Field operation method for improving straw carbon conversion rate in northern dry land

Abstract

The present invention belongs to the technical field of straw return to fields, and specifically relates to a field operation method for improving the carbon conversion rate of straw in dry land in northern China, comprising the following steps: preparing fertilizer; applying base fertilizer; sowing corn; applying the remaining fertilizer; harvesting corn and collecting the corn straw for later use; collecting soil from the topsoil layer of the field and measuring the available phosphorus content of the soil, and ensuring that the available phosphorus content of the topsoil layer is 30-60 mg / kg ‑1 Used to participate in the carbon conversion operation of corn straw; measure the soil pH. When the soil pH is greater than 7.5, add a pH regulator to the soil to adjust the soil pH to 6.5-7.5. The soil pH adjustment range is 0.2-3; plow the corn straw into the field and maintain the soil at 58-65% of field capacity. The amount of straw returned to the field is (6.8-7.3) t / hm ‑2 This method standardizes the operation process of returning straw to the fields, which is conducive to improving the effect and operability of returning straw to the fields, effectively improving the straw carbon conversion efficiency, and solving the problem of increased organic carbon content in the soil of northern drylands.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of straw returning to field, and particularly relates to a field operation method for improving straw carbon conversion rate in northern dry land. BACKGROUND

[0002] Soil organic matter (organic carbon) is the core of soil fertility and the basis of high and stable crop yield. Straw organic material is the main source of soil organic carbon. Straw returning to field is a main measure for agricultural waste resource reuse, environmental pollution reduction, and soil organic carbon improvement. Straw returning to field can improve soil nutrients, improve soil physical and biological properties, and thus improve crop yield and quality.

[0003] How to improve the conversion efficiency of straw carbon has been a core problem of efficient utilization of straw for a long time. In the farmland ecosystem, straw carbon is gradually converted into soil organic carbon under the action of microorganisms, and its conversion efficiency is significantly affected by soil nutrient availability. However, the difference and degree of soil nutrients and straw carbon conversion efficiency are not clear, and the regulation mechanism of different nutrient availability on straw carbon conversion efficiency is not clear, which seriously limits the research and application of farmland nutrient management technology for efficient utilization of straw.

[0004] Therefore, it is a problem to be solved by those skilled in the art to develop a farmland nutrient management method for soil organic carbon, improve the straw carbon conversion efficiency in northern dry land of China, and solve the fertilizer management technical bottleneck of improving soil organic carbon in dry land. SUMMARY

[0005] In order to solve the problems existing in the prior art, the application provides a field operation method for improving straw carbon conversion rate in northern dry land, which standardizes the operation process of straw returning to field, controls soil available phosphorus and soil pH, is beneficial to improving the effect and operability of straw returning to field, effectively improves the straw carbon conversion efficiency, and solves the problem of improving soil organic carbon content in northern dry land.

[0006] The specific technical scheme adopted by the application is:

[0007] A field operation method for improving straw carbon conversion rate in northern dry land, which comprises the following steps:

[0008] S1, preparing fertilizer, wherein the fertilizer comprises phosphorus fertilizer;

[0009] S2, using 50%-70% of the total weight of the fertilizer as base fertilizer;

[0010] S3, sowing corn;

[0011] S4, applying the remaining fertilizer during the growth period of corn;

[0012] S5, harvesting corn and collecting corn straw for later use.

[0013] S6, collecting the soil of the plough layer of the field and determining the effective phosphorus content of the soil, controlling the effective phosphorus content of the plough layer soil to be 30-60 mg / kg when the corn stalks are returned to the field -1 , the effective phosphorus content being obtained directly or after adding phosphorus fertilizer; determining the soil pH, when the soil pH is greater than 7.5, adding a pH regulator to the soil to adjust the soil pH to 6.5-7.5, the adjustment range of the soil pH being 0.2-3;

[0014] S7, returning the corn stalks to the field and keeping the soil at 58-65% of the field water holding capacity, the amount of returned stalks being (6.8-7.3) t / hm -2 .

[0015] Preferably, in step S6, the effective phosphorus content of the plough layer soil after corn harvesting is 53 mg / kg -1 .

[0016] Preferably, in step S5, the stalks are dried after collection and crushed to 2-10 cm of broken pieces.

[0017] Preferably, in step S7, the soil is kept at 60% of the field water holding capacity.

[0018] Preferably, the phosphorus fertilizer is heavy superphosphate or diammonium phosphate.

[0019] Preferably, in step S7, the amount of returned corn stalks is 7 t / hm -2 .

[0020] The beneficial effects of the present application are:

[0021] 1. Controlling the effective phosphorus content of the plough layer soil: the present application controls the effective phosphorus content of the plough layer soil by determining the effective phosphorus in the plough layer soil and applying fertilizer, ensuring sufficient soil phosphorus content, alleviating the nutrient limitation of microorganisms, optimizing the microbial community structure, and improving the activity of microorganisms, so that the stalks maintain a high rate of decomposition, increase the amount of straw decomposition; sufficient soil available phosphorus can also promote microorganisms to secrete more enzymes to decompose soil organic matter to obtain carbon, thereby increasing the amount of soil organic carbon mineralization.

[0022] 2. Combination of soil effective phosphorus content and straw returning time: the soil effective phosphorus content is controlled to be 30-60 mg / kg -1 when the straw is returned to the field, so that there is enough effective phosphorus in the soil during the peak period of straw decomposition (the fastest rate of straw decomposition in the early stage of straw decomposition), avoiding carbon limitation of microorganisms caused by nutrient deficiency, optimizing the microbial community structure, further ensuring rapid straw decomposition and soil organic carbon mineralization, and releasing nutrients into the soil after straw decomposition for crop absorption and utilization.

[0023] 3. Adjustment of soil pH: By adjusting the soil pH, the survival environment of soil microorganisms is optimized, the fungal dominance is promoted, and the decomposition efficiency of lignin and cellulose in straw is improved. Under higher pH conditions, the exchangeable calcium ions in the soil increase, the small molecular organic matter produced by the decomposition of straw is adsorbed through calcium bond, the direct mineralization of the small molecular organic matter into carbon dioxide is reduced, the transformation of carbon into mineral-bound organic carbon is promoted, and the soil carbon sequestration capacity is enhanced.

[0024] On the other hand, long-term fertilization can easily lead to soil acidification in northern dry land, and by adjusting the pH, the damage of acidity to the cell membrane of microorganisms can be reduced, the energy consumption of microorganisms for maintaining cell stability can be reduced, and more energy can be used for carbon transformation.

[0025] 4. Control of the amount of straw returned to the field: By controlling the amount of straw returned to the field, the imbalance of carbon and nitrogen ratio caused by excessive amount of straw returned to the field is avoided, and the lack of carbon source caused by insufficient amount of straw returned to the field is avoided. Microorganisms rapidly reproduce by using straw carbon as the energy source for their growth and proliferation. After the easily decomposable components in straw are reduced and the decomposition is slowed down, microorganisms will use more carbon to synthesize and decompose the original soil organic matter, causing an increase in soil carbon mineralization.

[0026] 5. Combination of straw returning mode and field water holding capacity: After corn straw is crushed into 2-10 cm fragments and returned to the field, it can be uniformly mixed with the soil to avoid water loss caused by overhead soil. The field water holding capacity of the soil is maintained at 58-65%, which can promote the metabolic activity of microorganisms, and the efficiency of the pre-movement of dissolved organic carbon and soil available phosphorus produced by straw decomposition is improved, and the ability of microorganisms to obtain nutrients is enhanced. On the other hand, the field water holding capacity of the present application makes the soil humidity suitable for the growth of microorganisms, which is also beneficial to increase the concentration of soil dissolved organic carbon and the migration and diffusion of nutrients in the soil, improve the availability of soil nutrients for microorganisms, and thus improve the number and activity of microorganisms, and promote the transformation and decomposition of organic carbon.

[0027] The present application combines the regulation and cooperation of soil available phosphorus, soil pH, straw returning amount and soil humidity, realizes the virtuous cycle of soil fertility enhancement-microorganism number structure optimization-microorganism promoting straw decomposition and nutrient release-soil fertility enhancement, and after 3-5 years of field management, the soil structure can be significantly improved, the soil organic carbon in dry land can be improved, the soil's ability to retain fertilizer and water can be enhanced, and nutrient loss can be reduced, which is helpful to provide stable nutrient supply for crop growth. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a schematic diagram of the steps of the present application;

[0029] Figure 2 is the dynamic change of carbon emission rate under different long-term fertilization and straw addition;

[0030] Figure 3Dynamic changes of cumulative carbon emission under long-term different fertilization and straw addition

[0031] Figure 4 Cumulative carbon emission at 176 days under long-term different fertilization and straw addition

[0032] Figure 5 Contribution rate of each factor to cumulative CO2 emission

[0033] Figure 6 Partial correlation analysis of soil properties and cumulative CO2 emission

[0034] Figure 7 Partial correlation analysis of soil properties and cumulative CO2 emission under straw addition

[0035] Figure 8 Structural equation model analysis of soil properties on cumulative carbon emission under straw addition

[0036] Figure 9 Dynamic changes of straw carbon decomposition rate under long-term different fertilization

[0037] Figure 10 Straw carbon cumulative decomposition amount under long-term different fertilization

[0038] Figure 11 Equation fitting of straw carbon cumulative decomposition amount under long-term different fertilization

[0039] Figure 12 Contribution rate of each factor to straw carbon cumulative decomposition amount

[0040] Figure 13 Partial correlation analysis of soil properties and straw carbon cumulative decomposition amount

[0041] Figure 14 Structural equation model analysis of soil properties on straw carbon cumulative decomposition amount

[0042] Figure 15 Dynamic changes of soil organic carbon mineralization rate under long-term different fertilization and straw addition

[0043] Figure 16 Soil organic carbon cumulative mineralization amount under long-term different fertilization and straw addition

[0044] Figure 17 Contribution rate of each factor to soil organic carbon cumulative mineralization amount under straw addition

[0045] Figure 18 Partial correlation analysis of soil properties and soil organic carbon cumulative mineralization amount under straw addition

[0046] Figure 19Structural equation model analysis of the effects of soil properties on soil organic carbon accumulation and mineralization under straw addition;

[0047] Figure 20 It is the dynamic change of the stimulation effect under different long-term fertilization conditions;

[0048] Figure 21 It is the cumulative stimulation effect under long-term different fertilization and straw addition;

[0049] Figure 22 is the contribution rate of each factor to the cumulative stimulation effect under straw addition;

[0050] Figure 23 Partial correlation analysis between soil properties and cumulative priming effects of straw addition;

[0051] Figure 24 Structural equation model analysis of the cumulative priming effect of soil properties on straw addition;

[0052] Figure 25 Heat map for correlation analysis between carbon emissions and soil properties under long-term fertilization and straw addition;

[0053] Figure 26 To analyze the correlation between available phosphorus and carbon emissions under long-term fertilization and straw addition;

[0054] Figure 27 To investigate the dynamic changes of DOC under different fertilization and straw addition in the long term;

[0055] Figure 28 The dynamic changes of MBC under different fertilization and straw addition in the long term;

[0056] Figure 29 The total microbial biomass under different long-term fertilization and straw addition;

[0057] Figure 30 The soil microbial community structure under different long-term fertilization and straw addition;

[0058] Figure 31 Heat map for correlation analysis between soil properties and microbial community structure;

[0059] In the accompanying figure, MOC is mineral-bound organic carbon; POC is particulate organic carbon; DOC is dissolved organic carbon; TDN is total dissolved nitrogen; SOC is soil organic carbon; AN is soil available nitrogen; and AP is soil available phosphorus. *, **, and *** indicate factor contributions that were significant at the p < 0.05, p < 0.01, and p < 0.001 levels, respectively. DETAILED DESCRIPTION

[0060] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0061] Example 1 Figure 1 As shown, the present invention relates to a field operation method for improving the carbon conversion rate of straw in dry land in northern China, comprising the following steps:

[0062] S1. Prepare fertilizers. The fertilizers include phosphate fertilizers. When nitrogen fertilizer is not applied, double superphosphate is used as phosphate fertilizer. When nitrogen fertilizer is applied, diammonium phosphate is used as phosphate fertilizer. Specifically, the fertilizer for jade in this embodiment includes 82.5 kg hm -2 of phosphate fertilizer and 82.5kg hm -2 Potash fertilizer;

[0063] S2. Take 50%-70% of the total weight of the fertilizer as base fertilizer. In this embodiment, the weight of the base fertilizer preferably accounts for 60% of the total weight of the fertilizer.

[0064] S3. Plant corn.

[0065] S4. Apply the remaining fertilizer before the jointing stage.

[0066] S5. Harvest corn and collect corn stalks for later use. After collection, dry the stalks and crush them into 2-10 cm pieces.

[0067] S6. Collect soil from the topsoil layer of the field and measure the available phosphorus content in the soil. When returning corn straw to the field, the available phosphorus content in the topsoil layer should be controlled at 30-60 mg kg -1 The available phosphorus content is obtained by direct measurement or after adding phosphorus fertilizer; the available phosphorus content of the preferred topsoil is 53 mg kg -1 The fertilizer prepared in step S1 of this embodiment ensures that the available phosphorus content of the tillage soil after corn harvest meets the standard, which not only eliminates the need to add fertilizer to ensure that the available phosphorus content of the soil meets the standard, but also ensures that there is sufficient phosphorus nutrient for the growth of corn in the previous season.

[0068] Measure the soil pH. If the soil pH is greater than 7.5, add a pH adjuster to adjust the soil pH to 6.5-7.5. The soil pH adjustment range is 0.2-3. If the operation area is a light saline-alkali area and the soil pH is less than 8, the soil pH can be lowered to within 1. If the operation area is a moderate saline-alkali area and the soil pH is less than 9, the soil pH can be lowered to within 2. If the operation area is a heavy saline-alkali area, the soil pH can be lowered to within 3. Gypsum or biochar can be used as pH adjusters.

[0069] S7. Plow the corn stalks and return them to the field until the soil maintains 58-65% of its field capacity, preferably 60%. The amount of corn stalks returned is (6.8-7.3) t hm -2 The optimal amount of corn straw returned to the field is 7t hm -2 .

[0070] The corn straw can be rolled before the straw returning to field to destroy the wax layer of the corn straw surface and promote the microorganism to invade the corn straw to decompose the corn straw.

[0071] The method in the embodiment is applied to a long-term positioning test station of black soil in Gongzhuling City, Jilin Province. The basic profile of the test station is shown in Table 1-1. Due to the climate, only one season of corn is planted in a year.

[0072] If applied in the north China region, before the straw returning to field, 30-60 mg kg -1 of effective phosphorus in the plough layer soil is ensured for the carbon conversion of the corn straw, and the amount of the base fertilizer is supplemented according to the nutrient content required by the crop planted after the corn is harvested to prevent the nutrient from being competed by the decomposition of the straw during the growth of the crop. The water holding capacity of the field is about 60% after the straw returning to field and the base fertilizer is applied, and the time is maintained for about one week to make the microorganism fully reproduce, and then the sowing of the next season of crop is performed.

[0073] By the regulation of the phosphorus nutrient availability and the soil pH value and the management of the field water holding capacity, the method can balance the soil nutrient, improve the soil nutrient environment, create good soil conditions for the efficient conversion of the straw carbon, and solve the problems of the low conversion efficiency of the straw carbon caused by the long-term unbalanced fertilization; the operation process of the straw returning to field is standardized, which is beneficial to improving the effect and the operability of the straw returning to field and promoting the efficient utilization of the straw in the farmland.

[0074] Under the operation method of the present application, the decomposition process of the corn straw returned to field is accelerated, the straw carbon can be more efficiently converted into the form available to the soil, the conversion efficiency of the straw carbon is improved, the accumulation and mineralization amount of the soil organic carbon and the accumulation stimulation effect are also improved, the efficient conversion of the straw carbon in the soil is realized, which is beneficial to the recycling of the straw carbon in the soil ecosystem, can promote the conversion and accumulation of the straw carbon to the soil organic carbon, and is helpful to improving the content of the soil organic carbon in the dry land and solving the problem of improving the soil organic carbon in the dry land.

[0075] Example 2 is basically the same as example 1, except that the fertilizer applied during the growth period of the corn in the present embodiment includes 82.5 kg hm -2 of phosphorus fertilizer, 82.5 kg hm -2 of potassium fertilizer and 165 kg hm -2 of urea.

[0076] The influence of the field operation method for improving the conversion rate of the straw carbon in the dry land in the north China region according to the present application on the carbon conversion process is verified by the following test comparison.

[0077] I. Test method

[0078] 1.1 Multiple treatments are set

[0079] The experiment relies on the black soil long-term positioning test station in Gongzhuling City, Jilin Province. The basic situation of the test station is shown in Table 1-1. Six fertilization treatments were set up in the test station, namely: no fertilizer (CK), nitrogen fertilizer (N), no organic fertilizer, nitrogen, phosphorus and potassium fertilizer (M0NPK), nitrogen, phosphorus and potassium fertilizer with straw returning (NPKS), nitrogen, phosphorus and potassium fertilizer (NPK), and phosphorus and potassium fertilizer (PK). The fertilization information of different treatments is shown in Table 1-2. 60% of the total weight of fertilizer is used as base fertilizer, and the rest of the fertilizer is applied before the jointing stage of the crop. Corn straw is covered on the soil surface after the jointing stage of the crop. The plot area is 400m 2 It is a randomized block design. Due to the early establishment of the test station, no repetition was set. Phosphorus fertilizer in the treatment without nitrogen was used as superphosphoric acid calcium, phosphorus fertilizer in the treatment of nitrogen and phosphorus combination was used as diammonium phosphate, and all the corn straw in the NPKS treatment was returned to the field in the season.

[0080] Table 1-1

[0081]

[0082] Table 1-2

[0083]

[0084] Table 1-3 Soil physical and chemical properties under different fertilization in the long-term

[0085]

[0086]

[0087] In the table, AP is the available phosphorus in soil, AN is the available nitrogen in soil, SOC is the soil organic carbon, MOC is the mineral-bound organic carbon, POC is the particulate organic carbon, and Ca-exe / SOC is the molar ratio of exchangeable calcium ion to soil organic carbon. Different lowercase letters represent significant differences between different fertilization treatments at the P<0.05 level.

[0088] 1.2 Collection of test soil samples

[0089] In October 2021, six fertilization treatments were collected from the Gongzhuling black soil long-term positioning fertilization test station, namely: no fertilizer (CK), nitrogen fertilizer (N), no organic fertilizer, nitrogen, phosphorus and potassium fertilizer (M0NPK), nitrogen, phosphorus and potassium fertilizer with straw returning (NPKS), nitrogen, phosphorus and potassium fertilizer (NPK), and phosphorus and potassium fertilizer (PK). Soil samples were collected from the above treatments in the plough layer (0-20cm). The area was divided into three replicates, and five points were taken from each replicate using the "S-type" soil drill sampling method. The collected soil was quickly transported back to the laboratory in a thermos box with a preservative ice bag. After removing the stone oaks and roots, one part was sieved through a 2mm sieve and used for indoor culture experiments. The other part was dried and used to determine the soil physical and chemical properties.

[0090] 1.3 Indoor culture test

[0091] This experiment used six different phosphorus nutrient availability treatment soils formed under long-term fertilization of Gongzhuling black soil as the experimental objects, corresponding to the addition / no addition 13 There were twelve treatments for corn straw labeled with C: low phosphorus: (1) no fertilizer (CK), (2) no fertilizer + straw (SCK), (3) nitrogen fertilizer (N), (4) nitrogen fertilizer + straw alone (SN); medium phosphorus: (5) reduced nitrogen, phosphorus, and potassium fertilizer (M0NPK), (6) nitrogen, phosphorus, and potassium fertilizer + straw without organic fertilizer (SM0NPK), (7) nitrogen, phosphorus, and potassium fertilizer and straw return (NPKS), (8) nitrogen, phosphorus, and potassium fertilizer and straw return + straw (SNPKS); high phosphorus: (9) nitrogen, phosphorus, and potassium fertilizer (NPK), (10) nitrogen, phosphorus, and potassium fertilizer + straw (SNPK), (11) phosphorus and potassium fertilizer (PK), (12) phosphorus and potassium fertilizer + straw (SPK). The available phosphorus contents in the soils treated with CK, N, M0NPK, NPKS, NPK and PK were 1.19, 2.08, 8.57, 16.64, 35.78 and 53.64 mg / kg, respectively. -1 The test used 13 C-labeled corn straw contains 42.16% carbon and 1.23% nitrogen. 13 The C value is 251.17‰. 13 Preparation of C-labeled corn stover: used during corn growth 13 CO2 pulse labeling (WANG et al., 2020). After corn harvest, the surface soil was washed clean, and the corn was dried in an oven at 105℃, dried at 60℃ until the weight no longer changed, and then ground evenly with a ball mill and passed through a 0.25mm sieve. 13 C value.

[0092] Before the experiment, the soil moisture content was adjusted to 40% of the field capacity with deionized water and pre-cultured at a constant temperature of 25°C in the dark for 10 days to stabilize the soil properties. After the pre-culture, 100 g of soil (dry weight) and 291 mg of corn straw (equivalent to 7 t ha -1 The mixture was thoroughly mixed and transferred to a 500 mL wide-mouth bottle, adjusted to 60% of the field water capacity with deionized water, sealed with a breathable membrane, and cultured in a 25°C constant temperature incubator in the dark for 180 days. During this period, deionized water was added every three days to maintain the moisture content.

[0093] 1.4 Test sample collection and measurement

[0094] (1) Gas sample collection and measurement

[0095] Gas samples were collected on days 1, 3, 5, 7, 11, 14, 21, 28, 45, 73, 95, 120, and 176 after the start of culture. To collect gas samples, remove the gas membrane from the culture bottle and replace it with a rubber stopper with two three-way valves. Connect one of the three-way valves and allow standard gas to flow for 30 minutes to remove CO2 from the bottle. After gassing, close the three-way valve, record the start time, and return the bottle to a 25°C incubator protected from light. The incubation time depends on the stage of culture (2 or 8 hours). After the incubation period, record the start time of gas extraction. Connect the three-way valve with a 50 mL disposable syringe. Open the three-way valve and repeatedly extract the gas ten times to homogenize the gas in the bottle. The extracted gas was then pumped into a vacuum-filled headspace vial. After gassing, the time taken was recorded. Remove the rubber stopper and allow the bottle to air naturally for 30 minutes. After that, replace the gas membrane and return the bottle to the incubator for continued culture. The CO2 concentration of the collected gas was determined by gas chromatography, and the δ 13 C value.

[0096] CO2 emission rate R (mgC kg -1 d -1 ) is calculated as follows:

[0097] R=ΔC / Δt×V / m×273.15 / (273.15+T)×12 / 22.4

[0098] Where ΔC / Δt is the daily CO2 emissions (ppmd -1 ), V is the volume of air above the soil in the jar (L), m is the dry weight of the soil used for the incubation test (g), T is the temperature during incubation (25°C), 12 is the mass of carbon per mole of carbon dioxide, and 22.4 is the volume occupied by each mole of gas under standard conditions (1 atm, 273.15K) (L mol -1 ).

[0099] Cumulative carbon emissions C t (mg C kg -1 The calculation formula of soil is as follows:

[0100] C t =∑(R i+1 +R i ) / 2×(t i+1 -t i )

[0101] Where i is the number of sampling times and t is the number of sampling days (d).

[0102] The CO2 in the gas sample originates from straw 13The proportion of C straw The calculation formula is as follows:

[0103] f straw =(δ 13 C treat -δ 13 C control ) / (δ 13 C straw -δ 13 C control ),

[0104] Where δ 13 Ctreat, δ 13 Ccontrol, δ 13 Cstraw is the gas sample treated with straw, the gas sample treated without straw, and the gas sample treated with straw added in the experiment. 13 C labeled corn stover 13 value;

[0105] The calculation formula for the cumulative decomposition amount of straw carbon (mgCkg-1soil) is as follows:

[0106] C s =C t ×f straw

[0107] Cumulative mineralization of soil organic carbon (mgCkg -1 soil) is the difference between the cumulative carbon emissions and the cumulative decomposition amount of straw carbon, and the calculation formula is as follows:

[0108] C SOM =C t -C s

[0109] Stimulating effect (mgCkg -1 soil) is the difference between the cumulative mineralization of soil organic carbon in the treatment with straw addition and the cumulative carbon emission in the treatment without straw addition, and the calculation formula is as follows:

[0110] C PE =C SOM -C control

[0111] (2) Determination of microbial biomass carbon and dissolved organic carbon content

[0112] Microbial biomass carbon and dissolved organic carbon were measured at the beginning of the 1st, 7th, 14th, 28th, 45th, 95th, 180th day. The method of K2SO4 extraction after CHCl3 fumigation was used to measure the soil microbial biomass carbon. In short, two 12.5 g fresh soil samples were accurately weighed in 25 mL beakers. Two vacuum desiccators were prepared, and two cups of NaOH solution were placed at the bottom of each vacuum desiccator on the diagonal. One of the vacuum desiccators contained two cups of CHCl3 with anhydrous calcium chloride particles, and the other contained two cups of ethanol-free CHCl3. The vacuum desiccators were sealed with vaseline, and the vacuum pump was connected to the vacuum desiccator containing CHCl3 using a rubber tube. After the CHCl3 in the vacuum desiccator boiled, the vacuum pump was connected for another 3 minutes. This process was repeated three times, and then the vacuum desiccator valve was closed. The samples were incubated in the dark for one day. After the incubation period, the samples were transferred to 200 mL plastic bottles, 50 mL of 10.5 M potassium sulfate solution was added, and the samples were shaken at 180 rpm for half an hour. The extracted solution was filtered and analyzed using a TOC analyzer (MultiN / C3100). The DOC content was measured without CHCl3 fumigation. 13 The samples were incubated in the dark for one day. After the incubation period, the samples were transferred to 200 mL plastic bottles, 50 mL of 10.5 M potassium sulfate solution was added, and the samples were shaken at 180 rpm for half an hour. The extracted solution was filtered and analyzed using a TOC analyzer (MultiN / C3100). The DOC content was measured without CHCl3 fumigation.

[0113] (3) Soil physical and chemical properties

[0114] The soil physical and chemical properties were measured using uncultured air-dried soil. pH was measured using an Orion pH meter with a 1:2.5 water-to-soil ratio; soil organic carbon (SOC) was measured using an elemental analyzer (EA3000) on soil samples after removing inorganic carbon with HCl; available phosphorus (AP) was measured using the NaHCO3 extraction-molybdenum antimony colorimetric method; available nitrogen (AN) was measured using the alkali hydrolysis diffusion method; mineral-bound organic carbon (MOC) and particulate organic carbon (POC) were measured: 10 g of air-dried soil samples were accurately weighed and passed through a 2 mm sieve, 0.5% sodium hexametaphosphate and glass beads were added, and the mixture was shaken at 180 rpm for 18 hours to completely disperse the soil. Then the dispersed soil was washed onto a 53 μm sieve, the part passing through the 53 μm sieve was MOC, and the remaining part on the sieve was POC. After drying at 65°C, the carbon content was measured using an elemental analyzer (EA3000) (POEPLAU et al., 2018). -1

[0115] 2. Statistical analysis

[0116] The data was statistically analyzed using Office 2021 Professional Edition, SPSS 27, and R language 4.2.2, and the data results were visualized using Origin 2021 and R language 4.2.2.

[0117] II. Carbon transformation characteristics and driving factors under long-term different fertilization and straw addition

[0118] 2.1 Total carbon emission characteristics and driving factors under long-term different fertilization and straw addition ​

[0119] 2.1.1 Characteristics of total carbon emissions under different long-term fertilization and straw addition

[0120] The soil CO2 emission rates under different long-term fertilization conditions were significantly different and showed obvious stage characteristics as the cultivation time increased.

[0121] like Figure 2 As shown in the figure, the CO2 emission rate of each treatment varied greatly from day 1 to day 45 of incubation. The soil CO2 emission rate of CK, N, MONPK, NPKS, NPK and PK treatments reached peak values ​​on day 7, 3, 7, 7, 1 and 11 of incubation, which were 6.7, 8.9, 6.2, 8.4, 10.0 and 9.8 mg C kg, respectively. -1 d -1 After reaching a peak, it rapidly declined and remained relatively stable until the 45th day. On the 45th day of incubation, the CO2 emission rates of the soil in the N, NPK, and PK treatments increased by 14.4%, 11.8%, and 10.5%, respectively, compared with the CK treatment, while the M0NPK and NPKS treatments showed no significant difference from the CK. During the first 45 days, the average CO2 emission rates of the treatments were in the following order: PK > NPK > N > NPKS > M0NPK > CK, with the PK treatment at 7.4 mg C kg -1 d -1 , CK treatment was 5.5 mg C kg -1 d -1 From the 45th to the 95th day of incubation, the CO2 emission rate of each treatment decreased rapidly. From the 95th to the 176th day of incubation, the soil CO2 emission rate of each treatment tended to be stable. The order of the average soil CO2 emission rate of each treatment was: NPK>N>PK>NPKS>M0NPK>CK. The soil CO2 emission rates of N, NPK and PK treatments were significantly higher than those of CK, M0NPK and NPKS treatments.

[0122] The CO2 emission rate of each treatment showed a similar trend. The CO2 emission rate of each treatment was the highest on the first day and decreased rapidly during the first 14 days. On the first day, the CO2 emission rate of SN, SNPK, and SPK was 85.3%, 114.1%, and 93.6% higher than that of SCK, respectively, while there was no significant difference between SM0NPK and SNPKS and SCK. During the first 14 days, the average CO2 emission rate of SN, SNPK, and SPK was significantly higher than that of SCK, SM0NPK, and SNPKS, which was 74.5%, 85.0%, and 88.5% higher than that of SCK, respectively. During the 14th to 95th day, the CO2 emission rate of each treatment gradually decreased, and the average CO2 emission rate of each treatment was in the order of SPK > SNPK > SN > SNPKS > SCK > SM0NPK. During the 95th to 176th day, the CO2 emission rate of each treatment was basically stable, and the CO2 emission rate of SN, SNPK, and SPK was significantly higher than that of SCK, SM0NPK, and SNPKS. The CO2 emission rate on the 176th day was only 2.56%-3.81% of that on the first day.

[0123] Compared with the treatment without straw addition, the CO2 emission rate of each treatment with straw addition increased significantly, with a larger increase in the early stage and a gradual decrease in the increase with the culture time. The increase of SN, SNPK, and SPK was significantly higher than that of SCK, SM0NPK, and SNPKS. The increase on the first day was 495.4%-738.8%, while on the 176th day, SCK, SN, SM0NPK, SNPKS, SNPK, and SPK increased by 4.1%, 14.7%, 3.9%, 10.0%, 16.1%, and 5.5%, respectively, compared with the treatment without straw addition.

[0124] As Figure 3 , Figure 4As shown, the order of cumulative soil CO2 emissions under different long-term fertilization conditions is as follows: PK = NPK > N > NPKS > M0NPK = CK. At day 176, compared with the CK treatment, cumulative soil CO2 emissions increased by 23.3%, 15.3%, 31.8%, and 33.6% in the N, NPKS, NPK, and PK treatments, respectively, while no significant difference was observed in the M0NPK treatment. Compared with the SCK treatment, cumulative CO2 emissions increased by 52.2%, 17.0%, 63.0%, and 66.6% in the SN, SNPK, SNPK, and SPK treatments, respectively, while cumulative CO2 emissions decreased by 6.4% in the SM0NPK treatment. Compared with no straw addition, cumulative CO2 emissions significantly increased in all treatments under straw addition, ranging from 77.1% to 120.8%. The increases in the SN, SNPK, and SPK treatments were significantly greater than those in the SCK, SNPKS, and SM0NPK treatments. The cumulative CO2 emissions of SCK, SN, SM0NPK, SNPKS, SNPK and SPK treatments increased by 77.1%, 118.6%, 58.3%, 79.6%, 119.0% and 120.8% respectively compared with the treatment without straw addition.

[0125] In this experiment, when no straw was added, the cumulative CO₂ emissions from treatments with high phosphorus availability (NPK and PK) were significantly higher than those with medium phosphorus availability (MONPK and NPKS), with increases ranging from 14.3% to 27.6%. Furthermore, the cumulative CO₂ emissions from treatments with high phosphorus availability were significantly higher than those from treatments with low phosphorus availability (CK and N), with increases ranging from 6.9% to 33.6%. Cumulative CO₂ emissions from the NPKS treatment were significantly higher than those from the CK treatment, with an increase of 15.3%.

[0126] The results showed that under straw addition, the cumulative CO2 emissions of the high phosphorus nutrient availability treatments (SNPK and SPK) under long-term fertilization were the highest, reaching 1614.3 and 1649.9 mg C kg -1 , which was significantly higher than the medium phosphorus nutrient availability treatment (SM0NPK, SNPKS) and the low phosphorus nutrient availability treatment (SCK, SN). The increase compared with the medium phosphorus nutrient availability treatment (SM0NPK, SNPKS) was 39.4%-78.0%, and the increase compared with the low phosphorus nutrient availability treatment (SCK, SN) was 7.1%-66.6%.

[0127] 2.1.2 Analysis of driving factors of total carbon emissions under different long-term fertilization and straw addition

[0128] The results of random forest model analysis show that Figure 5As shown in Table 4, the model explained 90.2% of the cumulative CO2 emissions without adding straw, and explained a total of 85.9% with straw addition. Regardless of straw addition, pH was the most important contributing factor, with a contribution of 18.8% and 21.2% to the cumulative CO2 emissions without and with straw addition, respectively, followed by AP, which contributed 15.4% and 15.1%, respectively. With straw addition, the contribution of AN and SOC to the cumulative CO2 emissions increased, with a contribution of 6.7%-8.7% and 5.9%-9.3%, respectively.

[0129] As shown in Table 4, the model explained 90.2% of the cumulative CO2 emissions without adding straw, and explained a total of 85.9% with straw addition. Regardless of straw addition, pH was the most important contributing factor, with a contribution of 18.8% and 21.2% to the cumulative CO2 emissions without and with straw addition, respectively, followed by AP, which contributed 15.4% and 15.1%, respectively. With straw addition, the contribution of AN and SOC to the cumulative CO2 emissions increased, with a contribution of 6.7%-8.7% and 5.9%-9.3%, respectively. Figure 6 As shown in Table 4, the model explained 90.2% of the cumulative CO2 emissions without adding straw, and explained a total of 85.9% with straw addition. Regardless of straw addition, pH was the most important contributing factor, with a contribution of 18.8% and 21.2% to the cumulative CO2 emissions without and with straw addition, respectively, followed by AP, which contributed 15.4% and 15.1%, respectively. With straw addition, the contribution of AN and SOC to the cumulative CO2 emissions increased, with a contribution of 6.7%-8.7% and 5.9%-9.3%, respectively.

[0130] As shown in Table 4, the model explained 90.2% of the cumulative CO2 emissions without adding straw, and explained a total of 85.9% with straw addition. Regardless of straw addition, pH was the most important contributing factor, with a contribution of 18.8% and 21.2% to the cumulative CO2 emissions without and with straw addition, respectively, followed by AP, which contributed 15.4% and 15.1%, respectively. With straw addition, the contribution of AN and SOC to the cumulative CO2 emissions increased, with a contribution of 6.7%-8.7% and 5.9%-9.3%, respectively. Figure 7As shown in the data, without controlling for other factors, MOC, pH, and SOC were significantly negatively correlated with cumulative CO2 emissions under straw addition, with correlation coefficients of -0.48, -0.84, and -0.54, respectively. AP was significantly positively correlated with cumulative CO2 emissions under straw addition, with a correlation coefficient of 0.69. The correlations between other factors and cumulative CO2 emissions under straw addition did not reach significant levels. After controlling for other factors, pH and AP remained significantly correlated with cumulative CO2 emissions under straw addition. The correlation between MOC and cumulative CO2 emissions under straw addition was no longer significant after controlling for POC and DOC, but it increased after controlling for TDN, AN, and AP, with increases of 32.3%, 32.3%, and 45.4%, respectively. The correlation between SOC and cumulative CO2 emissions under straw addition was no longer significant after controlling for MOC and pH, but increased after controlling for TDN, AN, and AP, with increases of 64.4%, 48.9%, and 15.6%, respectively. The correlation between AP and cumulative CO2 emissions under straw addition increased after controlling for MOC, pH, and SOC, with increases of 16.9%, 19.5%, and 7.5%, respectively. The correlation between DOC and cumulative CO2 emissions under straw addition was significantly negative after controlling for AN, with a correlation coefficient of -0.67. TDN and cumulative CO2 emissions under straw addition were significantly positively correlated after controlling for SOC, with a correlation coefficient of 0.84. AN and cumulative CO2 emissions under straw addition were significantly positively correlated after controlling for MOC, DOC, TDN, and SOC, with correlation coefficients of 0.60, 0.73, 0.61, and 0.77, respectively.

[0131] like Figure 8 As shown, structural equation model analysis results also showed that pH and AP were the main contributing factors to cumulative CO2 emissions under straw addition, with influence coefficients of -0.63 and 0.54, respectively. MOC content significantly inhibited cumulative CO2 emissions under straw addition, with an influence coefficient of -0.17. In this experiment, pH significantly altered the microbial community structure, with influence coefficients of -0.77 and 0.86 on G+ / G- and F / B, respectively. AP content had no significant effect on G+ / G- or F / B. G+ / G- represents the ratio of Gram-positive to Gram-negative bacteria in the soil, and F / B represents the ratio of fungi to bacteria in the soil.

[0132] 2.2 Characteristics and driving factors of straw carbon transformation under different long-term fertilization

[0133] 2.2.1 Characteristics of straw carbon decomposition under different long-term fertilization conditions

[0134] like Figure 9As shown in the figure, there are significant differences in the carbon decomposition rate of straw under different long-term fertilization, and the carbon decomposition of straw is fast at the beginning and slow at the end. In the first 45 days, the carbon decomposition rate of straw decreases rapidly and tends to be stable after 45 days. In the first 45 days, the carbon decomposition rate of straw decreases rapidly compared with the SCK treatment (21.42 -1 0.33mg C kg -1 d -1 ) compared with the control group, the carbon decomposition rate of straw treated with SN, SNPK and SPK increased significantly, with the rates ranging from 46.16 to 3.49 mgCkg -1 d -1 、56.03-3.61mg C kg -1 d -1 and 51.81–3.72 mg C kg -1 d -1 The decomposition rate of straw carbon in the SM0NPK treatment was slightly lower than that in the SCK treatment, with a rate of 19.11-1.10 mg C kg -1 d -1 From day 45 to day 94 of incubation, the carbon decomposition rates of straw in each treatment slowly decreased with incubation time. Among them, the carbon decomposition rates of straw in the SN, SNPK, and SPK treatments were still significantly higher than those in the SCK treatment, while there was no difference between the SMONPK and SNPKS treatments and the SCK treatment. During this period, the average carbon decomposition rates of straw in the SCK, SN, SMONPK, SNPKS, SNPK, and SPK treatments were 0.7, 1.6, 0.5, 0.5, 1.6, and 1.7 mg C kg, respectively. -1 d -1 From day 95 to day 176, the carbon decomposition rates of the straw in each treatment reached a stable state, with the SN, SNPK, and SPK treatments maintaining relatively high rates. On day 176, the carbon decomposition rates of the straw in the SCK, SN, SMONPK, SNPKS, SNPK, and SPK treatments were only 0.30%, 0.81%, 0.25%, 0.28%, 0.73%, and 0.49% of those on day 1, respectively.

[0135] like Figure 10 As shown in the results, the cumulative decomposition of straw carbon in the SN, SMONPK, and SNPKS treatments was significantly higher than that in the SCK, SMONPK, and SNPKS treatments on day 176. Compared with the SCK treatment, the cumulative decomposition of straw carbon in the SN, SNPKS, SNPK, and SPK treatments increased by 104.7%, 15.6%, 117.6%, and 111.2%, respectively, while the cumulative decomposition of straw carbon in the SMONPK treatment decreased by 14.8% (P < 0.05).

[0136] The results showed that the cumulative decomposition amount of straw carbon in the high phosphorus nutrient availability treatment (SNPK, SPK) under long-term fertilization was the highest, which was 722.5 and 701.2 mg C kg, respectively.-1 The straw carbon accumulation and decomposition amount of the high phosphorus nutrient availability treatment (SM0NPK, SNPKS) was significantly higher than that of the medium phosphorus nutrient availability treatment (SM0NPK, SNPKS), with an increase of 82.7%-155.5%. Under long-term fertilization, the straw carbon accumulation and decomposition amount of the next high phosphorus nutrient availability treatment (SNPK) was significantly higher than that of the low phosphorus nutrient availability treatment (SCK, SN), with an increase of 117.6% and 6.3%, respectively.

[0137] 2.2.2 Straw carbon residual characteristics under long-term different fertilization

[0138] The maximum decomposition amount of straw carbon under long-term different fertilization was fitted using y = C0(1-e bx ) and the straw carbon residual rate was calculated, as shown in Table 2.2.2. Figure 11 The straw carbon residual rate of the SCK, SM0NPK, and SNPKS treatments was significantly higher than that of the SN, SNPK, and SPK treatments. Compared with the SCK treatment, the SN, SNPKS, SNPK, and SPK treatments significantly reduced the straw carbon residual rate by 36.1%, 5.7%, 40.8%, and 38.5%, respectively. However, the SM0NPK treatment significantly increased the straw carbon residual rate by 5.9% compared with the SCK treatment.

[0139] 2.2.3 Driving factor analysis of straw carbon decomposition under long-term different fertilization

[0140] The random forest model analysis results showed that the model explained 83.8% of the cumulative decomposition amount of straw carbon, and pH was the most important contributing factor, accounting for 21.2% of the cumulative decomposition amount of straw carbon, followed by AP, which accounted for 12.1%. MOC, SOC, and TDN accounted for 10.2%, 9.9%, and 7.8%, respectively, as shown in Table 2.2.3. Figure 12

[0141] ​Without controlling for other factors, MOC, pH, and SOC were significantly negatively correlated with straw carbon accumulation and decomposition, with correlation coefficients of -0.56, -0.91, and -0.60, respectively. AP was significantly positively correlated with straw carbon accumulation and decomposition, with a correlation coefficient of 0.60. The correlations between other factors and straw carbon accumulation and decomposition did not reach significance. After controlling for other factors, pH and AP remained significantly correlated with straw carbon accumulation and decomposition. The correlation between MOC and straw carbon accumulation and decomposition was no longer significant after controlling for pH and SOC, but it increased after controlling for TDN, AN, and AP, with increases of 21.9%, 29.0%, and 30.7%, respectively. The correlation between SOC and straw carbon accumulation and decomposition was no longer significant after controlling for MOC and pH, but increased after controlling for TDN and AN, with increases of 50.0% and 45.3%, respectively. The correlation between AP and the amount of accumulated carbon decomposition in straw increased when MOC and pH were controlled, with increases of 25.1% and 30.1%, respectively, and weakened after controlling POC, DOC, and AN, with decreases of 2.0%, 2.1%, and 9.4%, respectively. The correlation between DOC and the amount of accumulated carbon decomposition in straw was significantly negatively correlated after controlling AN, with a correlation coefficient of -0.69. The correlation between TDN and the amount of accumulated carbon decomposition in straw was significantly positively correlated after controlling SOC, with a correlation coefficient of 0.83. The correlation between AN and the amount of accumulated carbon decomposition in straw was significantly positively correlated after controlling MOC, DOC, TDN, and SOC, with correlation coefficients of 0.65, 0.75, 0.69, and 0.83, respectively. Figure 13 shown.

[0142] like Figure 14 As shown in the figure, the results of structural equation model analysis showed that pH and AP were important factors affecting the cumulative decomposition of straw carbon, with influence coefficients of -0.70 and 0.40, respectively. MOC content significantly inhibited straw carbon decomposition, with an influence coefficient of -0.19. G+ / G- and F / B had no direct effect on the cumulative decomposition of straw carbon.

[0143] 2.3 Characteristics and driving factors of soil organic carbon mineralization under different long-term fertilization and straw addition

[0144] 2.3.1 Characteristics of soil organic carbon mineralization under different long-term fertilization and straw addition

[0145] like Figure 15 As shown in the figure, the soil organic carbon mineralization rate showed a downward trend with the incubation time and showed obvious stage characteristics. In the first 45 days, each treatment reached its maximum value on the first day of incubation. The soil organic carbon mineralization rates of SN, SM0NPK, SNPKS, NPK and SPK treatments were 23.93 mg C kg, respectively. -1 d -1 、16.75mg C kg -1 d -1, 19.19 mg C kg -1 d -1 , 24.96 mg C kg -1 d -1 and 21.43 mg C kg -1 d -1 , increased by 45.9%, 2.1%, 17.0%, 52.1% and 30.6% respectively compared with SCK. The soil organic carbon mineralization rate of SN, SM0NPK, SNPKS and SNPK reached the minimum value at the 14th day, which were 5.80 mg C kg -1 d -1 , 3.28 mg C kg -1 d -1 , 2.91 mg C kg -1 d -1 and 7.48 mg C kg -1 d -1 , decreased by 13.5%, 51.1% and 56.6% respectively compared with SCK, and increased by 11.5% for SNPK compared with SCK. The soil organic carbon mineralization rate of SPK increased after reaching the minimum value at the 7th day, and then gradually decreased, which was 11.02 mg C kg -1 d -1 at the 14th day, increased by 64.2% compared with SCK. From the 45th to 176th day of incubation, the soil organic carbon mineralization rate of each treatment further decreased, and basically reached a stable state after 95 days, and the soil organic carbon mineralization rate of SN, SNPK and SPK was significantly higher than that of SCK, SM0NPK and SNPKS. At the 176th day, the soil organic carbon mineralization rate of SN, SM0NPK, SNPKS, SNPK and SPK was only 7.7%, 7.8%, 7.7%, 9.0% and 7.6% of the peak value respectively compared with SCK, and all significantly decreased (P<0.05).

[0146] As Figure 16 shown, the cumulative mineralization amount of soil organic carbon under long-term different fertilization and straw addition increased gradually with incubation time. Compared with SCK, the cumulative mineralization amount of soil organic carbon of each fertilization treatment significantly increased, and showed obvious stage characteristics. From the 1st to 45th day of incubation, the increase rate of the cumulative mineralization amount of soil organic carbon of each fertilization treatment was larger. Among them, the cumulative mineralization amount of soil organic carbon of SN, SNPK and SPK was significantly higher than that of SCK; while the cumulative mineralization amount of soil organic carbon of SM0NPK was significantly lower than that of SCK. At the 45th day, the cumulative mineralization amount of soil organic carbon of SN, SNPK and SPK was significantly higher than that of SCK, which were 413.45 mg C kg -1 , 443.27 mg C kg-1 and 495.06 mg C kg -1 The cumulative mineralization of soil organic carbon in the SNPKS treatment was 328.79 mg C kg -1 The cumulative mineralization of soil organic carbon in the SNPKS treatment was 328.79 mg C kg -1 The cumulative mineralization of soil organic carbon in the SCK treatment was 332.19 mg C kg -1 From the 45th to the 176th day of incubation, the rate of increase in the cumulative mineralization of soil organic carbon in each fertilization treatment decreased, and the cumulative mineralization of soil organic carbon in the SN, SNPKS, SNPK, and SPK treatments was significantly higher than that in the SCK treatment. The cumulative mineralization of soil organic carbon in the SM0NPK treatment was still significantly lower than that in the SCK treatment. At the 176th day, the cumulative mineralization of soil organic carbon in the SN, SNPKS, SNPK, and SPK treatments was increased by 25.8%, 17.6%, 35.5%, and 44.1% (P < 0.05), respectively, compared with the SCK treatment, while the cumulative mineralization of soil organic carbon in the SM0NPK treatment was not significantly different from that in the SCK treatment. Meanwhile, the cumulative mineralization of soil organic carbon was significantly different among the SN, SM0NPK, SNPKS, SNPK, and SPK treatments.

[0147] The results showed that under the addition of straw, the cumulative mineralization of soil organic carbon in the highest phosphorus nutrient availability treatment (SPK) under long-term fertilization was the highest, reaching 948.7 mg C kg -1 which was significantly higher than that in the second highest (SNPK), medium phosphorus (SM0NPK, SNPKS), and low phosphorus (SCK, SN) nutrient availability treatments, with an increase of 6.4% compared with the second highest nutrient availability treatment (SNPK), 47.2% and 22.5% compared with the medium phosphorus nutrient availability treatments (SM0NPK, SNPKS), and 44.1% and 14.6% compared with the low phosphorus nutrient availability treatments (SCK, SN), respectively. The cumulative mineralization of soil organic carbon in the second highest phosphorus nutrient availability treatment (SNPK) under long-term fertilization was significantly higher than that in the medium phosphorus (SM0NPK, SNPKS) and low phosphorus (SCK, SN) nutrient availability treatments, with an increase of 38.4% and 15.2% compared with the medium phosphorus nutrient availability treatments (SM0NPK, SNPKS), and 35.5% and 7.7% compared with the low phosphorus nutrient availability treatments (SCK, SN), respectively.

[0148] 2.3.2 Analysis of the driving factors of soil organic carbon mineralization under long-term different fertilization and straw addition

[0149] As Figure 17As shown in Fig. 6, the random forest model analysis results showed that the model explained 74.6% of the cumulative mineralization of soil organic carbon, and pH was the most important contributing factor, accounting for 19.1% of the cumulative decomposition of straw carbon, followed by AP, which accounted for 16.1%. MOC, TDN accounted for 9.0%, 7.4%, respectively.

[0150] As shown in Fig. 6, the random forest model analysis results showed that the model explained 74.6% of the cumulative mineralization of soil organic carbon, and pH was the most important contributing factor, accounting for 19.1% of the cumulative decomposition of straw carbon, followed by AP, which accounted for 16.1%. MOC, TDN accounted for 9.0%, 7.4%, respectively. Figure 18 As shown in Fig. 6, the random forest model analysis results showed that the model explained 74.6% of the cumulative mineralization of soil organic carbon, and pH was the most important contributing factor, accounting for 19.1% of the cumulative decomposition of straw carbon, followed by AP, which accounted for 16.1%. MOC, TDN accounted for 9.0%, 7.4%, respectively.

[0151] As shown in Fig. 6, the random forest model analysis results showed that the model explained 74.6% of the cumulative mineralization of soil organic carbon, and pH was the most important contributing factor, accounting for 19.1% of the cumulative decomposition of straw carbon, followed by AP, which accounted for 16.1%. MOC, TDN accounted for 9.0%, 7.4%, respectively. Figure 19 As shown in Fig. 6, the random forest model analysis results showed that the model explained 74.6% of the cumulative mineralization of soil organic carbon, and pH was the most important contributing factor, accounting for 19.1% of the cumulative decomposition of straw carbon, followed by AP, which accounted for 16.1%. MOC, TDN accounted for 9.0%, 7.4%, respectively.

[0152] 2.4.1 Characteristics of priming effect under long-term different fertilization and straw addition

[0153] 2.4.1 Characteristics of priming effect under long-term different fertilization and straw addition

[0154] As shown in Fig. 6, the random forest model analysis results showed that the model explained 74.6% of the cumulative mineralization of soil organic carbon, and pH was the most important contributing factor, accounting for 19.1% of the cumulative decomposition of straw carbon, followed by AP, which accounted for 16.1%. MOC, TDN accounted for 9.0%, 7.4%, respectively. Figure 20As shown in Fig. 2, the rate of priming effect under different fertilization treatments was significantly different, and showed obvious stage characteristics. During the first 45 days of incubation, the rate of priming effect of each treatment first decreased and then increased with time. The rate of priming effect of each treatment reached the maximum value on the first day. The rate of priming effect of SN, SNPKS, SNPK and SPK treatments increased by 41.1%, 25.2%, 36.1% and 15.6% respectively compared with SCK, while the rate of priming effect of SM0NPK treatment had no significant difference with SCK. Negative priming effect appeared in SCK treatment on the 7th day, SN and SM0NPK treatments on the 14th day, and SNPK treatment on the 7th-14th day. On the 14th day of incubation, the rate of priming effect under fertilization treatments was the lowest value. The rate of priming effect of SN, SM0NPK, SNPKS and SNPK treatments decreased by 204.9%, 291.7%, 318.5% and 85.3% respectively compared with SCK, while the lowest value of the rate of priming effect under SCK was on the 7th day of incubation. During the 45th-176th day of incubation, the rate of priming effect of SN, SM0NPK, SNPKS, SNPK and SPK treatments gradually tended to 0.

[0155] As shown in Fig. 2, the rate of priming effect under different fertilization treatments was significantly different, and showed obvious stage characteristics. During the first 45 days of incubation, the rate of priming effect of each treatment first decreased and then increased with time. The rate of priming effect of each treatment reached the maximum value on the first day. The rate of priming effect of SN, SNPKS, SNPK and SPK treatments increased by 41.1%, 25.2%, 36.1% and 15.6% respectively compared with SCK, while the rate of priming effect of SM0NPK treatment had no significant difference with SCK. Negative priming effect appeared in SCK treatment on the 7th day, SN and SM0NPK treatments on the 14th day, and SNPK treatment on the 7th-14th day. On the 14th day of incubation, the rate of priming effect under fertilization treatments was the lowest value. The rate of priming effect of SN, SM0NPK, SNPKS and SNPK treatments decreased by 204.9%, 291.7%, 318.5% and 85.3% respectively compared with SCK, while the lowest value of the rate of priming effect under SCK was on the 7th day of incubation. During the 45th-176th day of incubation, the rate of priming effect of SN, SM0NPK, SNPKS, SNPK and SPK treatments gradually tended to 0. Figure 21 As shown in Fig. 3, the cumulative priming effect under different fertilization treatments showed a gradually increasing trend with the extension of incubation time. Compared with SCK, the cumulative priming effect of SN, SNPK and SPK treatments was significantly increased, while the cumulative priming effect of SM0NPK and SNPKS treatments was significantly reduced, and showed obvious stage characteristics. During the first 45 days of incubation, the cumulative priming effect of SN, SNPK and SPK treatments was significantly higher than that of SCK, while the cumulative priming effect of SNPKS and SM0NPK treatments was significantly lower than that of SCK. On the 28th day of incubation, the cumulative priming effect of SN, SNPK and SPK treatments was significantly higher than that of SCK (66.88 mg C kg -1 ), which was 85.24 mg C kg -1 , 106.08 mg C kg -1 and 121.70 mg C kg -1 , increased by 27.5%, 58.6% and 82.0% respectively, while the cumulative priming effect of SM0NPK and SNPKS treatments was significantly lower than that of SCK, which was 18.53 mg C kg -1 and 0.88 mg C kg -1, decreased by 72.3% and 98.7%, respectively. From the 45th to the 176th day of incubation, the cumulative priming effect of different fertilization treatments increased at a slower rate, and the cumulative priming effect of SN, SNPK, and SPK treatments was significantly higher than that of the SCK treatment. The cumulative priming effect of the SM0NPK treatment was still significantly lower than that of the SCK treatment. At the 176th day of incubation, the cumulative priming effect of the SNPK and SPK treatments increased significantly compared with the SCK treatment, by 56.0% and 103.1%, respectively (P < 0.05), while the cumulative priming effect of the SN, SM0NPK, and SNPKS treatments showed no significant difference compared with the SCK treatment.

[0156] The results showed that the highest cumulative priming effect was observed in the highest phosphorus nutrient availability treatment (SPK), reaching 201.5 mg C kg -1 , which was significantly higher than that of the next highest (SNPK), medium phosphorus (SM0NPK, SNPKS), and low phosphorus (SCK, SN) nutrient availability treatments. The cumulative priming effect of the SPK treatment was 30.2% higher than that of the SNPK treatment, 243.2% and 55.6% higher than that of the SM0NPK and SNPKS treatments, respectively, and 103.1% and 45.6% higher than that of the SCK and SN treatments, respectively.

[0157] 2.4.2 Analysis of the driving factors of priming effect under long-term different fertilization and straw addition

[0158] As shown in Figure 22 , the random forest model analysis results showed that the model explained 40.0% of the cumulative mineralization of soil organic carbon, and AP was the most important contributing factor, accounting for 14.3% of the cumulative priming effect, followed by pH, which contributed 14.0%.

[0159] As shown in Figure 23 , without controlling factors, pH and SOC were significantly negatively correlated with the cumulative priming effect, with correlation coefficients of -0.51 and -0.48, respectively. AP was significantly positively correlated with the cumulative priming effect, with a correlation coefficient of 0.69. The correlation between other factors and the cumulative priming effect did not reach a significant level. After controlling other factors, AP remained significantly positively correlated with the cumulative priming effect. The correlation between pH and the cumulative priming effect was no longer significant after controlling MOC, SOC, and AP. DOC was significantly negatively correlated with the cumulative priming effect after controlling AN, with a correlation coefficient of -0.54. TDN was significantly positively correlated with the cumulative priming effect after controlling SOC, with a correlation coefficient of 0.60. AN was significantly positively correlated with the cumulative priming effect after controlling DOC, with a correlation coefficient of 0.50.

[0160] As shown in Figure 24As shown in the figure, structural equation model analysis results showed that pH, AP, and MOC were important factors influencing the cumulative amount of soil organic carbon mineralization, with influence coefficients of -0.35, -0.71, and -0.28, respectively. G+ / G- had an inhibitory effect on soil organic carbon mineralization (influence coefficient of -0.26), but it did not reach a significant level. F / B was not significantly associated with the cumulative stimulating effect.

[0161] like Figure 25 、 Figure 26 As shown in the figure, the correlation analysis results showed that phosphorus nutrient availability was significantly positively correlated with the cumulative decomposition of straw carbon, the cumulative mineralization of soil organic carbon, and the cumulative stimulation effect, and was significantly negatively correlated with the residual rate of straw carbon, R 2 They are 0.36, 0.61, 0.48 and 0.36 respectively.

[0162] This experiment also revealed that AP and pH are the primary factors influencing carbon emissions under different long-term fertilization and straw addition conditions. In this experiment, AP did not significantly affect soil microbial community structure, but may indirectly regulate carbon emissions by affecting the stoichiometric ratio of soil nutrients, modulating microbial activity and physiological processes. However, at higher pH, lower G+ / G- and F / B ratios, as well as higher mineral protection status, all contribute to reduced carbon emissions under straw addition.

[0163] 3. Effects of long-term fertilization and straw addition on soil microbial community structure

[0164] 3.1 Dynamic changes of DOC and MBC under different long-term fertilization and straw addition

[0165] like Figure 27As shown, except for PK treatment, long-term fertilization significantly increased soil dissolved organic carbon (DOC) content, and showed obvious stage characteristics with incubation time. Without straw addition, DOC content under different long-term fertilization generally decreased slightly at first, then increased, and reached the maximum before 45 days and tended to be stable. DOC content decreased generally in the first 14 days, and NPKS treatment had the highest DOC content, followed by M0NPK treatment, which was significantly higher than other treatments, and increased by 69.2% and 61.3% compared with CK treatment (P<0.05). After 45 days, DOC content of NPKS treatment was significantly higher than N, NPK and M0NPK treatments, and higher than CK and PK treatments. After straw addition, DOC content of each treatment increased first and then decreased in the first 14 days, and reached the peak at the 7th day. Compared with SCK treatment, DOC content of SM0NPK and SNPKS treatments increased by 71.9% and 113.8%, respectively, while there was no significant difference in DOC content between SN and SNPK treatments and SCK treatment, and DOC content of SPK treatment was significantly lower than SCK treatment, decreasing by 27.9%. After 14 days, DOC content of each treatment increased rapidly, and reached the maximum at the 45th day and tended to be stable. At the 45th day, SNPKS treatment was significantly higher than SN, SM0NPK and SNPK treatments, and higher than SCK and SPK treatments. DOC content of each treatment at the 176th day was 125.68%-209.65% of the beginning, and increased significantly (P<0.05). In the first 28 days after straw addition, except for SPK treatment, straw addition significantly increased soil DOC content (30.8%-47.0%). But the increment gradually decreased with incubation time, and at the 95th day, except for SN, SM0NPK and SPK treatments, which increased by 11.1%, 10.6% and 20.7%, respectively, compared with no straw addition, there was no significant difference between other treatments and no straw addition. At the end of incubation, there was no significant difference between SM0NPK and SNPKS treatments and no straw addition, while SCK and SN treatments decreased by 14.3% and 12.1%, respectively, compared with no straw addition, and SNPK and SPK treatments increased by 7.0% and 9.6%, respectively.

[0166] As Figure 28As shown, long-term fertilization significantly affected soil microbial biomass carbon (MBC) content, but the response of MBC content under different fertilization treatments was inconsistent. The MBC content under NPKS treatment was significantly higher than that under M0NPK treatment, which was higher than that under CK treatment, while the MBC content under NPK and PK treatments was significantly reduced, and there was no significant difference between PK and CK treatments. The MBC content showed a phased change. Under the treatment without straw addition, the soil microbial carbon content under different long-term fertilization treatments first increased and then decreased within 1-14 days. At the 7th day of incubation, the MBC content reached a peak value, among which the MBC content under M0NPK and NPKS treatments increased by 17.1% and 39.6% respectively compared with that under CK treatment, while the MBC content under N and NPK treatments decreased by 49.0% and 41.0% respectively compared with that under CK treatment, and there was no significant difference in the MBC content between PK and CK treatments. The MBC content under each treatment increased and reached a stable value within 14-28 days, among which the MBC content under NPKS treatment increased by 77.3% compared with that under CK treatment, while the MBC content under N and NPK treatments decreased by 54.9% and 42.6% respectively compared with that under CK treatment, and there was no significant difference in the MBC content between M0NPK and CK treatments. Within 28-176 days, the MBC content under each treatment basically remained stable, and the order was NPKS > M0NPK > CK > PK > NPK > N treatment. Under the treatment with straw addition, the dynamic change of MBC content with time prolonging was basically consistent with that under the treatment without straw addition. At the 7th day of incubation, the MBC content reached a peak value, and at the 7th day, the MBC content under SN, SNPK and SPK treatments decreased by 42.9%, 41.8% and 18.1% respectively compared with that under SCK treatment, while there was no significant difference in the MBC content between SM0NPK and SNPKS treatments and SCK treatment. Within 7-176 days of incubation, the MBC content gradually decreased with the gradual increase of incubation time. Compared with the treatment without straw addition, straw addition significantly increased the MBC content, and at the 7th day, the increase amplitude of SCK and SM0NPK treatments was the largest, reaching 115.8% and 126.6% respectively, while the increase amplitude of SN, SNPKS, SNPK and SPK treatments was 81.8%, 45.6%, 65.3% and 56.7 respectively. At the end of incubation, there was no significant difference in the MBC content among the treatments except that the MBC content under SN and SNPK treatments increased by 77.6% and 73.6% respectively.

[0167] 3.2 Long-term different fertilization and straw addition on soil microbial community structure

[0168] As Figure 29As shown, long-term fertilization and straw addition affected soil microbial biomass. Compared with the CK treatment, the N treatment significantly reduced soil microbial biomass in the absence of straw addition, while the MONPK, NPKS, NPK, and PK treatments showed no significant differences in soil microbial biomass compared with the CK treatment. With straw addition, the SN and SM0NPK treatments showed no significant differences compared with the SCK treatment, while the SNPKS treatment significantly increased soil microbial biomass by 22.3%, while the SNPK and SPK treatments decreased soil microbial biomass by 20.5% and 34.6%, respectively. Compared with the absence of straw addition, the SN and SNPKS treatments significantly increased soil microbial biomass by 24.3% and 19.6%, respectively (P < 0.05). There was no significant difference in soil microbial biomass between the SCK, SM0NPK, SPK, and SNPK treatments and the absence of straw addition.

[0169] like Figure 30 As shown, long-term fertilization and straw addition significantly affected the soil microbial community structure, but different microbial species responded differently to fertilization and straw addition. Specifically, in the absence of straw addition, the content of Gram-negative bacteria in the N and PK soils was significantly reduced, by 32.8% and 21.9%, respectively, compared with the CK treatment (P < 0.05). There were no significant differences between the MONPK, NPK, and NPKS treatments and the CK treatment. However, the order of Gram-negative bacteria content under straw addition was SNPKS > SM0NPK = SCK = SN > SNPK = SPK. The SNPKS treatment was significantly higher than the other treatments, by 26.9% compared with the SCK treatment (P < 0.05). The SNPK and SPK treatments were 30.4% and 43.8% lower than the SCK treatment, respectively (P < 0.05). The content of Gram-negative bacteria in the SN and SM0NPK soils was not significantly different from that in the SCK treatment (P > 0.05). Compared with the treatment without adding straw, the content of Gram-negative bacteria increased significantly in the treatment with SN and SNPKS added to the straw, which increased by 36.9% and 20.4% respectively.

[0170] There were no significant differences in the Gram-positive bacteria content in the N, NPK, and PK treatments compared with the CK treatment (P>0.05). However, the Gram-positive bacteria content in the SNPK and SPK treatments was significantly lower than that in the SM0NPK and NPKS treatments (P<0.05). Straw addition did not significantly alter the Gram-positive bacteria content in the soil.

[0171] Without straw addition, the actinomycete content in the N and NPK treatments decreased significantly compared to the CK treatment, by 21.5% and 25.3%, respectively. With straw addition, the SNPKS treatment increased significantly by 25.2% compared to the SCK treatment, while the NPK and PK treatments decreased by 24.6% and 40.3%, respectively. Compared to the absence of straw addition, no significant changes were observed in the other treatments, except for the PK treatment, which decreased significantly by 33.8%.

[0172] Compared to the CK treatment, the N, NPK, and PK treatments significantly decreased their arbuscular mycorrhizal fungal content in the absence of straw addition, decreasing by 54.6%, 51.3%, and 31.5%, respectively. Compared to the SCK treatment, the SNPKS treatment significantly increased its content by 20.7%, while the SN, SNPK, and SPK treatments decreased their content by 41.4%, 56.9%, and 56.9%, respectively. Compared to the absence of straw addition, the SCK, SN, and SNPKS treatments significantly increased their content by 17.9%, 52.2%, and 30.7%, respectively, while the SPK treatment decreased its content by 25.8%.

[0173] Without straw addition, the bacterial content in the soil of the N treatment decreased by 24.0% compared with the CK treatment (P < 0.05), while no significant changes were observed in the MONPK, NPKS, NPK, and PK treatments. With straw addition, the bacterial content in the SNPKS treatment was significantly higher than in the other treatments, increasing by 22.9% compared with the SCK treatment (P < 0.05). The bacterial content in the soil of the SNPK and SPK treatments decreased by 23.8% and 37.5%, respectively, compared with the SCK treatment (P < 0.05). There were no significant differences in the bacterial content in the soil of the SN and SM0NPK treatments compared with the SCK treatment (P > 0.05). Compared with the absence of straw addition, the bacterial content in the SN and SNPKS treatments increased significantly after straw addition, increasing by 26.7% and 18.0%, respectively, compared with the absence of straw addition (P < 0.05).

[0174] Without straw addition, soil fungal content in the N, NPK, and PK treatments decreased by 49.9%, 39.5%, and 28.1%, respectively, compared with the CK treatment (P < 0.05). There were no significant differences in soil fungal content in the MONPK and NPKS treatments compared with the CK treatment. With straw addition, soil fungal content in the SN, SNPK, and SPK treatments decreased by 26.8%, 36.1%, and 48.4%, respectively, compared with the SCK treatment (P < 0.05). However, soil fungal content in the SNPKS treatment increased by 25.3% compared with the SCK treatment (P < 0.05). There was no significant difference in soil fungal content in the MONPK treatment compared with the SCK treatment. Straw addition significantly increased fungal content in the SCK, SN, SM0NPK, SNPKS, and SNPK treatments (P < 0.05), respectively, compared with the absence of straw addition. There were no significant changes in the SPK treatment.

[0175] Without straw addition, compared with CK, N and PK treatments increased G+ / G- by 25.2% and 9.1% (P<0.05), respectively, while M0NPK and NPKS treatments decreased G+ / G- by 13.4% and 13.2% (P<0.05), respectively. There was no significant difference between NPK and CK. Compared with no straw addition, SN decreased G+ / G- by 9.9%, and other treatments had no significant change.

[0176] Without straw addition, compared with CK, N and PK treatments increased G+ / G- by 25.2% and 9.1% (P<0.05), respectively, while M0NPK and NPKS treatments decreased G+ / G- by 13.4% and 13.2% (P<0.05), respectively. There was no significant difference between NPK and CK. Compared with no straw addition, SN decreased G+ / G- by 9.9%, and other treatments had no significant change.

[0177] As shown in Fig. 6, the results of correlation analysis showed that after straw addition, the correlation between MOC, SOC and AN and microorganisms weakened, while the correlation between DOC and AP and microorganisms strengthened. Figure 31

[0178] 3.3 Conclusion

[0179] (1) Straw addition significantly increased the F / B of soil. Under straw addition, a large amount of lignin and cellulose could provide nutrients and energy for fungi, and the dominance of fungi was enhanced.

[0180] (2) The results of this experiment showed that F / B was significantly positively correlated with pH.

[0181] (3) After straw addition, the correlation between microorganisms and MOC, SOC and AN weakened, while the correlation between microorganisms and AP strengthened, which indicated that soil microorganisms were transformed from carbon and nitrogen limitation to phosphorus limitation.​

Claims

1. A field operation method for improving the carbon conversion rate of straw in dry land in northern China, characterized in that: The following steps are involved: S1. preparing fertilizer, wherein the fertilizer includes phosphate fertilizer; S2, take 50%-70% of the total weight of fertilizer as base fertilizer; S3, sowing corn; S4. Apply the remaining fertilizer during the corn growth period; S5, harvesting corn and collecting corn stalks for later use; S6. Collect soil from the topsoil layer of the field and measure the available phosphorus content in the soil. When returning corn straw to the field, the available phosphorus content in the topsoil layer should be controlled at 30-60 mg kg -1 The available phosphorus content is obtained by direct measurement or after adding phosphorus fertilizer; the soil pH is measured. When the soil pH is greater than 7.5, a pH regulator is added to the soil to adjust the soil pH to 6.5-7.

5. The adjustment range of the soil pH value is 0.2-3; S7. Return corn stalks to the field and maintain the soil at 58-65% of its field capacity. The amount of stalks returned to the field is (6.8-7.3) t hm -2 ; use 13 C marks the corn straw returned to the field, collect 13 The soil marked with corn straw was used as the test sample and placed in a container. The emission rate of CO2 in the soil sample was R (mg C kg -1 d -1 ) is calculated as follows: R=△C / △t×V / m×273.15 / (273.15+T)×12 / 22.4, Where △C / △t is the daily CO2 emission (ppm d -1 ), V is the volume of air above the sample soil in the container (L), m is the dry weight of the sample soil (g), T is the Celsius temperature of the environment where the sample soil is located (25°C), 12 is the mass of carbon in each mole of carbon dioxide, and 22.4 is the volume occupied by each mole of gas under standard conditions (1 atm, 273.15K) (L mol -1 ); Cumulative carbon emissions of sample soil C t (mg C kg -1 The calculation formula of soil is as follows: C t =∑(R i+1 +R i ) / 2×(t i+1 -t i ), Where i is the number of sampling times, t is the number of sampling days (d); The CO2 in the gas sample originates from straw 13 The proportion of C straw The calculation formula is as follows: f straw =(δ 13 C treat -d 13 C control )(d 13 C straw -d 13 C control ), Where δ 13 Ctreat, δ 13 Ccontrol, δ 13 Cstraw is the gas sample treated with straw, the gas sample treated without straw, and the gas sample treated with straw added in the experiment. 13 C labeled corn stover 13 value; Cumulative decomposition amount of straw carbon (mg C kg -1 The calculation formula of soil is as follows: C s =C t ×f straw ; Cumulative mineralization of soil organic carbon (mg C kg -1 soil) is the difference between the cumulative carbon emissions and the cumulative decomposition amount of straw carbon, and the calculation formula is as follows: C SOM =C t -C s ; Cumulative stimulating effect (mgCkg -1 soil) is the difference between the cumulative mineralization of soil organic carbon in the treatment with straw addition and the cumulative carbon emission in the treatment without straw addition. The calculation formula is as follows: C PE =C SOM -C control 。 2. The field operation method for improving the carbon conversion rate of straw in dry land in northern China according to claim 1, characterized in that: In step S6, the available phosphorus content of the cultivated soil after corn harvest is 53 mg kg -1 .

3. The field operation method for improving the carbon conversion rate of straw in dry land in northern China according to claim 1, characterized in that: In step S5, the straw is collected, dried, and crushed into pieces of 2-10 cm.

4. The field operation method for improving the carbon conversion rate of straw in dry land in northern China according to claim 1, characterized in that: In step S7, the soil maintains 60% of its field capacity.

5. The field operation method for improving the carbon conversion rate of straw in dry land in northern China according to claim 1, characterized in that: The phosphate fertilizer is triple superphosphate or diammonium phosphate.

6. The field operation method for improving the carbon conversion rate of straw in dry land in northern China according to claim 1, characterized in that: In step S7, the amount of corn straw returned to the field is 7t hm -2 .

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