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

Abstract

The invention belongs to the technical field of straw returning, and particularly relates to a field operation method for improving the straw carbon conversion rate of northern dry land. Applying a base fertilizer; corn sowing; topdressing residual fertilizer; corn is harvested, and corn straw is collected for standby application; the method comprises the following steps: collecting soil of a field soil plough layer, measuring the available phosphorus content of the soil, and enabling the available phosphorus content of the plough layer soil to be 30-60mgkg <-1 > for participating in carbon conversion operation of corn straws; the pH value of the soil is measured, when the pH value of the soil is larger than 7.5, a pH regulator is added into the soil to adjust the pH value of the soil to 6.5-7.5, and the adjusting range of the pH value of the soil is 0.2-3; the corn straw is ploughed and returned to the field, the field capacity of the soil is kept at 58-65%, and the returning amount of the straw is (6.8-7.3) t / hm <-2 >; according to the method, the straw returning operation process is standardized, the straw returning effect and operability are improved, the straw carbon conversion efficiency is effectively improved, and the problem that the organic carbon content of northern dry land soil is increased is solved.

Description

Technical Field

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

[0002] Soil organic matter (organic carbon) is the core of soil fertility and the foundation for high and stable crop yields. Straw-based organic materials are the primary source of soil organic carbon. Returning straw to fields is a key measure for reusing agricultural waste resources, reducing environmental pollution, and increasing soil organic carbon. Returning straw to fields has multiple functions, including increasing soil nutrients, improving soil physical, chemical, and biological properties, thereby increasing crop yield and quality, and maintaining a virtuous cycle and sustainable development of the ecological environment. Currently, the overall organic carbon content in dryland farmland in northern my country is relatively low, seriously threatening the goal of achieving sustainable agricultural development. my country produces approximately 900 million tons of crop straw annually. Therefore, identifying the efficient conversion and utilization mechanisms of carbon in straw return is of great significance to national strategies such as improving the farmland ecological environment, enhancing soil health, and sequestering carbon and reducing emissions.

[0003] Improving the conversion efficiency of straw carbon has long been a core issue in the efficient use of straw. In farmland ecosystems, straw carbon is gradually converted into soil organic carbon by microorganisms, and its conversion efficiency is significantly influenced by soil nutrient availability. However, the differences and extent of soil nutrient and straw carbon conversion efficiencies remain unclear, as do the mechanisms regulating straw carbon conversion efficiency by varying nutrient availability. This has severely limited the development and application of farmland nutrient management technologies for efficient straw utilization.

[0004] Therefore, developing a farmland nutrient management method for soil organic carbon, improving the carbon conversion efficiency of straw in dryland areas in northern my country, and solving the technical bottleneck of fertilization management for increasing soil organic carbon in dryland areas are issues that need to be addressed by those skilled in the art. Summary of the Invention

[0005] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a field operation method for improving the carbon conversion rate of straw in northern dryland, standardizes the operation process of returning straw to the field, and controls the effective phosphorus and soil pH of the soil, which is conducive to improving the effect and operability of returning straw to the field, effectively improving the carbon conversion efficiency of straw, and solving the problem of increasing the organic carbon content in the soil of northern dryland.

[0006] The specific technical solution adopted in the present invention is:

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

[0008] S1. preparing fertilizer, wherein the fertilizer includes phosphate fertilizer;

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

[0010] S3, sowing corn;

[0011] S4. Apply the remaining fertilizer during the corn growth period;

[0012] S5, harvesting corn and collecting corn stalks for later use;

[0013] 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;

[0014] S7. Return corn stalks to the field and maintain the soil at 58-65% of field capacity. The amount of stalks returned to the field is (6.8-7.3) t / hm2. -2 .

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

[0016] Preferably, in step S5, the straw is collected, dried, and crushed into fragments of 2-10 cm.

[0017] Preferably, in step S7, the soil maintains 60% of its field capacity.

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

[0019] Preferably, in step S7, the amount of corn straw returned to the field is 7t / hm2. -2 .

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

[0021] 1. Regulating the content of available phosphorus in the cultivated soil: The present invention measures the available phosphorus in the cultivated soil and accurately regulates the content of available phosphorus in the cultivated soil through fertilization, thereby ensuring sufficient soil phosphorus nutrient content, alleviating nutrient limitations on microorganisms, optimizing the microbial community structure, and improving microbial activity, thereby maintaining a high decomposition rate of straw and increasing 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 available phosphorus content and straw return timing: When returning straw to the field, ensure that the soil available phosphorus content is 30-60mg / kg -1 , so that there is enough available phosphorus in the soil during the peak period of straw decomposition (the decomposition rate is fastest in the early stage of straw decomposition), avoiding microbial carbon limitation caused by nutrient shortage, 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 crops to absorb and utilize.

[0023] 3. Soil pH regulation: By regulating soil pH, the living environment of soil microorganisms is optimized, the dominance of fungi is enhanced, and the decomposition efficiency of lignin and cellulose in straw is improved. Moreover, under higher pH conditions, the exchangeable calcium ions in the soil increase, which adsorbs small molecular organic matter produced by straw decomposition through calcium bonds, reducing its direct mineralization into carbon dioxide, promoting the conversion of carbon to mineral-bound organic carbon, and enhancing the soil's carbon sequestration capacity.

[0024] On the other hand, long-term fertilization can easily lead to acidification of soil in northern drylands. By adjusting the pH, the damage caused by acidity to microbial cell membranes can be reduced, and the energy consumption of microorganisms to maintain cell stability can be reduced, allowing them to use more energy for carbon conversion.

[0025] 4. Control of the amount of straw returned to the field: By controlling the amount of straw returned to the field, we can avoid the imbalance of carbon-nitrogen ratio caused by excessive straw return, which will lead to microbial nitrogen limitation. At the same time, we can avoid insufficient carbon source caused by insufficient straw return. Microorganisms use straw carbon as the energy source for their own growth and proliferation to reproduce rapidly. After the easily decomposable components in the straw are reduced and the decomposition slows down, the microorganisms will use more carbon for enzyme synthesis to decompose the original organic matter in the soil, causing an increase in soil carbon mineralization.

[0026] 5. Combining the straw return method with field water holding capacity: After the corn straw is crushed into 2-10 cm segments and returned to the field, it can be evenly mixed with the soil, avoiding water loss caused by overhead soil. The field water holding capacity of the soil is maintained at 58-65%, which can promote microbial metabolic activity, and the efficiency of the forward movement of dissolved organic carbon and soil available phosphorus produced by straw decomposition is improved, thereby enhancing the ability of microorganisms to obtain nutrients; on the other hand, the field water holding capacity of the present invention makes the soil moisture suitable for microbial growth, and is also beneficial to increasing the concentration of soil dissolved organic carbon and the migration and diffusion of nutrients in the soil, thereby improving the effectiveness of soil nutrients for microorganisms, thereby increasing the number and activity of microorganisms and promoting the conversion and decomposition of organic carbon.

[0027] The present invention combines the regulation and coordination of soil available phosphorus, soil pH, straw return amount and soil moisture to achieve a virtuous cycle of soil fertility enhancement - microbial population structure optimization - microorganisms promoting straw decomposition and nutrient release - soil fertility enhancement. After 3-5 years of field management, the soil structure can be significantly improved, the organic carbon in dryland soil can be increased, the soil's fertilizer and water retention capacity can be enhanced, nutrient loss can be reduced, and a stable nutrient supply can be provided for crop growth. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0031] Figure 4 Cumulative carbon emissions on the 176th day under different long-term fertilization and straw addition;

[0032] Figure 5 is the contribution rate of each factor to the cumulative CO2 emissions;

[0033] Figure 6 Partial correlation analysis between soil properties and cumulative CO2 emissions;

[0034] Figure 7 Partial correlation analysis between soil properties and cumulative CO2 emissions under straw addition;

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

[0036] Figure 9 The dynamic changes of straw carbon decomposition rate under different long-term fertilization conditions;

[0037] Figure 10 is the accumulated decomposition amount of straw carbon under different long-term fertilization conditions;

[0038] Figure 11 The equation fitting for the amount of accumulated decomposition of straw carbon under different long-term fertilization conditions;

[0039] Figure 12 is the contribution rate of each factor to the cumulative decomposition of straw carbon;

[0040] Figure 13 Partial correlation analysis between soil properties and straw carbon accumulation and decomposition;

[0041] Figure 14 Structural equation model analysis of the effects of soil properties on straw carbon accumulation and decomposition;

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

[0043] Figure 16 The cumulative mineralization of soil organic carbon under different long-term fertilization and straw addition;

[0044] Figure 17 is the contribution rate of each factor to the cumulative mineralization of soil organic carbon under straw addition;

[0045] Figure 18 Partial correlation analysis between soil properties and soil organic carbon accumulation and mineralization under straw addition;

[0046] Figure 19 Structural 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 30The 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] Before returning the straw to the field, the corn straw can be crushed to destroy the waxy layer on the surface of the corn straw and promote microorganisms to invade the corn straw and decompose it.

[0071] The method in this embodiment was applied at the Black Soil Long-Term Positioning Experiment Station in Gongzhuling City, Jilin Province. A basic overview of the experimental station is shown in Table 1-1. Due to climatic conditions, only one corn crop is grown each year.

[0072] If applied in North China, when there are two crops per year, before returning the straw to the field, in addition to ensuring that 30-60mg / kg -1 In addition to using available phosphorus in corn straw for carbon conversion, the soil should also be supplemented with base fertilizer based on the nutrient requirements of the crops to be planted after corn harvest to prevent competition for nutrients with the decomposed straw during crop growth. After returning straw to the field and applying base fertilizer, the field water holding capacity should be brought to approximately 60% and maintained for about a week to allow microbial growth before sowing the next crop.

[0073] The present invention can balance soil nutrients, improve the soil nutrient environment, create good soil conditions for efficient straw carbon conversion, and solve problems such as low straw carbon conversion efficiency caused by long-term unbalanced fertilization by regulating the effectiveness of phosphorus nutrients and soil pH value, combined with the management of soil field water holding capacity. It also standardizes the straw return operation process, which is conducive to improving the effect and operability of straw return and promoting the efficient use of straw in farmland.

[0074] Under the operation method of the present invention, the decomposition process of corn straw returned to the field is accelerated, and the straw carbon can be more efficiently converted into a form that can be used by the soil, thereby improving the straw carbon conversion efficiency. It can also increase the cumulative mineralization amount and cumulative excitation effect of soil organic carbon, thereby realizing the efficient conversion of straw carbon in the soil, which is beneficial to the recycling of straw carbon in the soil ecosystem, and can promote the conversion and accumulation of straw carbon into soil organic carbon, thereby helping to increase the organic carbon content of dryland soil and solving the problem of increasing organic carbon in dryland soil.

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

[0076] The following experimental comparison verifies the influence of the field operation method for improving the carbon conversion rate of straw in dry land in northern China on the carbon conversion process.

[0077] 1. Test methods

[0078] 1.1 Setting up multiple processing

[0079] This experiment was based on the Black Soil Long-term Positioning Experiment Station in Gongzhuling City, Jilin Province. The basic profile of the experimental station is shown in Table 1-1. Six fertilization treatments were set up at the experimental station: no fertilization (CK), nitrogen fertilizer application (N), nitrogen, phosphorus and potassium fertilizers without organic fertilizer (M0NPK), nitrogen, phosphorus and potassium fertilizers and straw return (NPKS), nitrogen, phosphorus and potassium fertilizers (NPK), and phosphorus and potassium fertilizers (PK). Fertilization information for different treatments is shown in Table 1-2. 60% of the total weight of fertilizer was used as base fertilizer, and the remaining fertilizer was applied before the jointing stage of the crop. Corn straw was applied as topdressing before the jointing stage and then covered on the soil surface. The plot area was 400m 2 It was a randomized block design. Since the experimental station was established earlier, no replicates were set. In the treatment without nitrogen application, double superphosphate was used as the phosphate fertilizer, in the nitrogen-phosphorus combination treatment, diammonium phosphate was used as the phosphate fertilizer, and in the NPKS treatment, all corn straw of the season was returned to the field.

[0080] Table 1-1

[0081]

[0082] Table 1-2

[0083]

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

[0085]

[0086]

[0087] In the table, AP is soil available phosphorus; AN is soil available nitrogen; SOC is soil organic carbon; MOC is mineral-bound organic carbon; POC is particulate organic carbon; and Ca-exe / SOC is the molar ratio of exchangeable calcium ions to soil organic carbon. Different lowercase letters indicate significant differences among 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 at the Gongzhuling Black Soil Long-term Positioning Fertilization Experimental Station. These treatments included: no fertilization (CK), nitrogen fertilizer (N), nitrogen, phosphorus, and potassium fertilizers without organic fertilizer (M0NPK), nitrogen, phosphorus, and potassium fertilizers with straw return (NPKS), nitrogen, phosphorus, and potassium fertilizers (NPK), and phosphorus and potassium fertilizers (PK). Soil samples were collected from the topsoil layer (0-20 cm) of the above treatments. The plots were artificially divided into three replicates based on area. Five points were sampled from each replicate using an "S-shaped" soil drill and thoroughly mixed to form a single sample. The collected soil was quickly transported back to the laboratory in an insulated box with ice packs. A portion was removed of the lithophyllum and roots, passed through a 2 mm sieve, and used for indoor cultivation experiments. The remaining portion was air-dried and the physical and chemical properties of the soil were determined.

[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‰. 13Preparation 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 13 The 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 -1soil) 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] Destructive sampling was performed on the first, 7th, 14th, 28th, 45th, 95th, and 180th days to determine the soil microbial biomass carbon and dissolved organic carbon. The soil microbial biomass carbon was determined by CHCl3 fumigation followed by K2SO4 extraction. Briefly, two 12.5g fresh soil samples were accurately weighed and placed in a 25mL beaker. Two vacuum desiccators were prepared, with two cups of NaOH solution placed diagonally at the bottom of each vacuum desiccator. Two cups of ethanol-removing CHC solution with anhydrous calcium chloride granules were placed in one of the vacuum desiccators. 13 After sealing with vaseline, connect the vacuum pump to a vacuum desiccator containing chloroform using a hose. After the CHCl3 in the vacuum desiccator boils, pump for 3 minutes. Repeat three times, close the vacuum desiccator valve, and incubate in the dark for one day. After incubation, transfer the sample to a 200mL plastic bottle, add 50mL of 0.5M potassium sulfate solution, and shake at 180rpm for half an hour. The filtered extract is then analyzed using a TOC analyzer (MultiN / C3100). The DOC content is measured in the extract of the sample fumigated without chloroform.

[0113] (3) Soil physical and chemical properties

[0114] Soil physicochemical properties were determined using uncultivated air-dried soil. The pH was determined using an Orion pH meter at a water-soil ratio of 1:2.5. Soil organic carbon (SOC) was determined using an elemental analyzer (EA3000) after removing inorganic carbon using HCl. Available phosphorus (AP) was determined using the NaHCO3 extraction-molybdenum-antimony countercolorimetric method. Available nitrogen (AN) was determined using the alkaline diffusion method. Mineral-bound organic carbon (MOC) and particulate organic carbon (POC) were determined by accurately weighing 10 g of air-dried soil sample, passing it through a 2 mm sieve, adding 0.5% sodium hexametaphosphate and small glass beads, and simmering for 180 min. -1The soil was shaken for 18 hours to completely disperse. The dispersed soil was then rinsed onto a 53 μm sieve. The portion passing through the 53 μm sieve was MOC. The portion remaining on the sieve, POC, was dried at 65°C and its carbon content was determined using an elemental analyzer (EA3000) (POEPLAU et al., 2018).

[0115] 2. Statistical analysis

[0116] Office 2021 Professional Edition was used for statistical analysis of the data, SPSS 27 and R language 4.2.2 were used for data analysis, and Origin 2021 and R language 4.2.2 were used to visualize the data results.

[0117] 2. Carbon transformation characteristics and driving factors under different long-term fertilization and straw addition

[0118] 2.1 Characteristics and driving factors of total carbon emissions under different long-term 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 -1From 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] Under different long-term fertilization and straw addition conditions, CO2 emission rates showed similar trends across all treatments. CO2 emission rates peaked on day 1 for each treatment and rapidly declined from day 1 to day 14. On day 1, CO2 emission rates increased by 85.3%, 114.1%, and 93.6% in the SN, SNPK, and SPK treatments, respectively, compared to the SCK treatment, while no significant differences were observed in the SMONPK and SNPKS treatments. Over the first 14 days, average CO2 emission rates in the SN, SNPK, and SPK treatments were significantly higher than those in the SCK, SMONPK, and SNPKS treatments, increasing by 74.5%, 85.0%, and 88.5%, respectively, compared to the SCK treatment. From day 14 to day 95, CO2 emission rates gradually declined across all treatments, with the order of average CO2 emission rates being SPK > SNPK > SN > SN > SNPKS > SCK > SMONPK. From the 95th to the 176th day of cultivation, the CO2 emission rates of each treatment were basically stable. During this period, the CO2 emission rates of SN, SNPK and SPK treatments were significantly higher than those of SCK, SMONPK and SNPKS treatments. The CO2 emission rate on the 176th day was only 2.56%-3.81% of that on the first day.

[0123] Compared to the treatment without straw addition, CO2 emission rates increased significantly in all treatments after straw addition, with a larger increase in the early stages that gradually decreased with incubation time. The increases in the SN, SNPK, and SPK treatments were significantly higher than those in the SCK, SMONPK, and SNPKS treatments. The increases on day 1 ranged from 495.4% to 738.8%. By day 176, compared to the treatment without straw addition, SCK, SN, SMONPK, SNPKS, SNPK, and SPK increased by 4.1%, 14.7%, 3.9%, 10.0%, 16.1%, and 5.5%, respectively.

[0124] like 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, the model explained 90.2% of cumulative CO2 emissions without straw addition and 85.9% with straw addition. pH was the most significant contributing factor, contributing 18.8% and 21.2% to cumulative CO2 emissions, respectively, without and with straw addition. AP was second, contributing 15.4% and 15.1%, respectively. The contribution of AN and SOC to cumulative CO2 emissions increased with straw addition, ranging from 6.7% to 8.7% and 5.9% to 9.3%, respectively.

[0129] like Figure 6 As shown in the figure, partial correlation analysis results showed that when straw was not added, pH was significantly negatively correlated with cumulative CO2 emissions, with a correlation coefficient of -0.74. AN and AP were significantly positively correlated with cumulative CO2 emissions, with correlation coefficients of 0.54 and 0.77, respectively. The correlations with other factors in the absence of straw addition did not reach significant levels. pH and AP remained significantly correlated with cumulative CO2 emissions after controlling for other factors. The correlation between AN and cumulative CO2 emissions was no longer significant after controlling for pH, but it increased after controlling for MOC, DOC, and SOC, with increases of 17.2%, 19.3%, and 35.6%, respectively. MOC showed a significant negative correlation with cumulative CO2 emissions after controlling for AP, with a correlation coefficient of -0.50. TDN showed a significant positive correlation with cumulative CO2 emissions after controlling for SOC, with a correlation coefficient of 0.68. SOC showed a significant negative correlation with cumulative CO2 emissions after controlling for TDN and AN, with correlation coefficients of -0.72 and -0.65, respectively.

[0130] like 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 .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 , significantly higher than the medium phosphorus nutrient availability treatments (SM0NPK, SNPKS), with increases of 82.7%-155.5%, respectively. The cumulative decomposition of straw carbon in the high phosphorus nutrient availability treatment (SNPK) after long-term fertilization was significantly higher than that in the low phosphorus nutrient availability treatments (SCK, SN), with increases of 117.6% and 6.3%, respectively.

[0137] 2.2.2 Characteristics of straw carbon residues under different long-term fertilization conditions

[0138] Use y=C0(1-e bx ) was fitted to obtain the maximum decomposition amount of straw carbon under different long-term fertilization conditions and the straw carbon residual rate was calculated, as shown in Figure 11 As shown in Figure 3, the carbon residue rates in straw treated with SCK, SMONPK, and SNPKS were significantly higher than those in the SN, SNPK, and SPK treatments. Compared with the SCK treatment, the carbon residue rates in straw treated with SN, SNPKS, SNPK, and SPK were significantly lower by 36.1%, 5.7%, 40.8%, and 38.5%, respectively. However, the carbon residue rate in straw treated with SMONPK increased significantly by 5.9% compared with the SCK treatment.

[0139] 2.2.3 Analysis of driving factors of straw carbon decomposition under different long-term fertilization conditions

[0140] The results of the random forest model analysis showed that the model explained 83.8% of the accumulated carbon decomposition of straw. pH was the most important contributing factor, contributing 21.2% to the accumulated carbon decomposition of straw, followed by AP, which contributed 12.1%. MOC, SOC, and TDN contributed 10.2%, 9.9%, and 7.8%, respectively. Figure 12 shown.

[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、19.19mgC kg -1 d -1 、24.96mg C kg -1 d -1 and 21.43 mg C kg -1 d -1 , which 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, SMONPK, SNPKS and SNPK treatments reached the lowest on the 14th day, which were 5.80 mg C kg -1 d -1 、3.28mg C kg -1 d -1 , 2.91 mg C kg -1 d -1 and 7.48 mg C kg -1 d -1 Compared with the SCK treatment, the mineralization rate of soil organic carbon in the SN, SMONPK and SNPKS treatments decreased by 13.5%, 51.1% and 56.6%, respectively, and that in the SNPK treatment increased by 11.5% compared with the SCK treatment. In the SPK treatment, the soil organic carbon mineralization rate first increased after reaching the lowest value on the 7th day, and then gradually decreased after the 14th day, reaching 11.02 mgC / kg on the 14th day. -1 d -1 , a 64.2% increase compared to SCK. From days 45 to 176, soil organic carbon mineralization rates in all treatments decreased further, reaching a plateau after day 95. The SN, SNPK, and SPK treatments had significantly higher rates than those in the SCK, SMONPK, and SNPKS treatments. On day 176, compared to the SCK treatment, the SN, SMONPK, SNPKS, SNPK, and SPK treatments accounted for only 7.7%, 7.8%, 7.7%, 9.0%, and 7.6% of their peak values, respectively, representing significant decreases (P < 0.05).

[0146] like Figure 16 The results show that the cumulative mineralization of soil organic carbon under different long-term fertilization and straw addition gradually increased with the incubation time. Compared with the SCK treatment, the cumulative mineralization of soil organic carbon in each fertilization treatment increased significantly, and showed obvious stage characteristics. From the 1st to the 45th day of incubation, the cumulative mineralization of soil organic carbon in each fertilization treatment increased rapidly. Among them, the cumulative mineralization of soil organic carbon in SN, SNPK and SPK treatments was significantly higher than that in SCK treatment; while the cumulative mineralization of soil organic carbon in SM0NPK treatment was significantly lower than that in SCK treatment. On the 45th day, the cumulative mineralization of soil organic carbon in SN, SNPK and SPK treatments was significantly higher than that in SCK treatment, which were 413.45 mg C kg -1 、443.27mg C kg-1 and 495.06 mg C kg -1 The cumulative mineralization of soil organic carbon in the SM0NPK treatment was significantly lower than that in the SCK treatment, reaching 284.68 mg C kg -1 The cumulative mineralization of soil organic carbon in the SNPKS treatment was not different from that in the SCK treatment, which 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. On the 176th day, compared with SCK, the cumulative mineralization of soil organic carbon in the SN, SNPKS, SNPK and SPK treatments increased by 25.8%, 17.6%, 35.5% and 44.1%, respectively (P<0.05), while the cumulative mineralization of soil organic carbon in the SM0NPK treatment was not significantly different from that in SCK. At the same time, the cumulative mineralization of soil organic carbon was significantly different between the SN, SM0NPK, SNPKS, SNPK and SPK treatments.

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

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

[0149] like Figure 17As shown in the figure, the random forest model analysis results show that the model explains 74.6% of the cumulative mineralization of soil organic carbon. pH is the most important contributing factor, contributing 19.1% to the cumulative decomposition of straw carbon, followed by AP, which contributes 16.1%. MOC and TDN contribute 9.0% and 7.4%, respectively.

[0150] like Figure 18 As shown in the data, without controlling for other factors, pH was significantly negatively correlated with soil organic carbon accumulation and mineralization, with a correlation coefficient of -0.69. AP was significantly positively correlated with soil organic carbon accumulation and mineralization, with a correlation coefficient of 0.78. The correlations between other factors and soil organic carbon accumulation and mineralization did not reach a significant level. After controlling for other factors, pH and AP remained significantly correlated with soil organic carbon accumulation and mineralization. After controlling for TDN and AP, MOC showed a significant negative correlation with soil organic carbon accumulation and mineralization, with correlation coefficients of -0.51 and -0.56, respectively. After controlling for AN, DOC showed a significant negative correlation with soil organic carbon accumulation and mineralization, with a correlation coefficient of -0.58. After controlling for TDN, AN, and AP, SOC showed a significant negative correlation with soil organic carbon accumulation and mineralization, with correlation coefficients of -0.83, -0.64, and -0.51, respectively. After controlling for SOC, TDN showed a significant positive correlation with soil organic carbon accumulation and mineralization, with a correlation coefficient of 0.80. The correlation between AN and the cumulative mineralization of soil organic carbon was significantly positively correlated after controlling MOC, DOC, and SOC, with correlation coefficients of 0.51, 0.67, and 0.64, respectively.

[0151] like Figure 19 As shown in the figure, the results of structural equation model analysis showed that pH and AP were important factors affecting the accumulation of soil organic carbon mineralization, with influence coefficients of -0.49 and 0.72, respectively. G+ / G-, F / B, and MOC had inhibitory effects on soil organic carbon mineralization, but the effects did not reach a significant level.

[0152] 2.4 Characteristics and driving factors of the priming effect under different long-term fertilization and straw addition

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

[0154] like Figure 20As shown, the rates of priming responses varied significantly among the different fertilization treatments, all exhibiting distinct phased characteristics. From culture days 1 to 45, the rates of priming responses in each treatment initially decreased and then increased. The rates of priming responses reached their maximum on day 1, with increases of 41.1%, 25.2%, 36.1%, and 15.6% in the SN, SNPKS, SNPK, and SPK treatments compared with SCK, respectively. There was no significant difference in the priming response between SMONPK and SCK. Negative priming responses occurred on day 7 in the SCK treatment, day 14 in the SN and SMONPK treatments, and days 7-14 in the SNPK treatment. The priming response reached its lowest value under all fertilization treatments on culture day 14, with decreases of 204.9%, 291.7%, 318.5%, and 85.3% in the SN, SMONPK, SNPKS, and SNPK treatments compared with SCK, respectively. The lowest priming response in SCK occurred on culture day 7. From the 45th to the 176th day of culture, the stimulation effect rate of SN, SMONPK, SNPKS, SNPK and SPK treatment gradually approached 0.

[0155] like Figure 21 As shown in the figure, the cumulative stimulating effects of different fertilization treatments showed a trend of gradual increase with the extension of culture time. Compared with SCK, the cumulative stimulating effects of SN, SNPK and SPK treatments increased significantly, while the cumulative stimulating effects of SMONPK and SNPKS treatments decreased significantly, and showed obvious stage characteristics. From the 1st to the 45th day of culture, the cumulative stimulating effects of SN, SNPK and SPK treatments were significantly higher than those of SCK treatment, while the cumulative stimulating effects of SNPKS and SMONPK treatments were significantly lower than those of SCK treatment. On the 28th day of culture, the cumulative stimulating effects of SN, SNPK and SPK treatments were significantly higher than those of SCK (66.88 mg C kg -1 ), respectively 85.24 mg C kg -1 、106.08mg C kg -1 and 121.70 mg C kg -1 , increased by 27.5%, 58.6% and 82.0% respectively. The cumulative stimulation effects of SM0NPK and SNPKS treatments were significantly lower than those of SCK treatment, which were 18.53 mgCkg -1 and 0.88mgCkg -1, decreasing by 72.3% and 98.7%, respectively. From culture days 45 to 176, the rate of increase in the cumulative priming effect of the different fertilization treatments slowed down. The cumulative priming effects of the SN, SNPK, and SPK treatments were significantly higher than those of the SCK treatment, while the cumulative priming effect of the SMONPK treatment was still significantly lower than that of the SCK treatment. On culture day 176, the cumulative priming effects of the SNPK and SPK treatments significantly increased compared with the SCK treatment, increasing by 56.0% and 103.1%, respectively (P < 0.05). However, the cumulative priming effects of the SN, SMONPK, and SNPKS treatments did not differ significantly from those of the SCK treatment.

[0156] The results showed that the maximum phosphorus nutrient availability treatment (SPK) under long-term fertilization had the highest cumulative stimulation effect, reaching 201.5 mg C kg -1 , which were significantly higher than the second highest (SNPK), medium phosphorus (SM0NPK, SNPKS) and low phosphorus (SCK, SN) nutrient availability treatments. The increase compared with the second highest nutrient availability treatment (SNPK) was 30.2%, the increases compared with the medium phosphorus nutrient availability treatment (SM0NPK, SNPKS) were 243.2% and 55.6%, respectively, and the increases compared with the low phosphorus nutrient availability treatment (SCK, SN) were 103.1% and 45.6%, respectively.

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

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

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

[0160] like 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 were the primary factors influencing carbon emissions under different long-term fertilization regimes and straw addition. 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 contributed 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, with the exception of the PK treatment, long-term fertilization significantly increased soil dissolved organic carbon (DOC) content, with distinct phased characteristics over time. In the treatments without straw addition, DOC content initially decreased slightly, then increased, reaching a maximum before day 45 and then stabilizing. DOC content generally decreased over the first 14 days, with the NPKS treatment achieving the highest DOC content, followed by the MONPK treatment, which were significantly higher than the other treatments, increasing by 69.2% and 61.3%, respectively, compared to the CK treatment (P < 0.05). After day 45, DOC content in the NPKS treatment was significantly higher than that in the N, NPK, and MONPK treatments, and higher than that in the CK and PK treatments. After straw addition, DOC content in each treatment increased and then decreased from day 1 to day 14, reaching a peak on day 7. Compared with the SCK treatment, the DOC content in the SMONPK and SNPKS treatments increased by 71.9% and 113.8%, respectively, while the DOC content in the SN and SNPK treatments showed no significant difference from the SCK treatment. The DOC content in the SPK treatment was significantly lower than that in the SCK treatment, decreasing by 27.9%. After 14 days, the DOC content in each treatment increased rapidly and stabilized after reaching a maximum on the 45th day. On the 45th day, the DOC content in the SNPKS treatment was significantly higher than that in the SN, SMONPK, and SNPK treatments, and higher than that in the SCK and SPK treatments. The DOC content in each treatment on the 176th day of incubation was significantly increased from 125.68% to 209.65% of the initial value (P < 0.05). In the first 28 days after straw addition, except for the SPK treatment where DOC content decreased, straw addition significantly increased soil DOC content (30.8%-47.0%). However, the increase in the culture time gradually decreased. By the 95th day, except for SN, SM0NPK and SPK, which increased by 11.1%, 10.6% and 20.7% respectively compared with no straw addition, there were no significant differences in the other treatments compared with no straw addition. At the end of the culture, there were no significant differences in the SM0NPK and SNPKS treatments compared with no straw addition, while the SCK and SN treatments decreased by 14.3% and 12.1% respectively compared with no straw addition, and the SNPK and SPK treatments increased by 7.0% and 9.6% respectively.

[0166] like Figure 28As shown in the data, long-term fertilization significantly affected the soil microbial biomass carbon (MBC) content, but the response of MBC content under different fertilization treatments was inconsistent. The MBC content in the NPKS treatment was significantly higher than that in the M0NPK treatment and higher than that in the CK treatment, while the MBC content in the NPK and PK treatments was significantly reduced, and there was no significant difference between the PK treatment and the CK treatment. The MBC content showed a staged change. Without the addition of straw, the soil microbial carbon content in different long-term fertilization treatments from day 1 to day 14 first increased and then decreased. It reached a peak on the 7th day of incubation. Among them, the MBC content in the M0NPK and NPKS treatments increased by 17.1% and 39.6% respectively compared with the CK treatment, while the MBC content in the N and NPK treatments decreased by 49.0% and 41.0% respectively compared with the CK treatment. There was no significant difference in the MBC content in the PK treatment and the CK treatment. MBC content increased across all treatments and reached a stable value between days 14 and 28. The NPKS treatment showed a 77.3% increase compared to the CK treatment, while the N and NPK treatments showed decreases of 54.9% and 42.6%, respectively. The MBC content in the M0NPK and PK treatments showed no significant differences from the CK treatment. From days 28 to 176, MBC content remained largely stable across all treatments, with NPKS > M0NPK > CK > PK > NPK > N treatment. The dynamic changes in MBC content over time in the straw-added treatments were largely consistent with those in the no-straw treatment. MBC content peaked on day 7 for each treatment. On day 7, MBC content in the SN, SNPK, and SPK treatments decreased by 42.9%, 41.8%, and 18.1%, respectively, compared to the SCK treatment. There were no significant differences between the SM0NPK and SNPKS treatments and the SCK treatment. From day 7 to 176, MBC content slowly decreased with increasing culture time. Compared with the treatment without straw addition, straw addition significantly increased MBC content. On day 7, the SCK and SM0NPK treatments showed the largest increases, at 115.8% and 126.6%, respectively. The SN, SNPKS, SNPK, and SPK treatments saw increases of 81.8%, 45.6%, 65.3%, and 56.7%, respectively. By the end of the incubation period, no significant differences were observed in the other treatments, except for the SN and SNPK treatments, which saw increases of 77.6% and 73.6%, respectively.

[0167] 3.2 Effects of long-term fertilization and straw addition on soil microbial community structure

[0168] like 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, soil F / B ratios in the N, NPK, and PK treatments decreased by 34.6%, 27.1%, and 12.7%, respectively, compared with the CK treatment (P < 0.05). There were no significant differences in soil F / B ratios between the MONPK and NPKS treatments and the CK treatment. Straw addition significantly increased soil F / B ratios. Compared with no straw addition, soil F / B ratios in the SCK, SN, SM0NPK, SNPKS, SNPK, and SPK treatments increased by 22.4%, 43.8%, 13.5%, 22.6%, 40.8%, and 16.3%, respectively (P < 0.05).

[0176] Without straw addition, compared with the CK treatment, soil G+ / G- ratios in the N and PK treatments increased by 25.2% and 9.1%, respectively (P < 0.05), while those in the MONPK and NPKS treatments decreased by 13.4% and 13.2%, respectively (P < 0.05). There were no significant differences between the NPK and CK treatments. SN decreased by 9.9% compared with the no straw addition treatment, while no significant changes were observed in the other treatments.

[0177] like Figure 31 As shown in Figure 3, the correlation analysis results showed that after straw addition, the correlation between MOC content, SOC content and AN content and microorganisms weakened overall, while the correlation between DOC and AP and microorganisms strengthened.

[0178] 3.3 Conclusion

[0179] (1) The addition of straw significantly increased the soil F / B. With the addition of straw, a large amount of lignin and cellulose can provide nutrients and energy for fungi, and the dominance of fungi is enhanced.

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

[0181] (3) After straw addition, the correlation between microorganisms and MOC, SOC, and AN weakened, while the correlation with AP strengthened, which indicated that soil microorganisms shifted from being limited by carbon and nitrogen to being limited by phosphorus.

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 .

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 .

7. 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: 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 CO2 emission rate R (mg C kg -1 d -1 ) is calculated as follows: R=ΔC / Δt×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 。

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