Regulation and control method for stabilizing carbon and increasing sink of cunninghamia lanceolata forest soil in karst region

Abstract

The invention discloses a regulation and control method for stabilizing carbon and increasing sink in soil of a Chinese fir forest in a karst region. Through comprehensive treatment of litter burying, moisture regulation and charcoal application, the stability of organic carbon in the cedarwood forest soil is improved, and the physical and chemical properties of the soil are improved. The method for stabilizing the organic carbon of the soil and improving the carbon sequestration capacity is suitable for ecological engineering under the goals of forest soil improvement and carbon neutralization.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil carbon sequestration, and relates to a regulation method for stabilizing carbon sequestration and increasing carbon sinks in the soil of Chinese fir forests in karst areas. Background Art

[0002] Soils in karst areas generally have problems such as thin soil layers, poor water and fertilizer retention capacity, and fast decomposition of organic carbon, resulting in low stability of soil carbon pools, limited carbon sink functions, slow natural decomposition rates of litter (only 30 - 50% of non-karst areas), and imbalance between carbon release and sequestration efficiency.

[0003] Traditional litter management mostly uses surface covering or burning. The former is prone to carbon mineralization loss due to wet-dry alternation, and the latter directly releases CO2 and destroys the soil microbial community. Moreover, existing burial technologies lack scientific designs for the physical treatment of litter (such as size control) and burial depth, and it is difficult to match the permeability and microbial distribution characteristics of karst soils.

[0004] Currently, there is no method to synergistically optimize the carbon form transformation path of karst Chinese fir forest litter (such as the proportion regulation of labile carbon and recalcitrant carbon) and the construction of soil microhabitats (mechanical composition) to achieve long-term stable carbon sequestration. The present invention realizes a method for stable sequestration of soil organic carbon and improvement of carbon sink capacity through refined treatment and directional burial of litter, biochar, and water, combined with the soil characteristics of karst areas, and is applicable to forest soil improvement and ecological projects under the goal of carbon neutrality. Summary of the Invention

[0005] The purpose of the present invention is to provide a regulation method for stabilizing carbon sequestration and increasing carbon sinks in the soil of Chinese fir forests in karst areas. The present invention improves the stability of soil organic carbon, reduces carbon emissions, and improves soil physical and chemical properties through comprehensive treatments of litter burial, water regulation, and biochar application.

[0006] The technical solution of the present invention:

[0007] A regulation method for stabilizing carbon sequestration and increasing carbon sinks in the soil of Chinese fir forests in karst areas, comprising the following steps:

[0008] (1) Forest land selection: Select a Chinese fir forest with a simple understory structure, canopy density > 0.8, and little or no vegetation under the forest. Dig cross-shaped deep trenches, each cross-shaped deep trench being 15 - 25 cm wide, 25 - 35 cm deep, and having a spacing of 40 - 60 cm for standby;

[0009] (2) Litter pretreatment: After collecting fallen leaves and dead branches that have fallen in the forest between October and December and collecting them uniformly, remove thick branches, retain fallen leaves and fine branches, cut them into segments of 1.5 - 2.5 cm, mix the fallen leaves and fine branches in a volume ratio of 6 - 8:2 - 4, mix well, and screen to remove powders with a particle size < 0.5 cm to obtain pretreated litter;

[0010] (3) Preparation of biochar: Using rice straw as raw material, crush the rice straw into particles with a size of 0.5 - 1.5 mm. After pyrolysis at 500 - 700 °C, crush it through a 80 - mesh sieve to obtain biochar for standby.

[0011] (4) Litter burial: Bury the processed litter into the well - shaped deep ditches prepared in step (1). The amount of litter buried is 0.8 - 1.2 kg·m -2 , and the litter is buried in a stratified manner. First, bury half of the litter at a depth of 8 - 12 cm at the bottom layer. After covering with soil of 5 - 10 cm and compacting, then bury the remaining litter and cover with soil of 4 - 6 cm.

[0012] (5) Moisture regulation: After the rainy season ends, install 2 water storage devices in each well - shaped deep ditch. The water storage device is a wide - mouth plastic bottle with a volume of 4000 - 6000 mL filled with water, and an anti - mildew chemical fiber cotton rope with a diameter of 4 - 6 mm is placed inside. One end of the anti - mildew chemical fiber cotton rope is placed at the bottom of the wide - mouth bottle, and the other end is evenly distributed in a cross - shape at a distance of 8 - 12 cm from the soil surface. Based on the principle of capillary action, supply water to the soil. Regularly check the water supply efficiency of the cotton rope and fill it up once every 55 - 65 days.

[0013] (6) Application of biochar: Take biochar and apply it at a rate of 0.5 - 1.5 kg·m -2 into the soil layer in the Chinese fir forest and plow and mix it. The mixed soil layer extends from the ground surface to a depth of 25 - 30 cm underground, and the biochar and soil are fully mixed.

[0014] (7) Burial period: Starting from the time of litter burial, bury for 11 - 13 months.

[0015] Each of the aforementioned well - shaped deep ditches is 20 cm wide, 30 cm deep, and 50 cm apart.

[0016] The soil of the aforementioned Chinese fir forest is mainly yellow soil, with a texture of clay loam.

[0017] The aforementioned litter treatment: Collect the fallen leaves and dead branches in the forest during October - December and collect them uniformly. Then, remove the thick branches with a diameter > 5 mm, retain the fallen leaves and the thin branches with a diameter ≤ 3 mm, cut them into segments of 1.8 - 2.2 cm. The fallen leaves and thin branches are mixed according to a volume ratio of 6.5 - 7.5:2.5 - 3.5, fully mixed, and sieved to remove the powder with a particle size < 0.5 cm to obtain the processed litter.

[0018] The aforementioned litter treatment: In October - December, the fallen leaves and dead branches in the forest are collected and unified. After removing the thick branches with a diameter > 5 mm, the fallen leaves and the thin branches with a diameter ≤ 3 mm are retained, cut into segments of 1.8 - 2.2 cm. The fallen leaves and thin branches are mixed according to a volume ratio of 7:3, fully mixed, and screened to remove the powder with a particle size < 0.5 cm to obtain the treated litter.

[0019] The aforementioned biochar preparation: Using rice straw as the raw material, the rice straw is crushed into particles of 1 mm, pyrolyzed at 600 °C, and then crushed through 80 - mesh to obtain biochar for standby.

[0020] The aforementioned litter burial: The treated litter is buried in the well - shaped deep ditch prepared in step (1). The amount of litter buried is 1 kg·m -2 , and the litter is buried by the method of layered burial. First, bury half of the litter at a depth of 10 cm at the bottom layer. After covering with 5 cm of soil and compacting, then bury the remaining litter and cover with 5 cm of soil.

[0021] The aforementioned water regulation: After the rainy season ends, 2 water storage devices are buried in each well - shaped deep ditch. The water storage device is a 5000 - mL wide - mouth plastic bottle filled with water, with a 5 - mm diameter mildew - proof chemical fiber cotton rope inside. One end of the mildew - proof chemical fiber cotton rope is placed inside the bottom of the wide - mouth bottle, and the other end is evenly distributed in a cross - shape at a distance of 10 cm from the soil surface. Based on the principle of capillary action, water is supplied to the soil. Regularly check the water supply efficiency of the cotton rope and replenish the water once every 60 days.

[0022] The aforementioned application of biochar: Take biochar and apply it at 1 kg·m -2 into the soil layer of the Chinese fir forest and plow and mix it. The mixed soil layer extends from the ground surface to a depth of 25 - 30 cm underground, and the biochar is fully mixed with the soil.

[0023] The aforementioned burial period: Starting from the time of litter burial, bury for 12 months.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention realizes a method for stable sequestration of soil organic carbon and improvement of carbon sink capacity through the refined treatment and directional burial of litter, biochar, and water, combined with the soil characteristics of the karst area, and is applicable to forest soil improvement and ecological projects under the goal of carbon neutrality.

[0026] 2. Through the comprehensive treatment of litter burial, water regulation, and biochar application in the present invention, the soil ROCI increases by 2.2 - 2.7%, achieving the purpose of improving the stability of soil organic carbon.

[0027] 3. Through the comprehensive treatment of litter burial, water regulation and biochar application in the present invention, the physical and chemical properties of the soil can also be improved, where the total phosphorus in the soil increases by 2.62%, the total potassium increases by 6.52%, the available nitrogen increases by 0.43%, the available phosphorus increases by 70.53%, the available potassium increases by 28.96%, the silt increases by 6.05%, and the bulk density decreases by 6.58%. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 : Actual map of the plot with two water storage devices buried (Area A is the plot without soil covering on the upper layer of the water storage device; Area B is the plot with soil covering on the upper layer of the water storage device);

[0029] Figure 2 : Schematic diagram of plot layout (Dig a 30 cm deep soil pit between trees and bury a 5000 mL wide-mouth plastic bottle water storage device, and cover the upper layer of the water storage device with 10 cm of soil);

[0030] Figure 3 : Comparison of ROCI indices and growth rates of different treatment groups. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be further described in detail below in conjunction with the embodiments and the drawings, but the embodiments of the present invention are not limited thereto.

[0032] The reagents used in the embodiments can be purchased routinely from the market without special instructions.

[0033] Example 1:

[0034] (1) Forest land selection: Select a Chinese fir forest with a simple understory structure, a canopy density > 0.8, few or no understory vegetation, the soil of the Chinese fir forest is mainly yellow soil, with a texture of clay loam, dig cross-shaped deep trenches, each cross-shaped deep trench is 20 cm wide, 30 cm deep, and the spacing is 50 cm, for later use;

[0035] (2) Litter pretreatment: Collect the fallen leaves and dead branches in the forest during October - December, after unified collection, remove the thick branches with a diameter > 5 mm, retain the fallen leaves and the thin branches with a diameter ≤ 3 mm, cut them into 1.8 - 2.2 cm segments, mix the fallen leaves and thin branches according to a volume ratio of 7:3, mix well, and sieve to remove the powder with a particle size < 0.5 cm to obtain the treated litter;

[0036] (3) Biochar preparation: Use rice straw as the raw material, crush the rice straw into particles with a size of 0.5 - 1.5 mm, pyrolyze at 600 °C, and then crush and pass through a 80 - mesh sieve to obtain biochar, for later use;

[0037] (4) Litter burial (FLB): Bury the treated litter into the cross-shaped deep trenches prepared in step (1), and the amount of litter buried is 1 kg·m -2, the litter is buried according to the method of layered burial. First, bury half of the litter at a depth of 10 cm at the bottom layer, cover it with 5 cm of soil and compact it, and then bury the remaining litter and cover it with 5 cm of soil;

[0038] (5) Water regulation (WR): After the rainy season ends, bury 2 water storage devices in each well-shaped deep ditch. The water storage device is a 5000 mL wide-mouth plastic bottle (diameter 176 mm, inner diameter 76 mm, height 316 mm) filled with water, with a 5 mm anti-mildew chemical fiber cotton rope inside. One end of the anti-mildew chemical fiber cotton rope is placed inside the bottom of the wide-mouth bottle, and the other end is evenly distributed in a cross shape at a distance of 10 cm from the soil surface. According to the principle of capillary action, supply water to the soil, regularly check the water supply efficiency of the cotton rope, and replenish the water once every 60 days;

[0039] (6) Application of biochar (BC): Take biochar at 1 kg·m -2 Apply it to the soil layer in the Chinese fir forest and plow and mix it. The mixed soil layer extends from the ground surface to a depth of 25 - 30 cm underground, and the biochar is fully mixed with the soil;

[0040] (7) Combined treatment of litter burial, water regulation and biochar application (FLB + WR + BC), the method is the same as described above in this section.

[0041] (8) Burial period: Starting from the litter burial time, it can be buried for 12 months.

[0042] Example 2:

[0043] (1) Forest land selection: Select a Chinese fir forest with a simple understory structure, canopy density > 0.8, and little or no vegetation under the forest. Dig well-shaped deep ditches, each with a width of 15 cm, a depth of 35 cm, and a spacing of 60 cm, for standby;

[0044] (2) Litter treatment: Collect the fallen leaves and dead branches in the forest during October - December, collect them uniformly, remove the thick branches, keep the fallen leaves and fine branches, cut them into 1.5 - 1.9 cm segments, mix the fallen leaves and fine branches according to a volume ratio of 6:4, mix them thoroughly, and sieve to remove powders with a particle size < 0.5 cm to obtain the treated litter;

[0045] (3) Biochar preparation: Use rice straw as the raw material, crush the rice straw into 1.5 mm particles, pyrolyze them at 500 °C, and then crush and sieve through 80 meshes to obtain biochar, for standby;

[0046] (4) Litter burial: Bury the treated litter into the well-shaped deep ditches prepared in step (1), and the buried amount of litter is 1.2 kg·m -2, the litter is buried according to the method of layered burial. First, bury half of the litter at a depth of 8 cm at the bottom layer. After covering the soil with 4 cm and compacting it, then bury the remaining litter and cover the soil with 4 cm;

[0047] (5) Moisture regulation: After the rainy season ends, bury 2 water storage devices in each well-shaped deep ditch. The water storage device is a wide-mouth plastic bottle with 6000 mL of water filled. It contains a mildew-proof chemical fiber cotton rope with a diameter of 6 mm. One end of the mildew-proof chemical fiber cotton rope is placed inside the bottom of the wide-mouth bottle, and the other end is evenly distributed in a cross shape at a distance of 8 cm from the soil surface layer. Based on the principle of capillary action, supply water to the soil. Regularly check the water supply efficiency of the cotton rope and replenish the water once every 60 days;

[0048] (6) Application of biochar: Take biochar and apply it at a rate of 0.5 kg·m -2 Apply it to the soil layer in the Chinese fir forest and plow and mix it. The mixed soil layer extends from the ground surface to a depth of 25 - 30 cm underground, and the biochar is fully mixed with the soil;

[0049] (7) Burial period: Starting from the time when the litter is buried, it can be buried for 13 months.

[0050] Example 3:

[0051] (1) Forest land selection: Select a Chinese fir forest with a simple understory structure, a canopy density > 0.8, and little or no vegetation under the forest. Dig well-shaped deep ditches, each of which is 25 cm wide, 25 cm deep, and the spacing is 40 cm, for standby;

[0052] (2) Litter treatment: Collect the fallen leaves and dead branches that have fallen in the forest from October to December, and after unified collection, remove the thick branches, retain the fallen leaves and thin branches, cut them into segments of 2.1 - 2.5 cm, and mix the fallen leaves and thin branches according to a volume ratio of 8:2, fully mix them, and sieve to remove the powder with a particle size < 0.5 cm to obtain the treated litter;

[0053] (3) Biochar preparation: Use rice straw as the raw material, crush the rice straw into particles of 0.5 mm, pyrolyze it at 700 °C, and then crush it through 80 meshes to obtain biochar, for standby;

[0054] (4) Litter burial: Bury the treated litter into the well-shaped deep ditches prepared in step (1). The buried amount of litter is 0.8 kg·m -2 , the litter is buried according to the method of layered burial. First, bury half of the litter at a depth of 12 cm at the bottom layer. After covering the soil with 6 cm and compacting it, then bury the remaining litter and cover the soil with 6 cm;

[0055] (5) Moisture regulation: After the rainy season ends, bury 2 water storage devices in each cross-shaped deep ditch. The water storage device is a wide-mouth plastic bottle with a capacity of 4000 mL filled with water, and an anti-mildew chemical fiber cotton rope with a diameter of 4 mm is placed inside. One end of the anti-mildew chemical fiber cotton rope is placed inside the bottom of the wide-mouth bottle, and the other end is evenly distributed in a cross shape at a distance of 12 cm from the soil surface to supply water to the soil based on the principle of capillary action. Regularly check the water supply efficiency of the cotton rope and replenish the water once every 60 days;

[0056] (6) Application of biochar: Take biochar and apply it at a rate of 1.5 kg·m -2 to the soil layer in the Chinese fir forest and plow and mix it. The mixed soil layer extends from the ground surface to 25 cm underground, and the biochar and soil are fully mixed;

[0057] (7) Burial period: Starting from the time of litter burial, it can be buried for 11 months.

[0058] Example 4:

[0059] (1) Forest land selection: Select a Chinese fir forest with a simple understory structure, a canopy density > 0.8, and little or no vegetation under the forest. Dig cross-shaped deep ditches, each with a width of 18 cm, a depth of 30 cm, and a spacing of 55 cm for standby;

[0060] (2) Litter treatment: Collect the fallen leaves and dead branches in the forest during October - December, collect them uniformly, remove the thick branches, retain the fallen leaves and thin branches, cut them into segments of 1.8 - 2.2 cm, mix the fallen leaves and thin branches according to a volume ratio of 8:3, mix them thoroughly, and sieve to remove powders with a particle size < 0.5 cm to obtain the treated litter;

[0061] (3) Biochar preparation: Use rice straw as the raw material, crush the rice straw into particles with a size of 0.8 mm, pyrolyze it at 650 °C, and then crush and pass through a 80 - mesh sieve to obtain biochar for standby;

[0062] (4) Litter burial: Bury the treated litter into the cross-shaped deep ditches prepared in step (1). The amount of litter buried is 1 kg·m -2 , and the litter is buried in a layered manner. First, bury half of the litter at a depth of 11 cm, cover it with 4 cm of soil and compact it, and then bury the remaining litter and cover it with 6 cm of soil;

[0063] (5) Moisture regulation: After the rainy season ends, bury 2 water storage devices in each cross-shaped deep ditch. The water storage device is a wide-mouth plastic bottle with a capacity of 5500 mL filled with water, and an anti-mildew chemical fiber cotton rope with a diameter of 4.5 mm is placed inside. One end of the anti-mildew chemical fiber cotton rope is placed inside the bottom of the wide-mouth bottle, and the other end is evenly distributed in a cross shape at a distance of 9 cm from the soil surface to supply water to the soil based on the principle of capillary action. Regularly check the water supply efficiency of the cotton rope and replenish the water once every 60 days;

[0064] (6) Application of biochar: Take biochar and apply it at 1.2 kg·m -2 into the soil layer in the Chinese fir forest and plow and mix it. The mixed soil layer extends from the ground surface to 25 - 30 cm underground, and the biochar is fully mixed with the soil;

[0065] (7) Burial period: Starting from the time when the litter is buried, it can be buried for 12 months.

[0066] Example 5:

[0067] (1) Forest land selection: Select a Chinese fir forest with a simple understory structure, a canopy density > 0.8, few or no understory vegetation. Dig cross-shaped deep trenches, each cross-shaped deep trench is 22 cm wide, 32 cm deep, and the spacing is 45 cm for standby;

[0068] (2) Litter treatment: Collect the fallen leaves and dead branches in the forest during October - December, uniformly collect them, remove the thick branches, keep the fallen leaves and thin branches, cut them into 1.8 - 2.2 cm segments. The fallen leaves and thin branches are mixed according to a volume ratio of 7:2, fully mixed, and screened to remove powders with a particle size < 0.5 cm to obtain the treated litter;

[0069] (3) Biochar preparation: Use rice straw as the raw material, crush the rice straw into 1.2 mm particles, pyrolyze at 550 °C, and then crush and pass through 80 - mesh to obtain biochar for standby;

[0070] (4) Litter burial: Bury the treated litter into the cross-shaped deep trenches prepared in step (1). The burial amount of litter is 1 kg·m -2 , and the litter is buried by the method of layered burial. First, bury half of the litter at a depth of 10 cm at the bottom layer, cover it with 5 cm of soil and compact it, and then bury the remaining litter and cover it with 5 cm of soil;

[0071] (5) Water regulation: After the rainy season ends, install 2 water storage devices in each cross-shaped deep trench. The water storage device is a wide-mouth plastic bottle filled with 4500 mL of water, with a mildew-proof chemical fiber cotton rope with a diameter of 5.5 mm inside. One end of the mildew-proof chemical fiber cotton rope is placed inside the bottom of the wide-mouth bottle, and the other end is evenly distributed in a cross shape at a distance of 11 cm from the soil surface. Based on the principle of capillary action, supply water to the soil, regularly check the water supply efficiency of the cotton rope, and fill it up once every 60 days;

[0072] (6) Application of biochar: Take biochar and apply it at 0.7 kg·m -2 into the soil layer in the Chinese fir forest and plow and mix it. The mixed soil layer extends from the ground surface to 25 - 30 cm underground, and the biochar is fully mixed with the soil;

[0073] (7) Burial period: Starting from the time when the litter is buried, it can be buried for 12 months.

[0074] The inventor conducted the following experiments to verify the effects of the present invention:

[0075] 1 Plot selection and design

[0076] Select site conditions with basically the same slope, aspect, altitude, and ecosystem community structure, and establish a field test monitoring point - Puding County (105°36′13″E, 26°12′26″N). Taking the Chinese fir forest ecosystem, which is widely distributed and typical in the karst area of Guizhou, as the research object, select a simple understory structure with a canopy density greater than 0.8, few or no understory vegetation, and try not to change the original vegetation community structure. The soil type of the test site is mainly yellow soil with a texture of clay loam.

[0077] 1.1 Treatment group design

[0078] The experiment was set with 5 treatments and a randomized block design with 3 replicates, for a total of 15 experimental plots. The size of each plot is 3m * 3m, and a 1.0m buffer zone is set between plots. The specific conditions of each treatment are shown in Table 1, and the layout effect of the plots is as Figure 1 and Figure 2 shown.

[0079] FLB (Litter Burial) preparation: After uniformly collecting the fallen leaves and dead branches in the forest, remove the thick branches with a diameter > 5mm, retain the fallen leaves and thin branches (diameter ≤ 3mm), cut them into segments of 2cm ± 0.5cm, mix the fallen leaves and dead branches in a volume ratio of 7:3, mix well, and sieve to remove the powder (particle size < 0.5cm). Uniformly dig 30cm deep trenches in each treatment plot, bury the weighed litter, with a dosage of 1kg·m -2 (10t·ha -1 ), and 9m for each treatment 2 for a total of 9kg.

[0080] WR (Water Regulation) preparation: Dig 30cm deep soil pits between the trees and bury a wide-mouth plastic bottle with a water storage capacity of 5000mL (inner diameter 76mm, bottle body diameter 176mm, total height 316mm). Place a water-absorbing cotton rope (mildew-proof chemical fiber cotton rope, diameter 10mm) at the bottom of the bottle to supply water to the soil based on the principle of capillary action. The water-absorbing cotton rope is evenly distributed in a "cross" shape at a depth of 5cm on the soil surface, and 2 water storage devices are set for each treatment.

[0081] BC (Biochar Application): Using the straw of the local main crop, rice, as the raw material, pre-treat it into 1mm rice straw with a pulverizer, and prepare biochar (pH = 9.23, moisture 5%, containing about 16.60% SOC, particle size 80 mesh) by pyrolysis at 600°C, at a rate of 1kg·m -2(10 t·ha -1 ) was applied to the 0 - 30 cm soil layer and plowed and mixed. The biochar was fully mixed with the soil, and the application rate was 1 kg·m -2 (10 t·ha -1 ).

[0082] Litter burial in layers: 10 cm of litter at the bottom (0.5 kg·m -2 ), and after covering and compacting the soil, another 0.5 kg·m -2 of litter was laid in the middle layer.

[0083] Arrangement of water storage devices: Cotton ropes were distributed in a "rice" shape in the top 10 cm of soil, with 2 devices for each treatment.

[0084] The combined treatment was FLB + WR + BC, that is, litter burial + water regulation + biochar application treatment.

[0085] 1.2 Specific experimental procedures

[0086] Plot construction: A Chinese fir forest with consistent site conditions was selected in Puding County, Guizhou (105°36′13″E, 26°12′26″N). The plots were divided into small areas of 3 m×3 m, and a buffer zone of more than 1 m was set up.

[0087] Litter treatment: Litter was collected from October to December and buried in layers in a "well" - shaped ditch network (single ditch width 20 cm, depth 30 cm, spacing 50 cm).

[0088] Water regulation: After the rainy season ended, water storage devices were buried, the water supply efficiency of the cotton ropes was regularly checked, and the water was replenished to full once every 60 days.

[0089] Biochar application: The biochar was evenly applied to the soil and plowed to avoid concentrated accumulation.

[0090] 2 Data monitoring: The soil total organic carbon (SOC), recalcitrant organic carbon index (ROCI), and soil physical and chemical properties (total nitrogen, total phosphorus, available potassium, etc.) were measured according to standard methods, and the data were recorded in Tables 1 and 2.

[0091] 2.1 Index detection: The determination of the mechanical composition of forest soil was carried out in accordance with the forestry industry standard (LY / T 1225 - 1999). The sand particles had a particle size of (2 - 0.05 mm); SOC was determined by the dichromate titration method; total nitrogen (TN), total phosphorus (TP), and total potassium (TK) were determined by soil physical and chemical analysis methods (Bao Shidan. Soil Agricultural Chemistry Analysis (Third Edition) [M]. Beijing: China Agricultural Press, 2010); pH was determined by extracting the supernatant with a soil - water mass ratio of 2.5:1; bulk density (BD) was measured using the core - cutter method (100 cm 3),The soil sample around the cutting edge of the soil knife is cut, covered at both ends, and weighed accurately to 0.01 g.

[0092] 2.2 Recalcitrant organic carbon (ROC), ROC is the main indicator of the stable carbon pool in the soil, and is measured by a two-step acid digestion method: After air-drying the soil, pass it through a 100-mesh soil sieve, and add 5 mL of 1 mol / L hydrochloric acid for acidification. Take 0.5 g of the acidified soil sample, add 20 mL of 5 mol / L sulfuric acid, hydrolyze at 105 °C for 30 min, recover the upper-layer solution, wash the lower-layer precipitate with water, and collect the upper-layer solution together. Dry the washed precipitate at 55 °C, add 2 mL of 26 mol / L sulfuric acid, let it stand overnight at room temperature, dilute it with water to 2 mol / L, and shake continuously to obtain a precipitate. Wash the obtained precipitate with water and dry it to measure the soil organic carbon content, which is the recalcitrant carbon (ROC). Use the recalcitrant organic carbon index (ROCI) to evaluate the stability of the soil carbon pool, ROCI = ROC / SOC × 100%.

[0093] 3 Technical effects and experimental data

[0094] Carbon stability:

[0095] After 12 months of implementation, the total soil organic carbon (SOC) value of the CK treatment soil is 40.65 ± 1.13 g·kg -1 , and the SOC of the FLB+WR+BC treatment increases by 1.23 - 2.06 g·kg -1 . The recalcitrant organic carbon index (ROCI) value of the CK treatment soil is 64.96 ± 0.86%, and the ROCI of the FLB+WR+BC treatment increases by 2.2 - 2.7%.

[0096] Soil improvement effect: Compared with the control group CK treatment, the total phosphorus of the FLB+WR+BC treatment soil increases by 2.62%, the total potassium increases by 6.52%, the available nitrogen increases by 0.43%, the available phosphorus increases by 70.53%, the available potassium increases by 28.96%, the silt increases by 6.05%, and the bulk density decreases by 8.10%.

[0097] Table 1 Basic physical and chemical properties of each treatment group 1

[0098]

[0099] Table 2 Basic physical and chemical properties of each treatment group 2

[0100]

Claims

1. A regulation method for stabilizing carbon sequestration and increasing carbon sink in the soil of Chinese fir forests in karst areas, characterized in that: It includes the following steps: (1) Forest land selection: Select a Chinese fir forest with a simple understory structure, a canopy density > 0.8, and little or no vegetation under the forest. Dig cross-shaped deep trenches, each cross-shaped deep trench being 15 - 25 cm wide, 25 - 35 cm deep, and with a spacing of 40 - 60 cm, for standby; (2) Litter pretreatment: Collect the fallen leaves and dead branches in the forest during October - December and collect them uniformly. Then, remove the thick branches, retain the fallen leaves and thin branches, cut them into 1.5 - 2.5 cm segments. The fallen leaves and thin branches are mixed in a volume ratio of 6 - 8:2 - 4, fully mixed, and screened to remove powders with a particle size < 0.5 cm to obtain the treated litter; (3) Biochar preparation: Using rice straw as the raw material, crush the rice straw into particles with a size of 0.5 - 1.5 mm, pyrolyze at 500 - 700 °C, and then crush and pass through a 80 - mesh sieve to obtain biochar, for standby; (4) Litter burial: bury the processed litter into the well-shaped deep trenches prepared in step (1), and the amount of litter buried is 0.8 - 1.2 kg·m -2 , and the litter is buried in a stratified manner. First, bury half of the litter at a depth of 8 - 12 cm at the bottom layer. After covering with soil 5 - 10 cm and compacting it, then bury the remaining litter and cover it with soil 4 - 6 cm, and that's it; (5) Moisture regulation: After the rainy season ends, bury 2 water storage devices in each cross-shaped deep trench. The water storage device is a wide - mouth plastic bottle filled with 4000 - 6000 mL of water, with a mildew - proof chemical fiber cotton rope with a diameter of 4 - 6 mm inside. One end of the mildew - proof chemical fiber cotton rope is placed inside the bottom of the wide - mouth bottle, and the other end is evenly distributed in a cross - shape at a distance of 8 - 12 cm from the soil surface layer. Based on the principle of capillary action, supply water to the soil, regularly check the water supply efficiency of the cotton rope, and refill the water once every 55 - 65 days. (6) Application of biochar: Take biochar at 0.5 - 1.5 kg·m -2 Apply it to the soil layer in the Chinese fir forest and plow and mix it. The mixed soil layer extends from the ground surface to 25 - 30 cm underground, and the biochar is fully mixed with the soil; (7) Burial period: Starting from the time of litter burial, bury for 11 - 13 months.

2. The regulation method for stabilizing carbon sequestration and increasing carbon sink in the soil of Chinese fir forests in karst areas according to claim 1, characterized in that: In step (1), each cross - shaped deep trench is 20 cm wide, 30 cm deep, and has a spacing of 50 cm.

3. The regulation method for stabilizing carbon sequestration and increasing carbon sink in the soil of Chinese fir forests in karst areas according to claim 1, wherein: In step (1), the soil of the Chinese fir forest is mainly yellow soil, with a texture of clay loam.

4. The regulation method for stabilizing carbon sequestration and increasing carbon sink in the soil of Chinese fir forests in karst areas according to claim 1, characterized in that: In step (2), the litter treatment: Collect the fallen leaves and dead branches in the forest during October - December and collect them uniformly. Then, remove thick branches with a diameter > 5 mm, retain the fallen leaves and thin branches with a diameter ≤ 3 mm, cut them into 1.8 - 2.2 cm segments. The fallen leaves and thin branches are mixed in a volume ratio of 6.5 - 7.5:2.5 - 3.5, fully mixed, and screened to remove powders with a particle size < 0.5 cm to obtain the treated litter.

5. The regulation method for stabilizing carbon sequestration and increasing carbon sink in the soil of Chinese fir forests in karst areas according to claim 4, characterized in that: In step (2), the litter treatment: Collect the fallen leaves and dead branches in the forest during October - December and collect them uniformly. Then, remove thick branches with a diameter > 5 mm, retain the fallen leaves and thin branches with a diameter ≤ 3 mm, cut them into 1.8 - 2.2 cm segments. The fallen leaves and thin branches are mixed in a volume ratio of 7:3, fully mixed, and screened to remove powders with a particle size < 0.5 cm to obtain the treated litter.

6. The regulation method for stabilizing carbon sequestration and increasing carbon sink in the soil of Chinese fir forests in karst areas according to claim 1, wherein: In step (3), the biochar preparation: Using rice straw as the raw material, crush the rice straw into particles with a size of 1 mm, pyrolyze at 600 °C, and then crush and pass through a 80 - mesh sieve to obtain biochar, for standby.

7. The regulation method for stabilizing carbon sequestration and increasing carbon sink in the soil of Chinese fir forests in karst areas according to claim 1, characterized in that: In step (4), the litter burial: bury the processed litter into the well-shaped deep ditch prepared in step (1), and the amount of litter buried is 1 kg·m -2 , and the litter is buried by the method of layered burial. First, bury half of the litter at a depth of 10 cm at the bottom layer. After covering the soil with 5 cm and compacting it, then bury the remaining litter and cover the soil with 5 cm. That's all.

8. The regulation method for soil carbon sequestration enhancement in Chinese fir forests in karst areas according to claim 1, characterized in that: In step (5), for the moisture regulation: after the rainy season ends, bury 2 water storage devices in each well-shaped deep ditch. The water storage device is a 5000 mL wide-mouth plastic bottle filled with water, with a 5 mm diameter mildew-proof chemical fiber cotton rope placed inside. One end of the mildew-proof chemical fiber cotton rope is placed inside the bottom of the wide-mouth bottle, and the other end is evenly distributed in a cross shape at a position 10 cm away from the soil surface. Based on the principle of capillary action, water is supplied to the soil. Regularly check the water supply efficiency of the cotton rope and refill the water once every 60 days.

9. The regulation method for stabilizing carbon sequestration and increasing carbon sink in the soil of Chinese fir forests in karst areas according to claim 1, wherein: In step (6), applying biochar: Take biochar at 1 kg·m -2 Apply it to the soil layer in the Chinese fir forest and plow and mix it. The mixed soil layer extends from the ground surface to 25 - 30 cm underground, and the biochar is fully mixed with the soil.

10. The regulation method for soil carbon sequestration enhancement in Chinese fir forests in karst areas according to claim 1, characterized in that: In step (7), for the burial period: starting from the time when the litter is buried, it can be buried for 12 months.

Images