Method for increasing content of organic carbon in purple soil

Abstract

A planting method for increasing the content of organic carbon in purple soil. White clover and ryegrass are separately compound-planted with tea oil camellia, and then the compound-planted white clover and ryegrass are all returned to the soil. The planting method can promote the formation of macro-aggregates in purple soil, improve aggregate stability, and facilitate the accumulation of organic carbon in purple soil. In addition, the binding of particulate organic carbon to minerals within macro-aggregates can be increased, thereby further improving the stability of organic carbon in purple soil by means of mineral protection, and significantly improving the carbon sequestration capacity of purple soil.

Description

A method to increase the organic carbon content of purple soil Technical Field

[0001] This invention belongs to the field of soil improvement technology and relates to a method for increasing the organic carbon content of purple soil through agroforestry management of camellia oleifera. Background Technology

[0002] Purple soil is mainly distributed in the basins, hills, and low mountainous areas of Hunan, Sichuan, and Yunnan provinces. It is rich in minerals and has a certain fertility, making it suitable for planting cold-resistant and barren-tolerant economic trees such as camellia oleifera. However, due to its weak weathering, soft texture, and loose structure, coupled with uneven terrain and rainfall, purple soil is prone to soil erosion. This results in poor soil structure, severe nutrient loss, and low soil fertility, which greatly limits the growth of camellia oleifera.

[0003] Soil organic carbon is the core of soil fertility, and its content and stability are the result of multiple factors. The physical protection of soil aggregates reduces the contact between organic carbon and microorganisms, lowering the probability of its decomposition. Therefore, the formation and stability of aggregates significantly affect the sequestration of soil organic carbon. Clay minerals and iron-aluminum oxides in the soil can fix organic carbon on the mineral surface through adsorption and co-precipitation, enhancing its stability. This mineral protection is also one of the key mechanisms for the stable storage of soil organic carbon. Therefore, effective measures can be taken to improve the physical protection of soil aggregates and the mineral protection of organic carbon, thereby increasing the organic carbon content of purple soil. This is of great significance for improving soil structure, enriching purple soil fertility, and promoting the growth of camellia oleifera.

[0004] Agroforestry is a mixed planting method that combines different plants at the same growth stage within the same plot of land. Intercropping can increase vegetation cover, improve soil structure, and reduce the risk of soil erosion, making it an important measure to prevent soil erosion and nutrient loss on sloping farmland. In recent years, intercropping has played a significant role as an important technology for improving soil quality. However, due to the influence of soil type, intercropped plant types, and intercropped plant management methods, different intercropping patterns in different regions have varying impacts on soil organic carbon. Based on the characteristics of purple soil and the influence of aggregate physical and mineral protection on the formation and stability of organic carbon, selecting suitable intercropped plants and adopting reasonable management methods for intercropped plants are of great significance for increasing the organic carbon content of purple soil. Summary of the Invention

[0005] The purpose of this invention is to provide a method for increasing the organic carbon content of purple soil. This method involves initially planting herbaceous plants under camellia oleifera forests, and then returning all the planted herbaceous plants to the field in the later stages. This provides a method to increase the organic carbon content and stability of purple soil by promoting the formation of large soil aggregates and synergistically enhancing the physical and mineral protection capabilities of these aggregates.

[0006] This invention provides a method for increasing the organic carbon content of purple soil. The technical solution adopted to achieve the above objective is as follows:

[0007] (1) Leveling and tilling the purple soil camellia forest land: Till and level the camellia forest land with a plant spacing of 2m x 3m and a planting density of 100 trees per mu, remove weeds and stones and other debris, till to a depth of 25cm, and apply nitrogen fertilizer (urea) and phosphorus fertilizer (superphosphate) at a rate of 6.67kg per mu.

[0008] (2) Intercropping with herbaceous plants in Camellia oleifera forests: Intercropping with herbaceous plants can increase root exudates, improve soil structure, promote the formation of large aggregates, and enhance aggregate stability. Specifically, white clover and ryegrass are intercropped in strips under the Camellia oleifera forest, with a seeding density of approximately 5 kg per mu. The strips are broadcast vertically at the outer edge of the Camellia oleifera canopy, with a sowing width of 2 m. One month after sowing, a compound fertilizer is applied at a rate of 10 kg per mu. The compound fertilizer contains 20% nitrogen, 15% phosphorus pentoxide, and 15% potassium oxide.

[0009] (3) All herbaceous plants in the intercropping: White clover and ryegrass in the intercropping are not cut and are directly returned to the field. After the plant residues are decomposed, they further increase the input of organic carbon, improve the soil structure, increase the content of mineral-bound organic carbon in the aggregates, and enhance the mineral protection effect on soil organic carbon.

[0010] (4) Improve soil aggregate stability and organic carbon mineral protection: The intercropping of herbaceous plants and the return of herbaceous plants to the field both promote the formation of large soil aggregates, improve aggregate stability, increase the content of mineral-bound organic carbon in aggregates, and synergistically enhance the physical and mineral protection capabilities of aggregates, thereby increasing the soil organic carbon content.

[0011] The beneficial effects of this invention are as follows:

[0012] This invention promotes the formation of large soil aggregates by initially intercropping white clover and ryegrass under camellia oleifera forests, followed by returning all intercropped herbaceous plants to the soil in the later stage. This improves the stability of soil aggregates and enhances their physical protection of organic carbon. Simultaneously, this technique significantly promotes the accumulation of mineral-bound organic carbon in fine and micro-aggregates, enhancing the mineral protection of organic carbon within the aggregates, increasing the organic carbon content of purple soil, and effectively improving soil fertility. The method of this invention increased the organic carbon content of purple soil by 24.7% and 13.3% (intercropping with white clover), and 26.4% and 17.2% (intercropping with ryegrass) during the intercropping and returning-to-soil stages, respectively. Attached Figure Description

[0013] Figure 1: Effects of intercropping on soil aggregate structure and stability

[0014] Figure 2: Effects of intercropping on soil aggregate organic carbon composition

[0015] Figure 3: Relationship between total soil organic carbon, soil aggregates, and organic carbon components

[0016] In Figures 1-3: different capital letters represent significant differences in the same Camellia oleifera planting pattern at different time periods, and different lowercase letters represent significant differences between different Camellia oleifera planting patterns within the same time period (p<0.05). Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1:

[0019] The study focused on Camellia oleifera forests in the middle-aged stage in typical purple soil areas, with a planting density of 100 trees per mu and a spacing of 2m x 3m between trees.

[0020] Leveling and tilling the purple soil of the camellia oleifera forest: Till and level the camellia oleifera forest, remove weeds and stones and other debris. The tilling depth is 25cm. Apply nitrogen fertilizer (urea) and phosphorus fertilizer (superphosphate) at a rate of 6.67kg per mu.

[0021] 1. Intercropping of Camellia oleifera forests with herbaceous plants: After tilling and fertilization, intercropping plots are divided, each maintaining a consistent slope and topography. Each plot measures 3m x 18m and contains 15 Camellia oleifera trees. Each intercropping pattern includes five repeating plots. White clover and ryegrass are intercropped in strips under the Camellia oleifera trees, with a seeding density of approximately 5 kg per acre. The seeds are broadcast in strips at vertical points on the outer edge of the Camellia oleifera canopy, with a sowing width of 2m. One month after sowing, a compound fertilizer containing 20% ​​nitrogen, 15% phosphorus pentoxide, and 15% potassium oxide is applied at a rate of 10 kg per acre.

[0022] 2. All herbaceous plants in intercropping should be returned to the field: White clover and ryegrass planted in intercropping should not be cut and should be returned to the field in their entirety. The main reason for returning them to the field without cutting is to reduce the damage to soil aggregates caused by human trampling, thereby avoiding affecting the physical protection of organic carbon by the aggregates. After the plant residues decompose, they further increase the input of organic carbon, improve soil structure, increase the content of mineral-bound organic carbon in the aggregates, and enhance the mineral protection of soil organic carbon.

[0023] 3. Improve soil aggregate stability and organic carbon mineral protection: Intercropping with herbaceous plants and returning herbaceous plants to the field both promote the formation of large soil aggregates, improve aggregate stability, increase the content of mineral-bound organic carbon in aggregates, and synergistically enhance the physical and mineral protection capabilities of aggregates, thereby increasing the soil organic carbon content.

[0024] Figure 1 shows the effects of intercropping on soil aggregate structure and stability. The effects of herbaceous plant intercropping and returning to the field on the soil aggregate structure and stability characteristics of Camellia oleifera soil were analyzed. Soil samples were collected from Camellia oleifera forests using a five-point sampling method. Three undisturbed soil samples were randomly collected from under the canopy of Camellia oleifera trees in each plot. Larger soil clods were gently broken apart along cracks, and fallen leaves, stones, and other debris were removed. The samples were then placed in a naturally ventilated area to air dry for the determination of soil aggregate characteristic indicators.

[0025] The soil aggregate grading method is as follows: First, the completely air-dried undisturbed soil sample is divided into uniformly sized blocks. 100 grams of each block is weighed and evenly spread on the sieves of a water-stable aggregate analyzer (the sieves are arranged from top to bottom in the order of 2mm, 0.25mm, and 0.053mm). Next, the sieves are slowly placed into the wet sieve container, with the water level below the edge of the top sieve. After soaking for 5 minutes, the sample is shaken up and down for 15 minutes (amplitude 3 cm, frequency 30 times / minute), ensuring the top sieve is completely submerged in water during shaking. After completing the sieving step, the aggregates on the sieves are completely rinsed into an aluminum box with distilled water. The remaining <0.053mm particles are allowed to settle completely. The supernatant is then carefully removed, and the turbid water-soil solution is transferred to a beaker. A second settling is performed in the beaker, and after removing the supernatant, the solution is transferred to the aluminum box and dried at 50℃ for later use. The following aggregates were obtained: coarse aggregates >2 mm, fine aggregates 2-0.25 mm, micro-aggregates 0.25-0.053 mm, and powder-sticky aggregates <0.053 mm.

[0026] Soil aggregate stability index calculation method: Using data on the mass percentage of aggregates of various particle sizes, soil aggregate stability indices are calculated, including mean weight diameter (MWD) and geometric mean diameter (GMD).

[0027] In the formula, Xi represents the average diameter (mm) of the i-th soil aggregate, Mi represents the mass (g) of the i-th aggregate, and Mt represents the mass (g) of all aggregates.

[0028] As shown in Figure 1, the agroforestry management model significantly increased the proportion of large soil aggregates and significantly decreased the proportion of micro-aggregates and silty-clay aggregates, indicating that agroforestry promoted the formation of large soil aggregates. Furthermore, the intercropping of herbaceous plants increased the average weight diameter and geometric mean diameter of soil aggregates, enhancing the physical protection of soil organic carbon by these aggregates.

[0029] Figure 2 shows the effect of intercropping on the organic carbon composition of soil aggregates. Particulate organic carbon is easily decomposed and mineralized, while mineral-bound organic carbon is tightly bound to clay minerals and iron and aluminum oxides in the soil, exhibiting high stability. Therefore, the higher the content of mineral-bound organic carbon in soil aggregates, the stronger the mineral protection effect on soil organic carbon, which is conducive to the accumulation of soil organic carbon.

[0030] Organic carbon components within soil aggregates were separated using a particle size grouping method: 5g of soil aggregates with particle sizes of 2-0.25mm and 0.25-0.053mm were weighed and placed in separate 100ml plastic bottles. 50ml of a 0.5% sodium hexametaphosphate solution was added, and the mixture was gently shaken until homogeneous. Then, 10-12 glass beads (6mm in diameter) were added, and the mixture was shaken on a reciprocating shaker for 16-18 hours (180rpm). The thoroughly shaken soil solution was passed through a 0.053mm sieve, and the residue on the sieve was repeatedly rinsed with pure water until the solution was clear. The component remaining on the sieve (>0.053mm) was particulate organic carbon, while the component passing through the sieve (<0.053mm) was mineral-bound organic carbon. The samples were collected, dried at 50℃, weighed, ground, and passed through a 100-mesh sieve for organic carbon content determination.

[0031] As shown in Figure 2, intercropping increased the total organic carbon content, the particulate organic carbon content in aggregates with a diameter of >0.25 mm, and the mineral-bound organic carbon content in aggregates with a diameter of <0.25 mm. In particular, the mineral-bound organic carbon content in the intercropping soil was significantly higher than that in the soil with Camellia oleifera monoculture, indicating that the intercropping of herbaceous plants enhanced the mineral protection of organic carbon in the aggregates, which is conducive to the accumulation and stability of soil organic carbon.

[0032] Figure 3 shows the relationship between total soil organic carbon, soil aggregates, and organic carbon components.

[0033] As shown in Figure 3, total soil organic carbon (TOC) exhibits a highly significant positive correlation with the percentage of macroaggregates, average weight diameter, and geometric mean diameter (p<0.001). The degree of protection of soil organic carbon is determined by the cementation and aggregation processes of soil particles, and the formation and stability of macroaggregates play a crucial role in the accumulation of TOC. TOC content increases with increasing macroaggregate particle organic carbon content and macroaggregate mineral organic carbon content, reaching significant (p<0.05) and highly significant (p<0.001) levels, respectively. Macroaggregate particle organic carbon mainly originates from fresh organic matter such as plant residues and root exudates. These substances undergo preliminary decomposition and transformation by microorganisms in the soil, forming relatively stable particle organic carbon. Mineral organic carbon, on the other hand, is a complex formed by organic carbon and soil minerals through chemical bonding and surface adsorption. As the content of these two types of organic carbon in soil macroaggregates increases, the TOC content accumulates accordingly.

Claims

1. A method for increasing the organic carbon content of purple soil, characterized in that, Includes the following steps: (1) Leveling and tilling the purple soil camellia oleifera forest land; (2) Intercropping of Camellia oleifera forests with herbaceous plants; (3) All herbaceous plants grown in the intercropping program are returned to the field; (4) Improve the stability of soil aggregates and the protective effect of organic carbon minerals.

2. The method according to claim 1, wherein: Step (1) of leveling and tilling the purple soil camellia oleifera forest land includes: The planting spacing for camellia oleifera is 2m x 3m, with a planting density of 100 plants per mu (approximately 667 square meters). The camellia oleifera forest land is tilled and leveled, and weeds, stones, and other debris are removed. The tilling depth is 25cm. Nitrogen fertilizer (urea) and phosphorus fertilizer (superphosphate) are applied at a rate of 6.67kg per mu.

3. The method according to claim 1, wherein: The herbaceous plants mentioned in step (2) include white clover and ryegrass, which are planted in strips under the camellia oleifera forest. The seeding density of white clover or ryegrass is about 5 kg per mu, and the seeds are sown in strips at vertical points on the outer side of the camellia oleifera forest canopy, with a sowing width of 2 m. One month after sowing, a compound fertilizer is applied at a rate of 10 kg per mu, which contains 20% nitrogen, 15% phosphorus pentoxide, and 15% potassium oxide.

4. The method according to claim 1, wherein: Step (3) involves returning all the herbaceous plants in the intercropping to the field, which means that the white clover and ryegrass in the intercropping are not cut and all the plants are returned to the field.

5. The method according to claim 1, wherein: Step (4) describes the improvement of soil aggregate stability and the protection of organic carbon minerals, which includes: during the vigorous growth period of herbaceous plants and after returning the soil to the field, the soil aggregates, the average weight diameter of the aggregates, the geometric mean diameter, and the content of mineral-bound organic carbon in the aggregates.

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