A method for applying a soil amendment for acidification of southern forest soils

Abstract

The application belongs to the field of soil improvement, and relates to a method for applying a modifier for soil acidification in southern forests, by which goethite as a mineral modifier can effectively increase soil pH, adjust soil acidity, improve soil carbon sink capacity, comprehensively improve the plant habitat, and further promote plant growth, so as to simultaneously realize soil habitat improvement and ecological function improvement of the southern forests.

Description

Technical Field

[0001] This invention belongs to the field of soil improvement, and relates to the application method of a soil conditioner for soil acidification in southern forests, and more particularly to the application method of a soil conditioner for improving soil acidification and enhancing carbon sequestration capacity in southern forests. Technical Background

[0002] Soil habitat restoration is beneficial for improving the quality of plantations and enhancing their ecosystem services. In the mountainous forests of southern China, irrational management and human activities have exacerbated acid rain problems, leading to particularly prominent soil acidification issues in the red soil regions: such as decreased available nutrient content, deterioration of soil health, and weakened ecological functions. It is well known that the large-scale combustion of fossil fuels in industrial, transportation, and energy production releases sulfur oxides and nitrogen oxides, which form acid rain in the atmosphere and eventually fall into the soil, causing soil acidification. In addition, natural factors can also contribute to soil acidification. For example, different types of vegetation have different effects on soil pH. Organic acids secreted by the roots of some plants can lower the soil pH, creating acidic soils. Coniferous species such as pine and fir trees are particularly prone to soil acidification. Furthermore, heavy rainfall in southern China can wash away alkaline substances from the soil, further increasing soil acidity. Dissolved carbon dioxide in rainfall can also form carbonic acid, further intensifying soil acidity. This results in a series of problems, including reduced soil fertility and weakened ecological functions. Faced with the vast and serious problem of soil acidification, research on soil acidification improvement technology has always been an important and comprehensive topic in the field of soil science. The research on soil acidification improvement technology in low-quality and low-efficiency forests involves multiple fields such as soil chemistry, biology, and forestry science, and is therefore a complex research system.

[0003] In numerous studies on soil conditioners, inorganic and organic acidic soil conditioners such as quicklime, organic fertilizer, and biochar have been explored (see Non-Patent Literature 1, 2). It was found that although applying these conditioners alone can increase the soil pH value to a certain extent and improve the problem of forest soil acidification, these studies have ignored the feedback process between soil acidification improvement and ecological function enhancement, and have failed to synergistically solve problems such as declining available nutrient content, deterioration of soil health, and low soil ecological service function.

[0004] Non-patent literature:

[0005] 1. Research progress on iron-mediated soil organic carbon sequestration and mineralization [J]. Advances in Earth Science, 2021, 36(12): 1-10.

[0006] 2. Effects of mineral conditioner dosage on nutrient status in acidic soil and rapeseed growth [J]. Chinese Journal of Soil and Fertilizer, 2021, 3. Summary of the Invention

[0007] Based on the aforementioned problems, researchers, through optimization and innovation of neutralizing agents, have discovered a new type of soil conditioner—iron oxides—that neutralizes acidity and enhances soil carbon sequestration. As a novel mineral conditioner, it has been found to effectively alleviate soil acidification. The study also revealed that iron oxides possess a neutralizing effect, reacting with excess hydrogen ions in the soil to form water and release corresponding metal ions, thereby neutralizing soil acidity. Furthermore, iron oxides can reduce soil acidity by maintaining charge balance, participating in redox reactions in the soil, and in the cementation and aggregation of soil particles. Among these, goethite, a hydrated iron oxide with the chemical formula FeO(OH), was found to be an effective soil conditioner. Goethite has a high pH value, typically between 7.5 and 9. When added to the soil, goethite reacts with acidic substances, neutralizing them and thus increasing the soil pH. Furthermore, goethite carries a positive charge on its surface, which can adsorb negatively charged ions in the soil, including hydrogen ions (H+), thereby reducing the H+ concentration in the soil and increasing the soil pH. It has also been found that, compared to traditional quicklime, goethite, as a mineral conditioner, can effectively increase soil pH, regulate soil acidity, and enhance soil carbon sequestration capacity, comprehensively improving plant habitats, promoting plant growth, and ultimately enhancing the function of low-quality and low-efficiency plantations.

[0008] To achieve the above objectives, the present invention provides a method for applying an amendment to improve soil acidification in southern forests, the specific steps of which are as follows:

[0009] ① Preparation of the modifier goethite: 1 mol·L -1 FeCl3·6H2O solution and 1 mol·L -1 NaOH was mixed and titrated to a pH of 12. After being kept in a water bath at 70°C for 60 hours, the mixture was washed with ultrapure water and then processed by precipitation, freezing, and drying to obtain goethite. The goethite product was sealed and stored at room temperature for later use.

[0010] ② Collect soil samples from the top 20cm of the forest and determine the total iron content, bulk density and pH value of the soil samples;

[0011] ③ Using the data obtained in step ②, calculate the total iron content in the surface soil per unit area;

[0012] ④ Based on the soil total iron content measured in step ③, and the soil weight per unit area of ​​surface soil obtained from the soil bulk density, clean up the surface litter in the sample plot and set it aside, then add the goethite obtained in step ① in situ to make the soil total iron content reach 25% to 50%.

[0013] ⑤ After adding goethite in step ④ above, restore the original litter on the ground to its initial state;

[0014] ⑥ Measure the surface carbon flux after step ⑤ above is completed every half month using the static box method. The monitoring period is 1 year, and the data is recorded.

[0015] ⑦ One year after completing step ⑥ data recording, collect surface soil samples from the treated area and surrounding untreated areas, and measure soil pH, nitrogen and phosphorus available nutrient content, as well as soil microbial biomass and enzyme activity to evaluate soil acidification improvement and carbon sequestration enhancement capabilities.

[0016] In step ④, goethite with a total iron content of 28% to 45% is added in situ to the soil from step ①.

[0017] Regarding the mechanism of action of goethite: Goethite has a high pH value, typically between 7.5 and 9. When goethite is added to the soil, it reacts with acidic substances in the soil, neutralizing them and thus increasing the soil pH. Furthermore, goethite has a positively charged surface, which can adsorb negatively charged ions in the soil, including hydrogen ions (H+), thereby reducing the H+ concentration in the soil and further increasing the soil pH. Simultaneously, as an iron oxide, goethite has a large specific surface area and strong adsorption affinity. Through adsorption or co-precipitation, it combines with SOCs to form iron, thus binding organic carbon and constituting a unique mineral protection mechanism for SOCs, improving SOC stability and enhancing soil carbon sequestration capacity. In addition, iron oxides can also act as a cementing agent for clay and organic carbon, promoting the formation of soil micro-aggregates and improving soil structure and permeability. The strength of the aggregation effect is related to the type of iron oxide. Because goethite has more hydroxyl groups on its surface, it is more conducive to binding with minerals such as kaolinite, resulting in a stronger cementing effect on the soil, which is more beneficial for enhancing soil carbon stability.

[0018] Invention Effects

[0019] According to the present invention, a method for applying a soil conditioner for soil acidification in southern forests is provided. Experimental results after one year of application show that the conditioner, containing goethite, significantly increases soil pH. Furthermore, monitoring soil carbon emission flux using a static chamber method after application reveals that the addition of iron oxides significantly inhibits soil carbon release intensity while simultaneously enhancing carbon sequestration capacity. Therefore, this mineral conditioner can effectively increase soil pH, regulate soil acidity, and enhance soil carbon sequestration capacity, comprehensively improving plant habitats and promoting plant growth, thus simultaneously improving soil habitats and enhancing ecological functions in southern forests. Attached Figure Description

[0020] Figure 1Image of the goethite modifier prepared according to this invention. Detailed Implementation

[0021] The specific method for applying the soil conditioner for soil acidification in southern forests according to the present invention is described below.

[0022] 1. Laboratory preparation of goethite: 1 mol·L⁻¹ -1 FeCl3·6H2O solution and 1 mol·L -1 NaOH was mixed and titrated to a pH of 12. After incubating in a water bath at 70°C for 60 hours, the solution was washed with ultrapure water. Goethite can be obtained by precipitation, freeze-drying, and then stored in a sealed container at room temperature. The properties of the obtained goethite are as follows. Figure 1 As shown, it is a lemon-yellow to brown powder (30-50 mesh) (α-FeO(OH)), with a molecular weight of 88.85 and a pH value of 8.0-8.5.

[0023] 2. Sampling conditions

[0024] Sampling was conducted after the growing season (November) because rainfall frequency and amount were low at this time, which was less likely to interfere with soil amendment measures; and the litter layer was thicker, which could reduce the loss of amendments due to rainwater erosion. After sampling, the surface litter in the sample plot was cleaned up and placed aside, while the total iron content, bulk density and pH value of the soil were measured.

[0025] Example

[0026] Example of soil improvement in plantations of Chinese fir in Jinzhai County, Anhui Province:

[0027] The Mazongling Forest Farm in Jinzhai County, Anhui Province, located in a subtropical region, was selected for goethite ore addition treatment. This area is situated on the northern slopes of the Dabie Mountains, at an altitude of approximately 1000 meters, with a terrain trending from southeast to northwest. The average annual precipitation is over 1600 mm, the average annual relative humidity is 78%, the average annual temperature is 13.3℃, ​​and the frost-free period is 220-230 days. The soil texture is loamy and slightly acidic.

[0028] Topsoil (0-20cm) samples were collected from a 20-year-old Chinese fir plantation in the forest farm during the 2022 planting season. The bulk density was determined to be 1.09 g / cm³ using the ring sampler method, and the pH (after water extraction) was 5.25. After acid digestion, the total iron concentration in the soil was measured to be 12.50 g / kg using the o-phenanthroline colorimetric method and a UV spectrophotometer.

[0029] In November 2022, nine sample plots were established in a 20-year-old Chinese fir plantation in the forest farm. Each plot was 5m × 5m in size and square in shape. To prevent mutual interference between plots, the distance between each plot was greater than five meters. The total iron content (total iron content refers to the sum of all forms of iron in the soil, which was determined by the o-phenanthroline colorimetric method, followed by spectrophotometry) of the top layer (0-20cm) of the soil in each plot was calculated to be approximately 58.83 kg. Goethite prepared above was added in situ to achieve a total iron content of 25% (Fe25) and 50% (Fe50) in the soil. A control treatment without added goethite was set up, with three plots for each treatment. Before adding iron oxides, clean up the surface litter in the sample plot and set it aside. After cleaning up the litter in the sample plot, evenly spread 11.76 kg or 23.52 kg of the goethite prepared above into the sample plot at one time. After completion, restore the original litter in the sample plot to its original state.

[0030] After the goethite was added, two static chambers were set up in each sample plot, for a total of 18. Starting from April 1, 2023, the static chamber method was used to collect gas every half month, and the data were analyzed using a carbon dioxide isotope gas analyzer to calculate soil carbon emission flux data. The monitoring lasted for one year.

[0031] In November 2023, soil samples from the improved topsoil (0-20cm) were collected, and a comprehensive quantitative analysis of the soil's physicochemical indicators was conducted, including soil pH, organic carbon, total nitrogen content, microbial biomass, enzyme activity, particulate organic carbon content, mineral-bound organic carbon content, iron-bound organic carbon content, and the content of free, complexed, and amorphous iron oxide.

[0032] Table 1 Soil index data collected in this invention

[0033]

[0034]

[0035] The effects of goethite addition on improving forest soil acidification, carbon sequestration capacity, and nutrient availability were evaluated by monitoring carbon dioxide emission flux and measuring a range of soil chemical properties. Data from Table 1 show that this embodiment found that the low-dose treatment (25%) reduced cumulative CO2 release from soil respiration by 12.96%, while the high-dose treatment (50%) reduced it by 23.91%. One year after goethite addition, the low-dose treatment increased soil pH by 1.09 units, while the high-dose treatment increased it by 1.68 units. This demonstrates that with increasing goethite addition, the soil conditioner's ability to improve soil acidity and inhibit carbon emissions is enhanced.

[0036] Furthermore, after treatments with low and high amounts of goethite, the soil organic carbon content did not change significantly, but the particulate organic carbon content decreased by 15.93-20.31%, while the mineral-bound organic carbon content increased by approximately 30%, and the iron-bound organic carbon content nearly doubled. The activity of extracellular enzymes in the soil involved in the carbon, nitrogen, and phosphorus cycles was significantly enhanced. In addition, the high-amount goethite treatment increased total nitrogen content by 38.46%, soluble organic carbon content by 35.47%, microbial biomass carbon by 33.64%, free iron oxide content by 32.08%, complexed iron oxide content by 14.10%, and amorphous iron oxide content by 12.81%; while the effect of the low-amount goethite treatment was not significant.

[0037] In summary, as the dosage of added goethite increases, it has a more significant effect on improving acidified soil, enhancing nutrient availability, and inhibiting carbon emissions and sequestering carbon. The overall improvement effect is better, but considering cost and cost-effectiveness, the optimal soil total iron content is 25% to 50%.

Claims

1. A method for applying an amendment to improve soil acidification in southern forests, comprising the following specific steps: ① Preparation of the modifier goethite: 1 mol·L -1 FeCl3·6H2O solution and 1 mol·L -1 NaOH was mixed and titrated to a pH of 12. After being kept in a water bath at 70°C for 60 hours, the mixture was washed with ultrapure water and then processed by precipitation, freezing, and drying to obtain goethite. The goethite product was sealed and stored at room temperature for later use. ② Collect soil samples from the top 20cm of the forest as quadrats, and determine the total iron content, bulk density, and pH value of the soil samples; ③ Using the data obtained in step ②, calculate the total iron content in the surface soil per unit area; ④ Based on the soil total iron content measured in step ③, and the soil weight per unit area of ​​surface soil obtained from the soil bulk density, clean up the surface litter in the sample plot and set it aside, then add the goethite obtained in step ① in situ to make the soil total iron content reach 25% to 50%. ⑤ After adding goethite in step ④ above, restore the original litter on the ground to its initial state; ⑥ Measure the surface carbon flux after step ⑤ above is completed every half month using the static box method. The monitoring period is 1 year, and the data is recorded. ⑦ One year after completing the data recording step ⑥, surface soil samples were collected from the treated area and surrounding untreated areas to measure soil pH, nitrogen and phosphorus available nutrient content, as well as soil microbial biomass and enzyme activity, thereby evaluating the soil acidification improvement and carbon sequestration enhancement capabilities.

2. The application method according to claim 1, wherein, In step ④, goethite with a total iron content of 28% to 45% in the soil from step ① is added in situ.

Images