Application method of modifier for acidification of southern forest soil

Abstract

The invention belongs to the field of soil improvement, and relates to an application method of a modifier for acidification of southern forest soil, by means of the method, goethite serving as a mineral modifier can effectively improve the pH of the soil, adjust the acidity of the soil, improve the carbon sequestration capacity of the soil, comprehensively improve the plant habitat and further promote plant growth. The soil habitat improvement and the ecological function improvement of the southern forest are synchronously realized.

Description

Technical Field

[0001] The invention belongs to the field of soil improvement, and relates to an application method of an improver for improving soil acidification in southern forests, and in particular to an application method of an improver for improving soil acidification and enhancing carbon sequestration capacity in southern forests. Technical Background

[0002] Soil habitat restoration is conducive to improving the quality of artificial forests and enhancing ecological services. In the mountain forests of the south, the acid rain problem has been exacerbated by unreasonable management and human activities, and the soil acidification problem in the red soil area of ​​the south has also been particularly prominent: such as the decline in effective nutrient content, the deterioration of soil health, and the low ecological function. It is well known that the large-scale burning of fossil fuels in industry, transportation and energy production will release sulfur oxides and nitrogen oxides, which will form acid rain in the atmosphere and eventually fall into the soil, thus causing soil acidification. In addition, natural factors can also cause soil acidification. For example, different types of vegetation have different effects on soil acidity and alkalinity. The organic acids secreted by the roots of some plants can lower the pH value of the soil and cause acidic soil. Coniferous trees such as pine and fir usually acidify the soil. In addition, large amounts of precipitation in the south can also wash away alkaline substances in the soil, causing the soil acidity to further increase, and the dissolved carbon dioxide in the precipitation can also form carbonic acid, making the soil more acidic. This has brought about a series of problems such as reduced soil fertility and weakened ecological functions. Faced with the huge and serious soil acidification problem, the research on acidified soil improvement technology has always been an important topic in the field of soil science, and it is also a comprehensive topic. The research on acidified soil improvement technology for 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] Among the 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 the application of these conditioners alone can increase the pH value of the soil to a certain extent and improve the problem of forest soil acidification, these have ignored the feedback process between soil acidification improvement and ecological function enhancement, and have failed to synergistically solve problems such as the decrease in effective nutrient content, the deterioration of soil health, and the 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. Effect of mineral conditioner dosage on nutrient status and rapeseed growth in acidic soil [J]. Chinese Soil and Fertilizer, 2021, 3. Summary of the invention

[0007] Based on the above problems, researchers have found a new type of soil conditioner that can neutralize acidity and improve soil carbon fixation capacity by optimizing and innovating neutralizers based on traditional conditioners: iron oxide. As a new type of mineral conditioner, it has been found to effectively alleviate the problem of soil acidification. In addition, it was found in the study that iron oxide has a certain neutralizing effect, which can react with excessive hydrogen ions in the soil to form water and release corresponding metal ions, thereby neutralizing soil acidity. In addition, iron oxide can also reduce soil acidity by maintaining charge balance, participating in redox reactions in the soil, and cementation and agglomeration of soil particles. Among these, we found that goethite, as a hydrated iron oxide with a chemical formula of FeO(OH), can also be an effective soil conditioner. Goethite has a high pH value, usually between 7.5 and 9. When goethite is added to the soil, it reacts with acidic substances in the soil, neutralizes acidic substances, and thus increases the pH value of the soil. In addition, the surface of goethite carries a positive charge, which can adsorb negatively charged ions in the soil, including hydrogen ions (H+), thereby reducing the H+ concentration in the soil and increasing the pH value of the soil. It was also found that compared with traditional quicklime, goethite as a mineral conditioner can not only effectively increase soil pH and regulate soil acidity, but also improve the soil's ability to fix carbon, comprehensively improve plant habitats, and promote plant growth, thus achieving the functional improvement of low-quality and low-efficiency artificial forests.

[0008] In order to achieve the above object, the present invention provides a method for applying an improver for acidification of southern forest soil, and the specific steps are as follows:

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

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

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

[0012] ④ According to the total iron content of the soil sampled and measured in advance in step ③, and the weight of the surface soil per unit area is obtained according to the soil bulk density, the surface litter in the sample is cleaned and placed aside, and the goethite obtained in step ① is added in situ to make the total iron content of the soil reach 25% to 50%;

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

[0014] ⑥ Use the static box method to measure the surface carbon flux after the completion of step ⑤ above every half month, with a monitoring period of 1 year, and record the data;

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

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

[0017] About the mechanism of action of goethite: goethite has a high pH value, usually between 7.5 and 9. When goethite is added to the soil, it reacts with the acidic substances in the soil, neutralizes the acidic substances, and thus increases the pH value of the soil. In addition, the surface of goethite carries a positive charge, which can adsorb negatively charged ions in the soil, including hydrogen ions (H+), thereby reducing the H+ concentration in the soil and increasing the pH value of the soil. At the same time, as an iron oxide, goethite has the characteristics of large specific surface area and strong adsorption affinity. It combines organic carbon by adsorbing or co-precipitating with SOC to form iron, forming a unique mineral protection mechanism for SOC, improving the stability of SOC, and thus improving the carbon sink capacity of the soil. In addition, iron oxides can also act as a binder for clay and organic carbon to promote the formation of soil microaggregates and improve the structure and permeability of the soil. The strength of the agglomeration effect is related to the type of iron oxide. Since the surface of goethite has more hydroxyl groups, it is more conducive to combining with minerals such as kaolinite, and has a stronger cementation effect on the soil, which is more beneficial to enhancing the stability of soil carbon.

[0018] Effects of the Invention

[0019] According to the present invention, a method for applying an amendment for soil acidification in southern forests is provided. According to the measured results one year after addition, the amendment goethite significantly increased the soil pH. In addition, after addition, the soil carbon emission flux was monitored using a static box method, and it was found that the addition of iron oxides significantly inhibited the carbon release intensity of the soil and improved the carbon fixation capacity. It can be seen that mineral amendments can not only effectively increase soil pH and regulate soil acidity, but also improve soil carbon sequestration capacity, comprehensively improve plant habitats, and then promote plant growth, and simultaneously achieve soil habitat improvement and ecological function improvement in southern forests. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1Picture of the improver goethite prepared by the present invention DETAILED DESCRIPTION

[0021] The application method of the improver for acidification of southern forest soil of the present invention is specifically described as follows.

[0022] 1. Laboratory preparation of goethite: 1 mol·L -1 FeCl3·6H2O solution and 1mol·L -1 NaOH was mixed and the mixed solution was titrated to a pH of 12. After 60 hours in a water bath at 70°C, it was washed with ultrapure water. Goethite can be obtained by precipitation, freeze drying, and sealed and stored 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 carried out after the growing season ended (November), because the frequency of precipitation was low and the amount of rainfall was small, which was not easy to interfere with the improvement measures; and the litter layer was thick, which could reduce the loss of the amendment caused by rain erosion. After sampling, the surface litter in the sample was cleaned and placed aside, and the total iron content, bulk density and pH value of the soil were measured at the same time.

[0025] Example

[0026] Example of soil improvement in the Chinese fir plantation in Jinzhai, Anhui:

[0027] Mazongling Forest Farm in Jinzhai County, Anhui Province, located in the subtropical region, was selected for the addition of goethite. The area is located at the northern foot of Dabie Mountain, with an altitude of about 1,000 meters and a terrain trend from southeast to northwest. The average annual precipitation for many years is more than 1,600 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] In the 2022 season, a soil sample from the surface layer (0-20 cm) of a 20-year-old fir plantation in the forest farm was collected. The bulk density was determined to be 1.09 g / cm by the ring knife method, and the pH (water extraction) was 5.25. After acid digestion, the soil sample was measured by the o-phenanthroline colorimetric method and the total iron concentration in the soil was 12.50 g / kg using an ultraviolet spectrophotometer.

[0029] In November 2022, a total of 9 plots were established in the 20-year-old fir plantation in the forest farm. Each plot was 5m×5m in size and was square. To prevent mutual influence between plots, each plot was more than five meters apart. The total iron content of the soil in the surface layer (0-20cm) of each plot was calculated to be about 58.83kg (total iron content refers to the sum of various forms of iron in the soil. The total iron was determined by o-phenanthroline colorimetry and then by spectrophotometer) and the prepared goethite was added in situ to make the soil total iron content reach 25% (Fe25) and 50% (Fe50) goethite, and a treatment without adding goethite was set as a control, with 3 plots for each treatment. Before adding iron oxide, the surface litter in the sample plot was cleaned and set aside. After the litter in the sample plot was cleaned, 11.76 kg or 23.52 kg of the above-prepared goethite was evenly sprinkled into the sample plot at one time. After completion, the original litter in the sample plot was restored to its original state.

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

[0031] In November 2023, improved surface layer (0-20cm) soil samples were collected for a comprehensive quantitative analysis of the soil's physical and chemical indicators, 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 free, complexed and amorphous iron oxide content.

[0032] Table 1 Soil index data collected by the present invention

[0033]

[0034]

[0035] The effect of goethite addition on forest soil acidification improvement, carbon sequestration capacity and nutrient effectiveness was evaluated by monitoring carbon dioxide emission flux and measuring a series of soil chemical properties. As can be seen from the data in Table 1, this embodiment found that the low-amount treatment (25%) reduced the cumulative respiration release of CO2 in the soil by 12.96%, and the high-amount treatment (50%) reduced it by 23.91%. One year after the addition of the modifier goethite, the soil pH value increased by 1.09 units when the low-amount treatment was used, and by 1.68 units when the high-amount treatment was used. It can be seen that as the amount of goethite added increases, the ability of the modifier to improve soil acidity and inhibit carbon emissions is enhanced.

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

[0037] On the whole, as the dosage of added goethite increases, it has more obvious effects in improving acidified soil, enhancing nutrient availability, inhibiting carbon emissions and carbon sequestration. The comprehensive improvement effect is better, but considering the cost and cost-effectiveness, the best soil total iron content is 25% to 50%.

Claims

1. A method for applying an amendment for acidification of southern forest soil, the specific steps of which are as follows: ① Preparation of the improver goethite: 1 mol·L -1 FeCl3·6H2O solution and 1mol·L -1 NaOH was mixed, and the mixed solution was titrated to a pH of 12. After being kept in a water bath at 70° C. for 60 h, it was washed with ultrapure water, and then processed by precipitation, freezing, and drying to obtain goethite, and the product goethite was sealed and stored at room temperature for standby use; ② Collect soil samples below 20 cm from the forest surface as sample plots, and determine the total iron content, bulk density and pH value of the soil samples; ③ Using the data measured in step ②, calculate the total iron content per unit area of ​​surface soil; ④ According to the total iron content of the soil sampled and measured in advance in step ③, and the weight of the surface soil per unit area is obtained according to the soil bulk density, the surface litter in the sample is cleaned and placed aside, and the goethite obtained in step ① is added in situ to make the total iron content of the soil reach 25% to 50%; ⑤ After adding goethite in the above step ④, restore the original litter on the surface to its initial state; ⑥ Use the static box method to measure the surface carbon flux after the completion of step ⑤ above every half month, with a monitoring period of 1 year, and record the data; ⑦ One year after completing the data recording step ⑥, collect surface soil samples from the treated area and the surrounding untreated areas to measure soil pH, available nitrogen and phosphorus nutrient content, and soil microbial biomass and enzyme activity, thereby evaluating soil acidification improvement and carbon sequestration enhancement capabilities.

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

Images