Soil improvement is not simply about "fertilizing" or "adjusting acidity"

Soil is the lifeline of agriculture, and its improvement is not only related to crop yield, but also affects ecological sustainability. From organic matter supplementation to microbial activation, from structural repair to acid-base regulation, every technology carries the wisdom of "using and nurturing in combination". Only by respecting the laws of the soil and implementing scientific policies can we achieve a virtuous cycle of "fertile soil nurturing fertile fields and good yields from fertile fields", laying a solid foundation for the high-quality development of agriculture.
As the foundation of agricultural production, the quality of soil directly determines the yield and quality of crops. However, long-term unreasonable farming methods, excessive reliance on fertilizers, and changes in the ecological environment have led to increasingly prominent problems such as soil impoverishment, compaction, and acidification worldwide. According to data from the Food and Agriculture Organization of the United Nations, about 33% of the world's soil is in a degraded state, and nearly 40% of China's arable land also has varying degrees of quality problems. Soil improvement is not simply about "fertilizing" or "adjusting acidity", but a systematic project that requires the combination of soil characteristics, crop needs, and ecological laws to achieve sustainable improvement of soil fertility through scientific methods.

1、 Organic matter supplementation: the cornerstone project for building soil fertility
Soil organic matter is a core indicator for measuring soil fertility. It is like a "nutrient reservoir" of soil, providing basic nutrients such as nitrogen, phosphorus, and potassium for crops, improving soil particle structure, and enhancing water and fertilizer retention capacity. The organic matter content in ideal soil should reach around 5%, but in most cultivated land in China, the organic matter content is less than 2%, and in some barren plots, it is even lower than 1%. This is also a key reason for low crop yield and poor quality. （1） Organic Fertilizer application: The combination of traditional wisdom and modern technology. The application of organic fertilizers such as farmyard manure and compost is a classic method for supplementing organic matter. Its core principle is to decompose organic matter through microorganisms, converting complex carbon and nitrogen compounds into small molecule nutrients that crops can absorb. Taking the apple planting base in Xingtai, Hebei Province as an example, the base has experienced a decrease in soil organic matter to 0.8% and fruit sweetness from 15 ° C to below 10 ° C due to the continuous planting of apples for 20 years and excessive use of chemical fertilizers. Since 2019, the base has adopted a plan of "applying 3000 kilograms of decomposed sheep manure per acre per year+deep plowing 30 centimeters", combined with planting hairy sweet potatoes as winter cover crops. After 3 years, the soil organic matter increased to 2.3%, the sweetness of apples recovered to 14 °, and the yield per acre increased by 15%.
It should be noted that organic fertilizers must be fully decomposed. Unfermented raw manure (such as fresh chicken manure) contains a large amount of pathogens and uric acid, and direct application can lead to "root burning" - a vegetable greenhouse in Liaocheng, Shandong once caused 10 acres of cucumbers to wilt due to the application of 5 tons of raw chicken manure, resulting in a loss of 200000 yuan. Modern composting technology can achieve rapid composting in 30 days by controlling the carbon nitrogen ratio (25:1 optimal), temperature (55-65 ℃ for 7 days), and humidity (60%). After composting, the organic fertilizer can kill 99% of pathogenic bacteria and increase nutrient conversion rate by 40%.

（2） Biochar application: Long term enhancement of soil carbon pool Biochar, as a new type of organic amendment, has shown unique advantages in soil improvement. It is made by high-temperature carbonization of agricultural and forestry waste (such as corn stalks and bamboo) in an anaerobic environment, with a porosity of over 70%, and can adsorb 3-5 times its own weight of water and nutrients. The tea gardens in the Ailao Mountain area of Yunnan Province have poor water retention capacity due to long-term soil erosion, with soil organic matter only 1.2%. In 2021, the bamboo charcoal improvement technology was introduced, with 500 kilograms of bamboo charcoal (particle size 2-5 millimeters) applied per acre, combined with organic fertilizer application. After one year, the soil water retention capacity increased by 50%, the fresh tea leaf yield increased by 20%, and the amino acid content increased by 8%.
The long-term effectiveness of biochar is particularly outstanding. Research has shown that the decomposition cycle of biochar in soil can last for over a hundred years and can continuously improve soil structure. The rice field experiment in Quzhou, Zhejiang Province showed that after a one-time application of biochar, even without supplementary application for 5 consecutive years, the soil organic matter was still 1.2 percentage points higher than the control group, effectively solving the problem of traditional organic fertilizers requiring annual application.
2、 Acid base balance regulation: creating a suitable "living environment" for crops
Soil pH is a key factor affecting crop growth, directly regulating nutrient availability and microbial activity. When the pH value is below 5.5, the activity of aluminum ions in the soil increases, which inhibits the absorption of phosphorus and calcium by roots; When the pH value is higher than 8.0, trace elements such as iron and zinc will form insoluble compounds, leading to crop "nutrient deficiency syndrome".

（1） Acidic soil improvement: The synergistic effect of lime and organic fertilizer in the red soil region of southern China severely restricts crop growth due to frequent rainfall and soil pH values ranging from 4.5 to 5.5. Citrus orchards in Hengyang, Hunan Province, once experienced extensive leaf yellowing and a fruit deformity rate of 30% due to soil acidification (pH 4.3). Adopting the combination of "quicklime+organic fertilizer" for improvement: in the first year, 80 kilograms of quicklime were applied per acre (spread and plowed 15 centimeters), followed by an interval of 20 days before applying 2000 kilograms of decomposed pig manure. The soil pH increased to 5.8 that year, and the yellowing phenomenon decreased by 60% the following year, resulting in a 2.5 ° increase in fruit sweetness.
It is worth noting that lime application needs to be done "in small amounts multiple times". The sugarcane fields in Nanning, Guangxi once experienced a sudden increase in soil pH to 8.2 due to the one-time application of 200 kilograms of quicklime per acre, which led to zinc deficiency symptoms and a 15% decrease in sugarcane yield. The scientific approach is to apply no more than 100 kilograms in the first year, and adjust it annually based on the pH test results (target pH 5.5-6.5), while also planting acid resistant green manure such as purple clover to form a long-term adjustment mechanism. （2） Alkaline soil improvement: The application of gypsum and desulfurization gypsum requires targeted measures for the improvement of northern saline alkali land (pH 8.0-9.5). Gypsum (calcium sulfate) can reduce soil alkalinity through ion exchange, while power plant desulfurization gypsum (industrial by-product) has become the preferred choice for large-scale improvement due to its low cost (only 30 yuan per ton). The sunflower planting area in the Hetao Plain of Inner Mongolia has a soil pH value of 8.8 and a sodium ion content that exceeds the standard by three times. In 2022, desulfurization gypsum was used for improvement, with 1.5 tons applied per acre and deep plowing of 30 centimeters. The soil pH dropped to 8.2 that year, and the sunflower shell rate decreased from 40% to 15%, resulting in a 30% increase in yield per acre.
For mildly alkaline soils (pH 7.5-8.0), planting alkali tolerant green manure is an economically effective method. The experiment in Baodi, Tianjin showed that after planting alfalfa (alkali tolerant pH 8.5) for 2 years, soil organic matter increased by 1.1%, pH value decreased by 0.6 units, and 3 tons of fresh grass could be harvested per mu as feed, achieving a "win-win situation of improvement and income".

3、 Structural repair: breaking the compaction and allowing the soil to breathe smoothly
Soil compaction is a common problem in modern agriculture, often caused by long-term rotary tillage (less than 15 centimeters deep) and excessive use of chemical fertilizers. The porosity of compacted soil is less than 20%, and the lack of oxygen in the root system can lead to weakened crop growth - in the wheat field in Zhoukou, Henan, due to continuous rotary tillage for 10 years, a 12 centimeter thick plow bottom layer is formed, and the wheat root system can only penetrate 15 centimeters, resulting in a 40% reduction in yield in case of drought. （1） Deep plowing and loosening soil: Physical obstacle breaking technology is the core measure to break through the bottom layer of the plow. The vegetable base in Weifang, Shandong Province adopts the "deep plowing 30 centimeters+straw returning" technology, which crushes corn stalks and applies 500 kilograms per mu. After deep plowing, the soil bulk density decreases from 1.5 grams/cubic centimeter to 1.2 grams/cubic centimeter, and the porosity increases to 35%. The depth of the tomato root system planted reached 40 centimeters, resulting in an increase of 5 fruits per plant and a significant enhancement in drought resistance.
For plots where crops have already been planted, topsoil (5-10 cm) can be used in conjunction with microbial agents. In the pepper greenhouse in Xuzhou, Jiangsu Province, the soil was scarified every two weeks with a tooth harrow during the fruit bearing period. At the same time, the number of soil actinomycetes increased 10 times, and the incidence rate of pepper blight decreased from 25% to 5%. （2） No tillage and mulching: The combination of no tillage and straw mulching in ecological restoration mode can effectively reduce soil disturbance and protect aggregate structure. The soybean field experiment in the Sanjiang Plain of Heilongjiang Province showed that using "corn straw full coverage (300 kilograms per mu)+no tillage sowing" for three consecutive years increased soil organic matter by 0.5%, the proportion of water stable aggregate structure (>0.25 millimeters) increased from 28% to 45%, increased soybean yield by 18% per mu, and reduced soil erosion by 60%.
In orchards, covering with grass is a mature technique. White clover is planted in apple orchards in Luochuan, Shaanxi. Three times a year, grass is cut and the tree disk is covered. After three years, the soil organic matter increases by 1.0%, and the surface temperature in summer decreases by 5-8 ℃. This effectively alleviates the phenomenon of fruit burning caused by "high temperature stress", reducing the burning rate from 15% to 3%.

4、 Biological activation: awakening the vitality of soil microorganisms
Soil microorganisms are the "engine" of nutrient transformation. 1 gram of healthy soil contains hundreds of millions of microorganisms that decompose organic matter, fix nitrogen and phosphorus, and inhibit pathogenic bacteria. Their activity directly reflects the health status of the soil. Microbial diversity in poor soils often decreases by more than 50%, leading to nutrient cycling disruptions. （1） Application of microbial agents: Accurately supplementing functional microbial communities for different soil problems, selecting specialized microbial agents can achieve "targeted improvement". The navel orange orchard in Ganzhou, Jiangxi Province has been continuously cultivated for 8 years, and the incidence rate of soil root knot nematodes has reached 70%. The root irrigation treatment of "Paecilomyces lilacinus+chitin" was adopted, and 2 kg of bacterial agent (200 million/g of bacteria) was applied per mu, combined with 10 kg of chitin. After three months, the decline rate of root knot nematodes reached 85%, and the growth of new roots increased by 60%.
The symbiotic nitrogen fixation between leguminous crops and rhizobia is a classic case. In the alfalfa planting area of Yili, Xinjiang, after inoculation with alfalfa rhizobia (10 grams of inoculant per kilogram of seeds), the nitrogen fixation per acre reached 80 kilograms, equivalent to a reduction of 170 kilograms of urea, and the yield of alfalfa hay increased by 25%, with a 3 percentage point increase in crude protein content. （2） Crop rotation and intercropping: Constructing a reasonable crop rotation can significantly enhance soil microbial diversity. The long-term continuous cropping of cotton fields in Yuncheng, Shanxi, has led to frequent occurrence of fusarium wilt. After the adoption of the three-year rotation model of "cotton mung bean wheat", the number of Bacillus in the soil has tripled, the incidence rate of fusarium wilt has dropped from 40% to 5%, and the per unit yield of cotton has increased by 15%.
Interplanting techniques can achieve 'species complementarity'. The rice field in Yuanyang, Yunnan Province adopts the intercropping of "rice+azolla". Azolla (Man Jianghong) and cyanobacteria symbiotically fix nitrogen. The annual nitrogen fixation per mu is up to 20 kg, and the amount of nitrogen fertilizer used for rice is reduced by 30%. Moreover, azolla can increase soil organic matter by 0.3% after plowing, forming a virtuous cycle of the "rice azolla fish" ecosystem.
5、 Practical strategy: tailored improvement plan
There is no universal formula for soil improvement, and personalized plans need to be developed based on soil testing results. The following are examples of improvement paths for different types of soil:
Degraded farmland (organic matter<1.5%, compacted): Using "biochar (300 kg/mu)+organic fertilizer (2000 kg/mu)+deep plowing of 30 cm", combined with planting alfalfa (2 years), the soil organic matter can be increased to over 2.5% and the porosity can reach 30% in the third year.
Acidic red soil (pH 4.5-5.0): Apply 50 kg/acre of quicklime in the first year, and switch to applying dolomite powder (containing calcium and magnesium) from the following year, combined with planting purple cloud quartz (plowing and returning to the field). After 3 years, adjust the pH to 5.5-6.0 and supplement calcium and magnesium elements.
Saline alkali land (pH 8.5-9.0): First, irrigate with water to wash the salt (100 cubic meters of water per acre), then apply 1 ton/acre of desulfurization gypsum, plant sweet sorghum (salt alkali resistant) for 2 years, and during this period, return straw to the field, which can lower the pH to below 8.0 and increase organic matter by 1.0%.
Soil improvement is a long-term process that requires adhering to the principle of "three parts improvement, seven parts cultivation". The practice in Wuxi, Jiangsu has shown that through the comprehensive measures of "organic fertilizer+crop rotation+no tillage", even severely degraded soil can be restored to a healthy state within 5-8 years, and the subsequent maintenance cost is only 60% of conventional cultivation.
Soil is the lifeline of agriculture, and its improvement is not only related to crop yield, but also affects ecological sustainability. From organic matter supplementation to microbial activation, from structural repair to acid-base regulation, every technology carries the wisdom of "using and nurturing in combination". Only by respecting the laws of the soil and implementing scientific policies can we achieve a virtuous cycle of "fertile soil nurturing fertile fields and good yields from fertile fields", laying a solid foundation for the high-quality development of agriculture.