Xinhua Net – The Role of Microbial Fertilizers in the Development of Modern Agriculture

Speaker: Ding Fangjun, Professor at the College of Resources and Environmental Sciences, Shandong Agricultural University, and Deputy General Manager of Shandong Nongda Fertilizer Technology Co., Ltd.

In recent years, agricultural production has placed excessive emphasis on inorganic fertilizers while neglecting organic ones, leading to significant changes in the soil’s physical, chemical, and biological properties. These changes are particularly evident in seven key aspects: acidity, nutrient deficiency, imbalanced nutrition, contamination, salinization, and compaction. In China, soil organic matter content has declined, with its quality deteriorating, activity diminishing, and turnover rates slowing, thereby weakening its overall function. Nutrient imbalances have emerged—between nitrogen, phosphorus, and potassium, as well as between these macronutrients and micronutrients—resulting in deficiencies or immobilization of micronutrients within the soil. Organic–inorganic clay‑particle complexes form stable colloidal systems, enabling nutrients to exist in a high‑molecular‑weight integrated state, with adsorption, desorption, and release occurring in a balanced and efficient manner. This allows plants to access water, nutrients, air, and heat as needed, ensuring steady, uniform, adequate, and optimal supply. Water and air coexist in the same soil space, yet they often conflict, leading to soil compaction that impedes root growth. Moreover, insufficient attention has been paid to the application of micronutrient fertilizers, exacerbating nutrient imbalances and increasing the incidence of physiological disorders in vegetables. The primary causes of soil compaction are:

1. Organic matter is low, resulting in poor buffering capacity; 2. Soil structure is degraded by chemical fertilizers; 3. Excessive flood irrigation; 4. Lack of deep tillage and meticulous cultivation. Harmful effects: 1. Poor aeration and low soil moisture; 2. Weak water- and nutrient-retention capacity; 3. Impeded root growth.

Current issues in the arable soil layer:

The plow layer has become shallower, while the plow pan has risen and thickened, hindering the infiltration of rainfall into deeper soil layers and impeding root penetration. This is detrimental to water conservation, drip‑irrigation efficiency, and the roots’ ability to absorb and utilize moisture from deeper soil horizons. The underlying causes include a thinner plow layer, a more compacted plow pan, reduced amounts of active soil, deteriorated soil structure, and declining productive capacity. Organic–inorganic clay‑particle complexes serve as crucial binding agents for soil aggregates; under the influence of calcium ions, they can form stable aggregate structures, regulate the soil’s water–air–heat balance, and render the soil loose, well‑aerated, and warm—enhancing its water‑retention and heat‑preservation properties. However, highly concentrated, high‑efficiency organic–inorganic composite colloids such as Jinli exhibit diminishing returns and pose environmental risks. The key issues in China’s land fertilization practices are:

Emphasis on quantity over quality, and on inorganic rather than organic inputs, has led to a gradual decline in the yield‑boosting effectiveness of chemical fertilizers. The average utilization rates are approximately 30%–35% for nitrogen, 10%–20% for phosphorus, and 35%–50% for potassium; by contrast, developed countries typically achieve utilization rates of around 50% for all three major nutrients. Soil acidification fosters fungal proliferation, exacerbating diseases such as bacterial wilt, root rot, gall formation, and nematode infestations. Moreover, hydrogen ions exert antagonistic effects on the uptake of other cations, disrupting soil structure, promoting compaction, and causing the leaching of various ions that can be toxic to crops. Beneficial microorganisms contribute to soil resilience, nutrient transformation, soil health, environmental capacity, nutrient cycling, and buffering capacity. Factors contributing to soil pollution include:

Agricultural plastic mulch, radioactive elements, pathogenic microorganisms, heavy metals, antibiotics, and chemical fertilizers and pesticides all adversely affect crop growth and agricultural product quality, thereby impacting human health.

In the history of fertilizer development in China, three distinct stages have emerged:

The first stage is the pre-1970s nitrogen-limited phase. At that time, ammonium hydroxide, ammonium bicarbonate, ammonium sulfate, and the like began to be used; The second phase, spanning the 1970s to the 1990s, was a phosphorus-limited stage. During this stage, they began to recognize and use calcium superphosphate, calcium‑magnesium phosphate fertilizer, diammonium phosphate, and other fertilizers. The third phase, spanning the 1990s to the early years of this century, was characterized by potassium limitation. At this stage, farmers begin to recognize and make extensive use of compound and formulated fertilizers. However, the current phase is characterized by limitations imposed by carbon and secondary and micronutrients. Why is this the case? Because, for microorganisms to thrive in the soil, in addition to favorable moisture, temperature, and pH levels, an appropriate carbon-to-nitrogen ratio is essential. Typically, a C:N ratio of 25–30 is optimal for microbial activity: too high a ratio slows decomposition, while too low a ratio accelerates it. Yet today, soil organic matter and carbon levels are low, which to some extent hinders microbial function. Consequently, microbial fertilizers have become particularly important in modern agriculture.

1. Bacillus subtilis: Enhances crop stress tolerance and fixes nitrogen.

II. Bacillus megaterium: Phosphate-solubilizing (phosphate‑solubilizing bacterium), with excellent efficacy in degrading organic phosphorus in the soil.

3. Bacillus mucilaginosus: Solubilizes potassium and releases soluble phosphorus and potassium, as well as secondary and micronutrients such as calcium, sulfur, magnesium, iron, zinc, molybdenum, and manganese.

4. Bacillus licheniformis: Resists disease and eliminates harmful bacteria.

5. Bacillus thuringiensis: Insecticidal, including activity against root-knot nematodes, with species-specific toxic activity against lepidopteran and other arthropod pests.

6. Bacillus laterosporus: promotes root growth, exhibits fungicidal activity, and degrades heavy metals.

7. Bacillus mucilaginosus: Possesses phosphate-solubilizing, potassium-releasing, and nitrogen-fixing capabilities; secretes a variety of enzymes, thereby enhancing crop resistance to certain diseases.

8. Streptomyces jingyangensis: Possesses the ability to enhance soil fertility and stimulate crop growth.

9. Mycorrhizal fungi: They expand the root system’s absorptive surface area and enhance the uptake of nutrients—particularly phosphorus—that lie beyond the reach of primary root hairs.

10. Azotobacter: Fixes atmospheric nitrogen, increasing crop yield.

11. Photosynthetic microbial communities: the key agents in enriching soil and promoting the growth of plants and animals.

12. Bacillus coagulans: It can reduce harmful gases such as ammonia and hydrogen sulfide in the environment and increase the amino acid content in fruits.

13. Aspergillus oryzae: Converts organic matter in crop residues into nutrients essential for plant growth, increases soil organic matter, and improves soil structure.

14. Paecilomyces lilacinus: Exhibits effective control against a wide range of nematodes and is one of the most promising biocontrol agents for managing root-knot nematodes. When formulated as a composite microbial preparation containing three or more strains, these microorganisms synergistically promote and complement each other, resulting in significantly greater efficacy against soil-borne diseases than that achieved with a single strain. The beneficial microbial community works in concert, jointly enhancing crop yield and productivity.

1. Promotes rapid growth: Beneficial microorganisms such as Bacillus megaterium and Bacillus mucilaginosus produce abundant plant‑derived enzymes during their metabolic processes, significantly enhancing the uptake of essential nutrients like nitrogen, phosphorus, and potassium by crops.

2. Regulating physiological processes and boosting yield and income: Beneficial bacteria such as Bacillus mucilaginosus, Bacillus laterosporus, and Bacillus licheniformis in the microbial community promote root growth and increase the number of fine roots. The plant‑endogenous enzymes and plant growth regulators produced by these beneficial microorganisms are absorbed through the roots into the plant body, thereby enhancing photosynthesis in the leaves.

3. Enhanced Quality: Strains such as Bacillus laterosporus, Bacillus subtilis, and Bacillus coagulans can reduce nitrate levels in plants, lower heavy metal concentrations, increase vitamin C content in fruits, and boost soluble sugar levels. Lactic acid bacteria, including Lactobacillus acidophilus, Bacillus coagulans, and Bacillus subtilis, can elevate the levels of essential amino acids, vitamins, and unsaturated fatty acids in fruits. As a result, the fruit exhibits superior taste, improved storage tolerance, and higher market value.

4. Decomposes organic matter and toxins, preventing continuous cropping: Beneficial microorganisms such as Aspergillus oryzae, Bacillus licheniformis, and Bacillus subtilis in the microbial community accelerate the breakdown of organic matter, producing readily available nutrients for crops and providing them with energy. They also degrade toxic and harmful substances accumulated from consecutive plantings, thereby mitigating the adverse effects of continuous cropping.

5. Protecting the soil‑root environment: After beneficial microorganisms such as Bacillus licheniformis are applied to the soil, they rapidly multiply and become the dominant microbial population, thereby controlling root‑associated nutrients and resources. This deprives pathogenic fungi and bacteria—responsible for diseases like continuous cropping disorders, root rot, damping-off, gumming, and gray mold—of the space and conditions necessary for survival. Additionally, it promotes thickening, fibrousization, and lignification of plant root cell walls, while inducing the formation of a cutin–silica double layer, thus establishing a robust barrier that inhibits pathogen invasion.

6. Enhancing crop stress tolerance: Beneficial microorganisms such as Bacillus licheniformis, Bacillus megaterium, and Bacillus laterosporus in the microbial community can improve soil buffering capacity and strengthen crops’ resistance to drought, cold, and waterlogging. Meanwhile, Bacillus laterosporus can also reinforce the protective cuticle on leaf surfaces, ward off pathogen invasion, and enhance the crop’s resistance to diseases and pests.

The five‑type composite microbial consortium exhibits the following benefits: it promotes rapid plant growth, regulates physiological processes, enhances fruit quality, degrades toxins to mitigate continuous cropping issues, and strengthens stress resistance. It also stimulates microbial proliferation, accelerates decomposition, shortens the composting period, delivers excellent composting results, and alleviates the problem of seedling death associated with continuous cropping after application.