Soil compaction is a common issue—find the solution here.

I. What is soil compaction?

Soil compaction refers to the hardening of the soil surface that occurs when the topsoil, lacking organic matter and exhibiting poor structure, undergoes structural breakdown and particle dispersion under external factors such as irrigation or rainfall, followed by hardening due to cohesive forces upon drying.

II. The main causes of soil compaction are the following seven factors:

Soil compaction poses significant risks.

1. The farmland soil is excessively clayey, and the plow layer is shallow.

The clay soil has a high content of clay particles, and with a plow layer averaging less than 50 cm in depth, it exhibits few capillary pores, resulting in poor aeration, water permeability, and heat‑retention capacity. After rainfall or irrigation, the pores are easily blocked, leading to the formation of a crust on the soil surface.

2. Severe shortage of organic fertilizer and reduced amounts of straw returned to the field

This leads to an insufficient replenishment of organic matter in the soil, resulting in low soil organic matter content and degraded soil structure. Consequently, microbial activity is impaired, which in turn hinders the formation of soil aggregate structures, causing the soil pH to become excessively acidic or alkaline and leading to soil compaction.

3. Excessive investment in plastic products

Plastic mulch films and plastic bags, among other materials, are not thoroughly removed and cannot fully decompose in the soil, forming harmful clumps. In China, waste plastics disposed of in landfills along with municipal solid waste account for 3% to 5% of the total landfill mass, with plastic bags making up the majority. Once applied to the soil, these materials are difficult to degrade, leading to soil compaction.

4. Long-term, one-sided application of chemical fertilizers

There is a severe shortage of farmyard manure, with an overemphasis on nitrogen at the expense of phosphorus and potassium. Soil organic matter is declining, and humus is not being replenished in a timely manner, leading to soil compaction and cracking.

(1) Excessive application of nitrogen fertilizer: For every unit of nitrogen supplied to microorganisms, 25 units of carbon are consumed. This carbon is derived from soil organic matter; when organic matter levels are low, microbial activity is impaired, which in turn hinders the formation of soil aggregate structure and leads to soil compaction.

(2) Excessive application of phosphate fertilizers: Phosphate ions in phosphate fertilizers combine with cations such as calcium and magnesium in the soil to form insoluble phosphates, which not only waste the fertilizer but also disrupt the soil’s aggregate structure, leading to soil compaction.

(3) Excessive application of potassium fertilizer: Potassium ions in potassium fertilizers have exceptionally strong exchange capacity, capable of displacing polyvalent cations that contribute to the formation of soil aggregate structures. Meanwhile, monovalent potassium ions lack bridging functionality; as a result, the bridging bonds within the soil aggregates are disrupted, undermining the aggregate structure and leading to soil compaction.

5. Agricultural practices such as tillage and plowing lead to the disruption of the topsoil structure.

Due to the effects of excessively deep mechanical tillage, the soil aggregate structure has been disrupted. Moreover, only a portion of the fertilizer applied annually is absorbed and utilized by the current season’s crops; the remainder is immobilized in the soil, leading to the accumulation of substantial salt–acid deposits and resulting in soil compaction.

6. Accumulation of Harmful Substances

In some areas, groundwater and industrial wastewater contain high levels of toxic substances; prolonged use for irrigation can lead to the excessive accumulation of these contaminants, resulting in the compaction of the surface soil.

7. Wind and sand, heavy rainfall, and soil erosion

After exposure to wind and sand or heavy rainfall, fine soil particles from the surface layer are washed away, disrupting the soil structure and leading to soil compaction.

III. What are the main adverse effects of soil compaction?

1. Reduced root system capacity

Under conditions of soil compaction, oxygen deficiency leads to reduced root vitality and impaired root development. Root cell respiration is weakened, while nutrients such as nitrogen predominantly exist in ionic form and require energy derived from cellular metabolism for uptake. With diminished respiration, the energy supply becomes inadequate, thereby hindering nutrient absorption.

2. Causes deficiency disorders

Deficiency symptoms do not always result from a lack of the nutrient in the soil; rather, they may stem from reduced root uptake caused by factors such as soil compaction, unsuitable soil pH, or uneven soil moisture distribution.

IV. Methods for Alleviating Soil Compaction  

         1. Increase the application rate of organic fertilizer: Such as Agricultural University Bio-Organic Fertilizer: One Product, Three Benefits Manure, stable manure, and mixed soil fertilizers, as well as high-quality organic fertilizers produced by composting crop residues, are recommended; it is best to apply microbial inoculants with a high microbial content.

         2. Reduce the application rate of chemical fertilizers: Enhancing farmers’ understanding of the roles of various fertilizers and adopting a rational, crop‑yield‑ and soil‑fertility‑based approach to fertilizer application can both curb indiscriminate fertilizer use and reduce inefficient inputs, thereby boosting economic returns.

         3. Further promote dryland farming: Implement sprinkler irrigation, or encourage the storage of rainwater during the summer to make full use of surface water. Where feasible, deep-well water may also be utilized.

         4. Break away from outdated farming practices: Further promote straw return to the field and no-till mulching, making every effort to minimize unnecessary soil erosion in order to preserve soil structure.