How Does Soybean Cultivation Improve the Soil? A Detailed Guide to Practical Techniques

1. Soil Conditions for High-Yielding Soybeans

Soil conditions are the foundation of high soybean yields. Soil moisture status, nutrient status, and certain physical properties of the soil are important factors affecting soybean yield.

Soybean seeds require more moisture to germinate than cereal crops. Soybean seedling roots are relatively tender and high in water content, so suitable soil moisture conditions are needed to promote deep elongation of the young roots. The main root of the plant can reach about 1 m, and lateral roots can extend horizontally to about 0.5 m. When soil moisture is insufficient, both vertical and horizontal root growth are affected.

Soybean roots are very sensitive to changes in soil oxygen. Under oxygen-deficient conditions, root growth decreases markedly. Therefore, moderate soil moisture content, a deep plow layer, and moderate looseness can provide good moisture content and aeration conditions, promoting root growth and development. In soil science, soil compaction is used as an indicator of the physical properties of moisture and aeration in the plow layer, generally expressed as bulk density (grams per cubic centimeter of dry soil). The suitable soil bulk density for soybeans is 1.0-1.4. Loam is most suitable for soybean growth, and clay loam, clay soil, and sandy loam can also support normal growth; sandy soil and clay soil, with weak water-holding capacity or poor aeration, are unfavorable for growth.

2. Land Preparation Techniques Soybean planting can use land preparation techniques such as flat plowing, ridge cultivation, harrowing stubble, and deep loosening.

(1) Flat plowing. This is mostly used in the northern spring soybean regions with one crop per year. Through plowing, soil maturation is accelerated, which helps make full use of nutrients. Creating a loose plow layer of a certain depth, burying farmyard manure, stubble, pests and diseases, and weeds, etc., creates conditions for improving sowing quality and seedling emergence.

The timing of plowing varies with the previous crop and sometimes also changes due to climatic limitations. For wheat stubble, summer plowing should be completed in August, and no later than early September. For black soil, plowing depth is 25-35 cm; for loess, albic soil, mildly alkaline soil, or where the soil layer is thin or the subsoil contains harmful substances, the plowing depth should not exceed the fertile soil layer. After summer plowing, in autumn, wait until the soil has fully absorbed rainwater, then harrow fine and level. Corn stubble, millet stubble, and sorghum stubble are plowed in autumn. The autumn plowing window is short; once there is excessive rain, it cannot be done, and one can only wait for spring plowing the following year. Autumn plowing should be finished before freezing, with a depth of up to 20-25 cm. Autumn-plowed land should be harrowed and leveled immediately after plowing, then harrowed level again and compacted before spring sowing the next year to prevent moisture loss. Spring plowing should be 15 cm deep.

Generally speaking, summer plowing is better than autumn plowing, as it helps the soil store rainwater; autumn plowing is better than spring plowing, preventing excessive moisture loss before spring sowing. However, if autumn plowing is not timely and there is too much moisture, large clods form, and the effect is instead worse than spring plowing.

(2) Ridge cultivation. This is a traditional tillage method commonly used in Northeast China. After plowing, ridges are formed, which can raise soil temperature, deepen the plow layer, and enhance drainage and drought resistance. When the previous crop is corn, sorghum, or millet, overwinter on the original ridges; before thawing in early spring, use a heavy harrow to break up the stubble rows, then ridge-plow and seed in the furrow; after ridge plowing, promptly compact the ridge tops with a wooden roller to prevent moisture loss.

(3) Harrowing stubble. This is used in both the Northeast spring soybean region and the Huang-Huai River valley summer soybean region. Harrowing stubble is a shallow tillage method for flat-sown soybeans. This method can prevent excessive plowing from destroying soil structure and causing soil compaction, and can reduce the cost of deep tillage machinery operations. In the Northeast spring soybean region, shallow tillage by harrowing stubble is mainly used on fields where the previous crop was @#@245@#@. After wheat harvest, use a double-row disc harrow to cut stubble, harrow twice diagonally, and then harrow once more before sowing the next year, after which sowing can be done. In the Huang-Huai River valley summer soybean region, after the previous crop of winter wheat is harvested, first broadcast basal fertilizer, then immediately use a disc harrow to cut stubble 2-3 times, with a harrowing depth of 15-20 cm, then use an animal-drawn light spike-tooth harrow for one shallow harrowing pass; after harrowing fine and level, sow.

(4) Deep loosening. The deep loosening tillage method uses mechanized operations, has diverse methods, and is flexible, making it a very promising tillage method. On farms with a relatively high degree of mechanization in Heilongjiang Province, more than 80% of soybean planting areas have already adopted it. Using deep loosening shovels, the soil is loosened without turning over the soil layer, and interval deep loosening is carried out to break through the plow pan formed by flat plowing or ridge tillage, creating a plow layer structure with both loose and firm zones. The depth of deep loosening at the ridge bottom is generally 15-20 cm and should not be too deep; deep loosening in the furrow can be slightly deeper, generally up to 30 cm. At the same time, using deep loosening as the means can also complete operations such as topdressing, weeding, and earthing up at the same time.