Key Technical Points and Precautions for Soybean Sowing

1. Soil preparation:

(1) Pre-sowing land preparation: Pre-sowing land preparation includes the soil tillage carried out before sowing as well as harrowing, leveling, and rolling. Because different land preparation techniques are used, the pre-sowing land preparation work also differs. Examples include flat plowing, ridge planting, stubble harrowing, and deep loosening.

(2) Pre-sowing irrigation: For plots with poor soil moisture, where irrigation conditions permit, water once 1-2 days before sowing, just enough to moisten the soil, to facilitate seed germination after sowing.

(3) Pre-sowing pre-emergence herbicide application: In some large farms in the main soybean-producing areas of Northeast China, soybean cultivation areas are large, and if management is not timely, weed damage is severe, so mechanical spraying of herbicides is often used before sowing for pre-emergence herbicide application in the field. Herbicides such as trifluralin and alachlor can be sprayed on the soil before sowing. Trifluralin can effectively control annual grass weeds and certain annual broadleaf weeds. Generally, before sowing, apply 135 [units] of trifluralin at a concentration of 48% per mu, add 15 liters of water, and use a tractor-mounted sprayer to spray the soil surface.

2. Seed selection: Seeds with good sowing quality have high germination rate and germination vigor, and the seedlings are uniform and robust. Therefore, before sowing, diseased seeds, insect-damaged seeds, small seeds, shriveled seeds, and broken seeds should be removed. At the same time, according to the typical characteristics inherent to this variety, such as seed shape, seed color, seed size, hilum size, and color depth, mixed seeds of other varieties should be removed to improve seed purity. Manual seed selection gives very good results. If the amount of seed used is large, a spiral soybean seed selector can be used; its mechanical structure is simple, easy to move, and suitable for specialized soybean growers. The selected seed is required to reach a purity of more than 97% and a varietal purity of more than 98%.

3. Seed testing and germination test: Selected seeds should be tested for grain weight and subjected to a germination rate test before sowing. These two tasks are the basis for calculating the sowing rate. Take the selected seeds and randomly sample 3 portions, randomly drawing 100 seeds from each portion, weigh each separately and calculate the average, which is the 100-seed weight of that variety. The unit is expressed in grams. Seed germination rate determination: Place the above 3 portions of 100 seeds each into 3 small dishes or germination dishes, with straw paper or river sand underneath. Add water to form a thin water layer, then arrange the seeds evenly and place them in a warm place at about 20°C (beside a stove or in an incubator) to absorb water, swell, and germinate. After 5-7 days, count the number of seeds that can normally grow roots and germinate, and average the 3 samples to obtain the germination rate of the seeds. A germination rate of more than 95% is required.

4. Seed treatment: To control seedling-stage pests and diseases such as white grubs, cutworms, root maggots, and root rot, commonly use 0.1%-0.15% phoxim or 0.7% lindane powder or 0.3%-0.4% carbendazim plus thiram (1:1), or 0.3%-0.5% carbendazim plus captan (1:1) for seed dressing, based on seed weight. When chemical seed dressing and molybdenum fertilizer seed dressing are carried out at the same time, it is necessary to air-dry after molybdenum seed dressing before proceeding. Note that after seed dressing with rhizobia, insecticides and fungicides must not be applied again.

5. Determination of sowing rate:

Step one: Convert the measured 100-seed weight of a certain variety into the number of seeds per kilogram. For example, if the measured 100-seed weight of a certain variety is 20 grams, then the number of seeds per kilogram is: 100 seeds * 1000 grams ÷ 20 grams = 5000 seeds.

Step two: Calculate the number of seeds sown per 667 sq m. Calculate the number of plants to be retained per 667 sq m according to the actual situation, then according to local cultivation conditions and management level, add a certain loss rate (such as losses caused by machinery, people, and livestock during field management and manual thinning). Generally, the field loss rate can be calculated at 15%-20%. The planned number of plants to be retained per unit area plus the field loss rate is the number of seeds sown per 667 sq m (1 mu). For example, if a certain variety is planned to retain 25,000 plants per 667 sq m, and the field loss rate is estimated at 20%, then the number of seeds sown per 667 sq m is: number of seeds sown per 667 sq m: 25000 + 25000*20% = 30000 seeds.

Step three: Calculate the sowing rate per 667 sq m. The formula is as follows: sowing rate per 667 sq m (kg) = number of seeds sown per 667 sq m / (number of seeds per kg * germination rate). For example, if the plan is to sow 30000 seeds per 667 sq m, the measured number of seeds per kg is 5000 seeds, and the measured germination rate is 95%. Substitute into the formula: sowing rate per 667 sq m: 30000 / (50000*0.95) = 6.3 (kg).

6. Reasonable close planting: Planting density is closely related to yield. So-called reasonable close planting means that under the specific local and current conditions, the relationship between individuals and the population is correctly handled, so that the population develops to the maximum extent and individuals also develop fully; the light energy and soil fertility per unit area are fully utilized; and under the same cultivation conditions, the best economic benefit can be obtained. Therefore, a suitable density is not unchanging, and it cannot simply be said that "fertile land should be sparse and poor land should be dense." The following factors should mainly be considered:

(1) Variety: The degree of luxuriance of the variety, such as plant height, number of branches, leaf size, etc., is closely related to density. For varieties with tall plants, more branches, an open plant type, and large leaves, the planting density should be smaller; for varieties with short plants and poor luxuriance, or varieties that are taller but have few branches and a compact plant type, a larger density should be adopted.

(2) Fertilizer and water conditions: For the same variety, when fertilizer and water conditions are better, the plants grow luxuriantly, and the density should be smaller; conversely, when fertilizer and water conditions are poor, the density should be larger. Trials show that soil fertility and fertilization level are closely related to planting density.