How to mitigate continuous and alternate soybean cropping? Integrated measures are key

To minimize yield losses from continuous and alternate cropping, continuous and alternate soybean planting should be avoided as much as possible, rational crop rotation should be maintained, alternate cropping should be reduced, and continuous cropping should be controlled. In the long term, the area of continuous and alternate soybean cropping should not be expanded without limit, so as to avoid declining soil productivity and creating a vicious cycle. When continuous and alternate cropping is unavoidable, alternate cropping should be arranged first, and continuous cropping should be used only when alternate cropping cannot be arranged, and continuous cropping must not exceed two years. In response to the causes of yield reduction under continuous and alternate cropping, with emphasis on regulating nutrition and controlling pests and diseases, existing scientific research results, new technologies and practical technologies should be integrated and implemented in a coordinated way to reduce the damage to a minimum.

Choose varieties with strong stress resistance

Under continuous and alternate cropping conditions in different ecological regions, different varieties differ greatly in yield. Therefore, selecting excellent varieties with suitable maturity and tolerance to continuous and alternate cropping according to local conditions in different regions can reduce soybean yield losses. In the eastern region of our province, selecting high-quality, high-yield varieties resistant to root rot, and in the western region, selecting high-quality, high-yield varieties resistant to cyst nematode, both have relatively good results.

Strengthen the control of pests and diseases

The main pests and diseases affecting soybean yield include cyst nematode, root rot and Phytophthora blight. These three pests and diseases cause different damage in different regions and different years. The arid western region of Heilongjiang Province is mainly harmed by cyst nematode; the northern region is mainly harmed by root rot and root maggots, and the damage from sclerotinia is also relatively severe; the eastern and central-southern regions are mainly harmed by root rot and root maggots, and the damage from white grubs is also relatively severe. In rainy years, excessive soil moisture makes root rot prone to occur; in dry years, cyst nematode occurs more severely, and continuous and alternate cropping also aggravates the damage from soybean black spot, purple spot, aphids and pod borers.

Deep plowing in summer and autumn and fine seedbed preparation

Deterioration of the soil environment is another important reason for yield reduction in continuous and alternate cropping soybeans. Therefore, implementing deep plowing or deep loosening and fine seedbed preparation, improving soil water, fertilizer, air and heat conditions, promoting soybean root development, and enhancing plant resistance can increase the yield of continuous and alternate cropping soybeans. At the same time, plowing the land can also deeply bury insect eggs, pathogens and weed seeds, preventing the spread of pests and diseases.

In the northern soybean-wheat production area of Heilongjiang Province, summer plowing should be carried out early, with plowing and harrowing combined, and ridging done in time; wheat stubble can also be deep loosened or harrowed and deep loosened before ridging. In the western and southern corn-soybean production areas, autumn plowing or deep loosening and ridging should be carried out early, spring seedbed preparation should be minimized, and plowing, harrowing, leveling, ridging and compacting should be done as continuous operations, with attention to storing moisture, drawing up moisture and preserving moisture. In the eastern region, waterlogging should be prevented and temperature increased through deep plowing or deep loosening and ridging. Fields that have not been deep plowed in time must be planted on inverted ridges, not on original ridges.

Apply organic fertilizer and use chemical fertilizer skillfully

Continuous and alternate cropping soybean plants are not as robust as those in normal rotation, and their nutrient uptake capacity is weaker. In addition, soil fertility under continuous and alternate cropping is also lower than under normal rotation. Therefore, fertilizer application should be increased to promote plant growth and development. Organic fertilizer is a multi-element complex. Increasing the application of organic fertilizer can improve the soil's physical and chemical structure, increase soil fertility, meet the requirements of soybeans for various nutrient elements at different growth stages, create good environmental conditions for soybean growth and development, and have an obvious yield-increasing effect, especially under medium and low fertility conditions. When applying organic fertilizer, quality must be emphasized; the organic matter content should reach more than 8%. Generally, 15000-22500 kg per hectare is applied, incorporated in one application together with summer and autumn seedbed preparation.

Integrated weed control and controlling weed infestation

Weed damage in continuous and alternate cropping soybeans is more severe than in normal rotation. Malignant weeds such as cocklebur, dayflower and parasitic dodder associated with soybeans spread rapidly, competing with soybeans for nutrients, water and light. At the same time, due to long-term or repeated use of soybean field herbicides with long residual effects such as Pursuit, weeds have developed increased resistance, and soil residual toxicity has also increased. As a result, chemical weed control is not effective against malignant weeds, and it also affects the growth of soybeans and sensitive subsequent crops. In severe cases, it can leave residues in soybean seeds, reduce quality and affect exports.

Use continuous and alternate cropping regulation techniques

Continuous and alternate cropping soybean plants are shorter than those in normal rotation, have poor root development and weak absorption capacity. The application of rooting powder can promote root development and reduce root pest and disease damage; the use of seed coating agents with both pesticide and fertilizer functions can both prevent pests and diseases and strengthen plants; the application of organic micro-compound fertilizer and foliar topdressing can supplement nutrient deficiencies, promote healthy plant growth and development, and has a very good effect on increasing the yield of continuous and alternate cropping soybeans. At present, there are some soybean continuous and alternate cropping regulators, mitigators, foliar sprays and special fertilizers, some of which have very good effects and can be selected after testing.

After continuous and alternate cropping soybeans are treated with ABT rooting powder, the emergence rate can be increased, the number of cyst nematodes in the soil can be reduced, soybean cyst nematode disease can be alleviated, the number of rhizosphere bacteria and root nodules at the seedling stage can be increased, and the number of roots, root weight, nodule weight, dry matter accumulation, number of seeds per plant and yield can be increased. Its yield is comparable to that of normal rotation and it has a yield-preserving effect.

Improve planting methods and increase density appropriately

In continuous and alternate cropping soybean planting, due to pest and disease damage and nutritional deficiencies, dead seedlings, diseased plants and weak seedlings are prone to appear, reducing the green area in the field. Improving planting methods, appropriately increasing seeding rate and rationally distributing the population can increase soybean yield. Under normal circumstances, continuous and alternate cropping soybeans can be sown at a rate 8%-10% higher than normal rotation soybeans. At present, relatively good planting methods include precision hill-drop sowing in double rows on ridges, the "three-ridge" cultivation method, and narrow-row dense planting techniques.

Sow early and shallowly at the right time, and make full use of accumulated temperature to achieve high yield. In high-cold regions, temperature is an important factor limiting soybean yield and quality. In order to expand the planting area of high-yield late-maturing varieties and ensure maturity and quality, adopt timely early sowing when the 5 cm surface tillage layer stably passes 4°C, and shallow sowing (2 cm after compaction), to promote early seed initiation, early germination, early emergence and early maturity. This can ensure the promoted planting area of high-yield varieties and achieve the goal of promoting early maturity and high yield of late-maturing varieties.