What are the key cultivation techniques for rice-following beans?

Rice-following bean cultivation is a method in which, after the autumn rice harvest, the field is not ploughed or harrowed; instead, trenches are made, the field is divided into beds, and drainage is carried out, then soybeans are broadcast or dibbled on the bed surface and covered with rice straw. It has the advantages of simple planting, saving labour and time, low input, and good results, and is a short, flat, and fast project for raising multiple cropping and increasing grain, feed, and income.

1. Select improved varieties

There are many local soybean varieties; after mass purification and rejuvenation, those with good ecological adaptability, high yield, and disease resistance and with a moderate growth period can all be selected; for soybean varieties bred by agricultural research institutions, those with a large promotion area and good yield and economic benefit can also be selected. For example, Jingxuan No. 1, Diancang No. 2, local green-skinned bean, medium yellow hilum bean, fine yellow hilum bean, fine black hilum bean, and others currently bred and promoted in Jingdong have a whole growth period of 80-100 days, while large-seeded yellow hilum bean has a whole growth period of 70 days. These varieties yield 1200-2250 kg per hectare, with a maximum of 3000 kg, and are very suitable for planting as rice-following beans in areas of our province south of the equator at altitudes of 700-1350 m. However, many other soybean varieties are not suitable for planting as rice-following beans; for example, varieties of the Jufeng and Beifeng series perform as short plants with a shortened growth period, few or no pods, and low yield when planted as rice-following beans.

2. Pre-sowing preparation

① Sun the seed for 1-2 days before sowing, but avoid exposure to the scorching midday sun, which can crack the seed coat and affect germination; ② At sowing, dress the seed with 75-150 g of 56% ammonium molybdate per hectare (dissolved in hot water and cooled) or with 75 kg of biological potassium; ③ Do a good job of trenching, bed division, and drainage; trenching, bed division, and drainage are the basic work that must be done well in rice-following bean cultivation. For clayey fields with a high groundwater table and difficult drainage, drainage and field control should be carried out 10-15 days before the rice harvest; after the rice harvest, divide the field into beds 2-3 m wide in good time and open trenches for drainage. The side trenches and middle trenches should be 24 cm deep, and the bed trenches 12 cm deep. For large fields, after opening the "three trenches" well, open another cross trench every 7-10 m along the beds, dividing the field into many small beds, which helps drain the field water and sow evenly, reduces the death of young sprouts caused by oxygen deficiency during soybean germination or by high-temperature scalding of sprouts due to field water, and ensures uniform and strong seedlings.

3. Sow at the right time, plant at a reasonable density, and pay attention to fertilisation

The sowing period for rice-following beans is from late July to early and mid-August; too early or too late will both affect soybean growth. Specifically, sowing should be done promptly within one week after the rice harvest. The sowing rate depends on seed size, plant height, degree of branching, soil fertility, and fertilisation level. For small-seeded varieties, sow 60-67.5 kg per hectare; for medium-seeded varieties, 75-90 kg; for large-seeded varieties, 90-105 kg. There are two sowing methods: uniform broadcasting on small beds and dibbling; for dibbling, the row spacing is 30-36 cm, the hill spacing is 6-8 cm, and 3-4 seeds are sown per hill, ensuring 675,000-825,000 seedlings per hectare. After sowing, use the cut rice stubble as mulch, and add some rice straw to cover places that are not well covered, so that the seeds are not exposed, which shades them during the sprouting stage and maintains soil temperature, favouring seed germination and emergence. However, the mulch must not be too thick, lest it cause uneven emergence or produce leggy seedlings that affect yield. In addition, increasing fertiliser application has varying degrees of yield-increasing effect on soybeans. Immediately after emergence, apply 45-75 kg of urea per hectare (3-6 kg/mu) plus 70 kg of potassium chloride (4-5 kg/mu) as a seedling fertiliser; at the branching stage, topdress once more with nitrogen and potassium fertiliser; at the early flowering stage, topdress, generally using 30-45 kg (2-3 kg/mu) of compound fertiliser as a flower fertiliser; at the pod-setting stage, carry out foliar spraying. For spring soybeans planted in autumn, under the principle of "valuing base fertiliser, applying seedling fertiliser early, applying flower fertiliser skillfully, and applying seed-filling fertiliser as appropriate," specifically master the application per hectare of 99.5 kg of pure nitrogen, equivalent to 216 kg of urea (6.6 kg of pure nitrogen per mu, equivalent to 14.3 kg of urea per mu), 157.5 kg of P2O5, equivalent to 1125 kg of superphosphate (10.5 kg of P2O5 per mu, equivalent to 75 kg of superphosphate per mu), and 9.75 kg of K2O, equivalent to 243.75 kg of potassium chloride (9.75 kg of K2O per mu, equivalent to 12.25 kg of potassium chloride per mu), to obtain high yields.

4. Control pests and diseases and strengthen field management

Soybeans like moisture and fear drought but are not tolerant of waterlogging. If continuous clear and hot weather occurs after sowing, water in the early morning and evening to moisten the hills and preserve moisture; if continuous rainy weather occurs, drain water to prevent waterlogging. After emergence, check the seedlings and fill gaps promptly, insisting on thinning where dense and keeping where sparse, thinning out weak and yellow seedlings and keeping strong ones, so that the whole field has an even and reasonable population, and aim to keep 525,000-675,000 seedlings per hectare. When thinning, combine this with pulling weeds and cutting rice ratoon seedlings, so that the bean seedlings have good ventilation and light and grow evenly, laying the foundation for high yield.

5-7 days after sowing, spray 1500 mL of omethoate per hectare mixed with 900 kg of water (100 mL of omethoate per mu mixed with 60 kg of water) to control bean stem leafminer, applying once every 7 days for 3 consecutive times. At the bud stage and flowering stage, spray once each with zineb to control root rot, and for rust disease among them, spray with a 1000-fold solution of 20% triadimefon. At the pod-setting and seed-filling stages, use sodium diphacinone bait to control rodents.

5. Harvest at the right time to ensure increased income

When one third of the pods in the whole field have lost their green colour and turned yellow-brown, they can be harvested and hung up to dry, preventing mildew and rot from cloudy and rainy weather.