Key Technical Points for Field Management of Rapeseed (Brassica napus) After Spring

After the beginning of spring, as temperatures gradually rise, the vegetative growth and reproductive growth of rapeseed gradually enter an vigorous period. The main stem rapidly elongates and thickens, branches continuously emerge, short-petioled leaves, sessile leaves and branch leaves all emerge during this period, and flower buds differentiate in large numbers. This is the fastest growing period in its entire life cycle. Therefore, it is recommended that farmers strengthen field management during this period to promote normal growth and development of rapeseed.
　　
1. Scientific fertilization. Rapeseed grows vigorously after spring. To promote high yield, attention should be paid to rational application of fertilizers. Generally, when the bolting stem of rapeseed is about 10 cm high, fertilizer should be applied appropriately according to the situation. For fields with poor growth, 3-5 kg of urea or 8-10 loads of human and livestock manure can be applied per mu to increase the number of effective branches, siliques and grains per plant, ensuring steady growth of rapeseed in the later stage; at the early bolting stage and early flowering stage, in addition to the basal application of boron fertilizer, about 50 kg of 0.1%-0.2% borax solution should be sprayed on the leaves separately to prevent boron deficiency causing the "flowers but no seeds" disorder, which leads to severe yield reduction, decreased oil content of rapeseed and deteriorated quality; from the beginning of flowering to full bloom, combined with boron fertilizer spraying, 0.2% potassium dihydrogen phosphate solution should be sprayed per mu, which can effectively reduce silique shedding and empty siliques and increase grain weight.
　　
2. Drainage and waterlogging prevention. After spring, the three ditches in the field should be cleared in time, and the ditches outside the field should be deepened at the same time, keeping the ditches connected and drainage unobstructed, so that accumulated water in the field can be drained and soil moisture reduced, ensuring normal growth of rapeseed in soil with suitable moisture, maturing well to the end, preventing premature death of lower leaves, improving disease resistance of rapeseed and obtaining higher yields.
　　
3. Disease control. After spring, insect pests of rapeseed are relatively few, and the main focus is on preventing sclerotinia stem rot. This disease is highly damaging to rapeseed. In mild cases, it reduces the number of siliques and grains and decreases grain weight; in severe cases, the plants wither prematurely, or even result in no harvest at all. It generally can cause about 15% yield reduction, and in severe cases more than 40%. This disease can occur from the seedling stage to the maturity stage, with the most severe incidence after the full flowering stage. Leaves, stems, branches, petals, siliques and seeds can all be affected. For the control of this disease, on the basis of strengthening ditch clearing and drainage to reduce soil and field humidity; removing old yellow and diseased leaves in batches during the full flowering stage to improve field ventilation and light penetration, control the spread of pathogens and reduce sources of inoculum, chemical control should be applied. The full flowering stage is the key period for field spraying. For fields with good growth, at the early flowering stage and full flowering stage, 1000-1500 times diluted 40% dimethachlon solution should be sprayed once each per mu, and at the final flowering stage, 1500 times diluted 70% thiophanate-methyl wettable powder should be sprayed once per mu to ensure control effectiveness.
　　
4. Timely harvest. If rapeseed is harvested too early, grain weight is light, oil content is low, and a high-yield crop cannot be fully harvested. If harvested too late, siliques are prone to splitting and grain shattering, causing losses. When the siliques on the main inflorescence all turn yellow, and 70%-80% of the siliques on the whole plant and in the whole field have lost their green color and turned yellow, the lower siliques on the main inflorescence are yellow and glossy, and the seeds show the inherent color of the variety, it is ready for harvest. Harvesting should be done in the morning before the dew has dried or on cloudy days, taking care to cut and lay down gently to reduce losses. If the weather is sunny, after drying off moisture, the plants can be stacked for after-ripening for 5-7 days, then spread out to sun-dry and thresh, to promote after-ripening of some green siliques, plump the grains, and increase rapeseed yield and oil content. If continuous rainy weather prevents timely threshing, then bundle the rapeseed plants one by one, with siliques facing upward, and place them upright. Never stack them in large piles, which causes heating, mold, rot and sprouting, affecting the quality of the rapeseed.