Under general soil fertility, do not apply nitrogen fertilizer before and after soybean branching. Tests have shown that applying nitrogenous fertilizer at the branching stage not only inhibits the growth and development of roots and root nodules, but also changes flower buds to leaf buds, resulting in prolonged production loss. Most experts at home and abroad believe that the topdressing of soybeans at the flowering stage increases nitrogen production. Experiments have shown that under general soil fertility conditions, it is best not to apply nitrogen fertilizer during flowering. If the soil fertility is insufficient, the amount of nitrogen fertilizer applied at the flowering stage should also be less, because the application of nitrogen fertilizer during flowering will cause buds and flowers to fall off. The application of nitrogenous fertilizer at the end of the scarring stage can reduce the pods, greatly increase the weight of 100 seeds, and allow a small number of plants to reproduce buds (mostly one or two pods) and increase the yield by 20% to 40%. Because the growth of vegetative growth at the end of crust was basically stopped, the growth rate of roots and root nodules was greatly reduced, and the ability of nitrogen fixation of rhizobia was gradually decreased. The amount of nitrogen and phosphorus absorbed by soybeans during the grain-filling period accounted for 60% to 65% of the total growth period, and the absolute amount of nitrogen required was 8 to 9 times that of phosphorus. Therefore, the supply of nitrogen is often insufficient in the soybean grains. The application of nitrogen fertilizer at the end of the scarring stage not only meets the needs of soybean grain, but also does not cause plant growth, so it can significantly increase grain yield. The phosphorus-deficient blocks can also be combined with nitrogen and phosphorus for topdressing. The suitable ratio of nitrogen and phosphorus is 9:1. After top dressing, we must pay attention to timely irrigation.
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