Why does the partial application of nitrogen fertilizer reduce the yield of crops? How much nitrogen do crops need?

Nitrogen is one of the essential nutrient elements for crops. proper supply of nitrogen fertilizer can increase crop yield and improve crop quality. However, if the partial application of nitrogen fertilizer, the crop yield will be reduced, what is the reason for this? How much nitrogen do crops need?

Partial application of nitrogen fertilizer will cause a large number of carbohydrates produced by crop photosynthesis to be used to synthesize proteins, chlorophyll and other nitrogen-containing compounds, and only a small amount of carbohydrates can be used as raw materials to make up the cell wall-- cellulose, hemicellulose and pectin, etc. as a result, the cells are large and thin, the tissue is soft, the leaves are covered with each other, and the canopy is poorly ventilated and transparent, resulting in the elongation of the basal internodes of rice and the excessive growth of cotton plants. Greedy green late ripening, drought resistance, cold resistance, disease resistance decreased, and even lead to lodging and yield reduction, so the amount of nitrogen fertilizer should be appropriate.

So how much nitrogen do crops need? According to the analysis and statistics of a large number of data, if you harvest 100 kg rice (including corresponding stem and leaf nutrients, the same below), you need to absorb about 1.6-3.2 kg nitrogen; to produce 100 kg lint, you need to absorb 12-15 kg nitrogen; to produce 100 kg rapeseed (Brassica napus), you need to absorb 6.8-7.8 kg nitrogen; to harvest 100 kg corn seed, you need to absorb about 2.5-4.0 kg nitrogen. To harvest 100kg fresh tea, it needs to absorb 1.2kg to 1.4kg nitrogen; to produce 100kg apple and citrus, it needs to absorb 0.3kg and 0.6kg nitrogen respectively; to produce 100kg sweet potato, it needs to absorb 0.35kg 0.42kg nitrogen. It can be seen that different crops, the need for nitrogen is very different, the application of nitrogen fertilizer, can not be uniform.