When nitrogen supply was appropriate, the root system grew rapidly and the number of roots increased, but excessive nitrogen supply inhibited the root system growth of rice. Nitrogen can obviously promote the growth of stems and leaves and the development of tillering primordia, so the higher the nitrogen content of plants, the faster the leaf area grows and the more tillers there are. Nitrogen is also closely related to spikelet differentiation and degeneration. Generally speaking, proper nitrogen application can improve photosynthesis, form more assimilated products, promote spikelet differentiation and increase glume size, thus increasing caryopsis content and grain weight.
The symptom of nitrogen deficiency is usually that the leaves turn green and yellow. It usually starts from the lower edge. Nitrogen deficiency will hinder the synthesis of chlorophyll and protein, thus weakening photosynthesis and affecting dry matter production. When nitrogen deficiency is serious, cell differentiation stops, which is characterized by shorter leaves, thinner plants, decreased tillering ability and weakened root function. When there is too much nitrogen, the leaves are elongated and drooping, the leaves are dark green, the stems are clustered, the number of ineffective tillers increases, and the population tends to grow excessively, resulting in poor light transmission, decreased seed setting rate, delayed maturity, lodging in the later stage and aggravated diseases and insect pests.
Physiological effects of phosphorus on rice: the content of phosphorus in rice stems and leaves is generally 0.4% ~ 1.0%. The phosphorus content in the ear is high, which is 0.5%- 1.4%. Phosphorus is one of the important components in cytoplasm and nucleus, and directly participates in the metabolism of sugar, protein and fat. Some high-energy phosphoric acid is the main place for energy storage. Adequate phosphorus supply, good rice root growth, more tillers, vigorous metabolism, enhanced stress resistance, and promote early maturity and yield increase. Phosphorus participates in energy metabolism and exists in parts with high physiological activity. Therefore, phosphorus is indispensable in cell division and meristem development, especially in seedling stage and tillering stage.
When rice is short of phosphorus, the plants tend to be dark green, the leaves are narrow and erect, the lower leaves die, the tillers decrease, the root system develops poorly, and the growth stagnates, which often leads to rice seedling shrinkage and red seedling, and the growth period is delayed, which seriously affects the yield.
Physiological effects of potassium on rice: the content of potassium in stems and leaves of rice at different growth stages is about 1.5% ~ 3.5%, and the content in panicle is low, generally below 0.5% ~ 1%. Potassium exists almost completely in the form of ions in plants, and some of it is adsorbed in protoplasm. Unlike nitrogen and phosphorus, potassium is not a component of protoplasm, fat and cellulose. However, in some important physiological metabolism, such as the decomposition and transfer of carbohydrates, potassium plays a catalytic role, which can promote these processes smoothly. Potassium also contributes to nitrogen metabolism and protein synthesis, so the more nitrogen is applied, the more potassium is needed. Potassium is an activator of many important enzymes in plants. Appropriate amount of potassium can improve the photosynthesis of rice, increase the carbohydrate content and thicken the cell wall, thus enhancing the disease resistance and lodging resistance of plants.
When rice is deficient in potassium, the root system development is stagnant, which is easy to cause root rot. The degree of leaf discoloration is similar to that when nitrogen is applied too much, but the leaves become shorter. When potassium deficiency is serious, yellow-brown spots first appear on the tip of the leaf, which gradually spread to the whole leaf, the stem becomes soft and the plant height elongation is inhibited. Potassium has great mobility in plants and can be transferred from old leaves to new leaves. Potassium deficiency first appeared in the lower leaves. When potassium is insufficient, starch, cellulose and carbohydrates decrease, and most of the growth of rice can be improved after applying potassium fertilizer in lush shade or insufficient light.