（1） Fertility and Nutritional Characteristics

Rice goes through two different stages of vegetative growth and reproductive growth: vegetative growth includes seedling stage, tillering stage, and jointing stage, mainly the growth of roots, stems, and leaves, and the accumulation of nutrients for reproductive growth; Reproductive growth includes the booting stage, heading stage, flowering stage, and maturity stage, which mainly involve the formation, growth, flowering, and fruiting of reproductive organs. Fertilization during this stage should focus on promoting larger panicles, more grains, and fuller grains. Research has shown that the nutrient content in plants during the growth period of double season early and late rice is generally highest during the greening to tillering stage for nitrogen, and during the jointing stage for phosphorus and potassium; Single season rice has a longer growth period, with the peak of nitrogen, phosphorus, and potassium uptake occurring during tillering and late panicle differentiation. Double season rice has a shorter growth period, often reaching the peak of nutrient uptake within 2-3 weeks after transplantation.

Rice has a high demand for elements such as nitrogen, phosphorus, and potassium, and the amount and proportion of absorption are influenced by the variety, soil, climate, and cultivation conditions. Generally, for every 100 kilograms of rice produced, it is necessary to absorb 1.6-1.9 kilograms of nitrogen (N), 0.8-1.3 kilograms of phosphorus (P2O5), and 1.8-2.4 kilograms of potassium (K2O). The average ratio of N: P2O5: K2O is 1:0.6:1.2. If the yield of double season rice is 450 kilograms per mu, the average absorption of N-P2O5-K2O is 8-5-10 kilograms; The yield of a single season of rice per mu is 550 kilograms, which requires absorption of 10-6-12 kilograms.

（2） Fertilization amount

A large number of experiments have shown that there is a close relationship between grain yield and nitrogen application rate. As the yield increases, the nitrogen application rate also increases accordingly. This is called“ Determine nitrogen production. The main rice producing areas in China are in the south, where the soil is acidic and rich in phosphorus. However, there is a potassium deficiency (the available K content in the soil is less than 80mg/kg), and 5-10 kilograms of potassium fertilizer (K2O) need to be applied per mu. The nutrient ratio of applying chemical fertilizers to rice is N: P2O5: K2O, with an average of 1:0.35:0.65. If the yield of double season rice is 450 kilograms per mu, 12-16 kilograms of nitrogen fertilizer (N) are required, and the average fertilization amount of N-P2O5-K2O is 14-5-9 kilograms; The yield of single season rice is 550 kilograms per mu, requiring the application of 16-22 kilograms of nitrogen fertilizer (N). The average ratio of N: P2O5: K2O is 1:0.45:0.35, and the average fertilizer application rate is 19-9-7 kilograms. Under moderate fertility conditions, the nutrient requirements of crops such as rice for the current season are approximately half from soil and half from fertilization. If the soil is thin, fertilization should be the main method, while soil should be the main source of fertilizer for the soil.

（3） Fertilization technology

Fertilization for high-yield rice, leaving about 40% nitrogen fertilizer as topdressing and the remaining fertilizer as base fertilizer. Double season rice should be fertilized with nitrogen fertilizer about 7 days after transplanting, and then the seedlings should be fertilized later to prevent denitrification; Single season rice has a long growth period, with Honda growing for 90-120 days. Topdressing nitrogen fertilizer can be applied 5-7 days before the differentiation of young panicles. Rice with low yield and early maturity has a growth period of only 60-70 days, and sufficient basal fertilizer should be applied to promote early development. Topdressing is not necessary. Rice specific fertilizer should be applied as topdressing early, with phosphorus fertilizer being more effective; When using urea as topdressing, the proportion of nitrogen in the specialized fertilizer formula should be reduced accordingly. Rice is prone to zinc deficiency, and 50-70 kilograms of 0.1-0.3% zinc sulfate solution can be used per mu for foliar spraying. Adding silicate fertilizers is also beneficial for rice fields with high stems that are prone to lodging. Southern acidic paddy fields should use less nitrate nitrogen and water-soluble phosphorus to reduce the leaching loss of nitrate nitrogen and avoid the formation of insoluble iron phosphate and aluminum phosphate from water-soluble phosphorus, thereby reducing the fertilizer efficiency of the season.


Symptoms of nutrient deficiency

（1） Rice nitrogen deficiency: The whole plant has a light color, yellow and withered lower leaves, short stature, few tillers, premature senescence, small panicles, and incomplete grains. Excessive nitrogen leads to excessive plant growth, wilting and lodging, delayed maturation, and an increase in empty grains.
（2） Phosphorus deficiency in rice: Plants are tightly packed and in a tight state; The plant type of "Yizhu Xiang" is slow growing and not closed. The leaves and stems are dark green or gray blue, and the leaf tips and edges often have a purple red color and no luster. Phosphorus deficient rice declines before it ages.
（3） Potassium deficiency in rice: The leaves start to show reddish brown tips and spots from the lower leaves, gradually expanding towards the upper leaves, and in severe cases, the rice surface turns red like a wildfire. The plant height decreases, the leaf color is dark, the heading is uneven, the rate of ear formation is low, the ear shape is small, the seed setting rate is poor, and the grains are not full. Due to differences in cultivation season, variety type, and soil conditions, symptoms may vary. The first type is potassium deficient Fusarium wilt disease that occurs during the greening and tillering stage, also known as; Bronze disease. The second type is potassium deficient brown spot disease. The third type is potassium deficient sesame leaf spot disease.
（4） Magnesium deficiency in rice: Symptoms first appear on low aged leaves, and magnesium deficiency mostly occurs in the later stages of growth, with diseased leaves hanging down at right angles from the leaf pillow.
（5） Calcium deficiency in rice: Young organs are first affected, growth points are damaged, and heart leaves wither and die.
（6） Rice sulfur deficiency: Upper leaves lose their green color, growth is hindered, especially nutrient growth, and symptoms are similar to nitrogen deficiency.
（7） Iron deficiency in rice: The leaf veins lose their green color, appearing as striped flowers and leaves. The symptoms become more severe near the heart leaf, and in severe cases, the heart leaf does not emerge, resulting in poor plant growth, dwarfism, delayed growth, and even inability to head.
（8） Zinc deficiency in rice: The midrib of new leaves and the base of both sides of the leaves first turn green and yellow, and some even turn yellow at the spine of the leaf sheath. Later, it gradually turns into brownish red spots, and some have a large number of purple brown small spots that cover the entire leaf. Plants usually have varying degrees of dwarfism, and the sheaths of old leaves are even higher than those of new leaves, which is called“ Shrinking seedlings "or"; Shrinking seedlings. The base of the young leaves undergoes chlorosis, resulting in incomplete unfolding of the leaves and a special morphology where the front end unfolds while the middle and rear parts fold, leading to an increased angle of leaf emergence. If the symptoms persist until maturity, the plant will be extremely stunted, dark in color, with small and short leaves resembling bamboo leaves. The leaf sheaths will be longer than the leaf blades, and the jointing will be difficult. The tillers will be loose and take on a grassy appearance, and maturity will be delayed. Although slender rice ears can be pulled out, most of them will not be solid.
（9） Manganese deficiency in rice: The green color between the veins of newly formed leaves fades and turns yellow, but the veins remain green and the veins are clear. When there is severe manganese deficiency, gray white or brown spots may appear.
（10） Rice copper deficiency: Top wilts, internodes shorten, leaf tips turn white, and leaves become narrower and thinner. Excessive copper in rice plants makes it difficult for them to survive after transplanting, and even if the roots survive, they are not easily rooted. White roots are exposed on the surface, leaves turn yellow, and growth stagnates.
（11） Boron poisoning in rice: yellowing of leaf tips and edges, appearance of light brown spots, early growth inhibition, fewer effective panicles, reduced number of grains per panicle, increased number of flowers and grains, increased empty shell rate, and advanced maturity period.