[Agricultural Chemistry] Fertilization Techniques for High-Yield Rice

   I. Characteristics of Rice's Nutrient Requirements

1. Nitrogen
   Rice is a crop that prefers ammonium nitrogen. When the supply of nitrogen is sufficient, new roots of rice can grow, tillering can proceed normally, and the leaves can elongate. However, excessive application of nitrogen fertilizer will lead to overly lush leaves, insufficient light for the lower leaves, which is likely to trigger the breeding of pests and diseases and cause lodging in the later stage. Excessive application of ammonium nitrogen is prone to cause ammonia poisoning, especially under conditions of low light and low temperature. Nitrogen fertilizer can enhance root activity. Surface application of nitrogen fertilizer can enhance the oxidation ability of the upper roots and promote tillering, while deep application can enhance the activity of the lower roots and increase the number of spikelets per panicle.

2. Phosphorus
   Phosphorus can promote the transportation of sugar and the synthesis of starch in the plant, accelerate the grain filling and ripening process, and is conducive to increasing the 1000-grain weight and seed setting rate. The supply of phosphorus during the seedling stage and tillering stage of rice is very important. Phosphorus deficiency at this time will have a significant impact on subsequent growth and yield. Therefore, phosphorus fertilizer must be applied early. Topdressing phosphorus fertilizer after rice flowering will inhibit the synthesis of starch in the body and hinder grain filling.

3. Potassium
   Potassium can improve the resistance of rice to adverse environments and reduce the occurrence of pests and diseases. Therefore, some people call potassium fertilizer "pesticide". By promoting carbon and nitrogen metabolism, potassium can reduce the carbon and nitrogen sources required by pathogens, enhance the activity of adenosine triphosphatase in plants, and promote the synthesis of phenolic substances, thereby improving the disease resistance of crops. Potassium can increase the silicon content in the roots, stems and leaves of plants, enhance the number of silicified cells on the leaves per unit area. The hardness, thickness and lignin content of the stems all increase with the increase of potassium application rate, and ultimately enhance the resistance of rice to pathogen infection.

4. Silicon
   Rice is a silicon-loving crop and absorbs the largest amount of silicon among various crops, and is known as a "silicic acid plant". Silicon is an essential nutrient element for rice.

5. Zinc
   Zinc plays an important role in the growth and development of rice. Zinc can promote the synthesis of auxin. The zinc content in rice is higher in vegetative organs than in reproductive organs. The seedling stage and panicle stage are the peak periods of zinc absorption in rice, and the absorbed zinc accounts for 84.6% - 96.1% of the total zinc absorption during the whole growth period. Zinc deficiency is a relatively common problem in rice production. The most obvious symptoms of zinc deficiency are stunted plants, white midribs of leaves, hindered tillering, slow leaf emergence rate, which seriously affect the yield. Therefore, some people list zinc as the "fourth element" of rice, second only to nitrogen, phosphorus and potassium.

   II. The Law of Fertilizer Requirements in Different Growth Stages of Rice
   From the greening stage to the booting stage of rice, the absorption amount of various elements increases rapidly. However, after the booting stage, the increase range of various elements is different. For nitrogen, 80% of the total amount required for the whole growth process has been absorbed by the booting stage, while for phosphorus it is 60%, and for potassium it is 82%. There are two peaks in the nitrogen absorption amount of the plant, which are the tillering stage and the booting stage. The peak of phosphorus absorption amount is from the tillering stage to the jointing stage (accounting for about 50% of the total amount), and the absorption amount at the heading stage is also relatively high. The absorption amount of potassium is concentrated from the tillering stage to the booting stage. After the heading stage, the absorption amounts of nitrogen, phosphorus and potassium are all very weak. Therefore, most of the nutrients required during the grain filling stage are stored in the plant before the heading stage.

   III. Fertilization Principles

1. Determination of Fertilization Amount
   The fertilization amount of rice can be comprehensively considered according to the nutrient requirements of rice, the supply amount of soil nutrients, as well as the nutrient content and utilization rate of the applied fertilizers. The degree of rice's dependence on the soil is closely related to soil fertility. The higher the soil fertility, the greater the proportion of nutrients supplied by the soil. Paddy fields generally lack nitrogen, most of them lack phosphorus, and some lack potassium. In order to give full play to the yield-increasing effect of applying chemical fertilizers, not only should nitrogen, phosphorus and potassium be applied in combination, but also soil testing and formula fertilization should be implemented. The approximate range of the utilization rate of chemical fertilizers in the rice-growing areas of China in the current season is: 30 - 60% for nitrogen fertilizer, 10 - 25% for phosphorus fertilizer, and 40 - 70% for potassium fertilizer.

2. Determination of Fertilization Period
   The fertilization periods for high-yield rice generally can be divided into four periods: base fertilizer, tillering fertilizer, panicle fertilizer and grain fertilizer.
   ① Base Fertilizer. The fertilizer applied to the soil before rice transplantation is the base fertilizer. The base fertilizer should combine organic fertilizer and inorganic fertilizer to meet the requirement of high available nutrient supply during the effective tillering period and also have a stable and long-lasting fertilizer effect. The base fertilizer should account for 40% of the total amount of chemical fertilizers, and it is generally applied in combination with the last plowing of the field.
   ② Tillering Fertilizer. The tillering stage is an important period for increasing the number of roots. It is advisable to apply the tillering fertilizer early on the basis of applying sufficient base fertilizer to promote tillering, improve the ear formation rate and increase the number of effective ears. It is generally applied half a month after transplantation or rice planting.
   ③ Panicle Fertilizer. According to the period of topdressing and the function of the topdressed fertilizer, it can be divided into flower-promoting fertilizer and flower-protecting fertilizer. The flower-promoting fertilizer is applied during the panicle axis differentiation stage to the spikelet differentiation stage. Applying nitrogen at this stage can promote the differentiation of branches and spikelets and increase the number of spikelets per panicle. The flower-protecting fertilizer is applied slightly before the pollen cell meiosis stage, which can prevent the degeneration of spikelets and increase the accumulation of storage substances in the stem and sheath. In production practice, the panicle fertilizer is generally not divided into flower-promoting fertilizer and flower-protecting fertilizer, but is applied 40 - 50 days after transplantation.
   ④ Grain Fertilizer. The grain fertilizer has the functions of prolonging the leaf function, increasing the photosynthetic intensity, increasing the grain weight and reducing the number of empty grains. Especially for paddy fields with a relatively small population and varieties with large panicles and a long grain filling period, the application of grain fertilizer is more meaningful.

   IV. Several Issues Needing Attention in Fertilization

1. Apply Sufficient Organic Fertilizer
   Organic fertilizer contains various nutrients. In addition to nitrogen, phosphorus and potassium, it also contains sodium, magnesium, sulfur, calcium and various trace elements. Applying organic fertilizer can improve the soil aeration and the characteristics of absorbing fertilizer and retaining water, and promote the stable growth of rice plants, which is conducive to achieving high yield and good quality of rice. Organic fertilizer is mainly used as base fertilizer.

2. Control Nitrogen Fertilizer
   Applying an appropriate amount of nitrogen fertilizer to rice can promote the growth of rice plants. However, excessive application will not only result in an increase in ineffective tillers, excessive greening, lodging, and aggravation of pests and diseases, but also lead to more empty grains, a decrease in the seed setting rate, and affect the rice yield. Therefore, attention should be paid to controlling the amount of nitrogen fertilizer during the growth and development process of rice. Nitrogen fertilizer is mainly used as topdressing. For the first time, apply 6 - 7 kilograms of urea per mu after rice transplantation, and for the second time, apply 4 - 5 kilograms of urea per mu in combination with field weeding 13 - 15 days after transplantation to facilitate the growth of strong tillers. In the middle stage, pay attention to drainage and fertilizer control. Only for the second and third-class rice seedlings with poor growth should some balanced fertilizers be applied as appropriate. In the later stage, topdress 3 - 4 kilograms of grain fertilizer according to the growth of the seedlings.

3. Pay Attention to Applying Phosphorus and Potassium Fertilizers
   Phosphorus and potassium fertilizers are essential elements for the growth and development of rice. They can enhance the internal activity of plants, promote the synthesis and transportation of nutrients, strengthen photosynthesis, prolong the function period of leaves, make the grains plump and full, and increase the yield. Phosphorus fertilizer is preferably used as base fertilizer, and potassium fertilizer is better applied as topdressing. Apply 20 kilograms of phosphorus fertilizer per mu as base fertilizer in the fields with sufficient organic fertilizer, and topdress 3.5 - 5 kilograms of potassium chloride per mu before tillering. Spraying potassium dihydrogen phosphate in the later stage of rice can promote grain filling and ripening. Spray it once in the later stage of heading and flowering and once during the grain filling stage. Each time, use 150 grams of potassium dihydrogen phosphate per mu, dilute it with 50 - 60 kilograms of water and spray it in the evening.

4. Increase the Application of Multi-element Fertilizers
   Trace elements such as silicon, zinc, manganese, and boron can improve the oxygen supply to the roots of rice, enhance the stress resistance of rice plants, improve the disease resistance of plants, promote the development of roots in the later stage, prolong the function period of leaves, and prevent premature aging. They can accelerate the development of flowers, increase the number of pollen grains, promote the germination of flower grains, and are conducive to improving the ear formation rate of rice. They can also promote large panicles and more grains, improve the seed setting rate and the plumpness of grains, and thus increase the rice yield. According to experiments, under the same cultivation and management measures, applying trace element fertilizers can increase the yield by 40 - 50 kilograms per mu compared with not applying them, while the production cost per mu only increases by about 2 yuan.

   Yishizhuang Organic Fertilizer
   Rich in nutrients. It is rich in organic matter, biochemical fulvic acid, amino acids, nitrogen, phosphorus, potassium and medium and trace elements such as calcium, magnesium, boron and zinc.
   Improve the soil. Long-term application can effectively improve the soil aggregate structure, enhance soil permeability, promote microbial activities, and regulate the soil pH.
   Resist stress and prevent diseases. The fertilizer effect is long-lasting, which can improve the cold resistance, drought resistance, disease resistance and continuous cropping resistance of crops and improve the quality of crops.
   Green and environmentally friendly. The fertilizer is safe, free of heavy metals and other harmful substances, and can effectively decompose the toxic and harmful substances remaining in the soil.

     Yishizhuang's formula fertilizer for rice is a national patented product. It is rich in organic matter, which can effectively improve the soil structure and increase the utilization rate of fertilizers. Medium and trace elements (silicon and zinc) are reasonably added, with comprehensive and balanced nutrients and outstanding fertilizer efficiency. It can meet the nutritional needs of rice growth and effectively improve the yield and quality of rice.