The amount of fertilizer absorbed by rice plants as a percentage of the amount of fertilizer applied is called the fertilizer absorption utilization rate. The utilization rate of the main fertilizer in paddy fields is as follows:
Nitrogen Fertilizer Utilization The utilization rates of nitrogen fertilizers were 45.4% ammonium sulfate, 34.8% urea, and 26.8% ammonium bicarbonate. The direction of nitrogen application into the soil can be divided into three parts: rice absorption, soil residue and loss. The loss of nitrogen fertilizer in rice fields, the first is the denitrification process, the loss is about 10% to 15%, the highest is about 20%; the second is improper application method, the ammonium nitrogen can reach 5% to 50% through the volatilization loss; Water leaching, such as urea applied to rice fields, is usually converted to ammonium ions after two or three days of hydrolysis to be absorbed by rice and adsorbed by soil colloid. If it is drained within 24 hours, the nitrogen loss can reach 10% to 20%. Fourth, in addition to being adsorbed by the soil colloid, nitrogen remaining in the soil is difficult to release by fixing it by clay minerals.
The utilization rate of phosphate fertilizer is generally 10% to 25%, and the average is 14% is significantly lower than nitrogen fertilizer, mainly because the phosphorus applied to the soil is quickly combined with iron, aluminum and calcium in the soil to form insoluble phosphate. (called chemical fixation). This kind of fixation also has a beneficial side, which can reduce the loss caused by the leaching effect. A part of the fixed phosphorus is weakly acid soluble and can be absorbed and utilized by the second year crop. Paddy fields contribute to the release of phosphorus under flooding conditions, so the available phosphorus content in paddy soils is higher than that of corresponding dry soils.
Potassium fertilizer utilization rate Due to the soil clay mineral type, water status and soil acidity and alkalinity, the fixed amount of potassium in the soil varies greatly, generally ranging from 11% to 77%. Potassium fixation can reduce the leaching loss and will be re-released under certain conditions. Usually, the dry-wet interaction is frequent, the pH is increased, and the fixed amount of potassium is increased.
The consumption of potassium in the soil is mainly the absorption and leaching of rice, while the replenishment of potassium is mainly from fertilizer, and the rainfall brings a small amount of potassium. In addition, the roots remaining in the soil supplement a certain amount of potassium. In general, the mobility of potassium in soil is less than that of nitrate nitrogen and greater than phosphorus, so there is also a certain amount of leaching. The utilization rate of potassium in the year is generally 50% to 60%. (Liu Zuowen)
Symptoms of rice deficiency and nutrient excess
In the growth and development of rice, if a certain nutrient is lacking, the metabolism of the crop will be hindered and destroyed, and the roots, stems, leaves, flowers and seeds will have unique symptoms.
Nitrogen deficiency: The plant is short and has few tillers. The leaves are small and erect, the leaves are yellow-green, the stems are short, the ears are small, and the rate of imperfections is high.
Phosphorus deficiency: often forms a "frozen seedling" in the early stage of fertility, which is characterized by slow growth, no tillering or delayed tillering, and the seedlings are not weak. The leaves are dark green or grayish green with purple, the leaves are narrow and long, the leaves are small, and the leaves are slightly curled. The old roots turn yellow, the new roots are few and slender, and when they are severe, they become black and rot. The maturity period is inconsistent, the ear small particles are small, the thousand grain weight is low, and the empty shell rate is high.
Potassium deficiency: brown spots often appear on the leaves. Generally, after tillering, the tip of the old leaf first appears as a smoke-like brown dot, and the mosaic is scorched along the leaf edge. At the peak of the tillering period, the brown spots develop into brown spots, the shape is irregular, and the edges are clearly defined, often distributed in strips or blocks between the veins. The brown spots continue to develop from the old leaves to the adjacent new leaves. When the potassium is severely deficient, the brown spots are contiguous, and the whole leaves are red and dead, like burning.
Zinc deficiency: The growth of the seedlings is stagnant, and there is no sputum. The brown plaques appear in the middle of the back of the old leaves, and the veins turn white. When severe, the sheaths turn white.
Excessive nitrogen: The rice plant is long, the leaves are dark green, the leaves are hypertrophy, the stems are soft, easy to fall and infected with pests and diseases, and the grass is late and ripe, and the valley is more.
Excessive phosphorus: often induced zinc deficiency in rice. Therefore, the symptoms of excessive phosphorus are similar to those of zinc deficiency, and there are few tillers. The "frozen seedlings" do not develop, the leaves are green, and the leaves gradually turn yellow-white along the midrib, and the old leaves appear brown. The whole leaves are brown in the late growth stage. The root system grows slowly, and when it is severe, the whole plant is dead.
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