Introduction: utilization rate and physiological function of phosphate fertilizer

The utilization rate of phosphate fertilizer is much lower than that of nitrogen fertilizer and potassium fertilizer. In China, the utilization rate of phosphate fertilizer is generally within the range of 10% to 25%. The utilization rate of legume is higher in vegetable crops. There are two main reasons for the low utilization rate of phosphate fertilizer: the first reason is that phosphate fertilizer is fixed in soil, regardless of water-soluble, wolfberry-soluble and insoluble phosphate fertilizer. The second reason is that the movement of phosphorus in the soil is weak. This reason is actually the result of the first reason. Low exercise leads to low utilization rate because nutrients must be in contact with the root system in order to be really absorbed by crops, which involves the issue of bioavailability. In the past, the research on nutrients focused on chemical availability, that is, the study of what chemical forms are effective for crops. However, some chemically effective nutrients cannot be absorbed and utilized by crops for various reasons, so they are actually "ineffective". Recently, the concept of bioavailability has been put forward, that is, the nutrients of chemical availability must be actually absorbed by crops in order to be really effective to organisms, so it is called bioavailability. Of course, the premise of bioavailability is chemical availability. Only when the nutrients in the soil are in direct contact with the roots can they be actually absorbed by crops. Those nutrients that do not come into contact with the root system must reach the root surface through root interception, mass flow and diffusion. Root interception refers to the growth of the root system itself, extending to the location of nutrients. Mass flow refers to the nutrients dissolved in the soil solution, which reach the root surface with the movement to the root liquid. Diffusion means that a deficiency area is formed due to the absorption of nutrients close to the root surface, and the nutrient concentration in this area is lower than that of the soil, resulting in the movement of soil nutrients to the root surface. For phosphorus, due to the low concentration in the soil solution (usually only 0.05 mg / kg or less), the mass flow can supply very little phosphorus. For example, at the concentration of 0.05 mg / kg, the mass flow can only supply 1% of the phosphorus requirements of crops, and crop phosphorus is mainly obtained by diffusion (more than 90%). However, the diffusion coefficient of phosphorus is very small (that is, very little movement), and its 24-hour moving distance is only 1mm to 4mm, so the utilization rate of phosphorus is very low. Although the phosphate fertilizer applied to the soil is less absorbed and utilized by vegetable crops in the current season, the rest is mainly residual in the soil, forming the after-effect of phosphate fertilizer. If phosphate fertilizer is applied continuously and systematically to certain vegetable crops, the after-effect will be superimposed, so that the utilization rate of phosphate fertilizer used by vegetable crops in the current season increases significantly with the extension of continuous fertilization years, and some can even be as high as 30%-40%. Close to the utilization rate of nitrogen and potash fertilizer. Inorganic forms of phosphorus in vegetables mainly play a role in physiological regulation, such as the synthesis and transportation of sugars, the metabolism of fat, the promotion of respiration and the absorption of water and nutrients by vegetables, and the promotion of cell division and the growth of buds and roots. The root system of vegetable crops often does not grow well when phosphorus is deficient. Vegetables absorb more phosphorus in the early growth stage, accounting for 60% to 70% of the total absorption during the growth period. The phosphorus entering the vegetable body first accumulates in the most active meristem for cell proliferation and has the characteristics of reuse. Phosphorus can obviously improve the ability of drought, cold and salt resistance of vegetable crops, and has the effect of maturing earlier, increasing yield and improving quality. Vegetable crops are short in phosphorus deficiency, with erect leaves and dark green leaves. When phosphorus deficiency is serious, due to the hindrance of sugar transport, anthocyanins accumulate in the leaves and form anthocyanins, and purplish red stripes or spots appear in the leaves or stems at the base of the plant. Click to get more nitrogen, phosphorus, potassium application techniques click to get more chemical fertilizer application techniques