Detailed Explanation of Phosphorus Fertilizer Utilization Rate and Physiological Role
The utilization rate of phosphorus fertilizer is much lower than that of nitrogen fertilizer and potassium fertilizer. In China, the utilization rate of phosphorus fertilizer is generally in the range of 10%-25%. Among vegetable crops, legumes have a relatively higher utilization rate. There are two main reasons for the low utilization rate of phosphorus fertilizer: the first reason is the fixation of phosphorus fertilizer in the soil, whether water-soluble, citrate-soluble...
The utilization rate of phosphorus fertilizer is much lower than that of nitrogen fertilizer and potassium fertilizer. In China, the utilization rate of phosphorus fertilizer is generally in the range of 10%-25%. Among vegetable crops, legumes have a relatively higher utilization rate. There are two main reasons for the low utilization rate of phosphorus fertilizer: the first reason is the fixation of phosphorus fertilizer in the soil, and this problem exists for water-soluble, citrate-soluble and sparingly soluble phosphorus fertilizers alike. The second reason is that phosphorus moves very weakly in the soil. This reason is actually a result of the first reason. The low mobility leads to a low utilization rate because nutrients must come into contact with the root system to be truly absorbed by the crop, which involves the issue of bioavailability.
In the past, research on nutrients focused on chemical availability, that is, studying which chemical forms are available to crops. However, some nutrients that are chemically available cannot be absorbed and utilized by crops for various reasons, so they are actually "unavailable." Recently, the concept of bioavailability has been proposed, that is, only when a chemically available nutrient is actually absorbed by the crop is it truly biologically available, so it is called bioavailability. Of course, the prerequisite for bioavailability is chemical availability.
Nutrients in the soil can only be actually absorbed by crops when they come into direct contact with the root system. Those nutrients that do not contact the root system must reach the root surface through three ways: root interception, mass flow and diffusion. Root interception refers to the root system extending to the location of the nutrients as it grows. Mass flow refers to nutrients dissolved in the soil solution moving to the root surface along with the flow of water toward the roots. Diffusion refers to the formation of a depletion zone because nutrients immediately adjacent to the root surface are absorbed, and the nutrient concentration in this zone is lower than that of the bulk soil, thereby causing nutrients in the bulk soil to move toward the root surface. For phosphorus, because the concentration in the soil solution is very low (usually only 0.05 mg/kg or lower), the amount of phosphorus that mass flow can supply is very small. For example, at a concentration of 0.05 mg/kg, mass flow can supply only 1% of the crop's phosphorus requirement, and the crop mainly obtains phosphorus through diffusion (more than 90%). However, the diffusion coefficient of phosphorus is very small (that is, its mobility is very low), and it moves only 1-4 mm in 24 hours, so the utilization rate of phosphorus is very low. Although the phosphorus fertilizer applied to the soil is absorbed and utilized less by the current season's vegetable crops, the remainder mainly remains in the soil, forming the residual effect of phosphorus fertilizer. If phosphorus fertilizer is continuously and systematically applied to a certain vegetable crop, its residual effect will accumulate, so that the utilization rate of phosphorus fertilizer used by the current season's vegetable crops increases significantly with the extension of continuous fertilization years, and some can even reach 30%-40%, approaching the utilization rate of nitrogen fertilizer and potassium fertilizer.
The inorganic form of phosphorus in the vegetable plant mainly plays a physiological regulatory role, such as the synthesis and transport of carbohydrates, fat metabolism, promoting respiration and the vegetable's absorption of water and nutrients, and promoting cell division and the growth of young buds and the root system. When vegetable crops are deficient in phosphorus, root growth is often poor. Vegetables absorb more phosphorus in the early growth stage, which can account for 60%-70% of the total absorption during the growth period. The phosphorus entering the vegetable plant first accumulates in the most actively growing meristematic tissues for cell proliferation, and it has the characteristic of being reusable. Phosphorus can significantly improve the drought resistance, cold resistance and salt resistance of vegetable crops, and has the effect of advancing maturity, increasing yield and improving quality. When vegetable crops are deficient in phosphorus, the plants are short, the leaves are upright and dark green. When phosphorus deficiency is more serious, because carbohydrate transport is blocked, it accumulates in the leaves and forms anthocyanins, and purple-red stripes or spots appear on the basal leaves or stems of the plant.
Click to get more nitrogen, phosphorus and potassium application techniques
Click to get more chemical fertilizer application techniques