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五.作物磷的供应 1.作物对磷的吸收特点 作物在土壤溶液中主要吸收一价H_2PO_4~-和二价HPO_4~=离子,大多数作物吸收一价磷离子比吸收二价磷离子容易。这两种离子在土壤溶液中的比例决定于土壤pH,在一般土壤PH的范围内,PH愈高,二价磷离子愈多,PH愈低,一价磷离子愈多。 作物在整个生长期中都可吸收磷,但是在生长早期吸收最多,在干物质只占成熟时的25％时,往往吸磷量已经达到50％。所以在某些含磷中等的土壤上,作物早期磷肥有效,但却不能在后期增产,原因之一就是作物早期需磷多。 磷在植物体中可以运动,在缺磷的情况下,磷可以由老的组织向新生组织移动,从而使缺乏症状从老叶开始。如作物成熟时,大量茎叶中的磷向种子运送,丰富的磷可以促进作物开花,成熟。所以施磷可
V. Crop Phosphorus Supply 1. Crops Phosphorus Absorption Characteristics Crops mainly absorb monovalent H 2 PO 4 - and bivalent HPO 4 - ions in soil solution. Most crops absorb monovalent phosphorus ions more easily than divalent phosphorus ions. The ratio of these two ions in the soil solution is determined by the pH of the soil. The higher the pH, the higher the pH, the more the divalent phosphorus ions, and the lower the PH, the more monovalent phosphorus ions are present. Crops absorb phosphorus throughout the growing season, but absorb most of them in the early stages of growth, often up to 50% of phosphorus uptake when dry matter accounts for only 25% of maturity. Therefore, in some medium-phosphorus soils, early-stage P fertilization of crops is effective, but it can not increase production in the later stage. One of the reasons is that the crop needs more phosphorus in the early stage. Phosphorus can move in plants, and in the case of phosphorus deficiency, phosphorus can migrate from old tissue to nascent tissue, causing the lack of symptoms from the old leaf. Such as crops mature, a large number of stems and leaves of phosphorus transported to the seeds, rich in phosphorus can promote crop flowering and maturity. So phosphorus can be applied