Effects Of High Phosphorus On Vegetable Growth And Its Potential Environmental Impact

Soil phosphorus accumulation because of increasing application of phosphate fertilizer caused enormous potential threat to the water environment and affected the growth of crops. In this study, the effects of high phosphorus on the growth and some physiological metabolisms of tomato using hydroponic experiment, and the potential environmental impact of phosphate fertilizer application using an outdoor simulating soil column were carried out. This would be of great importance for the efficient application of phosphate fertilizer and the protection of agricultural ecological environment. The results were as follows:1. Effects of high phosphorus on vegetable growth and some physiological metabolisms1.1 Compared with normal phosphorus (0.66mmol.L^-1) treatment, the tomato plants treated with high phosphorus (6.60mmol.L^-1) was of shot height, small dark green and thick leaves. The root activity and the absorbing area of the roots decreased while the biomass decreased significantly. These showed that high phosphorus affected thegrowth of tomato plants.1.2 Compared with the normal phosphorus treatment, the content of the organic phosphorus in the tomato plants was no difference while the content of the inorganic phosphorus was increased positively significantly by high phosphorus treatment. Along with the enhances of phosphorus concentration (0-6.60mmol.L^-1), phosphorus concentration ratio of tomato's upper-position leaves to roots dropped, showing high phosphorus inhibited the transportation of phosphorus from the roots to the tip in tomato plants.1.3 The phosphorus use efficiency decreased while increasing the phosphorus concentration in nutrition liquid. The phosphorus use efficiency of high phosphorus treatment decreased significantly by 37.5% ,compared with normal phosphorus treatment. 1.4 High phosphorus inhabited the absorption of K⁺ and transportation of N,Ca²⁺,Mg²⁺,Zn²⁺ fr°m roots to tip in tomato plants, and decreased the absorption and transportation of Fe²⁺, compared with the normal phosphorus treatment.1.5 High phosphorus treatment had not obvious effect on the contents of chlorophyll and carotenoid, but decreased photosynthesis rate, the light compensation points, apparent quantum production, sugar and starch content, aggravated the phenomenon of photosynthetic "Midday Depression", while increased dark respiration, compared with normal phosphorus treatment.1.6 Compared with normal phosphorus treatment, high phosphorus treatment reduced nitrate reductase activity and the ratio of protein nitrogen to whole nitrogen ,showing protein synthesis was inhibited.2. Effects of phosphate fertilizers application on potential leach ability of phosphorus2.1 The content of total P and inorganic P increased with the increase of phosphate fertilizer applied. Compared with inorganic phosphate fertilizer, combined application of inorganic and organic increased the content of organic phosphorus at the surface and the bottom of the soil column, thus causing phosphorus leaching.2.2 With the increasing application phosphate fertilizer, the content of Olsen-P and CaCl₂-P in every layers of soil increased. Compared with inorganic phosphate fertilizer, combined application of inorganic and organic increased Olsen-P and CaCl₂-P content in the bottom of soil, showing phosphate fertilizer enhanced the potential leach ability of phosphorus.2.3 The production of Brassica campestris couldn't be enhanced and the excessive absorption of the phosphate in Brassica campestris was caused by using a lot of phosphate fertilizer in the soil with high contents of phosphate, which caused the waste of phosphate fertilizer.