Alleviation of Copper Toxicity to Maize by Phosphorus Fertilizer in Purple Soil

A pot experiment was conducted to evaluate the effects of phosphorus fertilizer in inhibiting the copper toxicity to maize(Zea mays L.) in neutral purple soil. Results indicated that the growth of the shoot and roots of maize plant was obviously reduced by copper and the height and biomass were significantly negatively correlated to the application levels of copper (r=-0.899**~-0.994**) at no P and low P (100 mg kg-1).However, the maize biomass was relatively increased and the high Cu (100 and 200 mg kg-1) induced toxicity of maize was greatly alleviated in all treatments with medium P (300 mg kg-1) and high P (500 mg kg-1).To maintain the normal growth of maize plant (≥3.68 g pot-1), the critical application rates of phosphorus fertilizer should be 160, 210, 300 and 500 mg P kg-1 at 10, 50, 100 and 200 mg Cu kg-1 levels of the soil,respectively. The increases in polyphenol oxidase and catalase activities in maize leaf and dehydrogenase activity in roots by phosphorus fertilizer were in the order of medium phigh plow pno P. Activities of polyphenol oxidase and catalase were significantly positively correlated to the application levels of copper (r=0.892**~0.924**), whereas that of dehydrogenase was just reverse (r=-0.966**) at no P. Medium and high P repressed the influence of copper on activities of three enzymes. Phosphorus fertilizer reduced the copper concentrations of maize roots and leaf and the change ranges of the P/Cu ratio of maize roots and the P/Cu, N/Cu and K/Cu ratios of maize leaf. The three ratios of maize leaf were 256±71.5, 2643±839 and 1133±440 at normal growth of maize plant, respectively. Soil available Cu could be markedly cut down by application of phosphorus fertilizer, especiallly at high phosphorus level.