Research On Treatments Of Phosphorus Application For The Soils Polluted With Cd And/or Simulated Acid Rain

Pot experiments were conducted in this research to study the effects of P application on growth of soybean plants in Cd-polluted soils and on species of soil Cd, and to study effects of P application on complex pollution of Cd and simulated acid rain. The main results were summarized as the follows:Cd inhibited growth of soybean plants. With increasing Cd concentrations in the soils, the biomass, chlorophyll contents, and SOD (superoxide dismutase) activities of the plants decreased remarkably, and MDA (malondialdehyde) contents increased. P application partly reduced the toxicity of Cd to the plant, and increased the biomass, chlorophyll, and SOD activities, and decreased MDA contents to some extent. If the Cd concentration in soil which resulted in 20% discount of soybean yield was used as the critical concentration (CC), CC was less than 5 mg/kg for the soil no P application and greater than 5 mg/kg for the soil with P application of 40 mg/kg. This indicated that P had an antagonism effect with cadmium to soybean plants. P application alleviated the toxicity of cadmium to plants and enhanced CC of Cd in soil. In this experiment, 80 mg/kg was the best application amount of P to the soil polluted with Cd of 5 mg/kg, and 160 mg/kg was the best application amount to the soil polluted with Cd of 20 mg/kg, meaning that excess application of P showed no more alleviating effects.The interaction of Cd and P in soil reduced the availability of soil Cd, and hence alleviated the toxicity of cadmium. Distribution of soil Cd fractions demonstrated that contents of exchangeable Cd decreased with increasing P application to soil. The exchangeable Cd was just the main source of available Cd to plants.Contents of Cd and some other elements in soybean plants were determined, and the results showed that the interaction of P and Cd in soil depressed plant availabilityof soil cadmium, and led to lower Cd concentrations in the plants. This interaction advanced plant uptake of Ca and Cu, but the uptake of Mg and Zn increased first and then decreased.Effects of single simulated acid rain on growth of soybean plants in this research, to some certain, were similar to those of Cd in soil, for example decreasing the biomass, chlorophyll contents, and SOD activities, and increasing MDA contents. These effects were much less than those of Cd. However, the complex pollution of Cd and simulated acid rain made the toxicity to soybean plants much more serious than ang single pollution of Cd or simulated acid rain. The effects of simulated acid rain and those of Cd showed an obvious synergetic toxicity to soybean, this synergetic effect became more apparently with increasing soil Cd concentrations. P application counteracted partly Cd toxicity and promoted growth of soybean plants, but showed little effects on toxicity of simulated acid rain.