| The soil cadmium (Cd) pollution has become a serious environmental concern as China's economy grows rapidly. Proper fertilization practices could remedy Cd contaminated soil effectively. But the knowledge regarding effects of phosphorus (P) fertilizers on Cd transfer within the soil-vegetable system had not been widely recognized. An incubation experiment using five P fertilizers at five rates P2O5(0,0.1,0.2,0.4,0.8g available P2O5/kg soil) was conducted to investigate effects of P fertilizers on Cd bioavailability in yellow brown and fluvo-aquic soils. A pot experiment was carried out to study the influences of five P fertilizers on Cd transference from soil to leaf vegetables, and the yield, quality, nutrients absorption and accumulation of four vegetables (spinach, pakchoi and two amaranth) growing in Cd contaminated soils.The main results were summarized as the following.1. After eight weeks of incubation experiment, pH of two soils was reduced significantly, soil available P and available Cd concentrations significantly increased with increasing rate of diammonium phosphate (DAP), monoammonium phosphate (MAP) and superphosphate (SSP); dicalcium phosphate (DCP) and tricalcium phosphate (TCP) had no significant effect on pH of two soils, but soil available P significantly was increased and available Cd concentration was decreased with increasing rate of DCP and TCP, both reduced the potential of soil Cd availability. The capability of five P fertilizers in acidifying soil varied in following order:DAP> MAP> SSP> DCP, TCP. All the P treatments except for DCP treatment, a significantly negative correlation was observed between soil pH and available Cd concentrations. The influences of five P fertilizers with five application rates on yellow brown soil available Cd concentrations and soil pH were smaller than that on fluvo-aquic soil. These probably due to the rich organic matter in the fluvo-aquic soil alleviating the soil acidification and Cd availability changes.2. P fertilizer treatments could significantly promote vegetables growth in the pot experiment, but the increases of vegetables yield among different P fertilizers were declined with increasing P fertilizer application rates. The responses of vegetable quality to P fertilization were similar with those of vegetable yield, while DCP resulted in the highest yield and better quality. Compared with the control treatment, the leaf chlorophyll content, the total P concentration and the nutrient accumulation of vegetables were raised whle the total K, Ca, Zn contents were decreased by P fertilizer treatments. The contents of Cd in vegetable shoots and roots and the Cd enrichment coefficients were significantly reduced by P fertilizer application particularly by DCP application. The Cd accumulation of the control treatment was the lowest, but the differences in Cd accumulation and translation coefficient were not remarkable among P fertilizer treatments. Those indicated that Cd accumulation declining of vegetables resulted from P fertilizer treatments was firstly attributed to the dilution effects of P fertilizer application, the antagonism between P and Cd was the secondary. Soil pH was the most important factor governing the availability of soil Cd, and the precipitation between P and Cd in soil was the secondary factor.3. The DCP treatment resulted in the greatest growth of vegetables, the highest soil pH, a higher availability of P fertilizer, the lowest soil available Cd, and consequently the lowest Cd transfer from soil to vegetables. Therefore in Cd contaminated vegetable field soils, dicalcium phosphate and calcium magnesium phosphate fertilizers mainly containing DCP or TCP should be preferably selected, while the overdose of DAP, MAP and SSP should be avoided. |
