Activation effects of N，P，K fertilization and phenol on Si, Al, Fe in Bleached Paddy Soils

The activation effects of urea (N), calcium dihydrogen phosphate (P), potassium sulfate (K) and catechol (Phy) on Si, Al and Fe in bleached paddy soils distributed in tea plantation region of west Sichuan Basin were studied by the soil extraction experiment. The results show that the concentration of Si in soil extracted solution is the highest, and the follows are Al and Fe. The concentrations of Si in soil extracted solution are in the order: NPK+Phy＞NPKP＞Phy＞KCKN, which indicates that the phosphate has the most important impact on Si activation by ligand adsorption of PO43-, HPO42-, or H2PO4-, and the phenolic also promotes Si activation through its weak acid role at the same time. The order of Al concentrations in soil extracted solution is: NPK+Phy＞Phy＞PNPKKNCK, which indicates that the phenolic plays a prominent role in activation of Al by formation of soluble complexes with free Al. In addition, K+ from potassium fertilizer and Ca2+ from phosphorus fertilizer could activate Al by exchanging a large number of Al3+ in strongly acidic tested soils. The Fe concentrations in soil extracted solution are ranked as follows: NPK+Phy＞Phy＞KPNPKCKN, indicates that the phenolic plays an important part in Fe activation by complexing and reduction of Fe. K+ from potassium fertilizer and Ca2+ from phosphorus fertilizer could activate Fe through exchanging Fe2+ adsorbed by soil colloid as well. The urea application has no significant activation effect on soil Si, Al and Fe. Above all, phosphate, potash and phenolics are important factors in activation of Si, Al and Fe in bleached paddy soils.