Effect of successive application of compost to no tillage-paddy field on inorganic phosphorus leaching during winter cropping

Effect of successive application of compost to no tillage-paddy field of crop rotation, paddy rice and Italian ryegrass on inorganic phosphate leaching during the Italian ryegrass cropping period was investigated. Cow manure composted with chaff (CMCC) and pelletized poultry manure composted (PPMC) mainly derived phosphate for eight crops was 430-1430, and 80-790 kg/ha P2O5, respectively. We investigated inorganic phosphate leaching using the resin method at the sixth and eighth crop. The following results were obtained. 1) Successive application of CMCC and PPMC to no tillage-paddy field caused the accumulation of soil available (Av-P) and water soluble phosphate (WS-P) at soil surface (0-3 cm depth) mainly and the cropping layer (3-13 cm depth) next, in proportion to the amount of phosphate applied. 2) Analysis of regression on the amount of inorganic phosphate leaching showed that a high R-squared value was obtained at the total amounts of phosphate applied from the first to fifth, or sixth crop, Av-P and WS-P at the soil surface and cropping layer, whereas, in the case of phosphate applied in the sixth crop or Av-P and WS-P at subsoil (13-26 cm depth), the R-squared value was very low. While inorganic phosphate leaching increased when precipitation was high, these data indicated that inorganic phosphate in soil moved downward by the depth of infiltration of water. 3) Temporary conversion to tillage-management before the seventh crop has remarkably decreased the content of the Av-P and WS-P at the soil surface. Therefore, inorganic phosphate leaching in the experimental plot of tillage-treatment remarkably decreased at the eighth crop in which the relation to precipitation was not clear. Between the two experimental plots of similar level for content of Av-P, the amount of phosphate leaching was lower in tillage-treatment. These data suggest that phosphate leaching in no tillage-paddy field is concerned with not only phosphate content at the soil surface and cropping layer, but also development extent of soil macro-pores.