EFFECT OF UREA APPLICATION AND SOIL AMENDMENTS ON YIELD AND NUTRIENT CONTENT OF RICE CROP AND FERTILITY OF PADDY SOILS IN TAIWAN

Increase N recovery % and grain yield upon USG deep placement, the first rice crop was superior than the second rice crop. For the first rice crop, grain yield increased up to 13%, while N recovery % increased up to 77%. However, it was found that grain yield of the second rice crop only increased about 3% at Pingtung Experiment Site, while the N recovery rate increased about 41%, lower than that of the first crop by 36%. The effect of USG deep placement on grain yield and N recovery rate found highly significant in Taichung soils, the grain yield increased by 18% and N recovery rate increased from 30% to 71%. At Pingtung Experiment site, grain yield only increased by 3% and N recovery rate also increase from 8% to 41.%. a high pH (7.4) at Pingtung field may cause a higher loss of NH3 and higher O. M. (4.4%) may reduce the response of applied N fertilizer to the yield. The coarse texture of Taichung soil also related to the higher N recovery rate. Increasing the fertilizer efficiency of USG deep placement may be partly attributed to the higher ammonium adsorptive nature due to the existence of expanding clay minerals in soils. In that case, Taichung soil has a higher amount of expanding clay minerals. This may explain why higher N recovery rate of USG deep placement at Taichung siteg and lower at Pingtung site. Appliation of rice husk increased not only with increasing N recovery rate, but also increased with uptake of N and K by rice plant. As respond to the grain yield, it increased about 9% for the second rice crop, and 4% for the first rice crop in general. The use of rice husk also depressed banded sclerotial disease of rice crop plant which in turn increased grain yield by 9% at Changhua Site. Based on our results, response of grain yield increase by application of rice husk was much significant than the use of slag. In Pingtung, use of slag even caused slightly yield decline. But with use of slag combined with rice husk, it significantly reduced the tendency of grain yield decline.