Influence of irrigation methods on soil fertility during the sabbath period

The purpose of this study is to investigate the influence of irrigation methods on soil fertility during the sabbath period.This study chose two blocks of paddy field,whose soil were turned over after the harvest.One of the blocks was irrigated continually to maintain ponding water and was called continual irrigation field.The other was without irrigation except natural precipitation and was called natural irrigation field.The sampling locations were at four corners and the center of the block.Each location was withdrawn six samples at six layers.Each layer was 10 cm in depth to a totality of 60 cm below ground surface.The soil samples in each layer were air dried and mixed homogeneously by passing 0.42 mm sieve.The mixed soils were analyzed for their pH,EC,organic matter,total nitrogen,effective phosphorous,Ca,Mg,K,and Na.The results showed that organic matter and effective phosphorous increased significantly after sab bath period due to the decay of rice roots.In natural irrigation field,the organic matter and effective phos phorous increased 51% and 88%,respectively.In cont inual irrigation field,the organic matter and effective phosphorous increased 13% and 69%,respectively However,in the natural irrigation field,Mg,K,and Na decreased 35%,24%,and 47%,respectively.In continual irrigation field,Mg,K,and Na decreased 29%,14%,and 41%,respectively.