Search

The decomposition characteristics of wheat straws and their effects on soil biological properties and nutrient status under different rice cultivation were studied in the 2007 and 2008 growth seasons,respectively.Wheat straws were wrapped in net nylon bags and embedded into the soil under conventional cultivation and a water-saving cultivation model.The rate of straw decomposition was greatest within the first 30 days and then decreased until the end of the experiment.Straw decomposition under the water-saving cultivation model was faster than straw decomposition under conventional cultivation,and the wheat straw cumulative decomposition rates were 48.9%—61.3%.The sequence of nutrient release rates were KPN≈C.The effect of the cultivation model and incorporation method on N,P and C release patterns followed almost the same trend as the decomposition of straw.Soil microbial biomass increased rapidly in the early growth stage after wheat straw was returned to the field,but decreased significantly in the middle growth stage and reduced slowly in the late growth stage.Urease,alkaline phosphatase and sucrase activities in the soil followed the same pattern as the microbial biomass after straw mulching.However,cellulase activity was different in that it increased rapidly in the early growth stage,improved slowly in the middle growth stage and decreased rapidly in the late growth stage.Microbial numbers and enzyme activities under the water-saving cultivation model were significantly higher than under conventional cultivation.Increasing the amount of wheat straw could improve microbial numbers and enzyme activities,but excessive straw would have a negative effect on bacterial and actinomycete numbers. The results also showed that soil nutrient contents could be improved noticeably by returning straw to the field.After straw mulching,organic carbon,total nitrogen,alkali-hydro nitrogen,and available phosphorus contents increased throughout the whole trial period.The available potassium content was highest after 30 days of straw mulching,and then decreased gradually.Nutrient contents under the water-saving cultivation model were higher than under conventional cultivation.Increasing the amount of straw had a positive effect on soil nutrient contents.