THE CHANGE OF ORGANIC,NITROGEN, PHOSPHORUS AND POTASSIUM NUTRIENT IN THE DIFFERENT CROPPING SYSTEM
稻田不同耕作制下有机质和氮磷钾的变化研究

A six year's follow up monitoring program was accomplished on the fields in east Dongting lake. It was found that, at the same condition, for four main cropping systems had different effects on soil fertility.Rice rice system lead to low yield,a decrease and retrogression of soil fertility,Rice rice green manure system lead to yield increase to some extent and bring about good economical benefit. Under this system,soil fertility appeared an increasing and evolution trend.Rice rice wheat and Rice rice rape systems could not only make a full use of the land and yield increase, but also could make the fertility increase and evolution.However, under latter two systems,economic benefit was relatively low.Comparing all the advantages and disadvantages of four systems,It is suggested that alternatively using Rice rice green manure system and rice rice rape(or rice rice wheat)system will probably be a better cropping system.