STORAGE OF SOIL ORGANIC C AND SOIL RESPIRATION AS EFFECTED BY LONG-TERM QUANTITATIVE FERTILIZATION

To understand the influence of organic manures composted with the wheat straws, oilcakes and cottonseed cakes, and chemical fertilizers on soil organic carbon and soil productivity, a long-term plot experiment was established in a calcareous fluvo-aquic soil (aquic inceptisol) in Fengqiu county, Henan province, China in September 1989 and was used to monitor soil respiration during the maize and wheat growth seasons from June 2002 to June 2003. The study involved 7 treatments: organic manure (OM), half organic manure plus half fertilizer N ((1/2OM),) fertilizer NPK (NPK), fertilizer NP (NP), fertilizer NK (NK), fertilizer PK (PK) and control (CK). The input of NPK as either organic manures or chemical fertilizers not only greatly improved soil productivity but also was of benefit to the soil as a carbon sink. However, the organic carbon in soils amended with organic manure was greatly higher than in the soil fertilized with chemical fertilizers and increased with the rate of organic manure applied. CO_(2) flux resulted from soil respiration mainly occurred during the maize growth period, accounting for 56%~59% of annual CO_(2) emission, whereas 32%~37% during the wheat growth period. The study suggests that the combination application of organic manures and chemical fertilizers should be the optimal measure from the viewpoint of environment and economy. A further study is necessary to elucidate the reasonable and feasible ratio of organic manure to chemical fertilizers, which will benefit the soil fertility, productivity and global environment.