| Soil productivity is strongly linked to soil organic matter (SOM) because SOM plays important roles in improving soil structure, soil water holding, infiltrating and capacities, and the nutrients supply to crops. It is significant that effect of land-use and management on soil organic matter turnover and land productivity is investigated for the sustainable agriculture and environment protection in gully area of the Loess Plateau. On the basis of long-term experiment, changes in soil organic C, N and dynamics of soil NOs-N of cropping systems were investigated in gully area of the Loess Plateau by means of analysis of the 15-year soil samples, crop yield hi following crop systems: 1) continuous winter wheat with unmanured (CK), nitrogen, organic manure (M), phosphorus and organic manure (PM), nitrogen and phosphorus (NP), nitrogen, phosphorus and organic manure (NPM), 2) continuous alfalfa, 3) pea-winter wheat rotation, winter wheat-sainfoin (Onobrychis viciifolid) rotation, and 4) bare fallow. A model was developed according to the organic C dynamics, and was tested by the long-term experiment. The potential yield of winter wheat and the approach were studied under the condition of local precipitation and fertilization. Some results were summarized as follows:(1) Land-use and management affected soil organic C and N. Soil organic C and N content in the continuous cereal was constant at the level of 6.50 g kg"1 and 0.82 g kg"1, respectively. Cereal-pea rotation could contribute a little to the accumulation of soil organic C and N. Winter wheat-sainfoin (Onobrychis viciifolid) rotation or continuous alfalfa (Medicago sativd) could significantly increase the soil organic C, N. Soil organic C and N slowly decreased in fallow.(2) Fertilization could evidently increase soil organic C, N. The increase of organic C varied from 9% to 13%, the increase of organic N varied from 22% to 35% among the different cropping systems.(3) Limited rainfall affected the accumulation of soil organic C, N in the pea-winter wheat rotation. However, low soil moisture due to crop strong evapotranspiration contributed more to the accumulation of soil organic C, N in the winter wheat-sainfoin (Onobrychis viciifolid) rotation.(4) Soil C/N ratio was constant at 8.3 in gully area of Loess Plateau, cropping and fertilization had little effect on the C/N ratio.(5) Land-use and management could result in significant changes in soil microbial biomass C, N. Soil microbial biomass C accounts for 1-4% of soil organic C, soil microbial biomass N accounts for 2-6% of soil organic N among cropping systems. There was a significant correlation between soil microbial C (N) and organic C (N). The changes in microbial C, microbial C/organic C ratio, in response to changes in soil management, occurred in the same direction as did in the changes in soil organic C, but microbial C and microbial C/organic C ratio were sensitive to similar soil management. So the microbial C and microbial C/organic C ratio could serve as a sensitive indicator of changes in SOM.(6) Soil moisture content depends on highly variable inter-year and inter-month rainfall. Cropping and fertilization could not change pattern of soil moisture change, and significantly affect intensity of soil moisture change. Effect of crops on soil moisture was in the order: continuous alfalfa > continuous winter wheat > bare fallow. Soil moisture on harvesting date and rainfall infiltration depth before winter wheat planting in continuous winter wheat was hi the order : unmanured, M, PM, N > NP, NM, NPM. Soil moisture content in continuous alfalfa was considerably lower than bare fallow, the rainfall infiltration depth in continuous alfalfa was reduced to 120 cm. Fertilization could not influence soil moisture in continuous alfalfa.Soil managements (cropping, fertilization, etc.) had a little effect on NH4-N change. Cropping and fertilization had a significant effect on soil NOa-N transport and accumulation. NOa-N level was low and constant in fallow treatment.
|
PDF Full Text Request