| Soil carbon and nitrogen transformation and management is the core problem of soil quality and environment for sustainable development in greenhouse vegetable field. Soil carbon and nitrogen in deep soil is important to soil quality, and it is also contribute to maintain the stability of the whole system. Five different land use, which were 20-years old greenhouse vegetable field, 10-years old greenhouse vegetable field, open vegetable field, crop field and waste land, respectively, were selected according to the intensification degree in Yuzhong County, Lanzhou, Gansu Province. The soil samples were taken to 0-200 cm at 10 cm intervals under every land use with three replicates. The objectice of the experiment is to study the change and mineralization of carbon and nitrogen in deep soil with the intensification degree by the measurement of soil C and N content,δ15N and soil C and N mineralization in topsoil and deep soil, Which could be heipful to understand the contribution of soil C and N in deep soil to soil quality and environmental and to propose suitable management of fertilization and tillage.Main conclusions were listed as follows:(1) Compared with other treatments, soil pH in greenhouse vegetable field decreased significantly in whole 0-200 cm soil profile. There was no significant difference of soil pH between 10-years old and 20-years old greenhouse vegetable field. It indicated soil pH could be to influnced to 200 cm soil depth under the land use of greenhouse vegetable cropping system, ahd soil pH kept stability after 10-years old.(2) In contrast with oter treatmens, soil C and N content with 10-years and 20-years old greenhouse vetetable field accumulated significantly in surface soil layer (0-20 cm). There was no significant difference of soil C and N content in deep soil (20-200 cm) among all treatments. No significant difference of soil dissolved organic C (DOC) was found both in top soil and deep soil among all treatmens. However, significant difference of inorganic N and soil dissolved organic N (DON) was observed both in top soil and deep soil among all treatments. The order was 20-years old greenhouse vegetable field> 10-years old greenhouse vegetable field >open vegetable field> crop field > waste land (P<0.05). Compared with crop field and waste land,there was higher percentage of inorganic N and DON accounted for total N with 20-years old,10-years old greenhouse vegetable field and open vegetable field in0-200 cm soil profile.(3) In the whole 0-200 cm soil profile, higher soil C mineralization rate was found with 20-years old greenhouse vegetable field. Higher C mineralization capacity was fould in 40-100 cm soil layer with waste land while higher C mineralization capacity was fould in 100-200 cm soil layer with crop field. In the cubation of 0-3d, the soil net N mineralization was positive with all tretments. The higher N net mineralization was found not only in top soil but also in deep soil with 10-years old and 20-years old greenhouse vegetable field.In the incubation of 4-56 d, the soil net N mineralization was negtive with all tretments. The higher N immobilization rate was found both in top soil land deep soil with 10-years and 20-years old greenhouse vegetable field. Soil(4) After the conversion of crop field to greenhouse field,δ15N increased significantly in top soil, but decreased in deep soil. With the soil depth,δ15N decreased in greenhouse vegetable field. Significant positive relationship was found between Soil 815N, SOC, TN, DOC, DON, inorganic N and N mineralization rate in 0-3 d incubation period while Significant negative relationship was found between these indicators and N mineralization rate in 4-56 d incubation period. Soil SOC, TN, DOC, DON, inorganic N was significantly negative related to soil C mineralization rate. Significant positive relationship was found between pH and C mineralization rate, N mineralization rate in 0-3 d incubation period while Significant positive relationship was found between pH and N mineralization rate in 4-56 d incubation period. |
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