Synchronizing Soil Nitrogen Supply to Vegetable Nitrogen Uptake By Available Carbon in Greenhouse Cultivation System.

Greenhouse vegetable production in China is increasing very fast, especially in sub-urban areas around big cities (like Beijing) in north part of China. The production system needs both of high quality of vegetables and less environmental impact. So, soil nitrogen (N) supplied by single organic fertilizer is one of the most important factors in this system. Although huge researches has been done on soil N, it is not clear yet how to synchronize soil N supply to crop N demand effectively, meaning low soil N supply when crop uptake is small and high supply when crop is in maximal growth. By synchronizing these two counterparts, N fertilizer use efficiency will be improved and N loss to environment will be lowered. This synchronization is especially difficult in cultivation system which the soil N supply comes from the single-applied organic fertilizer at the beginning of growing season. Available carbon (AC) is the main driving force behind the process of immobilization and mineralization turnover (MIT) of soil N. Through soil microbial MIT, AC can induce significantly the immobilization of soil mineral N and then impact on the re-mineralization, during which soil mineral N supply ability to crop is changed. Laboratory and greenhouse experiments based on the above facts were carried out to test the effectiveness of types and dose of AC on soil mineral N supply. Result showed that soil mineral N dynamics were changed with different types and dose of AC, and some vegetable quality indicators also changed. Behind this difference, soil microbial biomass, net and gross N mineralization measured by 15N pool dilution method varied accordingly and controlled this process. Based on the results, new concept to make organic fertilizer is under constructing. Key words: available carbon, synchronization, soil nitrogen supply, vegetable quality, greenhouse