Responses Of Microbial Biomass Turn Over And Nitrogen Mineralization To Exogenous Carbon And Nitrogen In A Dryland And Paddy Soil

The regulated mechanism of soil microbial on soil nitrogen is becoming one of the key research directions in the field of agricultural ecology. A typical dyrland and paddy soil in subtropical zone is the target of this research, the incubation experiment (Temperature: 25 ?,Air Relative Humidity:100%) was conducted to investigate the impacts of adding 15N-(NH4)2SO4and 15C-Glucose, adding rice straw and its biochar product on the amounts of soil microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) and the mineralization of soil organic nitrogen of a typical dryland soil and a paddy soil in subtropical region of China. The results showed that:The impacts of adding 15N-(NH4)2S04and 15C-Glucose on the soils MBC, MBN and the mineralization of soil organic nitrogen show that:1) In comparison with CK, the addition of glucose increased MBC by 126.0% and 142.1% respectively in the JinJing and TaoYuan dryland soil, and the MBC was increased by 72.8% and 36.6% respectively in the paddy soil; the addition of (NH4)2SO4 increased MBN by 10.1%-109.5% and 12.8%-170.0% respectively in the JinJing and TaoYuan dryland soil, the MBN was increased during 10 d in the paddy soil; the addition of Glucose and (NH4)2SO4 increased MBN by 6.3%-356.7%, 48.5%-316.6% respectively in the JinJing and TaoYuan dryland soil, the MBN was increased during 10 d in the paddy soil.2) The turnaround time of MBC was 357 d and 370 d respectively in the JinJing and TaoYuan dryland soil, and the turnaround time of MBC was 132 d and 137 d respectively in the paddy soil; the turnaround time of MBN was 238 d and 204 d, respectively in the JinJing and TaoYuan dryland soil, and the turnaround time of MBC was 111d and 115 d respectively in the paddy soil. (3) The nitrogen mineralization was increased by adding exogenous carbon and nitrogen. The dryland soil nitrogen mineralization with the extension of the incubation time is gradually increased to stabilize, and after the paddy soil nitrogen mineralization with prolonged incubation time first and then decreased again stabilized. The results show that:the addition of (NH4)2SO4 and glucose increased the nitrogen mineralization and microbial biomass, particularly in the dryland soil. The turnaround time of dryland soil was longer than paddy soil, the turnaround time of MBN was faster than MBC.The impacts of adding biomass charcoal and straw on the soils MBC MBN and the mineralization of soil organic nitrogen show that:1) In comparison with CK, after 35 days of incubation, the addition of biochar increased MBC and MBN by 34.6% and 163.1% in the dryland soil, and increased MBN by 23.0% in the paddy soil; the addition of biochar could also make nitrogen mineralization higher than the no biochar addition treatment in the dryland and paddy soil.2) In comparison with CK, after 35 days of incubation, the addition of rice straw increased MBC and MBN by 90.4% and 203.8% respectively in the dryland soil, and increased MBC and MBN by 13.4% and 19.9% respectively in the paddy soil; the addition of rice straw could make nitrogen mineralization lower than the no biochar addition treatment in the dryland soil, and make nitrogen mineralization little difference with the no biochar addition treatment in the paddy soil. In conclusion, both additions of biochar and rice straw increased microbial biomass in croplands, particularly with the rice straw. The nitrogen mineralization was also increased by the additions of biochar and rice straw, except for in the dryland soil with the rice straw addition. The contribution of rice straw and its biochar product to the dynamics of soil MBC and MBN and the turnover of soil organic nitrogen needs further investigations to clarify, such as by using the isotope techniques.