Dynamics of Soil Microbial Biomass Carbon, Mineral Nitrogen and Nitrogen Mineralization in Long-Term Field Experiment, Northern China

Abstract

ABSTRACT A long-term field soil fertility and crop yield experiment was carried out at China Agricultural University's Qu-Zhou experiment station in Hebei Province, Northern China. The station is in a continental temperate monsoon tone, and the climate in the region is warm, sub-humid, and consists of summer rainfall and dry-cold winters. The soil at study site is an improved silt fluvo-aquic soil. Three different farming systems were established in 1993: traditional compost (TC), chemical fertilizer (CF), and a control (CK). Soil samples were collected in October 2004 before the fertilizer application, during the crop growing stage (November 2004; March, April, May 2005) and at harvest (June 2005). The soil microbial biomass carbon (MBC), mineral nitrogen concentration, and nitrogen mineralization rate were evaluated. The results showed that soil MBC, mineral nitrogen concentration, and nitrogen mineralization rate were higher in TC and CF than in CK. The microbial biomass C in TC were significantly higher compared with CF and CK; although only slightly higher in CF compared with CK. Mineral nitrogen (NH4-N and NO3-N) concentration on 14 October 2004 and 25 May and 10 June 2005 among treatments followed the order: CK < CF < TC. Nevertheless, the order in November 2004 and March, April, and 10 May 2005 among treatments followed: CK < TC < CF. NH4-N concentration was always lower than NO3-N concentration. Significant differences in the nitrogen mineralization rate were observed between treatments and incubation dates. Nitrogen mineralization rate among treatments followed the order: CK < CF < TC. Nitrogen mineralization rate was positively correlated with microbial biomass carbon and wheat yield. Microbial biomass carbon was a good indicator for changes of soil fertility and quality.