Responses of soil nitrogen and carbon mineralization rates to fertilization and crop rotation

PurposeThe mineralization rate of soil carbon (C) and nitrogen (N) is important for determining soil C storage as well as nutrient supply and retention. Soil C and N decomposition processes are microbially driven and are therefore expected to be influenced by the balance between soil resource availability and microbial resource demand. However, we lack understanding of how the microbial uptake and mineralization of soil C and N is affected by different levels of fertilization and crop rotation patterns in agricultural systems.Materials and methodsSoils from a field experiment including five levels of N fertilization (0 kg N ha-1 (control, 0), 84 kg N ha-1 (low N application), 95 kg N ha-1 (moderate N application), 105 kg N ha-1 (conventional N application) and 115.5 kg N ha-1 (high N application)) were used to determine soil C and N mineralization and retention, in either a tobacco plantation either under tobacco monoculture or tobacco-maize rotation.Results and discussionNitrogen fertilizer application increased net N mineralization (40-307%), net nitrification (150-400%), microbial NUE (131-373%) and CUE (16-57%) but decreased respiration (11-42%) in monoculture system, due to the significant higher DOC concentration and microbial C limitation. However, N fertilizer application increased net N mineralization (67-400%), net nitrification (50-544%), and microbial NUE (84-438%) but reduced microbial respiration (56-71%) and CUE (8-39%) in rotation system, due to the lower microbial activity caused by significant higher microbial C and N limitation and poorer C quality. Therefore, fertilization aggravated microbial resource limitation and lowered quality indicated by elemental stoichiometry in rotation system, leading to decoupling of microbial respiration and metabolism.ConclusionsTogether, our results suggest that elemental stoichiometry and enzyme activities can be used to predict soil C and N cycling under different agricultural management practices.