Denitrification and mineralization in agricultural soil in Eastern Canada, as affected by nitrogen fertilizer, tillage, and crop rotation

The fate of fertilizer N is of primary concern for both agricultural productivity and environmental quality. Concerns include denitrification, leaching losses, mineralization of organic N as plant available N. Denitrification is an important source of N{dollar}sb2{dollar}O, a greenhouse gas but field measurements are difficult. Two methods of measuring denitrification are soil core (SC) incubation and closed chamber (CC) methods. These methods were assessed on soil under monoculture corn, monoculture soybean, and alfalfa in a corn soybean alfalfa rotation. Greater concentrations were found in the CC method than the SC method. Denitrification rates ranged from less than 15 g N ha{dollar}sp{lcub}-1{rcub}{dollar}h{dollar}sp{lcub}-1{rcub}{dollar} to nearly 2000 g N ha{dollar}sp{lcub}-1{rcub}{dollar}h{dollar}sp{lcub}-1{rcub}{dollar}. The CC method was more sensitive to treatment effects. The denitrification rates were dependent on the soil type, being higher on soils with high clay content. The variables that had the highest degree of relationship with denitrification were water filled pore space, soil NH{dollar}sb4{dollar}-N and NO{dollar}sb3 {dollar},-N concentrations. Higher rates of N increased denitrification. As to assessment of available soil N, this was accomplished N and C mineralization measurements. Potentially mineralizable N(N{dollar}sb0{dollar}) ranged from 144 mg N kg{dollar}sp{lcub}-1{rcub}{dollar} to 30.3 mg N kg{dollar}sp{lcub}-1{rcub}{dollar}. Higher rates of organic amendment resulted in higher measured values on Brandon soil while higher rates of inorganic N on Chicot and Ste. Rosalie soils caused no change in mineralizable N or respired C. Total N, organic C, water soluble organic C (WSOC) and microbial biomass C (MBC) increased with increasing amounts of organic or inorganic N amendment on Brandon soil. Higher rates of inorganic N resulted in lower WSOC and MBC on Chicot and Ste. Rosalie soils. Nitrogen mineralized, C respired, total N, organic C, WSOC and MBC were all related to soil texture. MBC and WSOC were found to have a strong positive relationship with potentially mineralizable N.