Impact of long-term tillage and N fertilization on labile soil N pools in a soybean-corn rotation

Tillage and N fertilization are known to significantly impact the productivity of agroecosystems. However, a greater understanding of their long-term and interactive influence on labile soil N pools is needed to implement sustainable soil and N management practices. Soil samples were collected at 0-5, 5-10 and 10-20 cm in the corn (Zea mays L.) phase of a long-term (24 yrs) soybean (Gylcine max L.)-corn rotation in eastern Canada. The experiment was designed as a split-plot with two tillage practices [no-till (NT) and mouldboard plough (MP)] as main plots and nine combinations of N and P levels as subplots randomized in the main plots, with four replicates. Our study focused on plots that received 0, 80 and 160 kg N ha-1 combined with 35 kg P ha-1. We measured the concentrations of soil mineral N, water-extractable organic N (WEON), microbial biomass N (MBN), particulate organic N (POMN), mineral-associated organic N (Min_Assoc_N), and soil total N. Preliminary results show a significant tillage effect on all parameters, except soil mineral N, and a significant N rate effect on soil mineral N and WEON concentrations. There was stratification of POMN, Min_Assoc_N, MBN and soil total N under NT but not under MP. Further in-depth analysis of results and implications of this study will be presented and discussed.