Influence of cropping intensity and nitrogen fertilizer rates on in situ nitrogen mineralization

Cycling of N through an agroecosystem can be managed more effectively if effects of N management and cropping sequence on soil N microbial processes are understood. Effects of cropping intensity and N fertilizer rate on net soil N mineralization were studied as well as their correlation with precipitation, air temperature and soil water content. Net soil N mineralization was measured by incubating undisturbed soil cores (15-cm depth) containing anion and cation exchange resins at their bottoms, Cores were incubated during each of five time periods (3-4 wk each) during the fallow phase (mid-April to mid-September) of two no-till cropping systems, wheat (Triticum aestivum L,)-fallow (WF) and wheat-corn (Zea mays L.)- fellow (WCF). Past N fertilizer applications were over four rates with total amounts applied during the previous 6 yr of 0, 95, 190, and 286 kg N ha(-1) in WF and 0, 134, 269, and 403 kg N ha(-1) in WCF, Soils were an Aridic Paleustoll at Sterling and an Aridic Argiustoll at Stratton in eastern Colorado, Total net N mineralization in WCF was half that in WP (22 vs. 43 kg N ha(-1); 2-site average), probably due to greater immobilization as evidenced by nearly three times greater accumulation of crop residue on the soil surface after 6 Sr of no-till management. Greater conservation of applied N and soil N can be expected in the more intensive WCF system, Total mineralized N increased with N rate by approximate to 0.2 kg ha(-1) for each kg ha(-1) of previously applied N, Precipitation in combination with air temperature and their interaction term gave the best prediction of average daily N mineralization at both sites.