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 ef fects of N management and cropping sequence on soil N microbial processes a re understood. Effects of cropping intensity and N fertilizer rate on net s oil N mineralization were studied as well as their correlation with precipi tation, air temperature and soil water content. Net soil N mineralization w as measured by incubating undisturbed soil cores (15-cm depth) containing a nion and cation exchange resins at their bottoms, Cores were incubated duri ng each of five time periods (3-4 wk each) during the fallow phase (mid-Apr il to mid-September) of two no-till cropping systems, wheat (Triticum aesti vum L,)-fallow (WF) and wheat-corn (Zea mays L.)- fellow (WCF). Past N fert ilizer 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 an d an Aridic Argiustoll at Stratton in eastern Colorado, Total net N mineral ization 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-t ill management. Greater conservation of applied N and soil N can be expecte d in the more intensive WCF system, Total mineralized N increased with N ra te 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 si tes.