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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.)- fallow (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 WF (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 yr 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 0.2 kg ha 1 for each kg ha 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. |
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