Effect of management systems on nitrogen mineralization and nitrification in soils

Nitrogen (N) management and spatial variability of soils have received considerable attention in recent years. The effect of long-term cropping systems on net N mineralization was studied in soils obtained from replicated plots from two sites: Galva-Webster Research Center (CWRC site) at Kanawha and Galva-Primghar Research Center (GPRC site) at Sutherland in Iowa, USA. Each experiment consisted of three cropping systems: continuous corn (CCCC), corn-soybean-corn-soybean (CSCS), and corn-oats-meadow-meadow (COMM), and treated before corn with (+N) and without (0N) ammoniacal fertilizer. Other studies involved assessing the effect of eight lime application rates (0-17,920 kg ha(-1) effective calcium carbonate equivalent, ECCE) on net N mineralization and nitrification in soils at the Northeast Research Center (NERC site) at Nashua, Iowa. The means of cumulative N mineralized at 30 degrees C for 24 weeks in soils from the CWRC and GPRC sites, expressed as percentage of organic N, were generally greater in N-treated plots than in control plots. The greatest amounts of N mineralized were in soils from the COMM rotation plots. Application of the log transformation of the data to calculate the potential mineralizable N (N(o)) and the first-order constants (k) showed that the data obeyed the exponential equation model. Expressed as percentages of total organic N in soils, the cumulative amounts of N mineralized ranged from 2.7 to 3.4% at 20 degrees C and from 5.8 to 7.5% at 30 degrees C. The cumulative amounts of N mineralized at 20 degrees C and 30 degrees C in soils from the plots under CSCS rotation were not affected by lime application. The Q10 values of N mineralization ranged from 1.9 to 2.2. Increasing the rate of lime application decreased the N(o) values at 20 degrees C, but not at 30 degrees C. Liming soils markedly increased the nitrification rate, from 27% of the NH4(+)-N added for untreated soils (0 kg ECCE ha(-1)) to 76% for the soil treated with 17920 kg ECCE ha(-1). N mineralization and nitrification rates varied among the replicated plots.