In situ soil nitrogen mineralization in no-till dryland agroecosystems

Research shows that increased cropping intensity under no-till management increases soil organic C and N, reduces NO{dollar}sb3{dollar}-N leaching, and increases biomass production compared to conventionally tilled monoculture agroecosystems. This study was conducted to: (1) evaluate the ion exchange resin/soil core method (IER/SCM) of determining in situ net N mineralization; and (2) to determine the effects of intensified no-till cropping systems, soil slope positions, and locations over an evapotranspirational (ET) gradient on net N mineralization. Cropping systems used to evaluate the IER/SCM and/or net N mineralization at Sterling, Stratton, and Walsh, CO included: (1) wheat (Triticum aestivum L.)- fallow (WF); (2) wheat-corn (Zea mays L.)-fallow (WCF); and (3) wheat-corn-(or sorghum (Sorghum vulgare L.)) millet (Panicum miliaceum L.)-fallow (WCMF/WSMF).; Variation with the IER/SCM is large so many cores are required to obtain N mineralization rates within acceptable confidence intervals. A precision of 1 ppm and probability level of 0.05 required from 28-36 cores, while increasing the probability level to 0.20 and precision to 1.5 ppm required 4-6 cores.; The highest levels of net mineralized N were at Stratton, Sterling, and Walsh, respectively. The high levels at Stratton were attributed to: (1) finer soil textures which enable the soil to better retain moisture; and (2) higher levels of SOM. The highest levels mineralization occurred on the toeslopes at all sites, followed by backslopes and summits. Net N mineralization followed the levels of soil moisture and SOM present in the soil slope positions. When soil water was equal, the more intensive WCMF/WSMF system had higher mineralization at all sites. Daily net N mineralization proceeded linearly in both cropping systems (r{dollar}sp2{dollar} = 0.63 and 0.98 for WCMF/WSMF and WF, respectively) in relation to the amount of SOM present in soil. The linear relationship indicates net N mineralization rates may be predicted by SOM levels. The majority of N mineralized during summer months preceding wheat planting illustrating the need for soil sampling to be close to fall planting.