NITROGEN MINERALIZATION IN NATIVE CULTIVATED AND ABANDONED FIELDS IN SHORTGRASS STEPPE

We conducted a set of in situ incubations to evaluate patterns of N av ailability among dominant land uses in the shortgrass steppe region of Colorado, USA, and to assess recovery of soil fertility in abandoned fields. Replicated 30 d incubations were performed in 3 sets of native (never cultivated), abandoned (cultivated until 1937), and currently cultivated, fallow fields. Net N mineralization and the percentage of total N that was mineralized increased in the order: native, abandoned , cultivated Higher soil water content in fallow fields is the most li kely reason for greater mineralization in cultivated fields, while hig her total organic C and C/N ratios in native and abandoned fields may explain differences in mineralization between these land uses. Recover y of soil organic matter in abandoned fields appears to involve accumu lation of soil C and N under perennial plants, but probable methodolog ical artifacts complicate evaluation of the role of individual plants in recovery of N availability. Higher N mineralization and turnover in cultivated fields may make them more susceptible to N losses; recover y of N cycling in abandoned fields appears to involve a return to slow er N turnover and tighter N cycling similar to native shortgrass stepp e.