Document: PEN-3-59-31

Effects of irrigation and cultivation on soil carbon and nitrogen in northeastern Colorado.

SINTON, P.J.*, I.C.BURKE and W.K.LAUENROTH

Colorado State Univerisity, Ft. Collins, CO 80523 USA 1

Abstract:
In the Colorado shortgrass steppe, the effects of dryland wheat-fallow cultivation on soil C and N have been well studied. However, no one has addressed the effects of irrigated crops on soil carbon contents in this region. In this study, we compared differences in total C and N and the distribution of C and N within the soil profiles of irrigated corn, dryland wheat-fallow, and uncultivated rangeland soils. We took 2m-deep soil samples for corn, wheat and rangeland fields, and analyzed them for total C and N. Irrigated corn fields averaged 21.2 kg C/m2, followed by rangeland and wheat fields with 13.2 and 7.8 kg C/m2, respectively. The distribution of C through the profile differed among fields, with net losses in the A horizon of dryland systems and net gains in irrigated systems, relative to rangelands. Total N content was highest in irrigated corn, averaging 0.85 kg N/m2, followed by rangeland and wheat fields with 0.59 and 0.32 kg N/m2. Irrigation significantly increased soil C and N in the semiarid steppe in Colorado. These findings have important implications for long term soil fertility and C storage.

Keywords: carbon, nitrogen, agroecosystem, soil fertility

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AGROECOLOGY