Nitrogen cycling assessment in a hedgerow intercropping system using 15N enrichment
Tóm tắt
Nitrogen (N) cycling was determined in monocultures of Sorghumbicolor (L.) Moench and alley cropped sorghum with Acaciasaligna (Labill.) H. Wendl. in semiarid Northern Kenya. N inputthrough biological N2 fixation of the acacia, N transfer from thelegume to the intercrop and losses of applied N through harvest and leachingwere estimated using 15N enrichment. The biological N2fixation and N transfer estimates clearly demonstrated the limitations of15N enrichment techniques in field experiments showing even highertransfer than actually fixed N. Therefore, N transfer in the hedgerowintercropping system could not be determined by the 15N dilutionmethodology. The 15N balance approach, however, yielded reliableresults even 1.5 years after 15N application. 74 to 88% of theapplied 15N was recovered after three cropping cycles, most of it inthe soil (0–1.2 m). Only about 10% of the15N was taken up by the above-ground vegetation of both monocultureand agroforestry. The trees took up more of the applied 15N(8.4%) than the sorghum (1.3%) in the agroforestry system,indicating nutrient competition between tree and crop. Leaching losses below 1.2m depth were low in this semi-arid environment with 3 and 6%of the applied 15N in the monoculture and agroforestry system,respectively. 15N losses from leaching were 2.5 times higher in thealley than under the tree row. Incorporating the leguminous tree into thesorghum cropping system had no effect on total leaching and total uptake ofapplied 15N in above-ground biomass.
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