| Lehmann, J; Gebauer, G; Zech, W: Nitrogen cycling assessment in a hedgerow intercropping system using 15N enrichment, Nutrient Cycling in Agroecosystems, 62, 1-9 (2002), doi:10.1023/A:1015403922358 | |
| Abstract: Nitrogen (N) cycling was determined in monocultures of Sorghum bicolor (L.) Moench and alley cropped sorghum with Acacia saligna (Labill.) H. Wendl. in semiarid Northern Kenya. N input through biological N2 fixation of the acacia, N transfer from the legume to the intercrop and losses of applied N through harvest and leaching were estimated using 15N enrichment. The biological N2 fixation and N transfer estimates clearly demonstrated the limitations of 15N enrichment techniques in field experiments showing even higher transfer than actually fixed N. Therefore, N transfer in the hedgerow intercropping system could not be determined by the 15N dilution methodology. The 15N balance approach, however, yielded reliable results even 1.5 years after 15N application. 74 to 88% of the applied 15N was recovered after three cropping cycles, most of it in the soil (0-1.2 m). Only about 10% of the 15N was taken up by the above-ground vegetation of both monoculture and 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 1.2 m 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 the alley than under the tree row. Incorporating the leguminous tree into the sorghum cropping system had no effect on total leaching and total uptake of applied 15N in above-ground biomass. |
