Microbial communities and residues in robinia- and poplar-based alley-cropping systems under organic and integrated management

Organic farming and agroforestry are considered as sustainable alternative agricultural practices for intensive agriculture. In a long-term field trial in Scheyern Germany, we evaluated the effects of 21-year organic farming and 4-year agroforestry (robinia and poplar) on microbial community and microbial residues. Microbial biomass and microbial community were determined by fumigation–extraction method and the analysis of phospholipid fatty acid (PLFA), respectively. Microbial residues were evaluated by the measurement of amino sugars. The results showed that organic farming had significantly positive effect on soil organic carbon (SOC) but that it tended to decrease microbial biomass C (MBC), PLFA functional guilds, muramic acid (MurN), and glucosamine (GlcN). Robinia system, however, significantly increased SOC and had the potential to enhance MBC, PLFA functional guilds especially Gram (+), but it tended to decrease MurN and GlcN, in comparison with poplar system. The hedgerow tree did not show significantly positive effect on SOC and microbial properties except the abundance of fungi and Gram (+) bacterial, after 4-year establishment period. The principal component analysis of the PLFA profile showed that in comparison with other investigated treatments, robinia system under organic farming had significantly a different microbial community structure. It also indicated tree species-specific effect on microbial community in the organic farming was stronger than that in the integrated farming. In summary, the short-term introduction of trees into an existing agricultural system will not substantially change the microbial biomass, but it has certain influence on the abundance of specific microbial groups in the hedgerow. Although organic farming did not show positive effect on overall microbial indices, we still see positive effect on SOC after 21-year organic farming and its additive effect with robinia on SOC in current study. We expect that alley-cropping agroforestry system that combines organic farming and robinia hedgerow has a great potential for sequestering SOC and developing sustainable agroecosystems with time.