Effects of mixed cropping, earthworms ( Pheretima sp.), and arbuscular mycorrhizal fungi ( Glomus mosseae) on plant yield, mycorrhizal colonization rate, soil microbial biomass, and nitrogenase activity of free-living rhizosphere bacteria

Abstract

Summary Sustainable agriculture uses nature as the model in designing agricultural systems. Because nature consistently integrates her plants and animals into a diverse landscape, a major tenet of sustainable agriculture is to create and maintain diversity. The effects of earthworm inoculation (Pheretima sp., Ew), arbuscular mycorrhizal fungi (Glomus mosseae, AMF) and mixed cropping systems on forage yield, mycorrhizal colonization rate, nitrogenase activity (NA) of free-living rhizosphere bacteria, soil microbial biomass (SMB) carbon, and the growth of clovers were studied at various mixed cropping ratios of berseem clover (Trifolium alexandrinum L., B) to Persian clover (Trifolium resupinatum L., P) (B:P=1:0, 3:1, 1:1, and 1:3). The effects of AMF and Ew on plant yield were positive. Mixed cropping gave more stable yields than monoculture. The greatest mycorrhizal colonization rate was observed at a B:P ratio of 1:1 with a combined AM+Ew inoculant. With the AMF+Ew inoculant, the greatest NA of free-living rhizosphere bacteria was observed with B:P=3:1. Although Ew had no significant effect on SMB, AMF increased SMB from 256 to 444 mg carbon kg−1. The greatest SMB (379 mg kg−1) was observed at B:P=1:1. The greatest nitrogen accumulation in the aboveground biomass, 31.5 mg g−1 forage dry matter, was obtained with mixed cropping (B:P=3:1) in the presence of the AMF+Ew inoculant. A combination of AMF, Ew, and mixed cropping increased the yield, mycorrhizal colonization rate, SMB, and nitrogen uptake of the clover plants, confirming the positive effects of diversity on an agriecosystem.