Effects of crop rotation on enhanced occurrence of arbuscular mycorrhizal fungi and soil carbon stocks of lowland paddy fields in seasonaly dry tropics

Abstract

The impacts of crop rotation systems on the arbuscular mycorrhizal fungal (AMF) spore density, mycorrhizal colonization of rice roots, soil C fractions and C stocks in seasonally dry climatic zone of Sri Lanka were examined in Rice–Soybean (RS) and Rice–Onion (RO) crop rotation systems during the subsequent rice cultivation season and, compared these with a rice monoculture, i.e. Rice–Rice (RR). The study also examined the correlations between AMF occurrence and soil carbon stocks. Results revealed that RS crop rotation system significantly enhances the occurrence of AMF spores in soil with a higher fraction of large sized spores, the total organic C (TOC), microbial biomass C (MBC), water soluble C (WSC), labile C and a high AMF colonization in rice roots in the subsequent rice cultivation season. The diversity of AMF morphospecies were also the highest in RS. Reduction in AMF density in the soil in RR crop rotation system may be due to prolonged anaerobic conditions prevailed. The growth of onion has drastically reduced the AMF colonization in rice and soil C contents. Soil carbon stocks showed positive correlations with % root colonization and AMF spore number in soil. Thus, the study confirmed that C stocks in paddy soils can be improved by intercropping with AMF supporting plants like soya bean. This is the first report that shows positive correlations of AMF sporulation and % root colonization in lowland rice with soil carbon stocks.