Root nodulation and yield of French bean (Phaseolus vulgaris) are altered by fallow length in slash-and-burn agriculture

ABSTRACT Shifting cultivation (Jhum) involves the conversion of forest land to agricultural land, and two successive Jhum cultivations in a patch of land make a Jhum cycle. Shortening of the cycle to meet population needs is a challenge, and one potential solution is to use N2-fixing, trees in fallow-phase and crops in cropping-phase. A pot experiment was conducted with soil from 2-, 4-, and 8-years fallows of alder-based (N2-fixed) and traditional Jhum agroecosystems, grown with surface-sterilized local French beans (design: CRD). A factorial micro-plot field experiment was also set up in alder-based Jhum sites in 2-, 4-, and 8-years fallow. In both, soil physico-chemical and biological properties, root nodulation and yield attributes of French beans were studied. Root nodulation and biomass yield attributes were higher in alder-based systems compared to traditional, with comparable improvements seen in shorter fallows. At harvest, yield parameters were in the order of 4->2->8-years in alder-based and 8->4->2-years in traditional Jhum soil. Rhizobium populations may decrease with longer fallow lengths without a host and fire stress of Jhum. Fallow length effect on all soil parameters, with increased values as length increased in both Jhum. Combination of soil-fertility and nodulation led to higher grain yield in 4-year-fallows of alder-based Jhum.