Construction of efficient nitrogen-fixing cropping pattern:Maize/faba bean intercrop with rhizobium inoculation in reclaimed low-fertility soils

Lighe sierozem in the Ningxia Yellow River Irrigation area is characterized as newly reclaimed soil due to lower fertility and land consolidation. To rational use land resources with environmental friendly way of the soil, leguminous/non-leguminous crops intercropping plus nitrogen-fixing rhizobium is an important measure. In order to construct an efficient nitrogen-fixing cropping pattern in reclaimed lands, the efficiency of Rhizobium species and the inoculation methods were investigated aiming to the construction of a maize/faba bean-rhizobium intercropping systems through the greenhouse and field experiments with newly-reclaimed low-fertility soils. Four Rhizobium leguminosarum biovar viciae (NM353, CCBAU, G254 and QH258) and four inoculation methods (seed inoculation with water absorbent, seed inoculation with water, dip root at 3-leaf stage and seed pelleting & inoculation) were used and the relative advantages determined with respect to crop productivity, aboveground nitrogen acquisition, nodule characteristics, biological nitrogen fixation, etc. The greenhouse experiment results showed that the order of total biomass of intercropped maize and faba bean for different rhizobium was CCBAU > NM353 > G254 > QH258 > intercropping without rhizobium > sole crop without rhizobium, and for inoculation method was seed inoculation with water absorbent > seed pelleting & inoculation > seed inoculation with water > dip root at 3-leaf stage. The field experiment showed that inoculation with NM353 with seed inoculation via water absorbent method produced significant increase in yield of intercropped faba bean and maize by 79.7% and 42.8%. The intercropping system with G254 and NM353 rhizobium showed obvious yield advantage, the land equivalent ratio was >1.5. Also nitrogen content of faba bean and maize was highest among different treatments. In addition, the number of nodules, nodule biomass and nitrogen derived from air (Ndfa) and percent Ndfa (%Ndfa) were all greater in the newly-established system compared to non-inoculated faba beans. Particularly, %Ndfa of faba bean inoculated with NM353 was respectively 19.1% and 11.1% higher than that inoculated with CCBAU at peak flowering and pod-filling stages, and both had significant differences. The differences in Ndfa of faba bean were significant between rhizobium inoculation NM353 and CCBAU at each growth stage. Relatively, the difference between NM353 inoculation and the other strains was more significant for either%Ndfa or Ndfa. The inoculation with water absorbent method showed best inoculation effect with respect to nodules number, nodule biomass, %Ndfa and Ndfa. Thus an efficient cropping system was successfully set up for nitrogen fixation. The maize/faba bean-rhizobium intercropping system based on seed inoculated with Rhizobium NM353 was the most sustainable development model for rational development and utilization of the low-fertility soil.