Legume Nitrogen Fixation and Symbioses in Low-Inputs Rainfed Rice Rotations

Abstract

Cropping systems with legumes play key roles in farming systems in sub-Saharan Africa. However, how commonly legume associations perform in low input-systems is not well-known. Here, we studied four legume species used in three systems in rotation with upland rice, i.e., groundnut monocropping, sorghum–cowpea intercropping, and velvet bean–crotalaria intercropping, in two fertilization managements on the previous rice, i.e., manure alone or complemented with mineral fertilization. Legume suitability was assessed using rhizobial and mycorrhizal colonization rates, plant biomass production, shoot N and P content, and biological N2 fixation based on their δ15N natural abundance. Shoot and root biomasses varied significantly between legume species and were positively correlated with nodule number (r = 0.49 and 0.74, p-value < 0.05 and <0.001, respectively) and the amount of fixed N (r = 0.73 and 0.50, p-value < 0.001 and <0.05, respectively). The proportion of plant N derived from N2 fixation also varied significantly between species, with a higher percentage for velvet bean (66%), compared to the other three species (50 to 60%). Legume roots were weakly colonized by AM fungi, with similar levels between species. Overall, fertilization management did not significantly impact legume biomass, symbioses, or N2 fixation, yet the organo-mineral fertilization significantly increased legume shoot P content. The lack of effect of mineral fertilization on N2 fixation and biomass could be due to other nutrient deficiencies (Ca, Mg, micronutrients), which can hamper symbioses with rhizobia and mycorrhizae.

Biochemical and Molecular Evaluation of Rhizobium spp. and its Growth Promotion Studies with Lentil (Lens culinaris Medik. L.)

“…Catalase and oxidase enzymes reduce the oxidative damage in crop while α-amylase enzyme in the aleurone layer of seed helps in hydrolyzing the endospermic starch into sugar molecules, which provide energy for vigour index parameter. [37][38][39][40][41][42][43][44] Similar results were found by Mumtaz et al 45 who reported positive results for catalase and protease activity of Bacillus strain. He also reported the cellulose degradation ability of Bacillus strains and these enzymes were comprehensively reported for their effectiveness in tolerating stress.…”

“…significantly improved the root and shoot weight and total dry biomass of rice, soybean and maize crop. [40][41][42] Bioprimed seed with selected strains of bacteria improved root and shoot length upto 2 fold when compared to untreated plant (control). Increased root length by growth promoting bacteria favoured plant growth by exploring a greater volume of soil thereby increasing nutrient obtainability.…”

The Potential of Three Summer Legume Cover Crops to Suppress Weeds and Provide Ecosystem Services—A Review

“…Cowpea is an annual tropical and subtropical legume that grows erect, tendrilous, semi-tendrilous, or bushy [26]. The average biomass production for cowpea and velvetbean is 3 and 2.7 tonnes per acre, respectively, with nitrogen fixation potentially reaching 18 and 8 kg N per acre for cowpea and velvetbean, respectively [27][28][29]. All three species are low-input cover crops, which means their need for fertilization and irrigation is limited while they can also adapt to marginal lands [30].…”