Variation of chickpea nodulation in a Mediterranean agroecosystem: relationship with soil characteristics and thresholds for significant contribution to plant growth
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This study was designed to investigate the influence of some environmental constraints on chickpea (Cicer arietinum L.) growth and nodulation in a reference agroecosystem. This multi-local field experiment, realized in the agroecosystem of Chlef in northern Algeria, involved 24 sites where the local well-adapted genotype Ain temouchent is grown. Determination of soil properties allowed the identification of three clusters of sites. Plant biomass (SDW) varied significantly among sites from 6.7 to 39.4 g SDW plant -1 and was highly correlated with nodule biomass (NDW). The slope of the regression function between NDW and SDW, defined as the efficiency in use of the rhizobial symbiosis (EURS) inside clusters ranged from 67 to 200 g SDW g-1 NDW. Analysis of the EURS highlighted the existence of a low nodulation threshold of 0.1 g NDW plant-1 below which the contribution of nodulation to the host plant growth was not significant and a high threshold above which the nodule biomass increase was not linked with an increase in shoot biomass. Thus, the significant regression of shoot growth as a function of nodulation ranged from 0.10 to 0.35 g NDW plant-1 (R 2 = 0.54, P < 0.001). Moreover, nodule biomass was positively correlated with soil Olsen-P, more particularly in cluster A (R 2 = 0.50, P < 0.05) and B (R 2 = 0.61, P < 0.01). This approach proved to be a rapid and efficient way to identify the major factors affecting nodulation in order to develop strategies to optimize nodule contribution to chickpea growth and yield.