Effect of biochar and rhizobium innoculation on nodulation, chlorophyll content, growth and yield of chickpea (Cicer arietinum L.)

Abstract

Soil infertility, water scarcity, and availability of high yielding and drought tolerant crop genotypes remain major constraints for agricultural production in semi-arid regions. These constraints are major threats to sustainable crop production and food security. Management practices in such areas should always be geared towards improving productivity at a low cost while sustaining soil fertility. Preliminary studies showed the huge potential of chickpea in the dry environments of the North Eastern South Africa. However, lack of nodulation in chickpea has been reported in these regions probably due to low soil pH, insufficient rhizobial populations or total lack of infective native rhizobia. Therefore this study assessed the effect of biochar and rhizobium inoculation on soil pH, nodulation, growth, yield and chlorophyll content of chickpea in Mpumalanga (Nelspruit) and Limpopo (Thohoyandou) Provinces, South Africa. Two field experiments were planted during winter 2015 and 2016. Treatments consisted of three levels of biochar (0, 10 and 20 t ha-1), two Rhizobium inoculation levels (with and without Rhizobium inoculation) and three chickpea genotypes (ACC #4, ACC #5, and ACC #6) in a factorial combination arranged in randomized complete block design replicated three times. Crop phenology (days to 50% emergence, flowering, podding, and physiological maturity), crop growth (plant height, canopy cover, number of primary and secondary branches), nodulation (number of nodules per plant and nodule dry weight), yield and yield components (number of pods per plant, number of seeds per pod and 100 seed weight [100-SW]), and chlorophyll content were determined at various crop growth stages. Identification and isolation of native rhizobia from soils was done using standard protocols. Data obtained were subjected to analyses of variance using the general linear model of Genstat software version 17. Significant differences between the treatments means were compared using the standard error of difference (SED) of the means at 5% level. Correlation analyses were performed to assess the relationship between parameters. Molecular data was subjected to BLASTn in National Centre for Biotechnology Information (NCBI) searches for identification of isolated strains Application of biochar at 10 and 20 t ha-1 increased soil pH by 0.7 pH units in Thohoyandou (clay soil) in 2015 and 2016, respectively. Soil pH increased by 0.77 pH units at 10 t ha-1 and 1.2 pH units at 20 t ha-1 in Nelspruit (loamy sand) in 2015 and 2016, respectively. Similarly, rhizobium inoculation increased soil pH by 0.2 (Thohoyandou) and 0.5 (Nelspruit) pH units in 2015 and 2016, respectively. There was a 100% increase in nodulation in inoculated compared to uninoculated treatments. There was no effect of biochar and rhizobium inoculation on number of days to 50% flowering, podding, v physiological maturity and on plant height. However, plant height varied with genotypes. Biochar application increased above ground biomass by 17% (10 t ha-1) and 12% (20 t ha-1), and 100 seed weight by 9% (10 t ha-1) and 7% (20 t ha-1) in Thohoyandou in 2015. Rhizobium inoculation increased yield and yield components in Thohoyandou in both seasons; biomass was greater by (31 and 23%), grain yield (26 and 24%), number of pods per plant (18 and 31%), and 100-SW (10 and 13%) in 2015 and 2016, respectively. Similarly, rhizobium inoculation increased biomass (53.4%), grain yield (81%), number of pods per plant (54%) and number of seeds per pod (89%) in Nelspruit in 2015. Genotype did not affect yield and yield components in Nelspruit. In contrast, genotype affected above ground biomass, grain yield, harvest index, number of pods per plant, and number of seeds per pod in 2015 in Thohoyandou with ACC #6 producing greater yield compared to ACC #4 and 5. The analysis for native rhizobia showed that agricultural fields in Nelspruit and Thohoyandou lack effective strains of rhizobium. The identified strains according to 16s gene region were Klebsiella variicola, Burkholderia cenocepacia, Bacillus subtilis and Ochrobactrum spp. The effects of biochar and rhizobium inoculation were more pronounced in Thohoyandou compared to Nelspruit. Therefore biochar and rhizobium inoculation may improve chickpea productivity in Limpopo and Mpumalanga Provinces through improved soil pH, nodulation, growth, yield and yield components.