Evaluation of granular rhizobium inoculant for chickpea
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Field and growth chamber experiments with chickpea (Cicer arietinum L.) were conducted to assess the efficacy of granular inoculants compared to seed-applied liquid or peat-based inoculants. In the field, granular inoculants were either placed in the seed furrow or side banded 2.5 or 8.0 cm below the seed. The nodule dry weight for the liquid inoculant was lower than that for the peat or granular inoculants. Nodule formation in the seed-inoculation treatments was restricted to the crown region of the root system, whereas soil inoculation in particular, below the seeding depth resulted predominantly in lateral root nodules. In the field, soil inoculation increased dry matter yield plant⁻¹ over seed inoculation, but the increase was minor in the growth chamber. In 1997 granular inoculant placed below seed increased kabuli seed yield by 36 and 14% over the liquid and peat-based inoculants, respectively, whereas desi seed yield increased 17 and 5%, respectively. However, yields were inconsistent in 1998. In the field, seed protein concentration, percentage N derived from atmosphere (%Ndfa) and amount of N₂ fixed for the seed were typically lower for the liquid inoculant than those for the peat and granular inoculants. Similar trend was observed for (%Ndfa) and N₂ fixed in the growth chamber. The rate of N₂ fixation in the growth chamber increased from the late vegetative stage (28 DAP) to a peak at the early pod-filling stage (56 DAP) and declined thereafter. The dry weight of lateral root nodules was highly correlated with both plant dry weight and seed yield but the relationship was inconsistent in kabuli in 1998, presumably due to droughty conditions. Based on the field results, placing granular inoculant 2.5 to 8.0 cm below the seed may be the optimum. The isotopic fractionation (β) values during N₂ fixation by desi and kabuli chickpeas, grown in N-free nutrient solution, were not influenced by the infecting rhizobial strain at the flowering stage, but the β values for the harvested seed in the desi were dependent on the rhizobial strain. Nodule dry weight, plant dry weight and N accumulation did not differ in either the desi or kabuli chickpea, except for plant N yield, which was lower in the mixed-strain inoculant in the kabuli chickpea. The survival of 'Rhizobium ciceri' on chickpea seed, treated separately with Apron, Arrest 75W, Crown or Captan, was examined under laboratory conditions Fungicide treatment decreased rhizobial viability on the seed. The toxicity of the fungicides in terms of rhizobial viability increased in the following order: Control = Crown < Arrest = Apron < Captan. In the growth chamber, Crown reduced nodulation, N₂ fixation and shoot dry matter. Seed treated with Arrest and Captan decreased nodule dry weight and N₂ fixation, but only Arrest reduced dry matter yield. Apron had no effect on any of the parameters measured at the early pod-filling stage and may be compatible with chickpea inoculum.