Impact of rock phosphate-enriched compost (RP-EC) and phosphate solubilizing microorganisms (PSM) on nodulation, growth and yield of chickpea and lentil

Abstract

In legumes, phosphorus (P) is required in large amounts due to its role in supplying energy in the form of adenosine triphosphate, nodulation and ultimately for biological nitrogen fixation. A series of pot and field experiments were conducted in order to study the impact of various combinations of rock phosphate (RP), compost and phosphate solubilizing microorganisms (PSMs) on nodulation, growth and yield of chickpea and lentil. Recommended dose of NPK fertilizers were used as control and N and K was used where P source was RP. Nodulation parameters regarding nodule number, fresh and dry weight of nodules were at flowering. Other growth and yield contributing parameters were taken at the harvest of the crops. Data collected was statistically analyzed using an appropriate statistical design i.e. completely randomized design (CRD) for pot experiments and randomized complete block design (RCBD) for field trials. The first study was conducted to find out the impact of phosphorus on nodulation, growth and allocation pattern of P in chickpea with and without rhizobia (Study 1). From the results, it was clear that ammonical form of nitrogen coming from the biological nitrogen fixation (BNF) enhances more shoot growth as compared to that with nitrate form in the form of Ca(NO3)2. The impact of P was more pronounced with ammonical form of N compared to the nitrate form, which clearly showed that P has an impact on nodulation of chickpea and lentil. So a clear linear relationship between nodulation and the applied P was observed. After finding the impact of P on nodulation, we planned to find out the cheaper and sustainable sources of P by using a combination of rock phosphate, compost and bio-inoculants (PSMs). So another pot trial was conducted to find out the impact of impregnation of rock phosphate with compost and PSMs on nodulation, growth and yield of chickpea and lentil (Study 2). From the results, it was clear that in most of the parameters like that of nodulation, grain and biological yield, the combination of RP, compost and PSM2 performed better as compared to recommended NPK taken from chemical fertilizer. After finding the better performing combination of rock phosphate, compost and PSM2, we then started to optimize this mixture for impregnation ratio of rock phosphate and compost, time of application and the rate of application were evaluated in study 3, 4 and 5. In study 3, effect of different ratios of effective formulation of rock phosphate found in study 2 on nodulation, growth and yield of chickpea and lentil was checked. From the results, it was found that the impregnation ratio of 50:50 of rock phosphate and compost with PSM2 performed better in case of parameters including nodulation, grain and biological yield as compared to that observed in other ratios (0:100, 25:75, 75:25, 100:0). Effect of different application times of the effective formulations of rock phosphate with optimized ratio found in study 2 and 3 on nodulation, growth and yield of chickpea and lentil was checked in study 4 which showed that the time of application of seven days before sowing performed better in case of parameters including nodulation, grain and biological yield as compared to the other evaluated times of application (30, 15, 3, 0 days before sowing). In the final study, a field trial was conducted to find out the effect of different application rates of the effective formulations of rock phosphate with optimized ratio and time of application on nodulation, growth and yield of chickpea and lentil (Study 5). The results showed that the application rate of 800 kg ha-1 performed better in case of nodulation, grain and biological yield as compared to the other evaluated rates. In all the studies, NP contents of straw and grain were improved as compared to NPK (recommended) control. In conclusion, the rock phosphate enriched compost (RP-EC) with PSMs could serve as a cheaper and easily available source of P for improved nodulation growth and yield of chickpea and lentil.