637 Nutrient uptake and phosphorus use efficiency of cowpea as influenced by genotypes, phosphorus levels and liquid based PSB MSR Kalyani, Ganajaxi Math*, Gurupad Balol AICRP on MULLaRP, MARS, University of Agricultural Sciences, Dharwad, Karnataka, India Abstract A study was conducted to evaluate the response of cowpea genotypes (DC-15, GC-3 and KBC-9) to phosphorus levels (0, 25, 50 and 75 kg P 2 O 5 ha -1 ) and liquid based PSB with respect to nutrient uptake and phosphorus use efficiency at MARS, University of Agricultural Sciences, Dharwad during kharif 2019 under rainfed condition. The results indicated that among the genotypes, the genotype DC-15 recorded significantly higher nitrogen (74.35 kg ha -1 ), phosphorus (11.00 kg ha -1 ), potassium uptake (48.57 kg ha -1 ) and recovery efficiency (0.040 kg kg -1 ) over other genotypes. Among the phosphorus levels, application of 75 kg P 2 O 5 ha -1 + liquid PSB @ 4ml kg -1 recorded significantly higher nitrogen (71.55 kg ha -1 ), phosphorus (11.32 kg ha -1 ) and potassium (46.33 kg ha -1 ) uptake over other levels. Whereas, application of 25 kg P 2 O 5 ha -1 + liquid PSB @ 4ml kg -1 seeds recorded significantly higher recovery efficiency (0.041 kg kg - 1 ) over other levels. Among the interactions, the genotype DC-15 with the application of 75 kg P 2 O 5 ha -1 + liquid PSB @ 4ml kg -1 seeds recorded significantly higher nitrogen (83.60 kg ha -1 ), phosphorus (12.02 kg ha -1 ) and potassium (49.66 kg ha -1 ) uptake over the control and other treatments. Further, genotype DC-15 with the application of 25 kg P 2 O 5 ha -1 + liquid PSB @ 4ml kg -1 seeds recorded significantly higher recovery efficiency (0.057 kg kg -1 ) over the control and other treatments. Keywords: Cowpea genotypes, phosphorus levels, liquid based PSB, phosphorus use efficiency Introduction Cowpea (Vigna unguiculata (L.) Walp) is an important protein rich legume in the semi tropics which occupy the unique position in agriculture by virtue of their high protein content, inherent capability to fix atmospheric nitrogen in root nodules. Among the edaphic factors (soil physiochemical characteristics), phosphorus deficiency is the most limiting soil fertility factor for cowpea production. This occurs as a result of either inherent low levels of P in the soils or depletion of the nutrient through cultivation. Phosphorus is among the most needed elements for crop production in most tropical soils, which tend to be phosphorus deficient. Phosphorus, although not required in large quantities, is critical to cowpea yield because of its multiple effects on plant nutrition. It plays a key role in many plant processes such as energy metabolism, nitrogen fixation, synthesis of nucleic acids and membranes, photosynthesis, respiration and enzyme regulation. It is critical to cowpea yield because it is reported to stimulate growth, initiate nodule formation as well as influence the efficiency of the Rhizobium-legume symbiosis (Nkaa et al., 2014). Phosphorus application influences the contents of other nutrients in cowpea leaves and seed. Compared to other major nutrients, phosphorus is the least mobile and available to plants, because a major portion of phosphorus in the form of soluble inorganic phosphate gets rapidly immobilized and thereby, it is unavailable, when applied as chemical fertilizers. Hence, the use of phosphorus solubilizing bacteria either in the form of carrier based or liquid based, can save the crop requirement of phosphatic fertilizer. Because, the quality standards of liquid based biofertilizers are good and stable for six months, they were considered as the best substitute for regaining soil health, enhancing crop yields and sustainable food production in the modern agriculture. Cowpea being a leguminous crop responds more to phosphorus than nitrogen and potassium. This fact necessitates determining the adequate supply of phosphorus to cowpea based on field experimentation for realising the genetic yield potential of newly evolved varieties. Therefore, this study is intended to govern the response of cowpea genotypes to differential P and PSB applications so as to determine suitable recommendations. Materials and Methods The experiment was conducted during kharif 2019 under AICRP, MULLARP at MARS, Dharwad which comes under Northern Transition Zone (Zone 8) of Karnataka. The texture of the experimental soil was clay loam having pH of 7.85 and electrical conductivity of 0.32 dS m -1 . The soil was low in available nitrogen (232.5 kg ha -1 ), medium in available phosphorus (22.6 kg ha -1 ) and high in available potassium (381.9 kg ha -1 ), respectively. The experiment was laid out in two factorial RBD with single control design with twelve treatment combinations and replicated thrice. The first factor consists of three genotypes (DC-15, GC-3 and KBC-9) and second factor consists of four phosphorus levels (0, 25, 50 and 75 kg P 2 O 5 ha -1 ) along with liquid based PSB @ 4ml kg -1 seeds and control (DCS-47-1+ RDF (25:50:25) N: P 2 O 5 : K 2 O kg ha -1 + carrier based PSB @ 500g ha -1 ). The spacing adopted was 45 cm × 10 cm. Phosphorus was applied through Single Super Phosphate (SSP) @ (0, 25, 50, 75 kg ha -1 ) as per the treatment requirements at the time of sowing and other agronomic management practices were followed as per standard recommendation. International Journal of Ecology and Environmental Sciences www.ecologyjournal.in Online ISSN: 2664-7133; Print ISSN: 2664-7125; Impact Factor: RJIF 5.28 Received: 26-10-2020; Accepted: 11-11-2020; Published: 25-11-2020 Volume 2; Issue 4; 2020; Page No. 637-639