Dr. R.V. KOTISAVITA F. HULLUR2018-01-112018-01-112014-06http://krishikosh.egranth.ac.in/handle/1/5810039197Field and pot experiments were conducted at College of Agriculture, Dharwad to screen the Soybean genotypes and to assess the genetic variability for P uptake, P content and Phosphorus use efficiency (PUE) along with morphological and physiological changes under P limiting condition. A laboratory experiment was conducted in selected genotypes to know the biochemical reasons for high P uptake and high PUE. The results of the field experiment revealed that shoot length, shoot dry weight, root dry weight decreased in P limited condition. Whereas root length and root to shoot ratio increased significantly and is one of the adaptive mechanisms to overcome the P deficiency in the vertisol. Leaf P and P uptake was reduced in P limiting condition and PUE increased in P limiting condition (- P). P limitation caused 17% decrease in seed yield. The phosphorus efficiency (relative value) of dry weight of the genotypes between –P and +P was identified as good indicator of the P efficiency genotypes. Bi-plot analysis of relative values (PE) of shoot dry weight against yield and PUE showed that the genotypes Gujarath Soybean-1, TAMS-38, TAMS-9821 Pusa-24, VL Soya-59, J 30 14-1 and J 20 47-18 were not only P efficient but also high seed yielder. Grain yield, PUE and P uptake exhibited high GCV, PCV and high heritability with high genetic advance over a mean under both P conditions. The photosynthetic rate, transpiration rate and WUE were decreased in -P condition. The soybean genotypes Shivalik followed by SL-296 and CO-3 were found to have high photosynthetic rate in P limiting condition. The root secretion of both citric acid and oxalic acid was maximum in the genotypes MACS-58, Shivalik and VL-Soya-59 under -P condition. The acid phosphatase activity was higher in -‘P’ condition and is an indication of ‘P’ sufficiency or deficiency in soybean. The genotypes viz., Pusa-24, TAMS-38, TAMS-9821, VL Soya -59, J 30 14-1 and J 20 47-18 were identified as phosphorus efficient with high PUE, dry matter and yield. The soybean genotypes ADT-1, CO-3, Bragg and JS-75-06 were identified for better root traits like higher root length, root dry weight, root to shoot length and root to shoot dry weight ratio.ennullThesis