EFFECT OF DIFFERENT PHOSPHORUS LEVELS ON XYLEM SAP COMPONENTS AND THEIR CORRELATIONWITH GROWTH VARIABLES OF MASH BEAN

Biological nitrogen (N) fixation is a reaction which needs 16 adenosine tri-phosphate (ATP) molecules to fix one molecule of atmospheric nitrogen. Nitrogen fixing crops need an optimum level of phosphorus (P) to attain maximum yield and nitrogen fixation. Mash bean (Vigna mungo) is a legume crop and it may fix efficiently atmospheric N if an adequate amount of P is present in the soil. A field experiment was conducted at the Research Farm Area, of the Department of Soil Science and Soil Water Conservation (SWC), Pir Mehr Ali Shah (PMAS), Arid Agricultural University, Rawalpindi, Pakistan to evaluate the effect of phosphorus fertilizer levels on grain yield, biomass yield, shoot and grain N yields and nitrogen fixation of mash bean. Four levels of phosphorus viz, 0, 40, 80 and 120 kg P2O5 ha^-1 were used as the treatment variables. The experiment was replicated three times in a randomized complete block design. It was measured that the application of 120 kg P2O5 ha^-1 produced the highest grain yield (711.3 kg ha^-1) and the highest N2 fixation (82.1 kg ha^-1). The correlation study showed that biomass yield (r^2 = 0.91), grain yield (r^2 = 0.96), shoot N yield (r^2 = 0.59) and grain N yield (r2 = 0.95) are positively correlated with the relative abundance of ureide-N in xylem sap which is the metabolic product of N2 fixation.