PJB-2008-78
ESTIMATION OF N2-FIXATION OF MUNG BEAN AND MASH BEAN THROUGH XYLEM UREIDE TECHNIQUE UNDER RAINFED CONDITIONS
RIFAT HAYAT*, SAFDAR ALI, SHAHZADA SOHAIL IJAZ, TAHIR HUSSAIN CHATHA AND MUHAMMAD TARIQ SIDDIQUE
Abstract
Xylem ureide is cost effective and inexpensive technique used for estimation of N2-fixation in legumes. Legumes transport large amount of nitrogenous compound in the form of ureide. To quantify N2-fixation through xylem ureide technique, field experiments were conducted on mungbean (Vigna radiata) and mashbean (Vigna mungo) during summer seasons of 2002 and 2003 at two different locations of Pothwar area i.e., Research Farm of University of Arid Agriculture, Rawalpindi (UAAR) and farmer’s field in Chakwal district. Treatments were T1) Mungbean, T2) Mashbean, T3) Mungbean + P @ 80 kg ha-1, T4) Mashbean + P @ 80 kg ha-1. Bean seeds were inoculated at sowing with effective brady rhizobia. Relative abundance of ureide-N (100×4×ureide/(4×ureide + nitrate + α amino-N) has been used as an indicator for relative dependence on N2-fixation. Concentration of ureide, nitrate and α amino-N were determined at pod filling stage to calculate the relative abundance of ureide-N (RUN%) and proportion of plant N derived from N2-fixation (%Pfix). Highest shoot dry matter (DM) yield 4.0 t ha-1 (85 kg N ha-1) of mash bean was recorded at UAAR site during summer 2003. Mung and mash beans fertilized with phosphorus produced 24 and 28% higher nodules when compared to beans without fertilizer, respectively. Ureide concentration (0.69 mM) was maximum in the xylem sap of mash bean with phosphorus at Chakwal site. The relative abundance of uredide-N (RUN%) in the xylem sap of beans, was in the range of 36-60 %. An increase of 32 % in the value of %Pfix was observed by addition of phosphorus fertilizer. N2-fixation by mung bean and mash bean was 47 and 80 kg N ha-1, which tended to increase up to 24 % with application of phosphorus fertilizer. Regression analysis indicated close association of N2-fixed with shoot DM (R2 = 0.88) and shoot N (R2 = 0.90) at UAAR site. Correlation amongst the parameters for the legumes showed that N2-fixation was positively and strongly correlated with all the legume parameters i.e., shoot dry matter (r = 0.90), shoot N (r = 0.79) and %Pfix(r = 0.99) at Chakwal site.
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