Effect of phosphorus application methods and zinc on agronomic traits and radiation use efficiency of wheat (Triticum aestivum L.)

Soils of Pakistan are generally sandy loam with alkaline pH. low organic matter and fertility, particularly nitrogen (N) and phosphorus (P), and around 90% of soils are deficient in available phosphorus coupled with 10-25% of phosphorus use efficiency (PUE). P is being considered as second major element and mainly responsible for stagnant yields in the past decade. Phosphatic fertilizers have become increasingly expensive that further widened already imbalance of N and P use ratio. The current study was conducted to evaluate the effect of phosphorus application methods and zinc on agronomic traits and radiation use efficiency (RUE) of wheat. The phosphorus application methods were side dressed, 3 inches aside seed (P-1), broadcasting at the time of seedbed preparation (P-2), and top dressing after first irrigation (P-3). Zinc was applied in the form of zinc sulphate 21% in Z(2) treatment and no zinc was applied in Z(1) treatment. The P-1 treatment significantly enhanced total dry matter (13.20 and 13.27 t ha(-1)) and grain yield (6.96 and 6.99 t ha(-1)) compared to P-2 and P-3 methods. The TDM and grain yield from P-1 was 13-14% and 16-18% greater than in P-3 application method, respectively. Zinc application gave 3-4% higher total dry matter (TDM) and grain yield (GY) over Zn-1 treatment. Net assimilation rate was significantly higher in P-1 and Zn-2 treatment in both years. Variation in yield with P application methods and zinc treatment were closely correlated with the number of grains m(-2) and mean grain weight. Leaf area index (LAI), leaf area duration (LAD), radiation use efficiency for TDM (RUETDM) and radiation use efficiency for grain yield (RUEGY) were significantly higher in side placement of P (P-1) and zinc application (Zn-2) as compared to all other treatments. Both TDM and GY were linearly dependent upon the cumulative LAD with correlation coefficient of 0.96 and 0.94, respectively. The P-1 application method enhanced intercepted PAR by 8.3% compared to P-2 and P-3 application methods. TDM production in both years was strongly and linearly related to cumulative intercepted PAR (R-2 = 96.4%) and gave a value of 2.03 g MJ(-1).