Nitrogen assimilation, grain protein and yield of wheat in response to irrigation and method of fertilizer n application

A field experiment was conducted with wheat (Triticum aestivum L. cv PBW 343) during 1999–2000, to assess the interactive effects of timings of irrigation and fertilizer N on nitrogen assimilation, grain yield and protein content on a sandy loam soil. The experiment consisted of nine irrigation treatments ranging from nil to four in the main plots and three N treatments viz. no fertilizer N and 120 kg N ha⁻¹ (a) drilled at the time of sowing and (b) broadcast before presowing irrigation (BPSI) applied one week before sowing in the sub-plots. Mineral N distribution in the soil profile, determined at the time of sowing, showed that presowing irrigation transported 63 percent of the applied N to the sub-soil.

Nitrate reductase activity (NRA) of the flag leaf during grain filling was significantly enhanced by both amount and method of N application. The grain protein content (GPC) increased significantly (p=0.05) from 10.3 percent in 120 kg N ha⁻¹ drilled at sowing to 12.7 percent in broadcast. However, there was a decline in GPC with increase in irrigation number. Further, NRA showed a curvilinear relationship with GPC and grain N uptake. N recovery was found to be 30 percent in drill and 60 percent in BPSI method.

There was a significant (p=0.05) increase in 1000-grain weight, grain yield, biomass and total N uptake with irrigation. Similarly, fertilizer N drilled at sowing increased total biomass, ears per m², grain number per ear, grain N uptake and total N uptake over no N. Application of the same amount of N with BPSI further brought a significant improvement in these parameters. However, the grain size was significantly reduced with both fertilizer N rate and method of application.