Aim : Genotypes, environment and nutritional management greatly influence physiological and agronomic performance of maize (Zea mays L), one of the important staple food crops. Among the plant nutrients, nitrogen is the most important nutrient that governs the maize growth and its productivity, but applied nitrogen fertilizer is subjected to various losses. These facts necessitate the determination of suitable planting time and precise N-Application schedule for maize. Hence, the current field experiment was conducted to assess the photosynthetically active radiation (PAR) interception, net photosynthetic rate (NPR) and production potential of maize varieties under variable growing environments and Soil Plant Analysis Development (SPAD) meter (also known as chlorophyll meter) guided N-Application rates. Methodology: The experiment consisted of twenty-four treatments comprising two-maize varieties, Pusa Extra Early Hybrid Makka 5 (PEEHM 5) and Pusa Composite 3 (PC 3), three-planting dates, July 9, July 24 and August 7 and four-nitrogen (N) application rates, no-N (control), 30 kg N ha(-1) as basal + 30 kg N ha(-1) top-dressed as and when average SPAD value dropped to < 37.5 (CMB), 30 kg N ha(-1) as basal + 30 kg N ha(-1) top-dressed at knee-high, pre-Tasseling and silking stages when average SPAD value dropped to < 37.5 and Soil Test Crop Response based N-Application (STCRB). The experiment was laid-out in a split-plot design assigning six-combinations of varieties and planting dates in main-plots and four-nitrogen application rates in split-plots. All the treatments were replicated thrice. Results: Hybrid PEEHM 5 recorded 5.23% higher grain yield, higher total biomass and net photosynthetic rate at early stages, while PC 3 showed 4.53 and 2.57% higher PAR at knee-high and tasseling stages, respectively. Among N-management practices, CMB N-Application improved grain yield by 9.25% and saved 10 kg N ha(-1) over STCRB N. Early planting on July 9 provided yield advantage of 5% over July 24 and 20% over late planting (August 7). Variety x N-rate interaction revealed highest NPR in PC 3 under CMB N application. Interpretation: The results of the investigation clearly demonstrated that planting of maize should not be delayed beyond second week of July in North Indian plains and chlorophyll meter reading i.e., average SPAD value < 37.5 of top-most fully expanded leaf, may be used in scheduling N-Top dressing to meet out in-season N-requirement, for achieving higher growth and productivity of maize crop.
