Impact of Nitrogen Addition on Physiological, Crop Total Nitrogen, Efficiencies and Agronomic Traits of the Wheat Crop under Rainfed Conditions

Abstract

Optimizing nitrogen (N) application timings and rate can improve nutrient uptake and nutrient efficiencies in wheat, particularly under rainfed conditions. Climatic stress in the form of high temperature and drought resulted in the decreased crop physiological traits, hastened maturity and, ultimately, caused lower grain yield. The impact of N application rates as full and split dose at three diverse locations of rainfed Pothwar, Pakistan was studied through field experiments for two years (2013–14 and 2014–15). Treatments include T1 = control (no fertilizer applied), full dose of N applied at the time of crop sowing, i.e., T2 = 50 kg N ha−1, T3 = 100 kg N ha−1 and T4 = 150 kg N ha−1, and split application of N at different timings at different stages of the crop, called split application of N, i.e., T5: application of 50 kg N ha−1 (15 kg N ha−1 (sowing, BBCH (Biologische Bundesanstalt Bundessortenamt und Chemische Industrie) 0): 20 kg N ha−1 (tillering, BBCH20): 15 kg N ha−1 (anthesis, BBCH 60), T6: application of 100 kg N ha−1 (30 kg N ha−1 (sowing, BBCH 0): 40 kg N ha−1 (tillering, BBCH 20): 30 kg N ha−1 (anthesis, BBCH 60) and T7: application of 150 kg N ha−1 (45 kg N ha−1 (sowing, BBCH 0): 60 kg N ha−1 (tillering, BBCH 20): 45 kg N ha−1 (anthesis, BBCH 60). The three study sites were Islamabad (high rainfall with optimum temperature), University Research Farm (URF)-Chakwal Road, Koont (medium rainfall with moderate temperature), and Talagang (low rainfall with high temperature). Results revealed that the highest stomatal conductance (0.80 mole H2O m−2 s−1), net photosynthetic rate (20.07 μmole CO2 m−2 s−1), transpiration rate (9.58 mmole H2O m−2 s−1), intercellular CO2 concentration (329.25 μmole CO2 mol−1 air), SPAD values (58.86%) and proline contents (35.42 μg g−1) were obtained from split application of N (T6 = split N100) compared to control and full dose N treatments. Among the sites, these physiological traits remained highest at Islamabad and lowest at Talagang, while between the years, the maximum values of the measured parameters were obtained during 2013–14. A similar trend was observed for crop total N, N efficiencies, and agronomic traits of the crop. The results suggested that the optimum N application rate at appropriate timings can help to harvest the real benefits of N. The split dose resulted in the maximum performance of the crop from the physiological parameters to the agronomic traits of the crop.