Optimizing water and nitrogen use for maize production under semiarid conditions

Water and nitrogen are among the most important crop inputs for optimum production of maize (Zea mays L.). A comprehensive experiment was conducted during 2009 and 2010 under the semiarid conditions of Pakistan to evaluate the effects of water and N applications on the growth and yield of irrigated maize. The objective was to formulate water and N best management practices (BMPs) for the above conditions. Three irrigation regimes (525, 450, and 375 mm ha^-1) with 5 N rates (0, 75, 150, 225, and 300 kg ha^-1) were tested using a split plot with a randomized complete block design. The results revealed that the irrigation and N treatments significantly affected growth and development of the crop plants. Photosynthesis and transpiration rates were influenced by the applied nutrients. The N application at 225 kg ha^-1 resulted in maximum values for photosynthesis (26.90 and 27.63 μmol m-2 s^-1 during 2009 and 2010, respectively) and transpiration (5.23 and 5.43 m mol m-2 s^-1 during 2009 and 2010, respectively). The highest values for leaf area index (4.93) and grain yield (8.40 t ha%-1) were also recorded at this N treatment during both growing seasons. On the other hand, the mean crop growth rate (19.23 g m^-2 day^-1) and biological yield (16.22 t ha^-1) were achieved with the 300 kg N ha^-1 treatments in 2009 and 2010. Nitrogen use efficiency (NUE) was optimum at 75 kg N ha-1 during both seasons. The highest water use efficiency (WUE) (16.48 and 18.64 kg ha^-1 mm^-1 during 2009 and 2010, respectively) was achieved by application of 225 kg N ha-1 with an irrigation water depth of 525 mm during both growing seasons. Water stress at the vegetative stage reduced the grain yield by 12.2%, whereas the same treatment at the grain filling stage reduced the grain yield by 22.6%. In the semiarid environment of Pakistan, the application of water at 525 mm ha^-1 with 225 kg N ha^-1 gave the optimum production of the irrigated maize tested in this experiment. These crop inputs may be considered as water and N BMPs for this region or for those with similar agricultural and environmental conditions. Agricultural inputsbased on these BMPs may result in similar NUE and WUE values.