A note on effect of nitrogen and irrigation regimes on some physiological traits of maize (Zea mays L.)

Worldwide, maize ranks first among the world cereals in both production and consumption. As a new introduced crop to Sudan, there is a growing importance for the crop reflected in both area ( 36,000 ha) and production (about 7000 tones). Crop production of many crops including maize in arid and semi-arid regions is restricted by deficiencies of both soil moisture and plant nutrients, especially nitrogen. The interplant competition for incident photosynthetic photon flux density, soil nutrients and soil water is more severe at high than at low plant density. In modern hybrids, tolerance to high plant density is a reflection of increased stress tolerance. The effect of water stress on physiological traits of many crops was widely studied (Ahmadi and Baker 2001; Calvino et al. 2003). Nitrogen is needed to form chlorophyll, proteins and many other essential plant growth molecules (Blackmer, 2000). As maize responds to water deficit by changing various physiological processes (Shahram and Roya, 2006), different genotypes differing in their response to nitrogen are evaluated by their nitrogen use efficiency. Nitrogen use efficiency (NUE) is the grain produced per unit of N applied to the soil (Moll et al. 1982). The objective of this trial was to study the response of Hybrid 351 under normal and stress irrigation at different nitrogen rates of various sources. The data recorded was canopy temperature depression, ground cover, chlorophyll content, nitrogen use efficiency and nitrogen uptake. The trial was carried during three seasons (2004 to 2006) using Hybrid 351 in split plot design with three replications. Treatments were two irrigation regimes, normal (every 10 days) and stress (Every 20 days) in the main plot and three nitrogen sources (urea, ammonium sulphate and ammonium sulphate nitrate at N rates of 0, 43 and 86 kg N/ha each in the subplot. The results showed that normal irrigation and N application irrespective of its source significantly increased canopy temperature depression (Table 1) and the ground cover (Table 2). Across the three seasons, canopy temperature depression ranged from 5.3 to 6.2 deg C for normal irrigation and from 3.2 to 3.4 deg C with stress irrigation and the mean ground cover across the seasons was 69.7 for normal irrigation compared to 59.3 for stress irrigation (Table 2). Though irrigation had no effect on chlorophyll content (46.2 for normal irrigation compared to 47.9 for stress irrigation), but N application significant increased it (from 38 to 49) as nitrogen is an integral part of chlorophyll formation (Table 2). Nitrogen use efficiency was reduced under stress irrigation by one third and decreased with increasing rates by nitrogen application (Table 3). Both normal irrigation and nitrogen application resulted in more nitrogen uptake (Table 4). The mean range in nitrogen uptake across the three seasons was 82-90 kg N/ha for normal irrigation and 69-75 kg N/ha for stress irrigation, a finding in conformity to Alan, (2005) and Patrick et al. (2004)