SUMMARYBecause of environmental and economic constraints, we need to determine the effects of nitrogen fertilizer application on nutrient availability and fertilizer recovery, especially in regions of limited rainfall. This study was conducted to provide information on effects of N rate on yields and N recovery by standard and semi-dwarf spring wheats (Triticum aestivum L.) sown at two dates.Ammonium nitrate was applied to spring wheat at rates up to 272 kg N/ha each year for 4 consecutive years. Only grain was removed from the plot at harvest. Wheat types did not differ in grain yields, but these yields were significantly reduced in 2 of 4 years by late sowing. Average grain yields for late sowing were greatest at 34 kg N/ha, but yields for early sowing approached maximum at the 68 kg N for semi-dwarf wheat and 136 kg N/ha for the standard wheat.Semi-dwarf wheat was lower than standard wheat in grain and flour protein concentration and baking absorption. Late sowing (May 30) reduced test weights, flour yield and baking absorption, but increased wheat protein concentration as compared with early sowing (April 30). Leaching of fertilizer N below the 90 cm depth ranged from 152 to 378 kg/ha at the 272 kg N/ha/year rate, and was greater for the late than for the early sowing. Fertilizer N that could be accounted for averaged 87 and 82% for early and late seeding respectively. Water-use efficiency was reduced by late sowing.Soil-water extraction by wheat to the 120 cm depth was greater for high N rates.These 4-year results showed that semi-dwarf and standard wheats had only slight differences in total grain production. Also, for efficient use of applied fertilizer and available soil water, wheat should be sown in the spring as soon as soil and weather conditions permit.
Nitrogen uptake and nitrogen fertilizer recovery in old and modern wheat genotypes grown in the presence or absence of interspecific competition
