Nitrogen and phosphorus requirements of different wheat plant types under dryland and irrigated conditions1

The wheat (Triticum aestivum L.) plant type in major producing areas of the U.S. is changing rapidly from tall cultivars to high‐yielding semidwarf cultivars. Objectives of experiments were to determine if nitrogen and phosphorus nutritional requirements differ between traditional tall cultivars and modern semidwarf cultivars under dryland and irrigated conditions. ‘Larned’, a tall cultivar; ‘Newton’, a semidwarf cultivar; and ‘Plainsman V, a high‐protein semidwarf cultivar, were grown with all combinations of three nitrogen fertilizer levels (0, 84, and 168 kg N/ha) and two phosphorus fertilizer levels (0 and 90 kg P2O5/ha) at Colby, Kansas for two years. Three levels of irrigation—dryland, limited irrigation, and full irrigation—were applied. Grain yields were highest with 84 kg N/ha under dryland and with 168 kg N/ha under irrigation. Phosphorus increased grain yield under dryland conditions one year, but had no effect under irrigated conditions. Cultivar X nutrition interactions from differential yield responses to fertility levels occurred under the dryland and limited irrigation regimes one year. Grain protein content was increased by nitrogen fertilization under all regimes both years and was decreased only by phosphorus fertilization under dryland conditions one year. Cultivar X nitrogen interactions for grain protein occurred under all irrigation regimes. We concluded that nutrient requirements do not differ between tall and semi dwarf wheat culti‐vars under any irrigation regime. Raising the recommended level of nutrients, particularly nitrogen, should be considered for all cultivars, both tall and semidwarf.