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Effect of N Fertilization on Yield and Water Use Efficiency of Dryland Winter Wheat as Affected by Stored Water and Rainfall¹

Dryland wheat is raised on stored water and limited precipitation. Nitrogen is known to increase grain yield and water use efficiency. But the crop response to N in relation to stored water, effect of N on water extraction, and effect of stored water and rainfall on water use are not sufficiently understood. Field experiments were conducted for a 3-year period on clay loam (Haplustaff) and loamy sand (Ustifluvent) soils using four rates of N viz. 0, 40, 80 and 120 kg N/ha to probe the above aspects in two-gene dwarf dryland winter wheat. Stored available water varied from 133 mm in a 180 cm profile to 204 mm in 120 cm profile and the rainfall varied from 62 to 141 mm.

Maximum grain yields and response to N application increased with increasing water storage irrespective of growing season rainfall. Compared with a control, N application increased yield, water use, and water use efficiency under all situations. Differences in water use and water extraction pattern by unfertilized and fertilized wheat were small during early stages. But after 80 days, 80 kg N/ha increased water depletion from 60 to 180 cm layer by 25 to 300%.

Under comparable rainfall, 52 mm higher initial available-water storage in clay loam than in loamy sand, caused 90 mm greater water depletion from 180 cm profile. With adequate moisture in the lower layers, a heavy rain during tillering followed by a long dry spell induced deeper rooting which depleted all the available water from 180 cm profile.

Key Words: N response • Water extraction pattern • Rainfall distribution and rooting

² Soil scientist, research assistant, professor of soil physics, and former research assistant, respectively.

Received for publication September 17, 1974.