Efficiency of nitrogen use by dryland wheat in a subhumid region in relation to optimizing the amount of available water

SUMMARY The effect of soil water supply on efficiency of N use in wheat and NO3-N accumulation in the soil profile was studied in a field experiment on loamy sand soil at Boothgarh in Hoshiarpur, Punjab, India in 1980/81. As the water supply increased from 509 to 548 mm, the response to N application increased by 11·5 kg grain/kg N and apparent N recovery by 11% at optimum N application rates. The increase in N recovery with additional water supply was related to the NO3-N use from the profile. The accumulation of NO3-N in the profile was related linearly to rate of N application but inversely to water supply up to an optimum value of 580 mm. Further increase in water supply did not increase fertilizer N use. If both the amount of moisture stored in the profile at sowing and the probable rainfall during the crop season are known, the efficiency of fertilizer N use can be predicted.