Irrigation frequency and nitrogen fertilizers modify cotton yield at Emerald, central Queensland

Abstract

Four irrigation frequencies and six nitrogen (N) fertilizer rates (0-300 kg ha-1) were applied to cotton (Gossypium hirsutum L.) grown on three Vertisols in the Emerald Irrigation Area, central Queensland. The purpose was to describe lint production responses to the plant available water before irrigation and N fertilizer, in terms of the crop N content and the efficiency of crop N use for lint production. Lint yield was greatest when the plant available water before irrigation was 50-80010 of the plant available water capacity (PAWC) of each soil. The rate of N fertilizer for maximum yield varied with plant available water and soil type. Plant available water before irrigation >60% and <37% PAWC, and rain after irrigation reduced the crop N content at the time of maximum leaf area index. Relative yield generally responded to 130 kg crop N ha-', although the range from 101 to 141 kg crop N ha-1 reflected differences in the maximum yield of each treatment. If the crop N was <130 kg ha-1, yield was mostly determined by the crop N content, whereas if the crop N content was >130 kg ha-1, yield and the efficiency of crop N use for lint production was determined by the plant available water before irrigation and soil type. Nitrogen fertilizer strategies to achieve the maximum yield of cotton (var. Deltapine 61) should focus on obtaining 130 kg crop N ha-1. This crop N content produced maximum yields for a range of plant available water contents before irrigation, and for three soil types.