Effects of supplemental irrigation and graded levels of nitrogen (N) on cotton yield and fiber quality were investigated in the Mississippi Delta in 2011 and 2012. Cotton was planted in 48 experimental plots with irrigation as main treatment unit and N application rate (0, 39, 67, 101, 135, and 168 kg ha -1 ) as subunit. Supplemental irrigation was conducted based on soil-water sensor measurements. Cotton yield was determined using a boll buggy equipped with load cells. Cotton samples were

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... cted and ginned, and the fiber quality was evaluated. Statistical analyses on the effects of irrigation and leaf N on the yield and fiber quality indicated that compared with non-irrigated cotton, the irrigated cotton increased seed cotton yield by 14%. Leaf N content varied in a range of 3.27% to 5.86% with an average of 4.34%. Leaf N of irrigated plants was 9.0% and 3.6% higher than that of the non-irrigated plants in 2011 and 2012, respectively. Soil water stress had a negative effect on N uptake of cotton plants. Yield showed a positive linear correlation with leaf N content in both irrigated and non-irrigated plots. Irrigation improved fiber quality, including all fiber length parameters. Upper half mean length (UHML) of cotton fiber in irrigated treatment was 2.7% and 1.8% greater than that in the non-irrigated treatment in 2011 and 2012, respectively. Micronaire decreased, and neps and yellowness increased with the increase of leaf N under irrigated and non-irrigated conditions. Excessive application of N would not be beneficial to fiber quality and could possibly create negative impact on some properties of cotton fibers.