The Importance of Residual Soil Nitrate in Upland Cotton Production Using Subsurface Drip Irrigation
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AbstractThe importance of residual soil nitrogen (N) in the production of upland cotton in Central Arizona has not been adequately studied. A subsurface drip irrigation experiment was conducted at the Maricopa Agricultural Center to examine the effect of residual soil nitrate content on lint yields of upland cotton, and to evaluate the validity of current cotton petiole nitrate interpretations under high yielding conditions. Different levels of water and N fertilizers applied to the plot area in previous years had resulted in a range of residual NO₃-N content ranging from 36 to 166 lbs /acre. Lint yields increased from 2.8 to 4.3 bales /acre as residual soil N increased from 5.7 to 27.7 ppm NO₃-N although the correlation between yield and soil N was relatively low. This was thought to be due to difficulty in obtaining soil samples that accurately reflect the true plant availability of N in soils irrigated with drip systems. The interpretation of cotton petiole data under high yielding conditions (> 4 bales/acre) proved to be essentially the same as that currently recommended for conventional furrow irrigated cotton.