Relationships between Leaf‐Blade Nitrogen and Relative Seedcotton Yields

Abstract

Nitrogen fertilization is a required production practice for cotton (Gossypium hirsutum L.) with risks arising from under‐ and over‐fertilization. Tissue testing for diagnosing N deficiencies in crops can use leaf blades and the total N concentration, but this practice has not been rigorously examined in cotton. The primary objective of these experiments was to determine the leaf‐N concentration of the uppermost, fully mature leaf blade below which yield loss could be expected. Nitrogen‐rate field experiments were conducted at 12 research station and farm sites in the Midsouth USA in Louisiana, Arkansas, Mississippi, and Alabama in 1996 and 1997. Leaf‐blade total N concentrations associated with yield loss were 4.3% N at early bloom (R2 = 0.50) and 4.1% N at mid‐bloom (3 wk after early bloom, R2 = 0.32). The likelihood of applying N when not needed could be reduced by lowering the early bloom critical value to 3.9%. Only 4% of all samples sufficient in N would have been incorrectly diagnosed N deficient at that critical value, but 44% of all deficient samples would have been misidentified as N sufficient. Reduced yields due to over application of N were evident in some samples with leaf N between 4.6 and 4.8% at early bloom. These concentrations were also common for N‐sufficient plants, making accurate diagnoses of the over application of N unlikely. Our leaf‐N critical values probably differ from previously established values because earlier values were derived via survey techniques and because faster fruiting cultivars may require higher leaf N.