ceed plant needs or when fertilizer applications are not synchronized with plant uptake. Today, methods for Nitrogen fertilization is a required production practice for cotton predicting N status of cotton grown in the Midsouth are (Gossypium hirsutum L.) with risks arising from under-and overeither inaccurate or require additional studies before fertilization. Tissue testing for diagnosing N deficiencies in crops can use leaf blades and the total N concentration, but this practice has the critical values used in tissue testing can be accepted not been rigorously examined in cotton. The primary objective of and used by farmers and extension personnel (Bock and these experiments was to determine the leaf-N concentration of the Adams, 1980;Sabbe and Zelinski, 1990). Critical values uppermost, fully mature leaf blade below which yield loss could be are used in tissue testing to separate N-deficient from expected. Nitrogen-rate field experiments were conducted at 12 re-N-sufficient plants. Plants with tissue samples that consearch station and farm sites in the Midsouth USA in Louisiana, tain N levels above the critical value are considered Arkansas, Mississippi, and Alabama in 1996 and 1997. Leaf-blade sufficient in N and no N fertilizer would likely be needed total N concentrations associated with yield loss were 4.3% N at early while those plants with N concentrations below the critibloom (R 2 ϭ 0.50) and 4.1% N at mid-bloom (3 wk after early bloom, cal value are considered deficient in N and N applica-R 2 ϭ 0.32). The likelihood of applying N when not needed could be tions might be advisable. Inaccurate critical values can reduced by lowering the early bloom critical value to 3.9%. Only 4% result in the over-application or under-application of N. of all samples sufficient in N would have been incorrectly diagnosed N deficient at that critical value, but 44% of all deficient samples The principal method for assessing cotton-N status would have been misidentified as N sufficient. Reduced yields due under irrigated conditions is the petiole nitrate test. The to over application of N were evident in some samples with leaf N test is a snapshot of N movement to leaves because it between 4.6 and 4.8% at early bloom. These concentrations were also is an analysis of a transportable form of N, and because common for N-sufficient plants, making accurate diagnoses of the petioles or leaf stems are the conduit for nitrate transover application of N unlikely. Our leaf-N critical values probably port from roots. Petiole nitrate is a sensitive measure of differ from previously established values because earlier values were N movement to leaves, but it is probably hypersensitive derived via survey techniques and because faster fruiting cultivars because of soil moisture effects on petiole nitrate. Remay require higher leaf N.searchers have found petiole nitrate testing a better measure of soil moisture status than cotton-N status (Bock and Adams, 1980; Touchton et al., 1981). Another

Peppermint (Mentha ×piperita) is currently not a common crop in the southeastern United States. Recently, there has been an interest in peppermint as an essential oil crop for this region. In 2007, a field experiment was conducted in Mississippi to determine the effect of nitrogen (N) (0 and 80 kg·ha−1), location (Verona and Stoneville), and harvesting stage (bud formation and flowering) on peppermint productivity, oil content, and composition. Peppermint biomass yields were higher at Verona (8.12 t·ha−1) than at Stoneville (6.12 t·ha−1). However, the essential oil content was higher at Stoneville (1.1%) than at Verona (0.6%). Generally, N rate at 80 kg·ha−1 did not affect oil yield and composition compared with 0 kg·ha−1. The concentrations of the major essential oil constituents were: (-)-menthol at 26% to 30%, (-)-menthone at 14% to 21%, (+)-menthofuran at 5% to 11%, and eucalyptol at 3% to 4% of total essential oil (wt/wt) and were generally within the values previously reported. The concentrations of (-)-menthone and (+)-menthofuran were significantly higher at Stoneville, 21% and 11%, respectively, than at Verona (14% and 6%). The (-)-menthol, (-)-menthone, and (+)-menthofuran yields/ha were higher at Stoneville than at Verona. Overall oil content and yields were higher at bud formation than at flowering, 1.3 and 1.8 times, respectively. In addition, the concentration of (-)-menthone and eucalyptol and the yields of (-)-menthone, (+)-menthofuran, and eucalyptol were higher at bud formation than at flowering. The results from this study demonstrated peppermint can be successfully grown in Mississippi and provide essential oil yields and composition comparable to those in the northwestern United States, the traditional peppermint-growing region.

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