No abstract

Information on nitrogen (N) fertilization of no‐till (NT) cotton (Gossypium hirsutum L.) is needed to optimize lint yields and earliness. We evaluated five N rates and three application methods for NT cotton production on Loring silt loam (fine‐silty, mixed, active, thermic Oxyaquic Fragiudalfs) with natural winter annuals as a cover; and on Memphis silt loam (fine‐silty, mixed, active, thermic Typic Hapludalfs) having corn (Zea mays L.) stover as a cover and on Lexington silt loam (fine‐silty, mixed, active, thermic Utlic Hapludalfs) having winter wheat (Triticum aestivum L.) as a cover. Nitrogen rates of 0, 34, 67, 101, and 134 kg ha−1 were either broadcasted as ammonium nitrate (AN) or injected as urea–ammonium nitrate (UAN) at planting. Additional treatments included broadcasting 67 kg N ha−1 as AN at planting with either 34 or 67 kg N ha−1 banded 6 wk later. Relative to no N, broadcasting 67 kg N ha−1 as AN increased 4‐yr average NT lint yields on Loring silt loam from 739 to 1281 kg lint ha−1 and 2‐yr average yields on Lexington silt loam from 1086 to 1535 kg ha−1. A higher N rate (101 kg N ha−1) was needed to increase 2‐yr average yields on Memphis silt loam from 821 to 1169 kg ha−1. Broadcasting AN was a satisfactory placement method producing yields equal to or higher than injecting UAN or splitting AN for NT cotton produced on these loessial soils despite different covers and residues.

Monocarpic senescence traits may influence adaptation to midseason drought by their effects on drought escape and dehydration avoidance. Adaptive attributes of two related cowpea [Vigna unguiculata (L.) Walp.] genotypes, contrasting in monocarpic leaf senescence, were evaluated under well‐watered and drought treatments in the field. Drought stress was imposed during flowering and pod filling for 19 consecutive days before irrigation was resumed. Delayed leaf senescence was expressed by genotype 8517 under both water regimes. Drought and monocarpic senescence concurrently reduced leaf area in both genotypes, but 8517 maintained greater leaf area and plant viability under either water regime than did the senescent cultivar, CB5. Both genotypes showed similar 13C discrimination under complete irrigation but 8517 discriminated significantly less against 13C than did CB5 under drought stress. Based on discrimination data, transpirational water‐use efficiency of droughted 8517 was estimated to be 10 to 14% higher than that of CB5. Plant survival was not significantly affected by the drought treatment, but a higher percentage of 8517 than CB5 plants survived the first podset and subsequently produced a large second podset. Total seed yields did not differ significantly between genotypes, but seasonal yield distribution differed markedly. Total reproductive duration of drought‐stressed 8517 was 50% greater than that of CB5, and 60% of its pod production escaped the drought. The delayed leaf senescence traits may enhance adaptation of cowpea to semiarid zones by improving the capacity to survive and recover from midseason drought.

No abstract

Producers of upland cotton (Gossypium hirsutum L.) are interested in alternative row spacings and planting patterns to improve productivity. We conducted factorial experiments for 3 yr in adjacent irrigated and nonirrigated fi elds at Milan, TN, of cotton grown in 25-, 76-and 102-cm rows, each planted in a solid and 2 × 1 skip-row pattern. Narrower rows and solid plantings tended to close canopy earlier and more completely, to suppress weed growth, and to mature earlier than in wider rows and skip-row patterns. Incomplete canopy closure in wider skip-row spacings resulted in less weed suppression, but weed growth in skipped rows diminished with narrower row spacing. Skip-row cotton matured later than solid planting, but this eff ect also diminished with narrower rows. Without irrigation, row spacing and confi guration for maximum lint yield depended on growing conditions of the particular year. Under irrigation, however, solid planted 76-cm rows consistently yielded more than either 25-or 102-cm solid or skip-row cotton. With or without irrigation, lint yields were 13 to 15% lower in 102-cm skip-row cotton than in 102-cm solid planting, but yields did not diff er between solid and skip-row in narrower rows. Across years and treatments, plant density was the most infl uential yield component in nonirrigated cotton, but plant density and bolls plant −1 had similar infl uence under irrigation. Cotton producers interested in skip-row planting should consider rows spaced 76-cm or less to minimize weed problems and yield loss.