Response of Solid‐Seeded Soybeans to Flood Irrigation. I. Application Timing1

Abstract

AbstractVariation in seasonal rainfall accumulation directly affects soybean [Glycine max(L.) Merr.] yields. In southwest Louisiana, where soybeans are primarily grown in rotation with rice (Oryza sativaL.), moisture shortages frequently occur due to the presence of a traffic‐induced hardpan 15 to 20 cm below the soil surface, which restricts root development. Field studies were conducted in southwest Louisiana on a Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualf) soil during 1981–1983 to study response of solid‐seeded ‘Dare’ (Maturity Group V) and ‘Ransom’ (Maturity Group VII) soybeans to flood irrigation. Water was applied at R2 bloom (B), R5– R6 pod fill (PF), B + PF, and full season (FS) as needed based on tensiometer readings (60 to 65 cbar). A nonirrigated control was included for comparison. In 1981 rainfall was adequate prior to bloom, but deficient when plants entered the reproductive stage. In 1982 and 1983, rainfall was generally deficient prior to bloom but adequate during the reproductive stage. Yield responses to the irrigation treatments varied among years and were directly related to rainfall distribution. Averaged over years, Dare yields were 161 kg ha−1higher (P=0.05) than the control where water was applied at B + PF and Ransom yields were 168 and 323 kg ha−1higher (P=0.05) than the control where water was applied at B + PF and FS, respectively. Seed/pod for Ransom and 100‐seed weight for Ransom and Dare averaged over years were significantly higher than the control only where water was applied FS. Pods/plant, seed/plant, plant height at maturity, lower pod height, and plant density were not affected by the irrigation treatments. Results indicate that in years where moisture is limited prior to bloom, early application of water can be beneficial, provided it is applied as needed throughout the remainder of the growing season. In years where moisture is adequate in early season prior to bloom, water should be applied during the reproductive stage if water shortage occurs.