NONIONIC SURFACTANT AND SUPPLEMENTAL IRRIGATION OF SOYBEAN ON CRUSTING SOILS

Agricultural land use in much of the Texas Coastal Prairie consists of 1 yr of rice (Oryza sativa L.) followed by 2 to 4 yr of native pasture. Replacing some of the native pasture with a cultivated rotational crop could benefit the area's agricultural base by reducing fixed costs and aiding pest management. Soybean [Glycine mar (L.) Merr.] fits the crop rotation system well but yields are highly variable and marginally economical. Research was initiated in 1985 near Eagle Lake, TX, to evaluate the potential of a nonionic surfactant and supplemental irrigation to increase and stabilize soybean yields on the Nada soil (fine loamy, silicous, hyperthermic Typic Albaqualf). tn addition the effect of the surfactant and irrigation on P and K fertilizer efficiency was evaluated. The nonionic surfactant (Amway ASPA 80; Amway Corp., Ada, MI) was injected through a lateral-move irrigation system at 0.00, 0.36, 0.71, and 1.42 L ha-1 during a 7 mm irrigation. Adjuvant rate, repeated adjuvant applications within 1 yr and over 3 yr, and P and K at the recommended and half the recommended rates were evaluated. Supplemental irrigation was applied so irrigation plus rainfall equalled 19 mm wk-1. No measurable yield differences between P and K rates were detected. The adjuvant at 0.36 L ha-1 increased soybean yields 37% above the check. Adjuvant at the 0.71 and 1.42 L ha-1 rate decreased yield from the 0.36 L ha-1 rate. No phytotoxicity was observed. Multiple adjuvant applications during 1 yr, and repeated applications to the same area over years, had no additional beneficial yield effect.