A single irrigation to improve early maturing soybean yield and quality

When irrigation sources are limited, deficit irrigation at selected growth stages may help avoid crop stress at critical times. The objective of this study was to determine the effect of a single irrigation at different reproductive growth stages on yield and quality of early maturing (Maturity Group 1) soybean [Glycine max (L.) Merr.] cultivars. The experiment was conducted from 1991 through 1994 on a Parsons silt loam (fine, mixed, thermic Mollie Albaqualf). The experimental design was a randomized complete block with a split-plot arrangement of treatments. Irrigation scheme (application of 2.5 or 5 cm at R4, R5, or R6) as the main plot was factorially arranged within each replicate, and cultivar (Hodgson 78 and Weber 84) was the subplot treatment. Also included was a randomized nonirrigated check whole plot planted with both cultivars. Yields from a single irrigation at R4, R5, or R6 were similar, and averaged approximately 20% more than yield with no irrigation (1.72 Mg ha(-1)). Irrigation at R4 increased seeds plant(-1), whereas R5 and R6 irrigations increased weight per seed. Irrigation had minimal effect on seed protein and variable effect on oil content. Visual quality of harvested seed frequently scored poor and irrigation improved quality only in 1992 when maximum air temperatures were <35 degrees C. A single irrigation at R5 in 1991 improved germination to nearly 60% compared with 30% with no irrigation. Germination averaged 81% in other years with no irrigation effects. These data show that a single irrigation at different reproductive growth stages can influence early maturing soybean yield and quality, but the improvements may be inadequate to justify the practice.