In 1985, when plentiful rains occurred during the seed-fill period, yields increased by only about 1 bushel per acre. The economics of achieving these yield increases are of paramount importance. The type of irrigation system and the water source greatly affect cost. Prospective irrigators should weigh potential costs against returns they can expect from the increased yields and reduced risks created by irrigation. In addition to influencing yields, irrigation may alter other characteristics of importance to soybean growers, such as maturity and lodging.
Irrigation delays the maturity of short- or midseason varieties only a few days.
Full-season varieties usually show no difference in maturity unless extended drought or charcoal rot infection occurs. Plant height normally increases under irrigation, which increases the chance of lodging. However, proper variety selection may reduce this problem. Weather patterns and crop water use Missouri rainfall patterns are characterized by sufficient winter and early spring rainfall that maintains the soil at or near saturation capacity until almost the first of June. During late June, July and August, the crop's need for moisture usually exceeds that available from either the soil or rainfall.