MONO- AND DOUBLE‐CROPPED WHEAT AND SOYBEANS UNDER RAIN‐FED AND IRRIGATED CONDITIONS1

In sufficient amounts and distribution of rainfall are often the major limiting factors to crop production in the southern Great Plains. This is especially true for summer crops, whether grown in mono- or double-cropping situations, for these factors have a significant impact on yields and profitability. This study was conducted at the Oklahoma Vegetable Research Station, Bixby, Oklahoma, from 1980–1984 on a Wynona silt loam soil (Cumulic Hapla-quolls) with 0–1% slope. The objectives were to compare yields and net economic returns of mono- and double-cropped wheat [Triticum aestivum (L.) EM. Thell] and soybeans [Glycine max (L.) Merr.], where all wheat was produced under rain-fed conditions and where mono- and double-cropped soybeans were produced under both rain-fed and irrigated conditions. Over the 5-year period, rain-fed monocropped wheat yielded an average of 3498, compared with 3008 and 2948 kg ha-1 for rain-fed, double-cropped wheat following irrigated and rain-fed double-cropped soybeans, respectively. Irrigated, conventionally tilled monocropped soybeans yielded an average of 2800 compared with 2162 kg ha-1 for rain-fed, conventionally tilled monocropped soybeans. Irrigated, no-till, double-cropped soybeans yielded an average of 2072 compared with 1546 kg ha-1 for rain-fed, no-till, double-cropped soybeans. Rain-fed double-cropped wheat and rain-fed, no-till, double-cropped soybeans produced the highest net economic return ($317 ha-1) of any of the five cropping systems. Net returns from rain-fed, double-cropped wheat and irrigated, no-till, double-cropped soybeans; rain-fed mono-cropped wheat; and rain-fed, conventionally tilled, monocropped soybeans were similar and ranged from $246, $238, and $233 ha-1, respectively. Irrigated, conventionally tilled, monocropped soybeans returned $183 ha-1. Irrigation increased the yields of mono- and double-cropped soybeans 638 and 526 kg ha-1, respectively. However, given these yields, the price of soybeans would have to increase from $0.25 kg-1 to $0.31 and $0.40 kg-1, respectively, for mono- and double-cropped soybeans before irrigation would become economically feasible.