Sequencing Sunflower in Semi-Arid Dryland Crop Rotations.

Sunflower extracts water to lower water contents and extracts water to deeper depths than most other crops in the central Great Plains, leading to reduced crop yield in subsequent crops. A study was established in 2010 at Akron, Colorado to investigate possible rotations with sunflower in the semi-arid Great Plains. Rotations included sunflower – extended fallow – winter wheat (Sun-exF-W), sunflower – proso millet – fallow – winter wheat (Sun-M-F-W), sunflower – field pea – fallow – winter wheat (Sun-P-F-W), and sunflower – grain sorghum – fallow – winter wheat (Sun-So-F-W). The experiment was conducted under natural Akron weather conditions and with supplemental irrigation to simulate the rainfall typical of central Kansas. Approximately 70% to 80% of the rainfall during the winter fallow period and approximately 40% to 50% of the water received by the fallow plots during the summer months was retained as stored soil water. Available water (AW) at wheat planting in 2012 was 2.5- to 5.0-cm less when a summer crop was included in the rotation compared with extended fallow for both water regimes. Lower AW at planting reduced wheat yields by 590 kg ha^-1 to 975 kg ha^-1 compared with extended fallow for Akron conditions and 130 kg ha^-1 to 650 kg ha^-1 compared with extended fallow under simulated KS conditions. Even though wheat yields were reduced due to water use by summer crops, total grain production was increased by including a summer crop such as millet or grain sorghum. For simulated KS conditions, even though there was a 20% reduction in wheat yield, total productivity doubled. When including sunflower in a winter wheat rotation, the producer may consider adding a short season spring/summer crop following sunflower. The summer crop will use summer rainfall more efficiently than fallow and still allow soil water recharge for the subsequent winter wheat crop.