Optimizing the planting density under the ridge and furrow rainwater harvesting system to improve crop water productivity for foxtail millet in semiarid areas

Abstract

The ridge and furrow rainwater harvesting (RFRH) planting system has many advantages for improving the use of water during dryland farming in semiarid areas, but the optimally matched planting density for maximizing the productivity of foxtail millet is not known. Therefore, field experiments were conducted during 2013–2015 to determine the soil water content with depth, evapotranspiration (ET), agronomic traits, grain yield, and crop water productivity under different planting densities when using RFRH planting (width of ridge and furrow is 60 cm, three rows were planted in furrow) compared with traditional flat planting. The results show that a high planting density would lead to soil drought conditions in the late reproductive growth stage, with reductions in individual plant traits and the harvest index (HI) in dry years. However, we found that RFRH planting could reduce ET and improve the soil water content at 0-120 cm soil layers in the jointing and filling stages, as well as mitigating the crop water deficit in the reproductive growth stage and the decreased HI caused by a high planting density. Compared with traditional flat planting, RFRH planting decreased the foxtail millet grain yield in the rainy year (2013) due to the relatively lower plant population, but it increased the yield in the normal rainfall years of 2014 and 2015, as well as significantly improving the crop water productivity by 7.9% and 14.0% under the optimized planting density, respectively. A relatively higher optimal planting density was always obtained in the furrows under RFRH planting compared with traditional flat planting in all three experimental years. Based on these results, we recommend increasing the planting density in the furrows to increase the grain yield and crop water productivity under RFRH planting, with a moderate planting density for foxtail millet (three rows in a 60 cm wide furrow and a plant spacing of 7.5 cm) in semiarid regions of China.