Determining Supplemental Irrigation Time for Rainfed Wheat by Monitoring Variations of Soil Water Content during Growth Period

Dry farming is an important method of crop production, particularly in semi-arid regions, where crop yield strongly depends on precipitation amount and its temporal variation during the growing season. Supplemental irrigation is a suitable practice for mitigating moisture stress and, consequently, improving crop yield in rainfed agriculture. This study was conducted to estimate the proper time of supplemental irrigation in rainfed land by measuring soil water content during growth period, in 2016-2017. A field experiment was conducted using two plowing directions (along the slope and on contour lines) in plots with 2 m × 5 m dimensions, in a rainfed farm with 10 % slope. Volumetric soil water content (SWC) was measured in root zone by a TDR set at 10-day interval during growth period, from November 2016 to June 2017. Based on the results, SWC in the plots plowed on contour lines was about 6 % higher than the plots plowed along slope, and this difference was statistically different (P< 0.05). The mean readily available water (RAW) during growth period in the plots plowed on contour lines (6.07 mm) was about 2.5 times higher than the plots plowed along slope (2.25 mm) and showed significant difference with it (P< 0.05). The highest RAW was observed at stem elongation and the lowest value was found at grain germination, at which stage, about 6.7 mm water deficit was observed in rainfed wheat. Thus, application of supplemental irrigation at this stage can efficiently prevent water stress and improve wheat grain yield in this semi-arid region.