Specific root length, soil water status, and grain yields of irrigated and rainfed winter barley in the raised bed and flat planting systems

Abstract

Understanding root growth characteristics is important for on-farm water management. The objectives of this study were to determine the root growth of barley under different irrigation water managements and planting systems. Raised bed (RB) and conventional flat (F) planting systems subjected to full (FI) and deficit irrigations (DI) managements, and rainfed (RF) conditions were applied. The FI addressed 100% crop evapotranspiration (ET) according to the Penman-Monteith equation, while the DI received 60% FI, and the RF just received precipitation. In the RB system, three rows of crops were grown on 60 cm wide beds that were 80 cm center-to-center apart. The height of each bed was 20 cm. In the F system, there was no land configuration. In total, there were nine barley rows separated 30 cm from each other in the F and RB systems. The F and RB systems were irrigated as basin irrigation and furrow irrigation, respectively. Root growth traits and characteristics, soil water depletion, and the total grain yields from the middle three rows were assessed. The RB significantly outperformed F in terms of root production under FI. However, this difference between RB and F was not significant under water stress conditions (DI and RF). The specific root length (SRL) decreased as soil water content decreased in the water stressed treatments through elevated soil water deficit progression after imposing irrigation treatments. Root development was considerable under all irrigation treatments and planting systems because RLD was at least 1 cm cm−3 at the 90–100 cm soil depth, which is recommended as the threshold for potential water uptake, and indicates that the barley Fasih cultivar produced more than 1 cm cm−3 of root length over the entire effective rooting zone of 0–100 cm under all experimental treatments. This might imply excess root production. Further analysis revealed that total grain yields were correlated with the RLD. Nevertheless the excess root growth might have negatively affected grain yield because more carbon and assimilate were translocated to the root system instead of grains. Under water limited conditions, it is thought to be important for barley crops that do not produce very large amount of roots, but rather produce less roots that do not negatively suppress grain yield.