ROOT-GROWTH AND SOIL-WATER EXTRACTION BY WINTER AND SPRING WHEAT

Efficiencies of soil-water extraction and use are important factors determining crop productivity in dryland regions. This study was conducted from 1986 to 1988 to compare root growth and soil-water extraction of Norstar and Norwin winter wheat (WW) (Triticum aestivum L.) and Katepwa and HY320 spring wheat (SW). Total root length and rooting depth increased with crop-development stage and level of available soil water. Preanthesis root development was concentrated at soils depths with temperatures greater than 15-degrees-C. Maximum rooting depth at crop maturity ranged from 110 to 130 cm and 60-80% of the total root length was found in the top 50 cm of soil. The rooting patterns of SW and WW were similar at each sampling date despite differences in the stages of development. However, the earlier development of WW resulted in a greater root length for WW by the end of May, an advantage maintained until WW maturity. Differences in the rooting patterns of semidwarf and tall cultivars were not detected. The average change in available soil water (0-130 cm depth) over all cultivars and locations between early May and crop maturity was 5 cm. Ninety-five percent of this water was extracted from the upper 70 cm of soil. Actual rooting depth and maximum depth of soil-water extraction were highly correlated (r = 0.87**). In six of eight trials, WW cultivars used significantly more water from the top 50 cm of the profile in May than SW. In one trial, WW extracted significantly more water from several soil-depth increments than SW over the entire growing season. In the remaining trials, levels of available soil water at SW anthesis and harvest were similar for all cultivars or were higher for WW cultivars because of soil-water recharge by late-season precipitation. Therefore, with the exception of greater early-season water extraction by WW, few consistent differences in soil-water extraction patterns were observed among cultivars considered in this study. Higher water-use efficiency for WW in these trials was attributed to differences in timing of water extraction and not to differences in depth of water extraction.