Soil water use and rooting depth of Italian ryegrass (Lolium multiflorum Lam.) in a small plot experiment

Abstract

Italian ryegrass is planted mainly under irrigation in the summer rainfall region of South Africa. Irrigation practices are often based on the assumption that Italian ryegrass has an extremely shallow root system. A small plot experiment was conducted to ascertain whether this assumption was true. It was shown that roots were, in fact, very shallow when plots were irrigated at weekly intervals, as is the usual practice. When stressed, however, the root system was much deeper and extracted water from depths of more than 1.0 m. Values for plant extractable water, determined in situ, ranged from 78 to 89 mm m⁻¹ for the two experimental seasons. The water extraction pattern during the season did not differ much between the slightly and severely stressed treatments. Thus, compared with the control treatment, the pastures did not have to be stressed much before water was utilized from the deeper layers.