Plant root distribution and water use patterns of some pasture and crop species

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Abstract
During a summer of lower-than-average rainfall, yield, root distribution, and soil moisture tension were measured for perennial ryegrass, white clover, ryegrass-clover mixture, cocksfoot, wheat, maize, and lucerne growng on a deep free-draining soil. In all species most roots occurred in the top 20 cm of soil, root numbers decreasing down to 100 cm, with smaller variable numbers at the maximum depth sampled. Cocksfoot and perennial ryegrass had the highest root numbers in the top 40 cm, cocksfoot roots continuing to be more numerous to 140 cm. The effective depth of the soil exploited for water by all species except lucerne was approximately 130 cm. Lucerne extracted water from at least 210 cm. Lucerne, maize, and cocksfoot produced at least twice as much dry matter as ryegrass and white clover, both of which had stopped growing by the final harvest. Maize which was not sown until late spring did not begin to deplete the soil water until the pasture species had used much of that which was available. Lucerne depleted the soil water uniformly at all levels of the profile to 150 cm, whereas all other plots showed depletion first near the surface and only later at greater depths This could be significant in maintaining nutrient availability under drying conditions.