Dry matter production and water use of lucerne and perennial ryegrass under dryland and irrigated conditions

Abstract

In dryland regions of New Zealand lucerne is sown as an alternative species to the most common pasture of perennial ryegrass and white clover. This is to maximise dry matter production and water use efficiency. This experiment compared the dry matter production of lucerne and perennial ryegrass pastures under full irrigation, irrigation every two weeks, irrigation every three weeks or no irrigation (dryland) on a Templeton silt loam and Eyre soil. Fully irrigated lucerne and perennial ryegrass had the highest dry matter yield of 18.7 t DM/ha. Unirrigated lucerne and perennial ryegrass had the lowest dry matter yields of 4.65 t DM/ha and 8.29 t DM/ha. The fully irrigated lucerne grew at the fastest rate of 6.69 kg DM/ha/˚Cd across the whole season. Unirrigated lucerne grew 3.03 kg DM/ha/˚Cd until soil moisture limited growth. After this point growth slowed to 0.39 kg DM/ha/˚Cd. Irrigated lucerne had the highest water use efficiency of 34.5 kg DM/ha/mm compared with 22.5 kg DM/ha/mm for all perennial ryegrass pastures and 11.2 kg DM/ha/mm for unirrigated lucerne. The low yield of unirrigated lucerne was unexpected and probably caused by an application of Glyphosate in June 2012. This experiment shows that lucerne could be sown instead of a perennial ryegrass/white clover pasture under irrigation due to higher dry matter production.