Spring water use efficiency of six dryland pastures in Canterbury

Abstract

The spring water use efficiency (WUE) of six pasture combinations was calculated from the 'MaxClover‟ grazing experiment at Lincoln University. Pastures have been established for six years and are grazed by best management practices for each combination. Measurements were from individual plots of four replicates of cocksfoot (CF)/subterranean clover (Sub); CF/balansa clover (Bal); CF/white clover (Wc); CF/Caucasian clover (Cc); perennial ryegrass (RG)/Wc or lucerne pastures. Actual water use was measured by time domain reflectometry (0-0.2 m) and a neutron probe (0.2- 2.3 m). Dry matter yield, botanical composition and herbage quality were measured at the end of seven regrowth cycles between 1 July 2008 and 30 June 2009 (33-85 d duration). The results highlight differences in spring WUE amongst species and these were related to legume contribution and grass nitrogen (N) yield. Lucerne had the highest spring WUE at 30 kg DM ha-1 mm-1 of actual water use. This was produced at a rate of 5.7 kg DM ha-1 °Cd-1 . For grass based pastures CF/Sub clover produced 18 kg DM ha-1 mm-1 at a rate of 5.9 kg DM ha-1 °Cd-1 compared with 14 kg DM ha-1 mm-1 for the other pastures at rates of 3.2 to 4.1 kg DM ha-1 °Cd-1 . These results highlight the importance of the spring period for dryland pasture production when soil temperatures are rising and moisture levels are high. The spring pasture WUE of dryland pastures was higher than in summer and autumn and therefore it is important that farmers maximise pasture production through combinations of pasture species that maximise spring legume content