Productivity and water use of lucerne and two lucerne-grass mixtures in Canterbury

Abstract

The long term trial, on a Templeton fine sandy loam, is a factorial combination of 3 pasture swards (pure WL320 lucerne, lucerne-‘Grasslands Matua’ prairie grass and lucerne-‘Grasslands Maru’ phalaris) and 2 grazing durations (long and short). The 0.04ha plots were sown in November 1986 with lucerne drilled across the grass rows. For the water use study, in 1988-89, 8 m² mini plots of pure lucerne, lucerne-phalaris, and lucerne-prairie in deep or shallow soil were selected. Pure lucerne plots produced annual dry matter (DM) yields of 12700 kg/ha, lucerne-phalaris 11600 and lucerne-prairie 10400. Deep soils had higher production (12600 kg/ha) than did shallow soils (10900 kg/ha). The lucerne-phalaris mixture had about 75-95% lucerne, while lucerne in the lucerne-prairie mixture ranged from 25% in winter to 65% in summer. The lucerne-prairie plots with deep soils had at least 60% lucerne while shallow soils had as little as 25%. Mean water use efficiency (WUE) was 25, 22 and 20 kg DM/ha/mm for pure lucerne, lucerne-phalaris and lucetne-prairie, respectively. Shallow soils had WUE of 21 kg DM/ha/mm H₂O and deep soils 24 kg DM/ha/mm. Soil water extraction ‘patterns differed little in shallow soils, but in deep soils pure lucerne extracted water to at least 100 cm while lucerne-phalaris and lucerne-prairie extracted soil moisture down to about 80 cm. Lucerne and phalaris roots were both found down to 90 cm and from O-20 cm most of the root mass was lucerne. With the lucerne-prairie mixture from O-20 cm, root mass was about 50% for each species and lucerne root mass was significantly reduced below 50 cm.