Lucerne pastures to sustain agricultural production in southwestern Australia

In two field experiments on sandy acidic soils, lucerne (Medicago sativa L.) was compared with subterranean clover (Trifolium subterraneum L.) in phase pasture-crop rotations. Soil water content, herbage production, lucerne persistence, soil nutrients and subsequent wheat yield and quality were measured. Compared to the annual pasture. the lucerne increased pasture biomass (5-7 t ha(-1) compared with 3-4 t ha(-1)) largely due to utilisation of summer rainfall. It reduced soil water content from the first summer of the study until a major rain event during the second summer. The wheat yield following lucerne was increased at one site (2 t ha(-1) compared to 1.7 t ha(-1)) with higher grain protein percentages at both sites. The more acidic site (pH = 4.4 in CaCl2, 0-30 cm, compared to >5.0) with higher lucerne plant densities (46 compared to 15 plants m(-2)) increased annual lucerne production (6-7 t ha(-1) compared to 5 and 6 t ha(-1)) reduced stored soil water (100 mm compared to 50 mm). However, it accrued less soil nitrogen in the top 10 cm and produced lower wheat yields (2.0 t ha(-1) compared to 2.2 t ha(-1)) and protein levels (9.8% compared to 11.8%). The results show that lucerne provides a high water-use phase farming system on sandy acidic soils common throughout the Western Australian cropping zone. (C) 2002 Elsevier Science B.V. All rights reserved.