Legumes for clay soils

Summary

There are some 15M ha of clay soils in Queensland and northern New South Wales which receive adequate rainfall for cropping or sowing of improved pastures. Maintenance of production is more difficult because of declining soil nitrogen levels. In cropping soils total and available nitrogen are declining causing a reduction in grain protein and yield, while in permanent grass pastures lower forage and animal production are the result of lower levels of available nitrogen.

One possible solution is to use legumes. Lucerne, annual medics, lablab and leucaena have, until recently, been the only legumes available for these soils. However, all these species have limitations. Lucerne and medics become increasingly unreliable as cool season rainfall decreases with decreasing latitude. Lablab, although very useful for a one year ley, seldom persists into a second year and leucaena is a specialist pasture, not likely to be used over wide areas. Desmanthus virgatus became commercially available in the first year of the "Legumes for Clay Soils" project, but little was known about its area of adaptation and management requirements. Two other legumes, Indigofera schimperi and Glycine latifolia, had shown promise in small plot testing.