Nutrient deficiencies in central Australian semi-desert rangelands, with reference to decline in range condition.

Abstract

Three central Australian' plant communities: Mitchell grassland, open woodland and mulga shrubland, were examined for evidence of nutrient deficiencies, particularly in association with poor range condition. Twelve nutrients were applied in various combinations to their soils in glasshouse pots trials. Two native grasses were grown in the Mitchell grassland and open woodland soils, while a native grass and a native chenopod were grown in the niulga shrubland soils. A field study with three nutrients was restricted to open woodland. The grasses grown in Mitchell grassland and open woodland soils responded to added nitrogen, phosphorus and sulphur. while the grass grown in mulga shrubland soil responded to added nitrogen and phosphorus only. The chenopod, grown in mulga shrubland soil, responded to calcium as well as to nitrogen and phosphorus. In the field study, nitrogen improved plant growth but not all species responded equally. Arisrida contorra, which acts as an indicator of poor range condition in open woodland. formed a greater proportion of the herbaceous biomass following the addition of nitrogen. No response to phosphorus and sulphur was detected in the field. In both Mitchell grassland and open woodland, decreaser species (those whose biomass contributes proportionately less to the total as range condition decreases) responded better under glasshouse conditions to phosphorus on soils from areas in poor range condition than on soils from areas in good range condition. Of the species which increase with decreasing condition. that from the grassland also responded better to phosphorus on soils from areas in poor range condition, while that from the woodland was insensitive to phosphorus. In the mulpa shrubland, range condition was not associated with nutrient status. Several nutrients may be deficient in central Australian rangeland soils but phosphorus is the only nutrient which is potentially more deficient in degraded rangeland soils than on healthy rangeland soils. The evidence for a relationship between range condition and phosphorus deficiency is, however, inconclusive.