Soil treatment, plant species and management effects on improved pastures on a solodic soil in the semi-arid subtropics. I. Dry matter and botanical composition

Abstract

Pastures of Rhodes grass (Chloris gayana), temperate legumes (annual medics) and a tropical legume (siratro) were established on a solodic soil in 1973-74 at Kogan in the semi-arid subtropics of southern Queensland. The effect of soil treatments, sown pasture species and cattle stocking rates on dry matter yields and botanical composition were measured during 1974-79. Nitrogen deficiency was a key factor limiting herbage production. Increased nitrogen in the ecosystem applied as fertilizer increased mean presentation dry matter of Rhodes grass pastures from 990 to 3443 kg/ha. Use of hydrated lime and gypsum (HLG) and annual medics with Rhodes grass increased dry matter yields from 990 to 1773 kg/ha. Where HLG had been applied, the annual medics re-established from seed each autumn and early winter throughout the period studied. Siratro established well at sowing and contributed initially to herbage production but then declined to almost zero. Deep subsoiling had no significant effect on dry matter yields or siratro persistence. Applied phosphorus at 48 kg Plha at establishment significantly increased herbage yields of Rhodes grass compared with 24 kg P/ha but no significant effects at either rate were found with a further 60 kg P/ha applied as 12 kg P/ha.year. Rhodes grass, which is tolerant of high soil sodium and magnesium status, maintained frequencies above 90% in treatments where the levels of nitrogen and phosphorus were high and when grazed at 0.62 steers/ha. However, deterioration occurred where nitrogen and phosphorus were lower or grazing pressure was higher, resulting in an ingress of native grasses. Twenty-five volunteer grass species were identified, the main genera being Eragrostis and Chloris. The need for a self-regenerating annual summer-growing legume in this environment is discussed.