Studies on some neutral red duplex soils (Dr 2.12) in north-eastern Queensland. 4. Field studies of nutrient responses with Caribbean stylo

The fertilizer requirements of Caribbean stylo (Stylosanthes hamata cv. Verano) grown on a neutral red duplex soil (Dr 2.12) have been examined in the field. The only nutrient limiting growth was sulfur. The severity of the deficiency increased through the four years of the experiment but good residual effects were obtained from an initial dressing of 40 kg sulfur/ha. It is shown that much of the applied sulfur was retained in a form extractable by calcium phosphate, and its distribution in the field corresponded closely with laboratory estimates of the sulfate sorption characteristics of this soil. In the final year, the growth of legume was closely related to the extractable sulfur in the soil. The absence of a response to phosphorus is unusual in virgin northern Queensland soils and was unexpected. The phosphate sorption characteristics of the surface soil implies that the external phosphate requirement of Caribbean stylo is below 0.015 pg phosphorus/ml.