Initial and residual effects of superphosphate on a Townsville lucerne pasture in north-eastern Queensland

Abstract

The responses to superphosphate of a Townsville lucerne (Stylosanthes humils)-grass pasture on a solodic soil near Townsville, were measured for three years. An initial dressing of 784 lb an acre gave the highest yield of dry matter for the three years, but 336 lb an acre was almost as effective. Applying 336 lb in equal annual dressings of 112 lb an acre gave less total dry matter but slightly more nitrogen and phosphorus per acre than 336 lb initially. On this soil type superphosphate had a good residual effect. Pastures with initial dressings of 336 1b or more outyielded the controls in all years, and did not respond to maintenance dressings applied in the second and third years. Superphosphate increased the yields of phosphorus per acre by increasing the phosphorus contents of both Townsville lucerne and grass as well as the dry matter yields. It had little effect, however, on the nitrogen contents. The relation between the phosphorus content of the pasture and the yield of dry matter was examined and tentative critical values were established.