ABSTRACT

Locations throughout tropical northern Australia are being evaluated as potential winter cotton production areas. The response of cotton to several different phosphorus fertilizers was recorded over two years in the Ord River Irrigation Area of north-western Australia. In 2000, when the starting soil P levels were low (bicarbonate extract 14mg kg^-1 in the 0-30cm zone of the soil profile), there was a yield response to both source and placement of P. However in 2001, when starting soil P levels were much greater (32mg kg^-1 in the 0-30cm zone of the soil profile), yields were higher than those in 2000 and there was no yield response to source or placement of P. It was concluded that source and placement of P fertilizer significantly af-fected cotton yield under conditions of low starting soil P. Deficiency levels appear to be substantially higher than indicated in the literature from temperate cotton growing areas.