Phosphorus Fertility Assessment of Intensively Farmed Areas of Catchments Draining to the Great Barrier Reef World Heritage Area; 1: Soil Phosphorus Status

Abstract

Australia's reef water quality protection plan has a key objective: "reduce the load of pollutants from diffuse sources in the water entering the Reef." This article reports on a survey to assess the contemporary phosphorus (P) status of fertilized cropping soils across 21 catchments in coastal Queensland, Australia. The survey focused on surface soils from cane farms, vegetable and subtropical/tropical fruit tree sites. There were sampling depth effects on P levels in sugar and fruit tree sites (lower with depth). Importantly, 84% of 105 sugarcane sites were excessively fertile and only 3% rated low (P deficient). Some 75% of 16 vegetable sites and 38% of 8 fruit tree sites had excess ratings for extractable soil P fertility. Highest total P levels (0-10 cm) occurred in fruit tree sites, followed by vegetable and sugarcane soils. There are regional differences in P soil fertility, and the recycling of mill by-products needs attention. Part 2 (Bloesch and Rayment 2006) examines the potential of these soils to release soluble P in a nutrient-sensitive area.

Phosphorus loss and speciation in overland flow from a plantation horticulture catchment and in an adjoining waterway in coastal Queensland, Australia

“…These benchmarks therefore imply that surface orthophosphate soil concentrations at the study site were ~1.5-2.25-fold higher than requirements for the optimum yield of macadamia. Soil surveys have found that excessive surface concentrations of orthophosphate are not uncommon in contemporary treecropping enterprises in coastal Queensland, as evidenced by a majority of the survey sites which had topsoil phosphate concentrations >60 mg/kg (Rayment and Bloesch 2006).…”