Assessing P fertiliser use in vegetable production: agronomic and environmental implications

Vegetable production is often located in the peri-urban areas close to large cities. In Sydney, Australia, excessive levels of phosphorus (P) have been reported in the soils, and vegetable farms have long been regarded as a potential source of the P that enters Sydney’s waterways. We report vegetable production under varying soil P conditions and the consequent changes in soil P, as well as water quality of runoff and leachate after growing 5 crops in a field trial where inputs in the form of garden organic compost were compared to current farmers’ practice. No difference in vegetable yield was observed between 100 and 400 mg/kg of soil Colwell P (0–0.10 m); therefore, our results indicate that the excessive soil P levels in the vegetable farms around Sydney are not important for optimal vegetable production. Results from runoff and leachate studies clearly demonstrate that high concentrations of P in soils used for vegetable production under the current farming practice around Sydney have increased the potential to export P and to negatively affect water quality of receiving environments. The significant increases in soluble P concentrations found in the soil and runoff water from the current farming practice can be attributed to the use of poultry litter. In contrast, using compost in place of poultry litter resulted in significantly reduced soil P accumulation and P concentration in runoff and leachate. Training and education programs for farmers and their advisors are recommended to encourage more sustainable fertiliser management practices and reduce the accumulation of P in the environment.