Title

Scope to improve phosphorus (P) management and balance efficiency of crop and pasture soils with contrasting P status and buffering indices

Document Type

Article

Publication Date

2011

Journal Title

Plant and Soil

Keywords

Agronomic efficiency, build up, critical value, environment, maintenance, subtropical, temperate, water

Abstract

Aims

Fluctuating phosphorus (P) fertiliser costs, water quality issues and on-going debate over global P supply and demand support the need to evaluate and ensure that P is used efficiently in agriculture. Methods We analysed the P balance of farming systems across southern Australia to south east Queensland in relation to P management and soil properties at farm and sub-farm scales. Phosphorus input, yield of products and soil data were collected from Mediterranean, temperate and sub-tropical farming environments to assess soil chemistry and P Balance Efficiency (PBE; percentage of P inputs harvested as P outputs) of sheep, beef, dairy and cropping systems.

Results

The median PBE was 11% for sheep, 19% for beef, 29% for dairy and 48% for cropping. Phospho- rus applied in excess of product removal (P balance) ranged from 18.1 for dairy to 6.1 kg P ha␣1 yr␣1 for cropping. The bicarbonate-extractable (Colwell) P concentration of surface soils increased with fertiliser application and this differed in relation to P Buffering Index (PBI), production history and the rate of P input. Soil test values for 63% to 89% of soil samples from pastures and crops exceeded critical values (CV; defined by PBI, bicarbonate-extractable P and land use) when little yield improvement would be achieved by applying additional P. A greater percentage of these soil test values exceeded environmental thresh- olds for water contamination.

Conclusions

A transition to using lower rates of P fertiliser to maintain soil P fertility at near optimal levels (P maintenance) has not occurred in farming systems represented by these soil samples. Over 50% of the samples had indications of more important constraints (soil acidity, potassium and sulphur deficiency) to yield. Alleviating these constraints is likely to improve PBE. For soils that exceed the CV for P, there is a need to adopt P maintenance practices to improve financial and environmental outcomes.