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

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. ResultsThe median PBE was 11% for sheep, 19% for beef, 29% for dairy and 48% for cropping. Phosphorus 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 thresholds 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.

Farm-scale nitrogen, phosphorus, potassium and sulfur balances and use efficiencies on Australian dairy farms

“…This in large part may be explained by the generally high levels of soil P, K and S measured on these dairy farms , suggesting that soil P, K and S reserves can be utilised for a period of time without a resulting decline in milk production. Levels of soil P in excess of agronomic requirements have also been reported recently in a range of agricultural industries across Australia (Simpson et al 2011;Weaver and Wong 2011).…”

“…Similarly broad ranges of P balances have been reported for commercial dairy farms in Northern Portugal (5-72 kg P/ha; Fangueiro et al 2008), Western Europe (4-36 kg P/ha; Raison et al 2006), New South Wales (1-127 kg P/ha; Lawrie et al 2004) and Western Australia (3-200 kg P/ha; Ovens et al 2008). A recent metaanalysis of P balances for sheep, beef, dairying and cropping in Australia (Weaver and Wong 2011) calculated a median P surplus for dairy farms of 18.1 kg P/ha, which was significantly greater than the other enterprises, and a median P-use efficiency of 19%.…”

“…While not considered as an immediate and directly quantifiable indicator of loss, P surplus appear to be resulting in increased soil P levels on Australian dairy farms, often well above agronomic levels Weaver and Wong 2011), which pose an increased risk of greater P losses in surface water (Sharpley 1995). In general, dairy farms that did not apply P fertiliser in any form had lower surpluses and higher P-use efficiencies.…”

“…There were a small number of farms with whole-farm P deficits, indicated a net removal of P, presumably largely from the soil. This appears to be warranted in some systems where existing soil P levels are above recommended thresholds of adequacy (Weaver and Reed 1998;Gourley et al 2006;Weaver and Wong 2011). Staines et al (2011) achieved P surpluses of 0-7 kg/ha.year and P efficiencies of 89-115% (average over 4 years) in a farmlet study when fertiliser P was applied only to paddocks where soil tests indicated a requirement for P fertiliser.…”

Diagnóstico de requerimiento de fósforo para alfalfa (Medicago sativa L.) en argiudoles

“…Para los suelos de la región pampeana húmeda, el fósforo (P) ha sido identificado como limitante para la producción de los cultivos (Sainz Rozas, Echeverría y Angelini, 2012) y se ha demostrado que su deficiencia restringe la producción forrajera de las pasturas de alfalfa (Quintero, Boschetti y Benavidez, 1995;Berardo y Marino, 2000b;Sevilla y Agnusdei, 2016). Por ello la fertilización fosfatada es una práctica recomendada, aunque aplicaciones en cantidades inadecuadas -ya sea por defecto (ganadería extensiva) o por exceso (ganadería intensiva)-ocasionan perjuicios productivos y ambientales (Weaver y Wong, 2011). Para ajustar la aplicación de P al mínimo requerido para alcanzar los rendimientos potenciales en cada ambiente (nivel crítico, NC), se han calibrado métodos de diagnóstico basados en el análisis de muestras de suelo (Echeverría y García, 1998;García, Picone y Ciampitti, 2015).…”