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Routes to improving the efficiency of phosphorus use in arable crop production

Research Review No. 83

Routes to improving the efficiency of phosphorus use in arable crop production

by

Tony Edwards1, Paul Withers2, Roger Sylvester-Bradley3 and Davey Jones2

1Crop & Soil Systems, SRUC Aberdeen Campus, Craibstone Estate,
Aberdeen AB21 9YA
2 School of Environment, Natural Resources and Geography, Bangor University, College Road, Bangor LL57 2DG
3ADAS Boxworth, Battlegate Rd, Boxworth, Cambridgeshire, CB23 4NN

 

Abstract

Phosphorus (P) fertilisers are essential to sustain and improve crop productivity but they contribute to P surpluses in soil and to P exports from crops to livestock and from land to water. Consequences of P use are economic cost, eutrophication, and depletion of finite rock phosphate reserves. This review examines evidence underlying current P nutrition strategies for cropping and assesses scope for innovations to achieve more sustainable approaches.

Current P recommendations largely rely on soil P storage rather than fresh P to optimise crop P supplies. This reliance results from poor capture of freshly-applied P by plant root systems and rapid immobilisation of plant-available P into less available forms in the soil matrix. Soil structure, moisture, temperature, pH and redox conditions can also constrain P supply from soil to root. Some inappropriate P use may also arise through growers justifiably lacking confidence in current soil P tests.

The balance method of assessing efficiency of fertiliser P use appears misleading because it discounts P contributions from non-labile soil sources. Long term studies indicate that soils release at least 5-9 kg/ha/year P without any fertiliser use, and net recoveries of conventional fertiliser P are only 10-15%. The philosophy of feeding the soil rather than the crop must therefore be questioned.

Three key strategies are proposed to improve sustainable P use: (i) minimising crop P requirements, (ii) maximising root recovery of soil P, and (iii) developing targeted fertiliser technologies with as complete P recovery as possible. Large genetic variations in leaf P and crop P (% DM) and in rooting and soil P acquisition offer much potential to improve crops and varieties by breeding; low phytate cereal mutants offer particular promise. Sites should be prepared and maintained to enable testing for and breeding of P-efficient varieties.

Integrated P management strategies including P fertiliser placement, seed P coatings, foliar P applications, industrially re-cycled products, and products that modify soil P availability provide many potential opportunities to improve fertiliser P recovery. These should be developed, and particularly targeted to meet crop P demand at the most susceptible stages (i.e. establishment to stem extension), so as to reduce reliance on soil P fertility. However, current high levels of soil P fertility inhibit P fertiliser improvement; networked experimental sites should be developed and sustained to facilitate development and validation of P fertilisers. New high-precision fertiliser testing methods are also required. Proven reliability of any P targeting technologies will be crucial to their general adoption. Successful innovations in crop P nutrition could offer significant progress in reducing growing costs, preserving finite global P reserves and reducing export of P to livestock and in runoff from land, whilst also facilitating renewed enhancement of crop productivity.

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