Phosphorus: Can We Farm Profitably on Low P Soils? Paul Withers, SENRGy, Bangor University

Transcription

1 Phosphorus: Can We Farm Profitably on Low P Soils? Paul Withers, SENRGy, Bangor University

2 Bangor University College of Natural Sciences School of Ocean Sciences (SOS) School of Biological Sciences (SBS) School of Environment, Natural Resources and Geography (SENRGy) Forestry, Environmental Sciences, (Soil science, catchment science) Links to the Centre for Ecology and Hydrology

3 The Phosphorus Dilemma Essential for life (energy, bones) Low solubility key limiting nutrient Food production systems reliant on mined P P inputs forecast to increase to meet food demand BUT P inputs inefficiently used (soil P fixation) P losses contribute to eutrophication High P diets can affect human health P reserves running out threat to global food security

4 The Global P Problem The global population continues to rise Increasing world demand for P, especially in Asia BUT resources may be limited and prices can soar due to energy demands and political instability SO P-fertiliser use must become more efficient and wastage reduced! (USGS 2010) Billions of People World Production Mt/yr Price $/t World P production Year 150 Global Population Year Rock P price Year

5 The Open Phosphorus Cycle The Open P cycle is inefficient and wasteful. Future food security depends on closing this cycle

6 Agricultural P Cycle in the UK (1993) 000 tonnes Surplus = 175,000 tonnesp or 15 kg P/ha Overall efficiency (outputs/inputs) is only 25% (Withers et al. 2001)

7 The UK Soil Surface P Balance (Defra 2010) Surplus P is equivalent to fertiliser consumption

8 The Cumulative UK P surplus Annual P surplus ('000 t) Years 10.0 Cumulative P surplus (M t) Cumulative P surplus = >1000 kg P/ha Soil P concentrations have doubled since the 1930 s (Withers et al. 2001)

9 Distribution of Soil Phosphorus Representative Soil Sampling Scheme ( ) 41% of soils in England and Wales are ADAS P Index 3 and above Data from the Professional Agricultural Analysis Group (2008/09) shows that 44% of soils in the UK are ADAS P Index 3 and above. P Index 0 Deficiency (0-9 mg/l) P Index 1 Low (10-15 mg/l) P Index 2 Optimal (16-25 mg/l) P Index 3 Maximum (26-45 mg/l) P Index 4 High (46-70 mg/l) P Index 5+ Very high ( 71 mg/l)

10 Land Use Distribution in the UK Segregation of farming systems exacerbates sustainable P management Only 20% of arable crops receive livestock manure 2.8 m tonnes of manures would have to exported from west to east UK each year to balance crop P demand by supply of manure (Bateman et al. 2011) Spatial disconnects: - arable to livestock - rural to urban

11 Sustainable Use of Phosphorus Sustainable Intensification Achieving higher yields from the same acreage without severely impacting the environment How can we reduce our dependence on inorganic fertilizers? Can we farm profitably on low P soils? Recognising the value of the soil P store Improving the efficiency of P that we do apply Recovering and recycling used P Reducing wastage (losses) of P in the cycle

12 Crop and Livestock Production Genetics Species & varieties Phosphorus requirement Product formulation Treatment & distribution P Application methods

13 Understanding Crop Requirement Crop yield P % Crop Demand Crop Requirement Fertiliser & Manure Soil Supply Immobilisation Adsorption Mineralisation Desorption Losses

14 Soil P Supply Fixed (residual) P 7 TgP = 4 million Various soil P tests (STP) (Syers et al. 2008)

15 What does a STP extract? Cummulative extractable P (mg/kg) f(x) = 3.87x f(x) = 2.1x Extraction number Meath I Linear Regression for Meath I Louth I Linear Regression for Louth I f(x) = 0.96x f(x) = 0.6x Meath II Linear Regression for Meath II Wexford I Linear Regression for Wexford I McDonnell and Walsh (1957) Acetic acid A single extraction only removes a proportion of the total labile pool

16 Issues over Sampling and Analysis Fertility status Colour- P (%) ICP-P (%) VL 7 0 L M M+ 0 6 H 8 8 Using ICP gave a different fertility class than using colour! Potential for misinterpretation of STP results

17 Mechanisms of Soil P Acquisition Root distribution morphology (lateral roots, root hairs) Symbiotic relationships (Mycorrhizal) Exudation of organic acid anions (carboxylates) Release of protons (H + ) Release of ectoenzymes(phytaseand phosphatases) Crop specific adaptations to reduced P supply

18 A New P Fractionation 0.01M Calcium chloride 0.1M Citric acid 0.02 EU Phosphatase and phytase 1M Hydrochloric acid 1:20, shake for 3 hours Filter/centrifuge and measure colorimetrically Solution P Organic acid labile P Enzyme labile P Acid labile P

19 A New P Fractionation New fractionation was applied to 100 soils covering differing habitats in the UK from 1998 and 2007 (200 in total). Solution P, citric acid P and occluded P all decreased, but enzyme labile P (organic P) increased!

20 Understanding Crop Requirement Crop yield P % Crop Demand Crop Requirement Fertiliser & Manure Soil Supply Immobilisation Adsorption Mineralisation Desorption Losses

21 Crop P Demand Low Phytate Mutants Grain P (mg/g DM) WT lpa1 WT lpa1 lpa2 WT lpa1 lpa2 WT lpa1 Wheat Maize Barley Rice Inorganic & low inositol P Phytate P Cell P After Guttieri et al. 2004; & Raboy 2002 J Nutrition 132-S,

22 Fertiliser P Recovery by Crop annual P uptake (kg/ha) P at Padstow(28 years barley) 0 mean optimum for grain yield full P recovery from inherent soil P mean recovery of optimum P = 14% annual P applied (kg/ha) Richards et al., 1996 Recovery of fertiliser P by the crop is often very low; usually < 30% and often <10%. Unused P remains in the soil for use by subsequent crops but also becomes gradually fixed by Fe/Al. Build-up and maintenance of soil P at optimum fertility level requires large amounts of P fertiliser.

23 NOW High soil P TARGETED P allowing low soil P Broadcast P fertilisers Foliar applications Crops yielding 10 t/ha grain contain ~90 kg/ha P 2 O 5 = 40 kg/ha P P run-off P run-off Seed dressings Placed fertilisers Reduce fixation of applied P Neutralise fixation sites e.g. AVAIL Recycled materials e.g. Struvite Slow release products e.g. Bauxsol

24 New LINK Project Improve the efficiency of P fertiliser use to reduce growers costs & help save global P reserves Reduce dependence on maintaining high soil P fertility (Index 2 down to Index 1) Utilise better the vast reserves of residual ( fixed ) P already in the soil Investigate potential for recycling of used P (e.g. Struvite) Reduce impacts of P use on the wider environment

25 Struvite Struvite technology is making significant advances to producing a product which is classed as a fertilizer and not a waste. Ammonium Magnesium Phosphate (6:13:0:10)

26 Struvite ph effects 1,4 [Pi] (M) 1,2 1,0 0,8 0,6 0,4 0,2 0, Time (days) ,0 Dissolution not affected by initial ph Dissolution raises local ph ph 7,5 7,0 6,5 6,0 5, Time (days)

27 Struvite dissolution Organic acid presence enhances Struvite solubility Oxalic acid Citric Acid Malic Acid [Pi] (mm) 2,0 1,5 1,0 Oxalic Acid 0.01 mm 0.1 mm 0,5 1 mm 0, Time (days)

28 Struvite Root branching 20 C Average number of LR per section A B B +P Homogenous 3.7 mm P A B -P mmoles P as Struvite at 6cm 0-4 cm 4-8 cm 8-12 cm Struvite placement stimulates increased root branching in the surrounding area

29 Enhancing Microbial Activity Pot Trial Barley in washed sand Phosphate = TSP AMP = Struvite RP Rock phosphate M Mycorrhizal innoc. PSB P solubilising bacteria By Mohammad Heydari, Bangor University

30 AVAIL One of a patented family of dicarboxylic copolymers Very high cationbinding capacity Designed to compete with phosphates for P-sorption sites in soil Used as a coating on granular phosphates or mixed into liquid phosphate fertilizers

31 AVAIL Harper Adams University College (from Carrs Fertilisers Website)

32 AVAIL AVAIL applied at recommended granular rate AVAIL applied at 100x granular rate P Sorped (µ.moles/g soil) TSP TSP % AVAIL P Sorped (µ.moles/g soil) K 2 HPO 4 K 2 HPO % AVAIL Solution P (µm) Solution P (µm)

33 AVAIL AVAIL is designed to be slowly biodegradable AVAIL is unlikely to diffuse far from the fertiliser without being broken down Soil respiration (pmol/s) Time (h) 1 mg, Glucose 20 ul, AVAIL 100 ul,1 M HCl DI Water 0 0,00 40,00 80,00 120,00 Avail added

34 Virotec TM A P-sorpingmix of minerals Used in water treatment to remove P Possible use in combination with readily soluble P- forms as a slow release fertiliser Spent material could also be used for P-fertilisation

35 Scotland (spring barley) 700 GS39 flag leaf emergence Dry weight g/m kg P/ha TSP inc TSP placed ST inc ST placed Avail inc Avail placed RP-S Foliar Non-calcareous loam, low P

36 Scotland (spring barley) 8,0 7,5 DM yiled (t/ha) 7,0 6,5 6,0 5,5 5, kg P/ha TSP inc. TSP pl St inc St pl Av inc Av pl Non-calcareous loam, low P

37 England (w. wheat) 8,40 8,20 DM yield (t/ha) 8,00 7,80 7,60 7,40 7,20 7, kg P/ha TSP inc. TSP pl St inc St pl Av inc Av pl Calcareous loam soil, low P

38 Conclusion: Future Research Redefining our food requirements Can P demand be reduced? Recognising the value of the soil P store Utilise existing soil P more efficiently, crop genetics, biological interventions Improving efficiency of P that we do apply Reducing fixation, placement, foliar P? Recovering and recycling used P Identify effective substitutes for inorganic fertilizers Reducing wastage (losses) of P in the cycle Reduce losses by better management but engineering solutions probably the main new research focus

39 LINK Project Improving the sustainability of phosphorus use in arable farming