Long term use of different organic fertilizer types and impact on phosphorus leaching Thijs Vanden Nest

The GLOBAL P cycle Soil cycle AQUATIC ENVIRONMENT Leaching, run-off, erosion dislocation Eutrophication FERTILIZER FARMLAND MANURE FOOD SEWAGE P Mines WASTE Recycling FEED LIVESTOCK The GLOBAL P cycle

The soil P cycle P intensity and soil P availability P readily available in the soil solution <10 kg P/ha P capacity and soil P stock P available for desorption 100 – 1000 – 5000 -… kg P/ha P leaching non-point vertical P losses <3 kg P/ha P treshold in surface waters (in Belgium 0.07 - 0.14 mg P/L) 50 mg NO3--N/L P uptake by crops 10-50 kg P/ha The amount of P in the soil solution is determined by The number of P sorption binding sites (soil property) The amount of P in the soil (fertilizer history)  van der Zee principle

Research methods What did we measure? Soil P availability HWP: hot water extractable P P-CaCl2: 0.01 M CaCl2 extractable P Soil P stock P-AL: ammonium lactate extractable P P leaching Laboratory leaching experiments TP: P concentrations in leachates

Research methods P leaching equipment

Research methods

Research methods What did we measure? Soil P availability HWP: hot water extractable P P-CaCl2: 0.01 M CaCl2 extractable P Soil P stock P-AL: ammonium lactate extractable P P leaching Laboratory leaching experiments TP: P concentrations in leachates Soil organic carbon (SOC%) Soil acidity (pH-KCl) Crop yield and P uptake Where did we measure? One year field trial with catch crops 5 long term field trials with organic fertilizer amendments

Prediction of P concentrations in leachates Pooled dataset of 5 long term fertilizer field trials Data of pH-KCl, SOC%, soil P stock (P-AL, PNaOH, Ptot), soil P availability (P- CaCl2, HWP), P leaching (TP and TDP concentrations) Fertilizer categories: no P fertilizers, mineral P fertilization, farmyard manure, cattle slurry, compost Can we predict the P concentrations in the leachates of upper soil layer? Impact of the fertilizer type?

Prediction of P concentrations in leachates   Model efficiency Model A.1 TP = 0.2810 + 0.6457 P-CaCl2 – 0.0003 Ca-AL 0.84 Model A.2 TP = -0.3821 + 0.6552 P-CaCl2 0.85 Model B.1 TP = 2.4374 + 0.2218 HWP – 0.0056 Ptot – 0.0020 Fe-AL 0.86 Model B.2 TP = -0.8393 + 0.1493 HWP 0.65 The P concentrations in the leachates are better predicted by the soil P availability, than by the soil P stock

Prediction of P concentrations in leachates

Prediction of P concentrations in leachates Impact of the fertilizer type? What determines P-CaCl2/HWP? ANCOVA’s with ‘fertilizer category’ as covariate P-CaCl2/HWP are determined by soil P stock (?) What does this mean??? The P leaching is in first place determined by the soil P stock, so in fact by the long term fertilizer history HOWEVER! In one particular field, organic fertilizer type A, will increase the soil P availability more than organic fertilizer type B

Conclusions Catch crop incorporation in soils with high P status does not increase the P leaching P leaching is influenced by the composition of the incorporated catch crop residues Different organic fertilizers have a different effect on P leaching In soils with high P status and low SOC, compost is preferred over farmyard manure Soil P availability is influenced by seasonal trends, but differences between fertilizers remain the whole year

Conclusions Zero P fertilization immediately reduces the soil P availability and P leaching, but no gradual further decrease was observed in the following 4 years P concentrations in leachates can be predicted with P-CaCl2 and HWP, but what with the seasonal trend? The soil P availability is mainly determined by the amount of P in the soil, which is the result of the long term fertilizer history BUT! In one particular field, organic fertilizer type A, will increase the soil P availability more than organic fertilizer type B

More information. T. Vanden Nest, B. Vandecasteele, G. Ruysschaert, R More information? T. Vanden Nest, B. Vandecasteele, G. Ruysschaert, R. Merckx. 2017. Prediction Of P Concentrations In Soil Leachates: Results From 6 Long Term Field Trials On Soils With A High P Load. Agriculture, Ecosystems And Environment 237, 55–65. Http://Dx.Doi.Org/10.1016/J.Agee.2016.12.015

Thanks for your attention Thijs Vanden Nest thijs.vandennest@ilvo.vlaanderen.be T + 32 (0)9 272 26 74 Instituut voor Landbouw- en Visserijonderzoek Burg. Van Gansberghelaan 109 9820 Merelbeke – België T + 32 (0)9 272 27 00 F +32 (0)9 272 27 01 plantTO@ilvo.vlaanderen.be www.ilvo.vlaanderen.be