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

2. 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

3. 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 – … kg P/ha
P leaching
non-point vertical P losses
<3 kg P/ha
P treshold in surface waters (in Belgium 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

4. 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

5. Research methods
P leaching equipment

6. Research methods

7. 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

8. 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?

9. Prediction of P concentrations in leachates
Model
efficiency
Model A.1
TP = P-CaCl2 – Ca-AL
0.84
Model A.2
TP = P-CaCl2
0.85
Model B.1
TP = HWP – Ptot – Fe-AL
0.86
Model B.2
TP = HWP
0.65
The P concentrations in the leachates are better predicted by the soil P availability, than by the soil P stock

10. Prediction of P concentrations in leachates

11. 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

12. 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

13. 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

14. More information. T. Vanden Nest, B. Vandecasteele, G. Ruysschaert, R
More information? T. Vanden Nest, B. Vandecasteele, G. Ruysschaert, R. Merckx 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.

15. Thanks for your attention
Thijs Vanden Nest
T + 32 (0)
Instituut voor Landbouw-
en Visserijonderzoek
Burg. Van Gansberghelaan 109
9820 Merelbeke – België
T + 32 (0)
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