1. Grassland P & K Advice Mark Plunkett Johnstown Castle, Wexford
Mark Plunkett, Teagasc
Grassland P & K Advice Mark Plunkett Johnstown Castle, Wexford

2. Soil P – Grassland Farms
Mark Plunkett, Teagasc
Soil P – Grassland Farms
Soil P for Grassland Soils
64% Index 1 & 2
Target Index 3
Soil P fertility decreasing over time
64% of soils P Index 1 and 2
Aim for P Index 3
Soil P fertility continues to decrease

3. Soil K for Grassland Soils
Mark Plunkett, Teagasc
Soil K - Grassland
Soil K for Grassland Soils
61% < Index 1 & 2
Target Index 3
Soil K fertility decreasing over time
57% of soils K Index 1 and 2
Aim for P Index 3
Soil Kfertility continues to decrease

4. Soil P & K Trends - Grassland Farms
Mark Plunkett, Teagasc
Soil P & K Trends - Grassland Farms
P and K Trends over time
42,572 Soils

5. Mark Plunkett, Teagasc
91% of soils sub optimal for pH, P & K

6. Step 1 - Reliable Soil Results
Mark Plunkett, Teagasc
Step 1 - Reliable Soil Results
“Soil results are only as good as the sample on which it is based on”
“Greatest potential for error is in field sampling”
Take a representative soil sample
Establish an accurate estimate of the soils nutrient status
10cm sampling depth represents a volume of approx. 1,500 tonnes/ha of soil
Sample every 4 to 5ha
Take soil samples as per soil sample guidelines to ensure reliable results
= 6,000 to 7,500t Soil

7. Peaty Soils & P Application
Peats type soils have no minerals such as and / silt / clay
Very little Iron / Aluminium
Therefore low ability to retain P
Increased risk of P loss to water
Apply maintenance P rates
Morgan’s P over estimates soil P
availability
Therefore poor indicator of peat soil P status

8. Soil Sampling Changes Check map & determine if peaty or not
Peat Soils Certification & Soil Organic Map
Check map & determine if peaty or not
Advisor signs off on peat or non peat
Where advisor signs off No Analysis required
If unsure test for SOM
>20% OM or Advisor signs off on peat only apply P Index 3 rates

9. Soil Organic Matter Layer Map

10. Role & Function of P Rooting & Tillering
Mark Plunkett, Teagasc
Role & Function of P
Rooting & Tillering
Kick starts spring grass growth
Extra 1.5t DM/ha
Animal health
0.35% P in Grass
Meat & Milk
Function and role of P in grass production

11. Irish Soils & P Fixation
Mark Plunkett, Teagasc
Irish Soils & P Fixation
Effect of soil pH on soil P availability – Aim for pH 6.3 to 6.5 to maximise soil P availability

12. Irish Soils & P Fixation
Mark Plunkett, Teagasc
Irish Soils & P Fixation
Irish soils are naturally acidic
High levels of Aluminium & Iron
Fix P applied to soils
Response to applied P very poor
Lime increases soil pH & unlocks soil P
Building Soil P will take time depending on the soil type and level of P fixation
Applying P to acidic soils results in P fixed by Al & Fe

13. Acidic Soils Fix P – Mineral Soils
Mark Plunkett, Teagasc
Acidic Soils Fix P – Mineral Soils
P Fertiliser
“Acidic soils competes for freshly applied P & its is Fixed by Al & Fe”
“Manure P more available in acidic soils” P Al
Explains soil P fixation Fe P
Acidic Soil

14. Unlocking Soil P with Lime!
Mark Plunkett, Teagasc
Unlocking Soil P with Lime!
Average change in soil test P (Morgan’s) across 16 soils (av. pH 5.5) treated with P (100 kg/ha of P), Lime (5 t/ha of lime), and P + Lime and incubated over 12 months in controlled conditions
Lime will increase soil P availability and freshly applied P is more available

15. Role & Function of K N & P Efficiency Prevents Lodging
Mark Plunkett, Teagasc
Role & Function of K
N & P Efficiency
Prevents Lodging
Silage Production
Extra 3t/ha
2 cut silage removes 250kg/ha
Slurry excellent K
Potassium vital role to play in N efficiency and water regulation in the plant
K vital in grass silage production. Ideally recycle slurry back to silage fields

16. Irish Soils & K Good levels of K 5% of total K is available
Mark Plunkett, Teagasc
Irish Soils & K
Good levels of K
5% of total K is available
K found in the clay component
Soil test very reliable
Easy to improve soil K compared to P
Soil type (light v heavy)
Some K fixing soils (for example Athy)
Peat soils and K??
Irish soils have good levels of soil K. Soil K will respond / change faster than soil P

17. Soil Test Results

18. Soil P & K Index System Basis to Index System
Mark Plunkett, Teagasc
Soil P & K Index System
Basis to Index System
Index 4 – Very Fertile Soils
Index 3 – Soil Feeding the crop & Replacing off-takes
Index 1 & 2 – Building soil fertility
Soil P & K Index system
Basis to Index system

19. Why Build Soil Fertility?
Mark Plunkett, Teagasc
Why Build Soil Fertility?
Index 3
Low response to fertilizer
Index 4
Soil supply sufficient to meet demands
Large variation between soil types!
Index 1 & 2
Yield response to increased soil P levels ~ 1.5 t/ha
Cost of not knowing soil is in Index 1 is approximately 1.5 t/ha of grass DM per year
Large variation around this average estimate (0-5 t/ha)
Average of response curves from 8 sites over 4 years. (32 repeated experiments).
K – Similar response in silage (1-3 t/ha/yr)

20. How much P and K to replace offtake?
Mark Plunkett, Teagasc
How much P and K to replace offtake?
P (kg)
K (kg)
Milk (1,000 litres)
Meat (Live wt.) (100 kg) 1
Silage (1 ton DM)
3 - 4 25
Grain (1 ton grain + straw)
3.8
10-15
P and K offtakes for milk / meat / silage / grain
Lalor – ASA Conference,
Killeshin Hotel, Portlaoise 20 Mar 2014

21. How much P & K Removed? Stocking Rate / ha Product P (kg) K (kg)
Mark Plunkett, Teagasc
How much P & K Removed?
Stocking Rate / ha
Product P
(kg)
K (kg)
10,000L Milk 10 15
15,000L Milk 23
1,200 kg
Meat 12
X 24
1,100kg 11
P & K Off takes by stocking rates
Lalor – ASA Conference,
Killeshin Hotel, Portlaoise 20 Mar 2014

22. P & K advice – replacing offtake
Mark Plunkett, Teagasc
P & K advice – replacing offtake
Stocking Rate (LU/ha)
> 3.0
Dairy
P – K advice
kg/ha
14 – 30
19 – 35
23 – 40
27 – 45
units/acre
11 – 24
15 – 28
18 – 32
22 – 36
Stocking Rate (LU/ha)
Beef/Sheep
P – K advice
kg/ha
7 – 10
10 – 15
13 – 20
16 – 25
units/acre
6 – 8
8 – 12
10 – 16
P and K advice for dairy & drystock
P and K rates for drystock are low

23. P & K Advice – Off takes Grass Silage
Mark Plunkett, Teagasc
P & K Advice – Off takes Grass Silage
Cut
1st
2nd
P – K advice
kg/ha
20 – 125
12 – 75
units/acre
16 – 100
10 – 60
P and K advice for 1st & 2nd cut silage

24. P & K – Build Up Rates Build-up Index 1 Index 2 P – K advice kg/ha +
Mark Plunkett, Teagasc
P & K – Build Up Rates
Build-up
Index 1
Index 2
P – K advice
kg/ha +
50 – 60
30 – 30
units/acre
40 – 48
24 – 24
P and K build up rates
P increased by 30kgP/ha at Index 1
P increased by 20kgP/ha at Index 2

25. How long does it take to change Index ?
Mark Plunkett, Teagasc
How long does it take to change Index ? P
Generally takes time to increase/decrease (5 to 10 years)
Lighter soils tend to move quicker
Organic matter content
% Clay
Advice
1st Correct Soil pH
Apply fertilizer as per fertiliser plan for a number of years
Re-test every 3-5 years to monitor changes over time K
Will change faster than P
Index 1 & 2
Apply off takes + build-up until next soil test
Index 4
Omit K for one year, then revert to Index 3 advice (off takes)
On av. 50kgP/ha req. for 1mg/L P
On av. 1kgK/ha req. for 1mg/L K
Changing soil P takes time while soil K will change faster

26. New Fertiliser P Allowances
Mark Plunkett, Teagasc
New Fertiliser P Allowances
Grassland Stocking Rate (kg/ha)
P Index 1 2 3 4 63 43 13 66 46 16
>250 69 49 19
50kg Index 1
30kg Index 2
1. Adjust for Conc. Feed (5kg/ton)
2. Slurry Removed from calculations
New P allowances
Complete Farm Fertiliser Plan to Determine P Allowances

27. Mark Plunkett, Teagasc
P & K advice – In Summary
Take good soil samples for reliable P & K results
Correct soil pH before building soil P
Determine P & K advice
Takes time to increase soil P while K will increase quicker
New Nitrates allow extra P for build up
Summary