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

2. Mark Plunkett, Teagasc
Presentation Notes
This presentation can be used for either drystock or dairy training groups as there is double slides for either group.
For example slides 3, 4 & 5, 6,7 & 8, 9 & 10
Mark Plunkett, Teagasc

3. Soil P for Grassland Soils
Mark Plunkett, Teagasc
Soil P - Drystock
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
Mark Plunkett, Teagasc, 2018

4. Soil K for Grassland Soils
Mark Plunkett, Teagasc
Soil K - Drystock
Soil K for Grassland Soils
57% < 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
Mark Plunkett, Teagasc, 2018

5. Soil P & K Trends - Drystock Farms
Mark Plunkett, Teagasc
Soil P & K Trends - Drystock Farms
P and K Trends over time
42,646 Soils
Mark Plunkett, Teagasc, 2018

6. Soil P for Grassland Soils
Mark Plunkett, Teagasc
Soil P - Dairy
61% < Index 1 & 2
Target Index 3
Soil P fertility decreasing over time
Soil P for Grassland Soils
61% of soils P Index 1 and 2
Aim for P Index 3
Soil P fertility continues to decrease
Mark Plunkett, Teagasc, 2018

7. Soil K for Grassland Soils
Mark Plunkett, Teagasc
Soil K - Dairy
54% < Index 1 & 2
Target Index 3
Soil K fertility similar to P declining slowing over time
Soil K for Grassland Soils
54% of soils K Index 1 and 2
Aim for P Index 3
Soil K fertility continues to decrease
Mark Plunkett, Teagasc, 2018

8. Soil P & K Trends - Dairy Farms
Mark Plunkett, Teagasc
Soil P & K Trends - Dairy Farms
P and K trends overtime
16,650 Soils
Mark Plunkett, Teagasc, 2018

9. Soils with Optimum Fertility
Mark Plunkett, Teagasc
Soils with Optimum Fertility
“90% of soils sub-optimal for Major Nutrients – pH, P or K”
91% of soils sub optimal for pH, P & K
Mark Plunkett, Teagasc, 2018

10. Soils with Optimum Fertility - Dairy
Mark Plunkett, Teagasc
Soils with Optimum Fertility - Dairy
“90% of soils sub-optimal for Major Nutrients – pH, P or K”
89% of soils sub optimal for pH, P & K
Mark Plunkett, Teagasc, 2018

11. 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
Mark Plunkett, Teagasc, 2018

12. 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
Mark Plunkett, Teagasc, 2018

13. 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
Mark Plunkett, Teagasc, 2018

14. 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
Mark Plunkett, Teagasc, 2018

15. Al Acidic Soils Fix P Fe P Fertiliser
Mark Plunkett, Teagasc
Acidic Soils Fix P
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
Mark Plunkett, Teagasc, 2018

16. 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
Mark Plunkett, Teagasc, 2018

17. 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
Mark Plunkett, Teagasc, 2018

18. 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)
Irish soils have good levels of soil K. Soil K will respond / change faster than soil P
Mark Plunkett, Teagasc, 2018

19. Soil Test Results
Mark Plunkett, Teagasc, 2018

20. 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
Mark Plunkett, Teagasc

21. 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)

22. 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
Mark Plunkett, Teagasc
Lalor – ASA Conference,
Killeshin Hotel, Portlaoise 20 Mar 2014

23. 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
Mark Plunkett, Teagasc
Lalor – ASA Conference,
Killeshin Hotel, Portlaoise 20 Mar 2014

24. 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
Mark Plunkett, Teagasc

25. 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
Mark Plunkett, Teagasc

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

27. 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
Mark Plunkett, Teagasc

28. 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
Mark Plunkett, Teagasc

29. 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
Mark Plunkett, Teagasc