1. MFS 2015 Soil Tests
Phil Graham

2. Why do we soil test”? To help fine tune our fertiliser decisions.
It is only part of the decision.

3. Long term graph of the Bookham site

4. Introducing P index
Richard Simpson come up with the P index to make graphing easier.
How do we get it?
Divide your Colwell P by Critical P we get from the PBI number.
Eg Hill paddock has colwell P of 19 and a critical P of 25,
19/25= 0.76

5. Bookham data expressed as a P index

6. S Index With the S index we divide our S reading from the test by 8.
Eg, 4.5 from test
4.5/8=0.56

7. What if you do not have access to a local pasture response curve?
95%
of max
yield
18 dse/ha
Pasture
supply
current
position
6 dse/ha
0.2 10 20
0.6 30 40 50 60
Soil test value: Colwell P (mg/kg)
P index
What if you do not have access to a local pasture response curve?

8. P & S index for PBI above 150 S I n d e x
P Index

9. P & S index for PBI between 150 and 90

10. P & S index for PBI between 90 to 30

11. Property numbers with PBI below 90 and a P index above 1

12. Property number for PBI above 160 and P index below 1S P

13. Do the results make sense?P

14. What if you do not have access to a local pasture response curve?
95%
of max
yield
18 dse/ha
Pasture
supply
current
position
6 dse/ha
0.2 10 20
0.6 30 40 50 60
Soil test value: Colwell P (mg/kg)
P index
What if you do not have access to a local pasture response curve?

15. Long term graph of the Bookham site

16. Should we always build soil P?

17. Should we always build soil P?