1. Nitrogen Application Modelling & Soil Carbon
Practical Application – a WIP.
David Watson

2. Background
Pasture Crop Sequence program - produce a user friendly in-crop nitrogen application calculator for the Vic HRZ with high yield potential.
Update, validate existing AgVise calculator
Used by AgVise for ~12 years
Based on an English model – Jon Midwood
Australianised over time
Balances N application against target yield & protein
It works!

3. Agronomist survey - Confidential
Phone interview
What method do you currently use? DSS tools?
What is good/bad about it?
Do you use deep N soil samples?
What depth?
What level of confidence that the N decisions maximise yield/quality (protein)?

4. What method do you currently use? DSS tools?
None use any formal tool or model and have little confidence in existing models
Range of approaches based on
nutrient budgets (20kgN/t)
Some estimates of mineralisation
Large element of “gut feel” applied to any calculation.

5. What is good/bad about it?
Low level of confidence on mineralisation estimates (for our region)
Scepticism about applicability of mineralisation calculations from other regions
Some use of soil OC, spring rainfall for min.
Some use of NUE factors
Little confidence in any method

6. Do you use deep N soil samples? Why not?
Most had moved away from deep N testing-few tests undertaken
Results are variable & unreliable
Time in getting results
Winter access to paddocks with rigs
Staff, contractors accessing right paddock (maps).
Questioned 60cm on our soils (subsoils)
Laborious

7. What level of confidence that the N decisions maximise yield/quality (protein)?
Consensus
A little science & a large component of gut feel.
Probably not optimising yield/quality
Quotes
“I tear my hair out every year over N decisions”
“Fly by the seat of my pants more often than not”
“Major issue for the industry with no clear process/tool available”
“The Holy Grail – good luck!”

8. AgVise calculator
In crop ~GS 24/30, canola, wheat (mill/feed), barley (malt/feed).
XLS spread sheet
Balance sheet approach
Soil N, 40cm, drill sample(next day results) Crop N est + mineralisation est
Less losses (vol, denit, leach, runoff) est
Graph crop requirement against range of yields

9. AgVise calculator

10. Shortcomings to address
Validate all crop N requirement assumptions for yield & protein
More accurate
crop N estimates
N loss estimates
Residual soil N estimates
Mineralisation estimates
Easier, quicker soil N sampling & testing

12. Mineralisation the biggest unknown
Soil temp, moisture & carbon
Mineralisation profile vs crop demand
5 Industry models/tools from other locations for entire growing season using rf & OC give a large range off values, typically kgN/ha
Take no account of soil temp.
APSIM (yield prophet)

13. APSIM default Carbon settings Lismore, 65 yrs
20-30kg N/ha
Too low
Something wrong!
Soil carbon ??????
Z30 to Maturity Mineralisation kg N/ha

16. SCaRP data for APSIM 146 sites SW Vic MIR assessment of soil carbon
Continuous crop >10yrs
Fraction definition similar/same as APSIM
Horizons different
SCARP 0-30
t/ha
Bulk density
Particulate OC
Humic OC
Resistant OC
Total OC
1.5
6.43
26.90
12.81
46.14
APSIM settings
BiomC
HumC
InertC
0.97
30.30
24.1
55.36

17. APSIM - SCaRP Carbon settings
~90kgN/ha

18. NAPP strategy going forward
Use basic AgVise calculator >>>> NAPP
Update all components to include
Likely distribution (range) of values, esp mineralisation.
Explanation of what factors influence range
Grower/advisor to use, knowledge, experience & intuition to determine component values - ownership
Growers/advisors to determine target yield/quality reflecting attitude to risk.

19. Industry Review Yield Prophet to include
existing SCaRP data where possible
Include MIR soil carbon assessment in all Yield Prophet soil characterisations- past & future
SCaRP data is available (ref CamN)