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

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!

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)?

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.

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

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

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!”

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

AgVise calculator

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

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 84-140kgN/ha Take no account of soil temp. APSIM (yield prophet)

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

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

APSIM - SCaRP Carbon settings ~90kgN/ha

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.

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)