A GRDC funded project was undertaken by Rural Management Strategies in 2013, to demonstrate the use of Yield Prophet and plant available water capacity (PAWC) mapping, to improve Nitrogen decision making in wheat.
Nitrogen represents the largest single cost in most continuous cropping enterprises. Nitrogen decisions are risky, relying heavily on future seasonal conditions, leading to uncertainty and stress for managers. The Yield Prophet model has potential to improve Nitrogen decision making, but relies on accurate soil characterisation data which can be expensive and time consuming to determine.
Many producers have yield mapping technology and the ability to apply varied fertiliser rates across a paddock, but are often unsure how to determine rates for different areas. PAWC mapping has been proposed as a method of clarifying differences across a paddock to allow soil types to be managed separately for Nitrogen, using predictions from Yield Prophet.
A paddock at Barmedman was split into three zones using yield maps plus EM38 surveys as an estimate of PAWC. Nitrogen allocations were determined using Yield Prophet modelling and applied using a variable rate spreader. Standard 100kg/ha Urea strips were placed at intervals across the paddock as well as a Nil treatment.
Nitrogen treatments, kg/ha of Urea.
There was no benefit from added Nitrogen at this site in 2013.
Managing Nitrogen separately using Yield Prophet and PAWC mapping, added $95/ha in costs compared to the Nil treatment and $35/ha compared to the standard Nitrogen treatment. This result was heavily influenced by seasonal conditions.
Average yield for the paddock was 3.27 t/ha, which is above the long term median yield, despite a number of years in crop.
Yield differences between treatments were not statistically significant.
Total rainfall for the year was 406mm (242mm April – October). However there were only two falls greater than 10mm after 12 June 2013.
Nitrogen decisions were influenced by the overly optimistic 3 month forecast from BOM (Bureau of Meteorology), which predicted a strong chance of exceeding median rainfall from July to September.
Potential remains for improving Nitrogen management using Yield Prophet and PAWC mapping, despite negative returns from this method in 2013.
The potential to identify situations where Nitrogen use can be reduced could lead to cost savings and reduced business risk. A decision making framework for Yield Prophet is proposed, which incorporates historical crop performance as well as model outputs to further improve Nitrogen decision making.
This project has been funded again by GRDC for 2014.
The full report can be found in our Knowledge-Base.