Understanding crop N requirements, and the dynamics of N within the soil, is an important skill for anyone involved in cropping. This assignment will give you the chance to improve your understanding of N within our farming systems.
Part 1
Choose Gunnedah paddock where you have access to 2 years of cropping history – especially yield (and hopefully protein) for last year (and maybe the previous year), possibly soil test N values, and N fertiliser used.
Paddock history for Gunnedah: 2 years ago, sorghum yielding 5t/ha at 12% protein from 150kg/ha urea and long fallowed from barley
Last year, barley 4.25t/ha at 10% protein, from 150kg Urea
This year, into barley again – target yield around 5t/ha
The paddock is black soil, low-mod fertility from long term cropping with little N inputs until
recently, and zero tilled.
Use any one of the N decision support tools available*, and estimate how much N should have been applied to this year’s crop (either this winters crop, or the next summer crop). Show enough of your calculations so that we can understand what you are doing, or describe/show the set up values you use in the computer models. Ideally, you would also discuss how well thepredictions matched the yield and protein results at harvest, but trimester timing doesn’t let us do this, so you will have to check the accuracy yourselves in December.
http://www.grdc.com.au/Resources/Bookshop/2011/10/Managing-Legume-and-Fertiliser– N-for-Northern-Grains-Cropping
· the simple N budgeting approach from the Qld and NSW DPI’s (which is described in files and a podcast on Moodle), and in “Soil Matters” at http://www.apsim.info/wiki/(S(2edr3dfgyhsuolithxmdat45))/public/Upload/ApSoil/SoilMatt ers/Default.htm
· the N budget in Howwet, a fallow modelling program based on the DPI approach and available at http://www.apsim.info/How/HowWet/how%20wet.htm,
· Yield Prophet (by inputting soil test values, and looking at N response for this year),
· CSIRO’s Yield and N calculator for southern regions found at http://www.clw.csiro.au/forms/ncalc/ncalcregistration.aspx
· Whopper cropper – a modelling program based on ‘typical’ soils, crops and N rates for each part of a region. It is easier to use, but much less specific than Yield Prophet, and doesn’t include the ‘real time’ updates. Whopper has only been available on CD due to the huge amount of data it contains, but it should be available on-line by the end of the year.
· Commercially available programs from Back Paddock, or Nutrient Advantage – these appear to be similar N budgeting approaches to most of the rest, but based on soil test values.
Something you may want to consider with the different models is how much they rely on soil test information. If the information is available (and enough cores were taken to be accurate), then these models can be very useful. However, most paddocks aren’t sampled each year, so another method which estimates N availability may have more impact across the industry as it could be used more frequently, and by more growers. David Herridge’s Nbudget, and the DPI N budget approach, are both able to estimate N for their calculations.
The “Managing Legume and Fertiliser N” booklet which is part of “Nbudget” is a good source of information for this assignment, and it has a great list of references which may be of use as well. Other references which may be of use include
