NBudget: A simple tool for farmers and advisors for N management in Australia’s northern grain cropping

Effective management of plant-available nitrogen (N) by farmers will generally have beneficial productivity, economic and environmental consequences. The reality is that farmers may be unsure of plant-avalable N levels in cropping soils at sowing and by necessity make decisions about how much fertiliser N to apply with limited information about soil N supply. NBudget is an excel-based decision-support (DS) tool developed to assist farmers/advisors in Australia's northern grains region estimate (i) plant-available soil N and water levels pre-sowing, (ii) target yields, (iii) fertiliser N requirements for cereals and oilseed crops and (iv) N₂ fixation by legumes. NBudget does not rely on soil testing either for nitrate-N, organic carbon or water. Rather, the tool relies on rainfall data plus basic descriptions of soil texture and fertility, tillage practice, information about the previous two years paddock use plus rules-of-thumb values and stand-alone or linked algorithms. Winter and summer versions of NBudget cover the major crops of the region. Groundtruthing of NBudget against three independent data sets (n=55) indicated generally close agreement between measured and predicted values for sowing soil nitrate (r²=0.76). A limitation of the tool is that it does not account for denitrification losses of soil N. The usefulness of NBudget would be enhanced by transforming the current Excel-based tool to a stand-alone app or web-based tool.