'NBudget' - a nitrogen management tool cropping systems

Abstract

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 as to the nitrate levels in their soils at sowing and often make decisions about what crop to grow and how much fertiliser N to apply using little information relevant to nitrogen supply. Current extension information on N, including legume N2 fixation, is often confusing, conflicting and inaccurate. With fertiliser N priced at about $1.50/kg, and with increasing pressure to reduce nitrous oxide (N2O) emissions in the agricultural sector, farmers need to maximise N inputs from N2-fixing legumes and to closely match fertiliser-N inputs to crop requirements.'NBudget' is an excel-based decision-support (DS) tool that will help farmers/advisers in Australia’s northern grains region (northern NSW and southern Qld) estimate soil nitrate levels pre-sowing, set target yields and determine fertiliser N requirements for winter cereals and oilseeds. A major difference between 'NBudget' and other DS tools for N management is that soil testing for either nitrate, organic carbon or water is not required. Rather, 'NBudget' contains rule-of-thumb values and algorithms for estimating the net release or immobilisation of nitrate-N in the soil and for estimating N2 fixation by a legume crop. Input data to generate the algorithms were derived from published and unpublished experiments conducted in the region during the past 30 years. Input data to run 'NBudget' are readily available to farmers. Details of the program are presented in this paper.