Managing Legume and Fertiliser N for Northern Grains Cropping

Abstract

The purpose for writing this manual was twofold. First, it was to provide an update of current information on fertiliser and legume nitrogen (N) in broadacre cropping in Australia's northern grains region, with particular emphasis on the legume N. Second, the manual was written to provide instructions, underpinning technical information and background science for 'NBudget' - the Excel-based calculator for estimating the fertiliser N requirements of cereal and oilseed crops and dinitrogen (N₂) fixation by legumes. The manual's target audience is likely to be the private and government agronomists, consultants and advisers who work with farmers to make decisions about N, rather than the farmers themselves. The manual may also provide useful material for tertiary-level education and training. ... Why focus on N? Plant-available (mineral) N is a major driver of agricultural productivity and profitability. Nitrogen is a component of chlorophyll, the green pigment found in almost all plants. It is responsible for photosynthesis in which carbon from carbon dioxide in the atmosphere is fixed by the plant into sugars in the presence of sunlight. Photosynthesis is the source of almost all of the energy for animal and human life. When plants are N-deficient they lack chlorophyll (termed chlorotic), appear yellow and are unthrifty. For grain crops, N deficiency means reduced yield and low grain proteins.