Estimates of the apparent net mineralisation of legume N and comparisons of the subsequent recovery of legume or fertiliser nitrogen by wheat

Mark Peoples, Tony Swan, Laura Goward, James Hunt - CSIRO Agriculture & Food

Type: Research Paper, Conference Paper
Knowledge level: Advanced

Farm Table says:

Elevated concentrations of soil mineral nitrogen (N) (i.e. nitrate+ammonium) are frequently observed after legume crops and pastures, but only a fraction of the legume N tends to be recovered by the next crop. It would be useful if grain-growers and their advisors had some means of predicting the N supplied by legumes to following crops when deciding how much N fertiliser to apply.

What is the problem?

This paper reports several approaches that were applied to crop and soil data collected from an on-farm field experiment to determine the apparent net mineralisation rate of N from either lupin stubble remaining after grain harvest, or a brown manured (BM) lupin killed with herbicide prior to grain filling (a strategy deployed by some local farmers to control herbicide resistant weeds), and the apparent recovery of the lupin N by a following crop of wheat


What did the research involve?

The experiment was located at an on-farm field site located near Junee, NSW, Australia

Each plot consisted of six crop rows 305 mm apart with measurements restricted to the four middle rows of
each plot.

At the end of April 2012, plots were sampled to 1.6 m for soil N analysis, and all treatments were sown to
wheat (cv Spitfire) in mid-May

What were the key findings?

Of the three different measures of apparent mineralisation of legume N examined here, perhaps the estimate
of around 7 kg additional soil mineral N/ha per tonne legume stubble DM might be the simplest ‘rules-of-thumb’
for farmers and their advisors to apply.

More experimental data for different legume species and diverse environments and soil types are currently being
collated to ascertain how robust the various determinations of mineralisation and crop recovery of legume and
fertiliser N may be for other dryland grain production systems of south-eastern Australia.

Final comment

Results from the experimentation indicated that concentrations of soil mineral (inorganic) nitrogen (N) measured just prior to sowing wheat in 2012 (0-1.6m) were 42 or 92 kg N/ha greater following lupin grown for either grain or brown manure (BM) than where the preceding crop in 2011 had been wheat or canola

2012 - Australia - Mark Peoples, Tony Swan, Laura Goward, James Hunt - CSIRO Agriculture & Food
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