The current temptingly high chickpea prices make them an attractive option. In paddocks with high soil nitrate (>100kg N/ha) chickpeas may not yield as well as expected, or deliver the usual legume break crop advantage of a net benefit to the paddock’s nitrogen (N) balance.
Paddocks can have high starting soil nitrate if they were left fallow over summer, especially coming out of a long fallow where nitrogen was applied, but a later decision made not to sow a crop.
When chickpeas are grown in low nitrate soils they can fix large amounts of nitrogen, adding to the soil’s N balance and, importantly for short-term productivity, increase the amount of nitrate-N in the root zone.
In soils with moderate to high nitrate-N the chickpeas take advantage of the available N in the soil and less N fixation occurs. By the end of the crop chickpeas may even have a negative impact on the paddock’s total soil N. Less Nitrate-N may be available at sowing for the crop following the chickpeas.
These nitrogen dynamics were derived from the N budget tool for the northern region calculated for a medium fertility no-till paddock, located at Moree in northern NSW.
More value from paddocks with high starting soil nitrate might be achieved sowing a winter cereal or oilseed crop and substantially reducing the amount of fertiliser N applied. High
nitrate paddocks could also be sown to faba bean, which continues to fix N in the presence of moderate to high soil nitrate.
Tim Weaver, NSW DPI, David Herridge, UNE, Rob Norton, IPNI
Photo courtesy of the GRDC