Making nitrogen applications pay this season was a hot topic at the Campbelltown GRDC Update. With Nitrogen(N) costs doubled, and the possibility it could stay expensive for years, do you cut back? Or as it is a production driver of grain yield, do you continue?

Wayne Pluske, a consultant from WA suggested that our nitrogen decisions were often emotional, based, on fear of missing out on yields or made based on past profitability.

The absolute yield and grain price while critical, may not necessarily drive profit, with the inflated cost of nitrogen. A bit like topping the market with livestock sales, if those weight gains have come from expensive supplementary feeding, then profit has not been optimised.

Wayne gave a great reminder that better N rate decisions was the biggest opportunity to maximise profit. Also, nitrogen profitability or return on nitrogen investment was not something that always guided our decisions, but should especially with increased prices.

Wayne drew on the law of diminishing returns to explain N investment. He used the analogy of having a beer on a Friday night. The first beer (or unit of N) provided the greatest benefit. The benefits of happiness optimised by the 13th beer, but then tips over and those benefits become reduced with every beer thereafter. We can all relate to the messiness that follows.

The same applies to N, at some point every unit of N applied no longer increases yield by the same amount and it can also tip over and cause disaster. I am sure everyone has experienced the gamble of putting out extra N and grown more biomass but with a dry spell, resulted in losing yield.

Wayne encouraged us to scrutinise return on investment on every incremental unit of fertiliser. To do this, develop a fertiliser response curve by working out N responses (yield) from four N rate strips. This helps determine which units of N deliver acceptable returns and which ones does not. Then calculate the rate that provides the greatest return on investment on all fertiliser N units (ROI % = Profit/Cost x 100).

While we commonly think 200kg N/ha is about right, I could not help reflecting that Wayne’s optimum happiness might be reached at 13 beers, it certainly is not for me, mines a measly two. So, I cannot help think, paddocks/districts will not all be the same.

Check out Wayne Pluske’s paper at  Making N applications pay this season – efficiencies of fertiliser usage. – GRDC