Ways to improve nitrogen efficacy

HOW many of us have heard the terms "nitrogen use transfer" or "nitrogen use efficacy"?

When doing a nitrogen budget for your wheat or barley crop, most accredited advisors can perform this integral part of your crop agronomy.

Having a recent soil test profile can give us residual levels of nitrogen (N) in mg/kg and from these numbers, we can work out the amount of the available residual N your plants will have in the next crop. Then throw in some usually over-estimated mineralisation figures of N release in-crop for a bonus in your N budget.

We also know how much nitrate nitrogen it takes to grow the next crop - and these figures really do scare some farmers by the impending cost structure at pre-plant time. For example, it can take more than 150kg/ha of N from somewhere - be it bag or residual in soil - to grow a four tonnes/hectare crop at 12% protein in barley.

Wheat, with a slightly higher protein factor, needs about 10% more N for similar yields and protein. I refer most definitely to growing a crop and not just paddock grain removal, which is a much lower figure.

Some have even applied urea by using an interrow disc between their 14-inch wheat rows, so the rainfall need is negated or reduced.

Work in a current price of urea at more than $600 a tonne and you can see why fellow farmers do struggle to apply even half of this amount of 75kg/ha of N, which is about 160kg/ha of urea. Factor in the cost and you have a fertiliser bill of more than $90/ha before you even start, for just this reduced rate. Unfortunately, cereal plants have a habit of releasing N from their tissues around flowering time, so as well as leaving N in your roots, stems and leaves, many of our varieties are just plain inefficient with your expensive N.

The N in these remaining plant parts will not go to waste, as these elements will be mineralised out in the future fallow months for the next crop. But due to all this inefficiency going on in this plant, we have made many calculations and finally make conclusions that our barley and wheat plants' "nitrogen use transfer" for pre-plant N can range from 35-55% efficacy, from pre-plant to eventual grain yield.

Of course, increasing your pre-plant N can just raise the inefficiency levels if going into a dryish soil profile condition. And, probably more importantly, this is compounded by other nutrient deficiencies, climate factors, soil compaction and leaf disease issues. So, what can be done - apart from breeding plants that are more frugal in their N demands?

For many years, I have pushed for an in-crop application of N. I can hear the sharp intake of breath now at this "silly" suggestion of trying to apply N into a crop of wheat.

Well, it has been done with solid products like urea and granam with an over-the-top broadcast at the critical stage around flowering, if trying mostly to bump up the protein.

Yes, an inch of rain or overhead irrigation needs to occur within a week of applying said fertiliser to solubilise and provide soil entry and root absorption of the N product.

This in-crop application can also include our options in the liquid N products, which can be dribble barred into a cereal crop or even mixed with water and used as a foliar spray on plant leaves.

More attuned to a row crop situation in summer, some have even applied urea by using an interrow disc between their 14-inch wheat rows, so the rainfall need is negated or reduced.

I will say being able to apply a level of N in these later stages of growth is very effective for the cereal plants' desire to grow and can have the double effect of yield and protein increase. The later application of N provides a higher level of efficacy - up to 80%, some researchers have reported.

So the plant likes it, your chequebook likes it - what can go wrong? Well, the biggest issues are the application method and time taken, plus achieving some rain as a follow-up with on-top application sites. But the farmer-driven solutions I have seen are many and varied.

Our nutrition stakes are critically important and if we can alter our fertiliser application methods without lifting our costs, then at least we need to consider it and even try it on our own paddocks.

We have so many yield-reducing issues - crown rot, nematodes and leaf diseases - we need some ups in yield to offset these downers.

Paul McIntosh is a former manager of Landmark Emerald, now based on the Darling Downs.

Topics:  fertiliser paul mcintosh

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