WithTheGrain: Spring decisions to chase protein with late nitrogen application

Author: Rachael Oxborrow | Date: 07 Oct 2017

Favourable spring conditions in parts of the southern region present an opportunity to raise wheat seed protein, with late applications of nitrogen (N) having the potential to unlock premium prices.

While there is some luck involved in pushing up protein, with the right N supply and a good finish to the season, protein concentrations can be raised.

However, the first issue is to see if the crop is actually running short on N.

This is where N rich strips or indications of low N status are seen – typically with yellowing of the lower leaves.

The incentive is clear, with prime hard wheat at a minimum of 13 percent protein quoted at a premium of upwards of $30 and reaching up to $60 a tonne over APW wheat of 10.5 percent in Victoria and South Australia this month.

International Plant Nutrition Institute Australia and New Zealand regional director Dr Robert Norton says there are a number of factors for growers to take into account this spring when thinking about chasing protein with late applications of N.

These include a healthy crop with a good canopy and no major weed, disease or pest issues, indications of inadequate N supply from the soil, sufficient rain to get applied fertiliser into the root zone, and adequate soil water to finish the crop.

Dr Norton outlines a general rule of thumb for cereals where early N applications before flag emergence often produce yield increase while later applications are likely to increase grain protein.

However, this is slightly different for canola where applications even at the early flowering stage can raise the yield.

This because canola is an indeterminate growth habit and keeps producing flowers at the same time that seed fill occurs.

With these factors in mind, Dr Norton says a protein increase can result from N applications from around growth stage 39 up until growth stage 55 in cereals – but with no guarantees.

 

Late nitrogen application wheat

Late nitrogen applications in wheat can provide gains in protein and yield with the right timing.

“Gains in protein require a ‘normal’ of better finish to the season, and too much N early can result in excessive vegetative growth, the crop may hay off and a protein increase may be at the expense of grain size,” he says.

Research shows protein gains through N applications are limited to a maximum of 1.5 percent, with the efficiency of the recovery of the N applied in the grain harvested dropping after booting stage (table 1).

“The science is that protein accumulation and starch accumulation are not necessarily linked, and in general grain N (and protein) accumulation finishes earlier than starch accumulation,” Dr Norton says.

“This means if N is in abundant supply, and the season has a long cool finish, the crop can still end up with lower protein because the carbohydrate keeps filling after the grain has stopped accumulating more N.

“Best results come from tactical use of late N fertiliser to shift grain protein into a higher price grade, when yield is already maximised with adequate N supplies earlier in the season.”

Table 1: A summary of yield and protein responses to application of 50 kilograms N per hectare as urea in trials in Victorian and South Australian high-rainfall cropping zones. Source: Charlie Walker, Incitec Pivot, 2004.
Method & timing of N applicationNo. of trials% increase vs control% fert N recovery in grain
  YieldProtein 
Mid row banded at sowing1213.35.529.9
Broadcast & incorporated by sowing712.83.826.8
Topdress at 5-leaf stage418.86.245.5
Topdress at fully tillered stage718.57.244.4
Topdress at boot stage1214.610.847.2
Topdress at mid flowering 125.512.434.1

*sites include: Dookie 2000-2002, Gnarewarre 2000-2002, Naracoorte 2000, Clare 2000-2001, Woorndoo 2000, glenthompson 2001, Lake Bolac 2002.

With significant premiums for high protein, Dr Norton says late N applications present southern region growers with the opportunity to take advantage of good soil moisture conditions.

It takes around 2 kilograms of N per tonne of grain to raise protein concentration by 1 percent - if all the applied N was taken up by the crop and transferred to grain.

This is not often the case as efficiency is lower with later applications, with maybe three to four times more N required to be supplied to meet that protein increase.

To guide growers in late N application, Dr Norton advocates the 4R nutrient stewardship principles of right time, right rate, right place and right source.

This takes into account timing to make nutrients available when crops need them, rate which matches amount of fertiliser to crop needs given the likely yield and protein target, place in terms of keeping nutrients where the crop can use them and source where fertiliser type is suitable for the crop’s need.

Also assisting with decision making around N applications is a recent GRDC investment available to growers and advisers.

This investment is supporting a review of decision support tools available to determine which are the most useful for the southern region.

Existing tools for these decisions have been developed independently in different parts of Australia when legume-based pastures contributed to soil fertility and supplies of N to crops.

Most of these tools have a fixed protein target given a range of yields, and Dr Norton said late N applications to boost grain protein are still risky.

Any decision must be made with a goal of lifting grain protein into the next grade for a profit increase.

GRDC research code: UA00165

More information

Dr Robert Norton
03 5382 1673
rnorton@ipni.net

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