An obligation on malting barley growers to deliver 25% to 30% of their malting barley at a distilling specification of under 8.8% protein would be challenging. Such an obligation would be eased considerably if the maximum threshold was raised towards 9.3%. The challenge of meeting the lower spec will be significant and costly for growers.

Nitrogen fertilisation and the targeting of low protein for distilling was one of the presentations at the Teagasc malting barley conference last week. Dr Richie Hackett from Teagasc outlined the massive variability that occurs, both in terms of grain yield response and protein content, to applied nitrogen on different sites and in different seasons. Protein content is actually the nitrogen content of the grain multiplied by a fixed multiplier, which is 6.25 for barley.

Richie introduced a less common measure of nitrogen description – protein yield. This is the grain yield multiplied by the percentage protein in the grain. Richie said that this measurement is highly correlated with the level of applied nitrogen.

However, the problem is that protein yield can be generated by low grain yield with high protein content or low protein content and high grain yield. The problem facing growers is that both of these are much less controllable on their own. Basically, if one can squeeze more starch into the grains, this extra yield will dilute the protein level already present in the grain.

The relationship between nitrogen application rate, grain yield and protein content is very complex. At low N rates, grain yield is very responsive. This uses up the majority of the available N and protein content remains relatively flat. As N rate increases, further grain yield responsiveness tapers off, either a little or a lot, and grain protein level shows much more response. Indeed, at very low nitrogen availability, grain protein level actually falls for a period as the plant tissues consume all available nitrogen to feed its growth.

Factors affecting protein

An additional challenge is to be able to predict the supply of nitrogen to the growing crop as this comes from both applied N and also from the soil, either from organic N or from mineralisation. Richie said that the combination of all these factors makes it extremely difficult to say with certainty what level of nitrogen rate reduction would be necessary to ensure that crops produce a protein level below a given threshold.

This is largely due to the dilution effect which grain yield can have on protein yield. As yield is increased through prolonged grain fill, the protein in the grain is diluted. This is traditionally given as the reason why high proteins are difficult to achieve for milling wheat.

Sites that used organic manures frequently had higher protein levels. A low phosphorus (P) site gave increased protein and increased yield when P was applied. However, continuously increasing the amount of P applied eventually resulted in a drop in protein content.

Richie reported no real effect on protein percentage from the use of sulphur. Use of non-leguminous catch crops had no predictable effect either. Disease control sometimes resulted in higher protein and sometimes the opposite, as increased grain yield diluted the protein. But, on balance, Richie said that there was no single silver bullet that could be employed to deliver low grain proteins.

Targeting protein

Richie emphasised that it is very difficult to predict a nitrogen rate to produce low protein. Over a series of trials, he reported that an application rate of 150kg N/ha produced grain protein levels from 7.7% to 12%. A series of trials that looked at nitrogen rates from zero to 240kg N/ha found very little effect of N timing on protein or yield, but late N increased protein slightly. The major protein effect came from extra nitrogen, but some of these were still below 8%.

From these results, he indicated that the chance of getting low protein was greatest when the nitrogen rate was below 90kg/ha. This would imply a grain yield reduction, but, again, there are no certainties due the site and year effect.

Average historical response to nitrogen is perhaps the best indicator of likely response, Richie suggested. In this regard, he indicated that, on average, protein increased by 0.2% for every additional 10kg/ha of applied nitrogen. But the starting level depends on the site. Some of the results from these 22 trial sites are shown in Table 1.

Using the results of these trials, Richie did an exercise which assumed that protein content was the only criterion on which grain would be accepted, or not, for distilling. He worked on the basis of squeezing in just under 8.8% protein and took three scenarios.

The first was to attempt to get as much grain as possible below 8.8% protein by reducing N rate to 120kg N/ha. The second scenario was to go for yield with 175kg N/ha and see how much made distilling grade. The third option was to just go for yield and feed. Results from the different scenarios are shown in Table 2.

While this does not and cannot indicate what level of premium might be required to safeguard grower income, it must be noted that this is targeting an 8.8% protein level. If a grower was obliged to get a proportion of grain into this category, he or she would have to target around 8% in the hope of getting most of the required area to qualify.

From what Richie said, this would mean cutting a further 40kg N/ha off the N rate and this would seriously hurt yield potential.

A big challenge

An obligation on growers to deliver a minimum proportion of their grain below 8.8% protein would be a serious challenge.

Anyone attempting to achieve this would be advised to target fields that had a history of producing low protein levels and especially fields that do this with high grain yields. This will inevitably mean a well-worn field with good fertility. Then drill as early as possible and ensure that all other fertility aspects are up to scratch.

After that, it’s about good crop protection to ensure that every grain is filled to its maximum to help dilute protein level. And, based on the results currently available, it looks like one should target around 120kg N/ha.

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