As featured in Arable Farming Magazine April 2021
Milling wheat N needs identified underground
by Arable Farming
Closer examination of wheat roots during the growing season should help growers
striving to achieve milling quality grain. Andrew Blake reports.
Roots, the gateway between nutrients in soil and crop, are key to understanding the latter’s needs, according to Mechteld BlakeKalff, of Hill Court Farm Research (HCFR), who is leading work on wheat samples collected during an AHDB research project*.
The project aims to give farmers a reliable diagnostic tool to help them apply nitrogen fertiliser for protein only if required.
During the past 10 years, Gloucestershire-based HCFR has developed a more accurate method of deciding whether to apply extra N to achieve milling-level protein than measuring leaf chlorophyll levels or analysing flag leaf N.
“The test accurately assesses the N status of the crop at the time of sampling and from that it’s possible to predict whether there’s enough N present to get high protein levels at harvest,” says Dr Blake-Kalff.
The test was launched commercially last year at a cost of £30 per sample.
In 2019, AHDB funded a three-year NIAB-led project on the effect of N application timings on quality in milling wheat.
In it, 40kg/hectare N was applied as solid at either GS32, GS37 or as foliar at GS73, as well as several combinations of these treatments.
“This project offered a great opportunity for HCFR to try their protein prediction test on replicated field experiments and for AHDB to gain an insight of the effect of treatments on the crop’s N status at different times through the growth season.
“HCFR funded the analysis of 600 root samples themselves in the first year and because the results were so successful AHDB agreed to provide a small amount of funding for the second and third year,” says Dr Blake-Kalff.
Signals
The latest research aims to see how well the test is predicting harvested protein and to understand how climate affects roots’ N status in the growing crop.
The work involved analysing root samples from the NIAB trials at three points in the growing season.
Sampling involves loosening the soil with a fork and then pulling out the whole plant, including the root ball.
“In the lab we remove the stems, thoroughly clean the roots and dry them in the oven.
The next day the roots are milled, weighed and extracted.
We analyse the extracts for signals involved with regulating the roots’ N uptake.
This gives us the crop’s N status at the time of sampling, from which we can forecast the protein levels.
“The surprise has been how varied the roots’ structures are from different fields.
Some are really thin and spindly,” says Dr Blake-Kalff.
“We always think the quantity of N applied is the main driver for crop growth but if you haven’t got a good root structure it doesn’t matter how much N is in the soil as the crop will have difficulty taking it up.
“Seeing those roots has made me think a lot more about how important it is to focus not just on application rates, but also on soil structure, compaction, climate change and all the other factors that can prevent efficient nutrient uptake.” The results in 2019 showed the test could accurately predict the effect of the treatments within 0.5%.
“For example, it predicted that in the variety Zyatt, adding 40kg N/ha at GS32 or GS37 would both increase protein levels by 0.5% compared to not adding any extra N, but that there wouldn’t be any difference between application timings.
That was exactly what we found at harvest.
“It also suggested that in Skyfall, adding 40kg N/ha at GS37 would increase protein levels slightly but significantly compared to adding N at GS32.
Again, this was borne out by the protein results at harvest.” The test showed that none of the treatments would achieve protein levels above 12.5%, the harvested average being about 12%, she adds.
Sampling
“Last year, N uptake was really hampered in the south east of the country by lack of rain at the critical time between April and May.
Although the test accurately assessed the low N status at the time of sampling, this wasn’t due to lack of N but to moisture shortage.
“N was present in the soil but couldn’t be taken up.
Once rainfall increased in June, a lot of N was still taken up and converted into protein.
“By contrast, the Scottish samples showed that plenty of N was taken up by the crop and this was reflected in the much higher protein levels at harvest.”
New root test a ‘promising’ tool
Combined with an N-Min test, the new HCFR test promises to help milling wheat growers use nitrogen fertiliser more efficiently, according to Sajjad Awan, company agronomist at CF Fertilisers.
He says: “If we could accurately predict grain protein at or around growth stage 37 [early to mid-May] when yield can also be predicted, we’d be well placed to manage N fertiliser applications to improve the way the crop uses that nutrient.” Modern wheat varieties such as Skyfall have high yield potential, he adds.
“But high yield usually dilutes grain protein, so it can be difficult to achieve both yield and good grain protein content.
Balance
“There needs to be the right balance. Too much applied nitrogen could see some being lost to the environment, but too little can result in loss of quality premium.
“We had pretty dry springs in 2019 and 2020, but the root test results from those two years have predicted a strong correlation between protein concentration in the roots at the time of sampling [GS37] and grains at harvest, suggesting the method is practically sound.” Soil sampling to account for soil mineral N, along with estimates of additionally available N which can be achieved with CF’s N-Min test, will remain key to determining milling crop needs, says Dr Awan.
“And as with soil sampling, it will be crucial for the roots to be removed carefully and as many as possible taken out at an appropriate depth.
“But compared with the cost of this test, the cost of missing milling specification could be much higher.”
