The early prediction of breadmaking quality of grain and its improvement through targeted late application of nitrogen fertilisers

Abstract

Grain protein content is important in terms of the market value of the crop, particularly for wheat breadmaking quality, and prediction systems based on this parameter have had varying success. A specific fraction of the grain proteins, known as the high molecular weight glutenin subunits (HMW-G), is believed to be influential in breadmaking quality. A previous study of samples of Hereward grown at one site during a single season had suggested that these components could be exploited as predictive markers for monitoring the crop and applying targeted fertiliser as late foliar urea. This three-year study aimed to:

1. validate and extend these preliminary results by examining additional varieties grown at several sites and over several seasons,

2. develop a simple and reliable test based on the HMW-G protein fraction, or a suitable alternative, which could be used to monitor the crop and predict the final quality in breadmaking wheat.

Growing trials were conducted by Levington Agriculture over three seasons. These involved several sites, selected breadmaking varieties, and a range of ammonium nitrate and late foliar urea treatments. Developing grains were sampled at growth stage (GS) 75, and analysed for HMW-G levels by gel electrophoretic methods, protein content and in later years by scanning near infrared (NIR) reflectance spectroscopy. Harvest samples were subject to the same analyses, in addition to a series of flour quality tests and performance in standard breadmaking processes.

In Year 1 trials, six varieties were grown with a basic fertiliser treatment of 200 kg N/ha of ammonium nitrate with or without the application of 40 kg N/ha of late foliar urea at GS 60 at five sites. With the exception of a minor effect on protein content, quality test results, breadmaking performance and HMW-G measurements generally proved to be inconclusive.

The Year 2 trials featured Hereward and Rialto, grown at four sites, and treated with 0, 150 and 200 kg N/ha applied as ammonium nitrate, plus 0, 25, 50 and 75 kg N/ha applied as foliar urea at GS 65.

In Year 3, Hereward was grown at two sites and Caxton grown at two other sites. Ammonium nitrate application ranged between 120 - 240 kg N/ha, plus a control of 0 kg N/ha. Foliar urea was added at levels of 20 and 40 kg N/ha to a set of plots receiving 160 and 200 kg N/ha of ammonium nitrate. The main conclusions from these trials were:

In most cases the optimal loaf volumes were achieved with the addition of 20-50 kg N/ha of late foliar urea and 150 kg N/ha of ammonium nitrate.
Site and variety significantly influenced HMW-G levels. HMW-G levels may be unsuitable as quantitative markers of breadmaking quality as there was no consistent relationship between HMW-G and protein content or loaf volume.
While the addition of both types of fertiliser influenced the protein content significantly, their effects on other measures of quality were less consistent.
The protein content of the harvested grain could be predicted well from the NIR spectral data of the immature grain at GS 75, a growth stage at which late-applied foliar urea can be effective in improving wheat quality.
Conclusions and Implications

This study has demonstrated that:

The non-destructive NIR technique can be applied to predict the final level of grain protein rapidly from measurements of immature grain samples, irrespective of variety.
NIR could become a reliable and a cost-effective tool to assist the grower in early decision making for effective crop management, which would be beneficial both economically and environmentally.
Recent developments in NIR technology offer the prospect of portable instruments suitable for field-testing being commercially available in the near future