Optimising durum wheat yield and quality

Abstract

Durum wheat (Triticum durum) produced in New Zealand is often of inconsistent yield and quality, where quality is specific to its utilisation in the pasta industry. Quality parameters include protein content and falling number of grain and flour, and flour and pasta colour. In this study, colour of grain, flour and pasta was quantified using the CIELAB colour space. High quality durum grain and flour was defined as that with high (>11.5%) protein content, high (>250 s) falling number and high (>18) b* value. The main research objective was to determine if the two management options available to growers, namely nitrogen (N) management and cultivar selection, could be used to produce high yielding crops with the desired quality characteristics including acceptable flour and pasta yellowness.

To do this the effects of different N fertiliser treatments on the yield and quality of 'CRDW17' and 'Waitohi' durum wheat were examined. Grain was produced from field experiments established at Darfield, Lincoln and Wakanui with a total of six N treatments applied early (tillering) and late (flag leaf emergence) during crop development.

At the dryland Darfield site, grain yield increased from 3.5 to 5.5 t/ha following 150 kg N/ha applied at tillering compared with increases from 4.5 to 7.0 t/ha at the irrigated Lincoln site after 175 kg N/ha. At Wakanui, early N did not increase yield due to 236 kg N/ha of available soil N at sowing.

Grain and flour protein percent were increased by both early and late N fertiliser. At all sites, crops which received early N achieved the industry standard of 11.5% for grain protein content. 'Waitohi' consistently had a protein content about 1% higher than 'CRDW17' across all N treatments, and the mean falling number value for 'Waitohi' was 20 to 90 s higher than for 'CRDW17'.

Grain b* value, or yellowness, was decreased by at least 1 unit when only early N was applied, and 'Waitohi' had a higher mean b* value than 'CRDW17' at all sites. In contrast, flour b* values for 'CRDW17' were increased by at least 1 unit at the three sites by early N application, leading to a negative correlation between grain and flour b* values. 'CRDW17' had a mean flour b* value at least one unit higher than 'Waitohi' at all sites and mean pasta b* values were higher for 'CRDW17' (27) than 'Waitohi' (24) at Darfield. The flour b* values were positively correlated with carotenoid concentration.

Optimal yield and required protein content can be consistently achieved by applying an appropriate amount of N fertiliser early in crop growth. In addition, early N application was not detrimental to flour and pasta b* values, and may increase yellowness. A definite method of increasing flour and pasta yellowness is to grow crops of 'CRDW17' rather than 'Waitohi'. However, industry should also consider the other poorer attributes of 'CRDW17' for improvement through plant breeding. A compromise between colour and other quality attributes such as grain soundness, grain protein content and flour rheological properties all of which were superior for 'Waitohi', may be necessary to compensate growers for using 'CRDW17'.