Managing micronutrient deficiencies in cropping systems of eastern Australia

Summary:
A range of delivery strategies for Cu were evaluated at this site, and these were assessed as responses in terms of shoot dry weights, grain yield, screenings and grain protein concentration. The nutrient concentrations in the YEBs were assessed as well.

Mean site yield was low where no Cu was supplied, and there was little response to Cu supplied in dry blended fertilizers or in-furrow fluid applications at seeding. The highest yields were achieved with one or two foliar applications of 90 g/ha of Cu as sulfate. and the response was to almost triple grain yield. The Cu concentraiton in YEBs were generally in the range of 1.2 to 2.0 which is around the critical values in Reuter and Robinson, but there was no particular relationship with tissue values and yields.


During the growing season, there were very hot temperatures across much of Australia. At this trial, the hot drying conditions of the early October weekend, severely scorched all plots with no or poorly effective Cu management strategies. See picture below.


Final yields:



Messages from the trial.
• The site was severely deficient in Cu for wheat so growers in this district with similar soil types should heed the warning provided by this trial.
• Under these severely deficient conditions, soil applications of Cu were poorly effective compared to foliar sprays but fluid applications performed better than Cu enriched granular fertilisers. However, soil applications of Cu can persist for decades so we hope to re-seed this trial in 2016 to assess residual benefits of the treatments applied in 2015.
• There was no evidence that a chelated source of Cu as a foliar spray was more effective than a sulphate source and less Cu seemed to end up in the grain with the chelated source.
• A single foliar spray of Cu prior to flowering is often sufficient to protect a cereal crop from Cu deficiency but under the severe deficiency encountered in 2015, two foliar sprays were necessary to overcome the problem completely (one at first node, the second prior to flowering).
• Cu deficiency can make a crop more sensitive to adverse conditions. In this trial, the hot drying conditions of the early October weekend, severely scorched all plots with no or poorly effective Cu management strategies.
• The soil and leaf tests taken during this trial support that the current guidelines for Cu deficiency are still relevant to modern farming systems and varieties. A DTPA Cu level in soil of less than 0.3 ppm in the top 10 cm is considered deficient, and 1.3 ppm Cu in YEBS is considered very deficient for wheat.