The effect of foliar copper application on grain yield and quality of wheat

Available Cu concentrations in prairie soils (DTPA-extractable Cu) are extremely variable, thus resulting in areas within fields that are Cu deficient. These areas are difficult to characterize by a soil test based on a composite field sample; thus, when they are identified in the growing season, foliar Cu application possibly represents the only method of correcting them. A project, carried out over a period of 8 yr that consisted of four experiments and a total of 22 trials, was designed to ascertain whether foliar Cu applications indeed provide a satisfactory means of correcting Cu deficiency. Experiments included comparison of foliar applications at Feekes growth stages 6 (first node of stem visible at base of shoot) and 6 plus 10 (sheath of last leaf completely grown out) to soil broadcast and incorporation of 4 to 5.5 kg Cu ha-1 as copper sulphate (CuSO4·5H2O) or seed placement of 2 kg Cu ha-1 in three forms (two oxysulphates and one sulphate); foliar application of a variety of products representing different chemistries (chelate, lignin sulphonate, humic acid, oxychloride and citric acid) on a number of wheat cultivars at Feekes growth stage 10 or one cultivar at Feekes growth stages 2 (beginning of tillering), 6, 10 and 2 plus 10. Foliar applications appear to provide a solution to Cu deficiency that is identified during the growing season. However, foliar applications were not always as effective as broadcast and incorporation of at least 4 kg Cu ha-1 in the form of CuSO4·5H2O, which still remains the preferred method to correct a Cu deficiency. Foliar application at Feekes growth stage 2 was ineffective, whereas a single foliar application at Feekes growth stage 10 was not as satisfactory as a single one at Feekes growth stage 6. Thus, the latter stage appears to be preferable; however, maximum grain yield in some cases was obtained by the combination of two foliar Cu applications, one each at Feekes growth stages 6 and 10. Responses of wheat to foliar Cu application were obtained on soils that contained DTPA-extractable Cu concentration of less than 0.4 mg kg-1. Foliar Cu applications did not have an appreciable effect on grain quality parameters, such as hectolitre weight, moisture or protein content.