Effect of Foliar and Soil Application of Copper on the Level and Quality of Winter Rapeseed Yields

In Poland nearly 40% of land under agricultural use is characterised by a progressing deficit of copper available to plants. Inventory studies revealed that 25% of rapeseed plantations are undernourished with this component. The objective of the study was to estimate the yield-forming effects of foliar and soil fertilisation of rapeseed with copper, to identify the optimum dose of Cu for the crop species, and to compare the effects of the two methods of application on the quality of the seeds. The study comprised two three-year strict field experiments, in which pre-sowing fertilisation of rapeseed with copper was applied at rates of 4, 8 and 12 kg Cu⋅ha-1, as well as foliar spraying at the optimum dose of 250 Cu g⋅ha-1 in the phase of closed bud. The experiments were set up on light soils of acid and light acid reaction and with a low or medium content of available copper. Significant increases in rapeseed yields, compared to the control treatment (without Cu), were obtained in treatments fertilised to the soil with doses of 8 and 12 kg Cu⋅ha-1 and in the treatment with foliar spraying. In plants from treatments without copper fertilisation, insufficient levels of the content of this component were found. Sufficient copper nutrition of plants caused a significant increase in yields of rape seeds. In some of the treatments, there was a tendency for the copper content in seeds to increase favourably, especially in the case of foliar application and of the higher copper doses applied to the soil. Also, some cases of increased oil content in seeds were recorded, even by several percent compared to seeds from treatments without Cu fertilisation. With the existing copper deficit in soils in Poland, fertilisation of rapeseed with this component appears to be crucial.