Effects of iron, manganese and zinc enriched coffee and tea wastes on lettuce – a field trial

Abstract

Ensuring proper microelement supply under alkaline soil conditions could be a challenge even with the application of synthetic chelates. In this study, the application of coffee and tea wastes enriched with water soluble inorganic iron, manganese and zinc compounds was compared to water solution application of the same compounds at the same amount on a field with an alkaline Calcaric Arenosol. One butterhead and two iceberg lettuce cultivars were used as test plants. The effects of microelement enriched wastes on microelement availability in the soil, measured by DTPA-TEA method, was not clear-cut. However, the soil application of those microelement enriched wastes increased the nutritional value of lettuce by resulting in significantly higher concentration in cores for all the three investigated microelements. The highest rate of increase was observed for iron. As a consequence, lettuce heads accumulated significantly higher amount of iron, while this was not the case for manganese and zinc. There were comprehensive differences in the microelement concentration of the cores of the three investigated cultivars, with the butterhead type having especially high iron concentration. Head weights were not affected by the treatments. Hence, under the field conditions of this study, higher microelement concentration and uptake in the lettuce heads was not a prerequisite for good lettuce yield, as it was proved by the results of a zero control. However, the soil application of microelement enriched coffee and tea wastes for supplying microelements for lettuce in alkaline soil proved to be promising, especially for iron.