Spent coffee grounds improve the nutritional value in elements of lettuce (Lactuca sativa L.) and are an ecological alternative to inorganic fertilizers

The element concentration in lettuces grouped in 5 categories (baby variety, cultivated in agricultural soils with low or high percentages of spent coffee grounds-SCG, without SCG and with NPK) were measured. Lettuces cultivated in agricultural soils amended with SCG had significantly higher levels of several essential (V, Fe, Co, V, and probably Mn and Zn) and toxic elements (Al and probably As), without reaching their toxicological limits. Additionally, blocking of N uptake and therefore plant biomass, and probably Cd absorption from agricultural soil was observed. Organic farming with SCG ameliorates element concentrations in lettuces vs. NPK fertilization. The linear correlations among element uptake and the amendment of SCG could be related with their chelation by some SCG components, such as melanoidins and with the decrease in the soil pH. In conclusion, the addition of SCG produces lettuces with higher element content.