In the last three years, we have developed over 100 compounds (JXB - Nisler et al., 2021; 2022, 2023 - submitted) which block the degradation of cytokinins in plants by inhibiting Cytokinin oxidase/dehydrogenase (CK😆. The compounds, called CKX-inhibitors, are derived from diphenylurea. The key compounds of the library are perfect candidates for use in agriculture when their cost of production, dose per hectare and predicted eco-toxicity are considered. Winter wheat and oil seed rape treated by key CKX inhibitors in low micromolar concentrations exhibited surprisingly fast growth and development of shoots and roots, resulting in more than doubled weight of these parts. The same results were obtained when these two species were grown with a half dose of nitrogen fertilizer, which clearly points to higher nutrient use efficiency by treated plants. It is of particular importance that CKX inhibitors caused greater root branching and overall root growth, which is in contradiction with current knowledge about the effect of cytokinins on root development. This issue, the development of the key compounds, their effect on the amino acid composition of one leguminous species and their effect on the yield of field-grown spring barley, winter wheat and winter oilseed rape will be presented.