Nutritional solution composition in fertigation must be designed according to crop needs. These needs are variable and depend on factors like plant growth rate, environmental conditions, and water uptake. The objective of this work is to study the influence of the N-form supply (N-NO₃^– or N-NH₄⁺) on the potassium uptake and potassium concentration changes on the recycled solution and the development of empirical models that permit the prediction of the potassium nutritional needs of Dieffenbachia amoena, ‘Tropic Snow’. To achieve this, potassium uptake has been correlated to temperature, vapor pressure deficit, global radiation, and leaf area index. The plants were placed in a Buried Solar Greenhouse, the plants being supplied with equal amounts of nitrogen, differing in the percentage of the N-form applied (NO₃^–:NH₄⁺): Ta (100:0), Tb (50:50), and Tc (0:100). Seasons (winter and summer) generate important differences in the potassium concentration changes in the recycled solution but are not influenced by the nitrogen form. In winter, the potassium concentration remains constant, whereas in summer conditions, there is a higher decrease. This difference in behavior should be considered in the nutritive solution formulation. The nitrogen form applied does not affect potassium uptake. The study also indicates the possibility of predicting the potassium (K) uptake using the proposed models. K uptake can be estimated with a model dependent on the leaf area index, and potassium uptake concentration can be estimated with K uptake through the model and the experimental water uptake.