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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.

The study of models for better nutrient uptake estimation can help to improve integrated fertigation management, allowing enhanced water and fertilization use efficiency. The aim of this work was the development of empirical models that permit the prediction of the phosphorus (P) nutritional needs of Dieffenbachia amoena to increase P use efficiency in a recycled system. To achieve this, P uptake was correlated to climate parameters, such as temperature (T), vapor pressure deficit, and global radiation (Rg), and to growth parameters such as leaf area index (LAI). In addition, the influence of the N form supply (NO₃ ^–-N or NH₄ ⁺-N) on P uptake was studied. The trial was carried out with Dieffenbachia amoena ‘Tropic Snow’ plants growing in a recycled system with expanded clay as substrate. The crop was placed in an INSOLE buried solar greenhouse, with the plants supplied with equal amounts of N, differing in the percentage of the N form applied: Ta (100 NO₃ ^– : 0 NH₄ ⁺), Tb (50 NO₃ ^– : 50 NH₄ ⁺) and Tc (0 NO₃ ^– : 100 NH₄ ⁺). The N form applied to Dieffenbachia amoena ‘Tropic Snow’ plants affects P and N uptake, but it does not influence K uptake. Nitrogen and P uptake rates are higher in the plants supplied with NH₄ ⁺ or NO₃ ^– + NH₄ ⁺ than in the plants provided with NO₃ ^– alone. The supply of a combination 50 NO₃ ^– : 50 NH₄ ⁺ improves P use efficiency. The study also indicates the possibility of predicting the P uptake rate and P uptake concentration using the proposed models. Phosphorus uptake can be estimated with a model dependent on the LAI in the NO₃ ^–-N treatments and on the LAI and Rg in the NH₄ ⁺-N treatments. The P uptake concentration can be calculated with the P uptake, estimated through the previous model, and the experimental water uptake. This parameter would permit the nutritive solutions design, decreasing nutrient losses in open systems.