The exchangeable potassium in soil was significantly influenced by the isolated factors Doses and Sampling time (Figures 3(a) and 3(b)). The nutrient concentration data, depending on the Doses and Sampling times, followed an increasing and decreasing linear model, respectively. The exchangeable potassium in the soil increased from
0.31 cmolc dm−3 to 1.08 cmolc dm−3 due to the application of cassava doses that were equal to 0 and 136 m3 ha−1 ,
respectively; however, we found that this nutrient decreased during the course of sunflower cultivation. At 21 and 105 days after the application of cassava wastewater (DAM), exchangeable potassium concentrations were equal to 0.88 and 0.34 cmolc dm−3 , respectively.