Development of tuberous roots and yield of cassava in response to potassium topdressing rates in Northwestern Paraná, Brazil

Potassium fertilization is essential for cassava cultivation, especially in sandy soils with low nutrient availability. This study aimed to evaluate the growth, development, and yield of cassava in response to increasing rates of potassium chloride (60% K2O), as well as to assess the feasibility of applying higher rates. The experiment was carried out in a randomized block design with four replications and five treatments: T1 - no potassium fertilization; T2 - 200 kg ha-1 of KCl applied 45 days after planting; T3 - 200 kg ha-1 of KCl at 45 days plus 200 kg ha-1 at 90 days after planting; T4 - 267 kg ha-1 of KCl at 45 days; and T5 - 267 kg ha-1 of KCl at 45 days plus 267 kg ha-1 at 90 days after planting. Five plants were harvested per plot to determine the number and mass (kg) of tuberous roots, allowing estimation of the total number of roots per hectare and yield (kg ha-1). From each harvested plant, one root was randomly selected for measuring length (cm) and diameter (cm). Starch content (g kg-1) was determined using the hydrostatic balance method. No significant differences among treatments were observed for root length, diameter, or starch content. However, treatments with 200 kg ha-1 of KCl (T2 and T3) showed higher root numbers per hectare and yield compared with the others. The management with doubled potassium rates was not economically feasible, since the productivity gain did not offset the increased fertilizer cost.