Multisite potassium fertilization effects on sugarcane ratoon yield and economic return in South-Central Brazil

The rate of potassium (K) applied during sugarcane (Saccharum spp.) ratoon cycles has been reduced due to the K-supply from straw recycling, but it may be insufficient to replace the K export by the stalks and maintain soil K at adequate levels. The aim of this study was to evaluate the multisite responses of sugarcane ratoon to K fertilizer rates, and the effects on soil K content, sugarcane production parameters, K removed by stalk, and economic returns including different price scenarios. Ten field trials were conducted during two consecutive ratoon cycles in South-Central Brazil in a randomized block design with five repetitions, and the treatments consisted of seven K rates (0, 40, 80, 120, 160, 200, and 240 kg K2O ha−1) applied as potassium chloride (KCl). Measurements included biomass traits, leaf K content, stalk yield, and technological quality. At selected sites, soil K content and K accumulated in stalks were also measured. The average K content in straw ranged from 11–74 kg K ha−1 from previous cycle. Our findings indicated a significant response of sugarcane to K rates observed at six sites in the first ratoon cycle, and seven sites in the second ratoon cycle. On average, sugarcane yield showed a linear response to K rates, with the rate of 240 kg K2O ha−1 promoting yield gains by 15 and 17 Mg ha−1 in the first and second ratoon cycles compared to no fertilizer application, respectively. The K content in leaves and soil as well as sugar yield were consistently improved with K fertilizer rates. The K removed per 100 Mg of stalks ranged from 23 to 164 kg K ha−1. Increased K rates were shown to be economically feasible at KCl prices up to USD 750 Mg−1 (high price scenario), ensuring a higher net profit of USD 48 to 96 ha−1 at 240 kg K2O ha−1 compared to the usual rate (120 kg K2O ha−1) and the control, respectively. Under sugarcane ratoon cycles with the presence of straw in soils with low K, K fertilization at a relatively high rate increased yield at different sites, resulting in a positive economic return and maintaining adequate soil and leaf K levels.