Adubação corretiva de potássio em solos da região noroeste do Rio Grande do Sul

Abstract

Potassium fertilization is crucial to raise potassium (K) levels in soils that have values below the critical level. The corrective doses for K levels can vary depending on soil characteristics such as Cation Exchange Capacity (CTC) and texture. The current recommended doses consider the same buffering power of potassium regardless of the variation in soil CTCpH7.0. This study aims to determine the necessary potassium doses to increase potassium levels to the critical level in soils in the Northwest region of the State of Rio Grande do Sul and provide insights for adjusting corrective recommendations. Thirty soils with potassium levels below the critical level from 16 municipalities within the Northwest region of the state were analyzed. Samples were incubated for a period of 20 days with 6 doses of K2O (0, 30, 60, 120, 180, 360 kg ha-1) with 3 repetitions. Potassium content extracted by Mehlich 1 was evaluated after incubation and related to the K2O doses used, obtaining the soil's potassium buffering capacity (PTK). From the PTK, it was possible to estimate the K correction dose. In the 30 soil samples analyzed, potassium content increased linearly after applying corrective doses. PTK correlated positively with CTCpH7.0 but negatively with clay content; thus, higher clay levels in the soil resulted in lower PTK. Soils with CTCpH7.0 between 7.6 to 15 cmolc dm-3 showed no variation concerning CTC. Soils with CTCpH7.0 from 15.1 to 30 cmolc dm-3 exhibited a linear behavior regarding PTK. The potassium doses required to increase potassium levels to the critical level in soils from the Northwest region of the State of Rio Grande do Sul with CTCpH7.0 7.6 to 15 cmolc dm-3 are 74, 108, and 39%, and for CTCpH7.0 15.1 to 30 cmolc dm-3 are 164, 217, and 111% (for the average CTC within the range), being higher than the recommended doses for soils with very low, low, and medium levels respectively recommended for the region by CQFS-RS/SC (2016).