Phosphorus and potassium fertilization in no till southern Brazilian soils

Abstract

Phosphorus (P) and potassium (K) levels in southern Brazilian (Rio Grande do Sul, RS) soils are largely below the critical concentrations more than four decades after implementation of the officially recommended system. This study aims to evaluate the increase in P and K levels in 0-10 and 0-20 cm deep samples from no-till soils using the Mehlich-1 (M1) and Mehlich-3 (M3) extractants as well as resin methods and to estimate the amount of P 2 O 5 and K 2 O fertilizers necessary to increase the P and K soil levels by 1 mg · kg -1 . The study was conducted in fields cultivated using a no-till system (direct planting) to grow soybeans, wheat, maize, pasture, and cover crops and fertilized with P 2 O 5 and K 2 O. Soil samples were collected from the 0-10 and 0-20 cm soil layers and analyzed by the M1, M3, and resin methods. The results demonstrated that the P and K levels increased in the 0-10 and 0-20 cm layers. However, the amount of these levels increased depending on the source of phosphate fertilization and on the P and K extraction methods used. The amount of P 2 O 5 fertilization needed to raise the P level by 1 mg · kg -1 was greater in the 0-20 cm layer than in the 0-10 cm layer, and the amount of K 2 O fertilization needed to raise the K level by 1 mg · kg -1 was higher in the 0-10 cm layer than in the 0-20 cm layer.