Nutrient Dynamics in a Highly-Weathered Soil Under Long-Term No-till System.

The nutrient dynamics in soils is affected by cropping systems, soil properties and environmental conditions. The repeated use of phosphorus (P) and potassium (K) fertilizers can significantly increase P and K contents in the soil leading to potential environmental impacts; therefore, their uses need to be evaluated and improved. The objectives of this study were to evaluate the effects of a long-term no-till (NT) system and continuously fertilization on P and K availability, plant uptake, and the yields of two soybean cultivars (cv) grown in an Oxisol in Brazil. The treatments included a control and four rates of P (0, 50, 95 and 110 kg ha^-1 of P₂O₅) and the same rate of K₂O (50 kg ha^-1), and K (0, 50, 90 and 130 kg ha^-1 of K₂O) and the same rate of P₂O₅ (50 kg ha^-1) with four replicates in a randomized block design. Soil available P and K were extracted by both Mehlich-1 and exchange resin. Nutrient contents in soybean tissues and soybean yields were also determined. Exchange resin extractable P and K were highly correlated with those of Mehlich-1. Phosphorus and K contents in soybean trifolium increased as the rates of both P and K application increased and were correlated with soybean yields. Soil test for plant available nutrients is important to guide annual fertilization and to ensure optimum crop yields.