Fertilization with Potassium in Crops Under no-tillage in Uruguay: Yield Response Based on Soil Testing

The objectives of this study were to summarize the recent information generated in the country related to the potassium fertilization and find a tentative critical level of Potassium (K) in soil for various crops in Uruguay, using the most widely used K soil test. The data come from 50 K-response experiments in barley, wheat, corn, soybeans, sorghum, and sunflower, conducted by different working groups from 2004 to 2010, in soils with different texture and exchangeable K levels. The fertilizer rates ranged from 0 to 240 kg/ha of K2O and in all cases the source of K was broadcasted KCl at planting date. Potassium fertilizer increased crop yield in 15 of 50 sites (Pr < 0.10). To determine the critical level, we included the control treatments (without K) and the average of the rates of 60 and 120 kg/ha of K2O. Across all sites and crops, the critical level of exchangeable K was 0.34 meq/100 g soil. This value should be taken as a preliminary indicator of K deficiency in soils. The results demonstrate the need for further studies of the dynamics of this nutrient in soils of Uruguay.