Phosphorus and potassium stratification in conservation tillage systems

Distribution patterns of phosphorus (P) and potassium (K) in soils under long-term conservation tillage systems were determined by intensive, quantitative sampling of the upper 25-cm (10-inch) soil layer and subsequent laboratory analysis for available P and available K. Results of the study show that pronounced vertical stratification of P and K occurred in the ridge till-plant, ridge slot-plant, and flat no-till systems studied. Available P and K values for the upper 5-cm (2-inch) soil layer were, on the average, 3.5 times greater than those for the 5- to 15-cm (2- to 6-inch) soil layer. In the ridge till-plant and ridge slot-plant systems, localized and high concentrations of P and K frequently were observed in the interrow zones. No marked row-interrow differences in soil P and K were detected in the flat no-till system. On the basis of nutrient distribution patterns observed in this study, yield-limiting problems potentially could develop in ridge till-plant, ridge slot-plant, and flat no-till systems due to positional unavailability of nutrients.