Potassium losses in runoff from cotton production fields

Potassium (K) loss in runoff represents a potential financial concern since fertilizer-K is routinely applied to sustain optimal crop K nutrition and yield potential. Our research objectives were to quantify and characterize the soluble-K loss in runoff from fields used for continuous cotton (Gossypium hirsutum L.) production while determining if the time of the year (growing season vs. nongrowing season), type of hydrological event (irrigation vs. rainfall), and cover crops influence K loss in runoff. Field-scale, edge-of-field monitoring of runoff water and its soluble-K concentration was performed on 10 site years in southeastern Arkansas across three production seasons. The mean K loss in surface runoff per event was 0.98 kg ha(-1) across all sites and events (n = 304). The relationship between loss of K mass to runoff volume was positive and significantly correlated (p < 0.0001) when both variables were transformed by the natural logarithm. K loss during the growing season was significantly higher (p < 0.001) in the cotton growing season whereas K loss resulting from runoff events generated by either irrigation or rainfall was not significant. Additionally, losses from fields with cover crops were significantly larger (p < -0.05) than from fields without covers. Cumulative annual-K loss, between annual fertilizer-K applications, averaged 32.2 kg K ha(-1) across all site years representing a significant economic loss to replace the lost K with fertilizer. This study illustrates the increased risk of K losses on poorly drained soils in the Southeastern United States. Runoff-K loss represents a significant amount of K that requires additional research on how to mitigate these losses.