Potassium retention and leaching in an organic crop rotation on loamy sand as affected by contrasting potassium budgets

Summary

. In organic farming, potassium (K) deficiency may become a significant problem due to import restrictions. Knowledge about potential K leaching in systems with different K budgets is therefore important for effective agricultural management. We investigated the effect of four organic farming systems (two livestock densities in combination with two types of organic manure) on crop yields, K leaching and K balances in a six course crop rotation from 1993/94 to 1997/98. Average K concentrations in soil water extracted by means of ceramic suction cups at 1 m depth were 0.6 mg K l-1 corresponding to a K leaching loss of 1.5 kg ha-1 yr-1,which was less than expected from values reported in the literature. Variation in K budgets from –12 to +30 kg ha-1 yr-1 did not affect K leaching. In an additional experiment with application of 988 kg K ha-1 as KCl, K leaching accounted for only 0.2% of the applied K although 40% of the accompanying Cl was leached. The main part of the applied K was retained in the topsoil. It was concluded that K leaching was a result of the fertiliser history rather than of the current K budget.