info:oai:orgprints.org:392info:ofi/fmt:xml:xsd:oai_dc Exchangeable potassium and potassium balances in organic crop rotations on a coarse sand Askegaard, Margrethe Eriksen, Jørgen Olesen, Jørgen E. Farming Systems Crops on sandy soils (<5% clay) are exposed to K deficiency due to the small release and high leaching losses of K. Reliable tools are needed to improve the K management in cropping systems with limited K input, such as organic farming where import of nutrients are restricted according to the EC regulations. We investigated K balances and exchangeable K (Kexch) changes in an organic crop rotation experiment. Potassium leaching decreased from 42 kg ha-1 in 1998/99 to 21 kg ha-1 in 2000/01 as an average of a crop rotation (spring barley, grass-clover, winter wheat and pea/barley) with manure application and without catch crops. In the same period, spring Kexch decreased from 5.0 to 3.0 mg K 100 g-1 soil (0-20 cm). The retention of the straw K left in the field after harvest increased with decreasing levels of Kexch. The cereal crops did not respond to K application but in the pea/barley mixture the pea yield increased by 46%. The concordance between measured K balances and changes in Kexch was weak. Exchangeable K is suitable as a tool for K management on a crop rotational basis, and a Kexch above 3 mg 100 g-1 soil in the autumn should be avoided to minimize K leaching. 2003 Journal paper NonPeerReviewed application/pdf http://orgprints.org/392/1/AEO2003.pdf Askegaard, Margrethe; Eriksen, Jørgen and Olesen, Jørgen E. (2003) Exchangeable potassium and potassium balances in organic crop rotations on a coarse sand. Soil Use and Management (19), pp. 96-113. http://orgprints.org/392/