?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.title=Exchangeable+potassium+in+soil+as+indicator+of+potassium+status+in+an+organic+crop+rotation+on+loamy+sand.++&rft.creator=Askegaard%2C+Margrethe&rft.creator=Eriksen%2C+J%C3%83%C2%B8rgen&rft.subject=+Farming+Systems&rft.description=In+organic+agriculture%2C+where+K+may+be+a+limited+resource%2C+reliable+tools+are+important+in+the+assessment+of+K+availability+in+the+soil+in+order+to+avoid+K+deficiency.++We+investigated+the+effect+of+four+organic+farming+systems+on+the+exchangeable+K+in+the+plough+layer+of+a+six-course+crop+rotation+from+1994+to+1997.+The+accumulated+K+balances+over+the+four+years+varied+between+%0D%0A-49+and++%2B120+kg+K+ha-1+and+the+corresponding+exchangeable+K+(0-20+cm)+in+autumn+1997+was+7.1+and+9.6+mg+K+100+g+soil-1%2C+respectively%2C+as+an+average+of+the+crop+rotation.+The+exchangeable+K+fraction+responded+to+the+K+application+in+manure+and+to+the+crop+in+the+rotation.+In+an+additional+experiment%2C+no+yield+response+to+K+was+found%2C+despite+a+low+level+of+exchangeable+K.+The+exchangeable+K+was+a+useful+indicator+of+changes+in+the+K+status+in+the+farming+system+with+the+largest+positive+K+balance+whereas+this+K+fraction+was+insufficient+as+an+indicator+in+the+other+three+farming+systems.+The+considerable+variation+of+exchangeable+K+through+the+crop+rotation+makes+the+soil+test+method+most+suitable+at+the+crop+rotation+level+where+fluctuations+caused+by+crop+and+management+are+smoothed+out.%0D%0A&rft.date=2002&rft.type=Journal+paper&rft.type=NonPeerReviewed&rft.format=application%2Fpdf&rft.identifier=http%3A%2F%2Forgprints.org%2F391%2F1%2FAE2002.pdf&rft.identifier=Askegaard%2C+Margrethe+and+Eriksen%2C+J%C3%83%C2%B8rgen+(2002)+Exchangeable+potassium+in+soil+as+indicator+of+potassium+status+in+an+organic+crop+rotation+on+loamy+sand.+Soil+Use+and+Management%2C+18%2C+pp.+84-90.&rft.relation=http%3A%2F%2Forgprints.org%2F391%2F