?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.title=Exchangeable+potassium+and+potassium+balances+in+organic+crop+rotations+on+a+coarse+sand&rft.creator=Askegaard%2C+Margrethe&rft.creator=Eriksen%2C+J%C3%83%C2%B8rgen&rft.creator=Olesen%2C+J%C3%83%C2%B8rgen+E.&rft.subject=+Farming+Systems&rft.description=Crops+on+sandy+soils+(%3C5%25+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%2C+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%2F99+to+21+kg+ha-1+in+2000%2F01+as+an+average+of+a+crop+rotation+(spring+barley%2C+grass-clover%2C+winter+wheat+and+pea%2Fbarley)+with+manure+application+and+without+catch+crops.+In+the+same+period%2C+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%2Fbarley+mixture+the+pea+yield+increased+by+46%25.+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%2C+and+a+Kexch+above+3+mg+100+g-1+soil+in+the+autumn+should+be+avoided+to+minimize+K+leaching.&rft.date=2003&rft.type=Journal+paper&rft.type=NonPeerReviewed&rft.format=application%2Fpdf&rft.identifier=http%3A%2F%2Forgprints.org%2F392%2F1%2FAEO2003.pdf&rft.identifier=Askegaard%2C+Margrethe%3B+Eriksen%2C+J%C3%83%C2%B8rgen+and+Olesen%2C+J%C3%83%C2%B8rgen+E.+(2003)+Exchangeable+potassium+and+potassium+balances+in+organic+crop+rotations+on+a+coarse+sand.+Soil+Use+and+Management+(19)%2C+pp.+96-113.&rft.relation=http%3A%2F%2Forgprints.org%2F392%2F