?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.relation=https%3A%2F%2Forgprints.org%2Fid%2Feprint%2F172%2F&rft.title=Spatial+variability+of+symbiotic+N2+fixation+in+grass-white+clover+pastures+estimated+by+the+15N+isotope+dilution+method+and+the+natural+15N+abundance+method&rft.creator=Hansen%2C+Jacob+P.&rft.creator=Vinther%2C+Finn+P.&rft.subject=+Nutrient+turnover&rft.subject=+Soil+quality&rft.subject=+Soil+biology&rft.subject=+Pasture+and+forage+crops&rft.description=Aiming+at+estimating+the+spatial+variability+in+N2+fixation%2C+and+to+evaluate+the+appropriateness+of+the+15N+isotope+dilution+(ID)+method+and+the+natural+15N+abundance+(NA)+method+in+reflecting+spatial+variability+under+the+influence+of+cattle+grazing%2C+the+symbiotic+N2+fixation+in+grass-white+clover+mixture+was+studied.+At+the+Foulum+site%2C+where+the+ID+method+was+used%2C+differences+in+the+climatic+conditions+between+the+two+years+of+investigations+caused+a+considerable+difference+in+plant+growth+rates+and+proportion+of+clover.+Consequently%2C+the+total+N2+fixation+in+ungrazed+reference+plots+was+significantly+less+in+1998+than+in+1997%2C+being+5.9+and+12.5+g+N+m-2%2C+respectively.+In+both+years+there+was+a+wide+range+in+concentration+of+inorganic+N+in+the+soil+with+coefficients+of+variance+of+approximately+60+%E2%80%93+190%25+for+ammonium+and+70+%E2%80%93+340%25+for+nitrate.+Significant+negative+correlations+between+pNdfa%2C+determined+by+the+ID+method%2C+and+the+log-transformed+values+of+inorganic+N+and+total+N+in+grass+were+found.+The+NA+method+was+applied+on+3+nearby+commercial+dairy+farms.+They+also+showed+high+coefficients+of+variation.+The+coefficient+of+variance+for+NO3--N+ranged+from+37%25+to+282%25+and+for+NH4%2B-N+from+29%25+to+237%25.+Average+estimates+of+pNdfa+values%2C+which+in+the+NA+method+were+calculated+using+apparent+B+values+ranging+from+%E2%80%932.10+to+%E2%80%932.59%E2%80%B0%2C+were+generally+lower+(0.7+%E2%80%93+0.87)+for+these+farms+than+for+the+Foulum+site+(0.89+%E2%80%93+0.95)+using+the+ID+method.+For+the+NA+method+the+d15N+values%2C+i.e.+deviation+in+15N+concentration+from+atmospheric+N2%2C+ranged+from+-7.0+to+5.7%E2%80%B0+for+the+grass+N%2C+which+in+several+cases+was+lower+than+for+clover+N.+Due+to+this+high+variability+of+the+d15N+values%2C+probably+caused+by+deposition+and+plant+assimilation+of+15N+depleted+urinary+N+in+the+pastures%2C+the+NA+method+was+marginal+for+accurate+determination+of+pNdfa.+Consequently+no+significant+correlation+between+the+pNdfa+determined+by+this+method%2C+and+the+log-transformed+values+of+inorganic+N+in+soil+or+total+N+in+grass+were+found.++&rft.date=2001&rft.type=Journal+paper&rft.type=NonPeerReviewed&rft.format=application%2Fpdf&rft.language=en&rft.identifier=%2Fid%2Feprint%2F172%2F1%2FHansen_og_Vinther_2001.pdf&rft.identifier=+++Hansen%2C+Jacob+P.+and+Vinther%2C+Finn+P.+++(2001)+Spatial+variability+of+symbiotic+N2+fixation+in+grass-white+clover+pastures+estimated+by+the+15N+isotope+dilution+method+and+the+natural+15N+abundance+method.+++Plant+and+Soil+(230)%2C+pp.+257-266.++++++++