Fræðaþing landbúnaðarins - 16.02.2007, Side 476

474 • Fræðaþing landbúnaðarins 4, 2007
fyrir flutning á nitri milli tegunda (Ledgard, 1991). í ljósi þessara niðurstaðna má ætla
að flutningur á nitri eigi sér stað með fleiri ferlum en niðurbroti í jarðvegi þar sem
umtalsvert magn fluttist frá smára í gras á fyrstu 20 dögunum (2. tafla). Þeir ferlar sem
þykja líklegastir er flutningur með beinum eða óbeinum hætti í gegnum svepprót og
upptaka á lífrænum efnasamböndum.
Ályktanir
Flutningur mældist í báðar áttir þó svo að flutningur frá smára yfir í gras hafi verið mun
meiri en í gagnstæða átt. Ljóst er að gagnkvæmur flutningur á nitri milli belgjurta og
annarra plantna er mjög mikilvægur þegar horft er til niturbúskapar og niturferla bæði í
ræktuðum og óræktuðum vistkerfum.
Heimildir
Áslaug Helgadóttir & Þórdís A. Kristjánsdóttir. 1993. Ræktun hvítsmára. Ráðunautafundur. 188-197.
Carlsson, G. & Huss-Danell, K. 2003. Nitrogen fixation in perennial forage legumes in the field. Plant and
Soil, 253: 253-372.
Sigríður Dalmannsdóttir, Þórey Gylfadóttir, Þórdís A. Kritsjánsdóttir & Áslaug Helgadóttir. 2007.
Niturbinding smára, mælingar með 15N aðferð. Fræðaþing landbúnaðarins 2007.
Frame, J., Charlton, JFL. & Laidlaw, AS. 1998. Temperate Forage Legumes. CAB Intemational, Walling-
ford.
Friðrik Pálmason, Jón Guðmundsson & Áslaug Helgadóttir. 1995. Symbiotic nitrogen fixation in lupin and
clover in Iceland. Nordisk jordbmksforskning, 77(3): 77.
Hertenberger, G. & Wanek, W. 2004. Evaluation of methods to measure differential 15N lebeling of soil and
root N pools for studies of root exudation. Rapid Communications in Mass Spectromerty, 18: 2415-2425.
Hogh-Jensen, H. & Schjoerring, J.K. 2000. Below-ground nitrogen transfer between different grassland
species: Direct quantification by 15N leaf feeding compared with indirect dilution of soil 15N. Plant and
Soil, 227: 171-183.
Hogh-Jensen, H. & Schjoerring, J.K. 2001. Rhizodeposition of nitrogen by red clover, white clover and
reygrass leys. Soil Biology and Biochemistry, 33:439-448.
Laidlaw, A.S., Christe, P. & Lee, H.W. 1996. Effect of white clover cultivar on apparent transfer of nitrogen
ffom clover to grass and estimation of relative tumover rates of nitrogen in roots. Plant and Soil, 179: 243-
253.
Ledgard, S.F., Freney, J.R. & Simpson, J.R. 1985. Assessing nitrogen transfer from legumes to associated
grasses. Soil Biologu & Biochemistry, 17: 575-577.
Ledgard, S.F. 1991. Transfer of fixed nitrogen from white clover to associated grasses in sward grazes by
dairy cows, estimated using 15N methods. Plant and Soil, 131: 215-223.
Paynel, F., Murray, P. & Cliquet, J.B. 2001. Root exudates: a pathway for short-term N transfer ffom clover
to ryegrass. Plant and Soil, 229: 235-243.
Shearer, G. & Kohl, D.H. 1986. N2-fixation in field settings: Estimations based on natural 15N abundance.
Australian Joumal of Plant Physiology, 13: 699-756.
Vallis, I., Haydock, K.P., Ross, P.J. & Henzell, E.F. 1967. Isotopic studies on the uptake of nitrogen by
pasture plants. III. The uptake of small additions of 15N-labelled fertilizer by rhodes grass and townsville
luceme. Australian Joumal of Agricultural Research, 18: 865-877.
Zhu, Y.-G., Laidlae, A.S., Christie, P. & Hammond, M.E.R. 2000. The specificity of arbuscular mycorrhizal
fungi in perennial reygrass-white clover pasture. Agriculture Ecosystems & Environment, 77: 211-218.