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Input of nitrogen from N2 fixation to northern grasslands

Carlsson, Georg (2005). Input of nitrogen from N2 fixation to northern grasslands. Diss. (sammanfattning/summary) Umeå : Sveriges lantbruksuniv., Acta Universitatis Agriculturae Sueciae, 1652-6880 ; 2005:76
ISBN 91-576-6975-9
[Doctoral thesis]

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Forage legumes form N2-fixing symbioses with rhizobia and may thus make substantial contributions to the N pool in grasslands. However, to optimize their use as sources of N, it is important to elucidate the effects of management factors that influence their N2 fixation rates, and to develop convenient methods for measuring N2 fixation quickly and reliably. An analysis of published data on N2 fixation in the field showed that lucerne (Medicago sativa L.), red clover (Trifolium pratense L.), and white clover (T. repens L.) grown in mixtures with grasses derived most of their N from N2 fixation, irrespective of geographic location and management practices – and despite large inter-annual variations in legume dry matter yield (kg ha-1 year-1). Consequently, there were strong correlations between legume dry matter yield and amounts of N2 fixed (kg N ha-1 year-1), which can be used very simply to obtain estimates of N2 fixation in these legumes. In experimental grassland plots where the species richness of neighbouring vegetation was varied, alsike clover (T. hybridum L.), red clover, and white clover consistently derived at least half of their N from N2 fixation, measured by the 15N natural abundance (NA) method using three different reference plants. This method is sensitive to the degree of discrimination against 15N in the N2-fixing plant (B value) and the choice of reference plant. B values were therefore established for each of the three clover species in symbioses with different Scandinavian Rhizobium leguminosarum bv. trifolii genotypes. In red clover, reductions following cutting in the activity of the N2-fixing enzyme, nitrogenase, and the rate of shoot regrowth were dependent on the cutting height. The recovery in nitrogenase activity after cutting followed the rate of leaf area increment, which confirms the correlation between N2 fixation and growth found in field experiments. The results of the work underlying this thesis show that perennial forage legumes growing in grasslands are highly dependent on N2 fixation. Awareness of this should facilitate the development of resource-efficient management regimes for northern grasslands.

Authors/Creators:Carlsson, Georg
Title:Input of nitrogen from N2 fixation to northern grasslands
Series Name/Journal:Acta Universitatis Agriculturae Sueciae
Year of publishing :September 2005
Number of Pages:50
ALLI. Carlsson, G. & Huss-Danell, K. 2003. Nitrogen fixation in perennial forage legumes in the field. Plant and Soil 253, 353-372. II. Carlsson, G., Palmborg, C. & Huss-Danell, K. 2005. Discrimination against 15N in three N2-fixing Trifolium species as influenced by Rhizobium strain and plant age. Acta Agriculturae Scandinavica Section B. Soil and Plant Science (in press). III. Carlsson, G., Palmborg, C., Jumpponen, A., Högberg, P. & Huss-Danell, K. N2 fixation in three perennial clover species in communities of varied plant species diversity. Submitted. IV. Carlsson, G. & Huss-Danell, K. Dynamics in nitrogenase activity and growth after cutting red clover (Trifolium pratense) at different heights. Submitted.
Place of Publication:Umeå
Associated Programs and Other Stakeholders:Z - SLU - Library > Odla mera
ISBN for printed version:91-576-6975-9
Publication Type:Doctoral thesis
Full Text Status:Public
Agris subject categories.:P Natural resources > P35 Soil fertility
F Plant production > F01 Crop husbandry
P Natural resources > P34 Soil biology
Subjects:Not in use, please see Agris categories
Agrovoc terms:nitrogen fixation, rhizobium, grasslands, soil fertility, medicago sativa, trifolium pratense, trifolium repens, trifolium hybridum, forage, feed legumes, plant production, models, sweden
Keywords:Acetylene reduction activity, clover, cutting height, δ15N, forage, legume, methods, N2 fixation, perennial, Rhizobium, species richness
Permanent URL:
ID Code:895
Department:(NL, NJ) > Dept. of Agricultural Research for Northern Sweden
(VH) > Dept. of Agricultural Research for Northern Sweden
Deposited By: Georg Carlsson
Deposited On:02 Sep 2005 00:00
Metadata Last Modified:21 Oct 2015 14:01

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