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Biological N2-fixation in grass-clover ley in response to N application in cattle slurry vs. mineral fertilizer

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Background: The nitrogen (N) response in grass-clover is influenced by quantity and timing of N-fertilizer, but less is known about the effect of fertilizer type (animal manure vs. mineral N) and N form (ammonium vs. nitrate). Method: A field trial was established in a mixture of white clover (Trifolium repens L.), red clover (Trifolium pratense L.) and perennial ryegrass (Lolium. perenne L.) with mineral N and slurry. DM yield in grass and clover and N2-fixation activity (%Ndfa) was determined in four cuts during the season. Results: Fertilization resulted in a peak in soil mineral N within 1-2 weeks of application and decreased to background rate prior to plant harvest. No differences in white clover N2-fixation activity were found between fertilizer types within each N level. Conclusions: The experiment showed that mineral N form does not affect the regulation of N2-fixation activity. The fertilizer N level was the only factor affecting white clover N2-fixation activity. Further, the results demonstrated an N threshold below which annual %Ndfa was always high (~90%). This was controlled by the companion grass’ ability to deplete the soil mineral N pool. When N fertilization exceeded this threshold (above 180 kg N ha-1 yr-1in our case) annual %Ndfa significantly decreased as did qBNF in the harvested biomass.

TidsskriftPlant and Soil
Sider (fra-til)629-641
Antal sider13
StatusUdgivet - feb. 2022

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