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Effektar av traktorkøyring, gjødsling og frøblanding på avling, botanisk samansetjing, fôrkvalitet, nitrogenopptak og nitrogenfiksering i eng Delrapport frå prosjektet: Proteinrike engbelgvekster under ulike dyrkings‐ og klimaforhold

The weight of tractors and farm machinery has increased in recent years. We have examined how tractor traffic affects physical properties of soil, grassland yields, botanical composition and forage quality of pure grass and mixtures of grass and clover stands at three locations in Norway; Tjøtta in Nordland county, Fureneset in Sogn and Fjordane and Løken in Oppland. Tractor traffic reduced yields (20 %) on silty soil at Løken, while there was a moderate decline (6 %) on silty sand at Fureneset, and no yield effect on sandy soil at Tjøtta. The tractor weight gave small yield effects, however, the results show that one should avoid traffic on silty soils under wet conditions whenever possible. Tractor traffic on silty soil changed the botanical composition at Løken. Red clover and dicot weeds decreased by traffic, while white clover and grass weeds (Poa annua, Alopecurus geniculatus) increased. Traffic on silty soil also reduced nitrogen uptake and biological N fixation. Use of clover in the seed mixture gave a large positive effect on yield and forage quality. Use of 60 kg N in mineral fertilizer after the first cut increased grass yields, but reduced the clover content and the biological N fixation. Nitrogen fertilizer and use of clover changed the grass composition in direction of more timothy and less meadow fescue. An increase from 15 % to 30 % clover in the seed mixture gave small effects on yields and botanical composition, but increased the biological N fixation by 5 kg N ha-1 year-1.