Nitrogen Fixation in an Establishing Alfalfa ( Medicago sativa L.) Ley in Sweden, Estimated by Three Different Methods

Abstract

In an investigation of the ability of alfalfa to fix nitrogen under field conditions in Scandinavia, N(2) fixation during the establishment year ranged between 7.85 and 10.37 g of N m, depending on the method used. The methods used were an in situ acetylene reduction method, a N isotope dilution method using two reference crops, and a total-N difference method. The dynamics of nitrogenase activity in relation to plant development was studied by using the acetylene reduction method. Also, the diurnal variation in N(2) fixation at the field site was studied with the acetylene reduction method; no diurnal change was detected, which is explained by the fact that the nodules within the soil were protected against short-term fluctuations in temperature. The significant amount of nitrogen fixed by alfalfa during its first year even at northern latitudes suggests that this crop offers an alternative to conventional field management of heavily fertilized nonlegume leys.