Über die Schätzung des Beitrags der symbiontischen N2-Fixierung durch Weißklee zur Stickstoffbilanz von Grünlandflächen

Based on a special evaluation of published data obtained by using the 15N dilution method, a method for estimating the N2 fixation by white clover in mixed grasslands swards is proposed. Two figures are distinguished. The first figure is the N yield of fixation defined as the amount of N from symbiontic origin within the harvestable herbage. Representing the annual gain of N avaiable for plant growth, it should be used in establishing the area-related N budget as a basis of fertilization planning. For estimating the N yield of fixation the following equation is recommended: kg N/ha/year = (4.0 x1 - 0.01 x12) (1 - 0.000036 x 22), in which x1 means the clover yield (100 kg units of DM per ha per year) and x2 the fertilization rate (kg N per ha per cut). The second figure is the total N input from fixation into the respective system. It also includes that part of N from symbiontic fixation which is subjected to nitrate leaching. This figure should be used when budgeting the N for the whole system in order to evaluate farming types with regard to their ecological acceptance. The total N input from N2 fixation can be roughly calculated by multiplication of the N yield of fixation, extimated according to the given equation, by the factor 1.25.