Contribution of red alder to soil nitrogen input in a silvopastoral system

摘要

Studies on Alnus rubra Bong. (red alder) were carried out to assess its potential for use as a component of a silvopastoral system. Comparison was between two treatments: red alder at 400 stems ha?1 (silvopasture) and red alder at 2,500 stems ha?1 (forestry control). δ15N values close to zero were recorded in all red alder plant parts except for root nodules, indicating that a large proportion of N in red alder was fixed from the atmosphere. Overall, it was estimated that there was 63.45 kg N ha?1 fixed N accumulated in red alder trees, and the rate of N fixation was estimated at 30.95 kg ha?1 year?1 in the silvopasture treatment. The total amount of N that could potentially be added to the soil in the silvopasture treatment as a result of decomposition of senescent leaves, roots, and dead nodules was estimated at 40.56 kg ha?1 year?1. Of the total N added to the soil, 27.1 kg ha?1 year?1 was due to N fixation from the atmosphere. These results show that red alder has a potential to improve and maintain soil fertility in a silvopastoral system.