Nitrogen fixation in a Mexican coffee plantation

Fertilizer studies in Mexico indicate that coffee production can be stimulated by added nitrogen. One traditional method of coffee cultivation employs leguminous trees for shade, but these species may also play an important role in coffee production by biologically fixing nitrogen. The presence and importance of nitrogen fixation was evaluated in four systems: coffee only, coffee plus the leguminous shade treeInga jinicuil Schletchter, coffee plus the leguminous treeInga vera H.B. and K., and coffee plus banana and orange trees. In all systems coffee leaves with epiphylls, wood litter, soil, roots, and root nodules were assayed for nitrogen fixing activity with the acetylene reduction technique. All components of these systems exhibited activity except roots. Total apparent fixation was highest in theInga jinicuil site, and equivalent to >40 kg N ha^?1 yr^?1 assuming a 3∶1 C₂H₂∶N₂ ratio. The activity was primarily associated withInga jinicuil nodules. Apparent fixation in the other three sites was less than 1 kg N ha^?1 yr^?1. Nitrogen fixed in theI. jinicuil site was 53% of the average amount of fertilizer nitrogen applied annually, suggesting that fixation by non-crop legumes can be an important nitrogen source for coffee agro-ecosystems.