Cycling Nitrogen for Productivity in Agroforestry: Nitrogen, Lignin, and Polyphenol Controls on Mineralization
Cody, M. J.. 1999. M.Sc. Thesis. Dept. Renewable Resources, University of Alberta, Edmonton, AB
Abstract
Soi1 productivity in the Humid Tropics depends on consenation and recychg of nutrients
within the soil-plant system. In agroforestry systems, efficient use of organic fertilizers
requires that nutrient reiease from them be timed for maximum uptake by crops and
minimal leacbing or gaseous loss. Chernical constituenîs such as nitrogen (N), lignin (L),
and poIyphenols (PP) are controis on rates of N reIease. Patterns of N release from the
pninings of two tree species and one herbaceous legume were hvestigated in relation to
the chemical characteristics of the materials. Also, N distriiution in the soil following
slash and burn disturbance was documented. Mixing of pruning types reduced the
predictability of N release; interaction between mixed components was consistent with the
action of soluble polyphenols. Overall, L PP:N ratio was the best chemical index for
prediction of N release. Slash and burn disturbance resdted in a mineral N flush in the
fïrst metre of soil; some of this N was leached below one metre.
