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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


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.