Dn. Mugendi et Pkr. Nair, PREDICTING THE DECOMPOSITION PATTERNS OF TREE BIOMASS IN TROPICAL HIGHLAND MICROREGIONS OF KENYA, Agroforestry systems, 35(2), 1997, pp. 187-201
Decomposition- and nitrogen-release patterns of biomass from three agr
oforestry multipurpose trees (Calliandra calothyrsus, Cordia africana
and Grevillea robusta) were investigated in four contrasting environme
nts (microregions) in the Kenyan tropical highlands during two croppin
g seasons. Dried leafy biomass was placed in 2-mm litter bags, buried
at 15-cm depth and recovered after 2, 4, 7, 10, 15 and 20 weeks. Decom
position patterns were best described by first-order exponential decli
ne curves. The decomposition rate constants ranged from 2.1 to 8.2 yr(
-1), and the rates of decomposition among the species were in the orde
r: calliandra greater than or equal to cordia > grevillea. There was a
species-by-environment interaction during both seasons, but the nitro
gen released did not follow such a pattern. Among the three tree speci
es, calliandra released the highest amount of cumulative N, followed b
y cordia and greviIlea. Using multiple regression techniques, decompos
ition pattern was described as a function of three groups of factors:
biomass quality (N, C, lignin and polyphenol), climate (soil temperatu
re and rainfall), and soil conditions (pH, soil organic C, total N and
P). For all the species and factors combined, the adjusted R-2 values
were 0.88 and 0.91 for seasons 1 and 2, respectively. Among the three
groups of factors, climate and biomass quality had the most influence
on decomposition rates. Climatic factors accounted for 75% of the tot
al rate of decomposition in season 1 ('irregular' season with less rai
nfall and more soil temperature fluctuations), whereas biomass quality
factors were more influential in season 2 ('regular' season), account
ing for 65% of the total variability.