Ba. Jama et Pkr. Nair, DECOMPOSITION AND NITROGEN-MINERALIZATION PATTERNS OF LEUCAENA-LEUCOCEPHALA AND CASSIA-SIAMEA MULCH UNDER TROPICAL SEMIARID CONDITIONS IN KENYA, Plant and soil, 179(2), 1996, pp. 275-285
In agroforestry systems, loppings from trees and shrubs are commonly u
sed, often as mulch, as sources of nutrients for interplanted crops. T
herefore, it is important to understand the rates of mulch decompositi
on. This paper reports the results of a study on the decomposition and
nitrogen (N)-mineralization patterns of the leaves, small twigs, and
mulch (leaves plus twigs) of Leucaena leucocephala and Cassia siamea i
n a field experiment in an Alfisol in semiarid Kenya. Plant materials
contained in 5mm nylon bags were placed below or on the soil surface i
n an alleycropping system involving the two tree species, with maize (
Zea mays L.) as the intercrop. For plant materials of both species (ex
cept Leucaena leaves), there were two phases of decompositions: an ini
tial rapid phase and a slower second one; Leucaena leaves had only a s
ingle phase. When placed below the soil surface, the decomposition rat
es of both Leucaena and Cassia mulch were similar (about 12% week(-1)
in the first phase and 1% week(-1) in the second phase). When placed o
n the soil surface, Leucaena mulch decomposed 1.3 times more rapidly t
han Cassia mulch in the first phase. The patterns of N release from th
e mulch of both species were similar to those of mass loss. In general
, mulch-decomposition and N-release rates of both species were related
more to their C:N ratios than to polyphenol contents; while C:N ratio
predicted the rate of first (rapid) phase, the rate of the second (sl
ow) phase appeared to be regulated by lignin and polyphenol contents.