Abstract:
Knowledge on the possible influence of mucuna green manure application rate, and variable soil
moisture conditions on decomposition of its biomass and available soil nitrogen levels is vital for
efficient resource management. Consequently, potted soil experiment was carried out on these factors
for 8 weeks under glasshouse conditions at Field Station-Kabete, University of Nairobi, Kenya in
March-April, and repeated in May-June, 2005. The objective was to determine potential effect of
mucuna green manure application rate and varying soil moisture level on decomposition pattern and
available nitrogen in sandy clay soil collected from an experimental site in southwest Kenya. The
treatments studied were: mucuna green manure applied at rates of 0, 60, 120 and 240 kg N ha-1
equivalent to 0, 3, 6 and 12 t DM ha-1 of the biomass and, soil water potentials at field capacity (-0.01 Mpa), wilt point (-1.5 Mpa), and intermediate (–0.75 Mpa) levels represented by moisture
contents of 22, 12 and 18 %, respectively. The two factors were combined factorially in a randomized
complete block design with three replications. The treatments were applied and maintained in 10-litre imperforated plastic pots filled with 4 kg soil. Destructive sampling of soil and observation were
done at 1, 3, 5 and 8 weeks after treatment. Results obtained showed that mucuna green manure
application rate had non-significant effect on decomposition pattern. But, effect of soil moisture level
on the pattern was significant. Mucuna green manure showed two phases of decomposition: an initial
rapid phase and a slower second one. Half-life of mucuna green manure under field capacity soil
moisture condition was one week. But, it took no less than 5 weeks for 50 % of the applied mucuna
biomass to disappear if soil water condition was varying from wilting point, intermediate to field
capacity as is likely to happen in field environment.
