Siam weed (Chromolaena odorata) is a plant that has infested a large area of agricultural
land in Serengeti district and has adversely reduced crop land and crop yields. It is
encroaching land and especially in the famous Serengeti National Park. The weed has
been reported to contain high amount of plant nutrients in its tissue, hence its probable
use as an organic soil amendments, with aspect to soil fertility improvement. A study was,
therefore, conducted to address the Siam weed growth requirements, nutrient contents in
its tissue and its suitability and use as an organic amendments as a way to manage the
weed accordingly and appropriately. Soil and Siam weed plant sampling was done in the
Serengeti district (Mara Region), an analysis was done in the Soil Science laboratory at
SUA, Morogoro. Composite topsoil (0 – 20 cm) samples were collected and analysed for
physico-chemical properties hence shows to have slightly acidity with pH (5.8 to 6.5),
low to high CEC (11.6 - 29.4 cmol (+) kg −1 ) and very low to very high soil organic
carbon (0.36 - 3.69%). Three soil profiles on a toposequence from the infested soil were
excavated, described and sampled for soil laboratory analysis, hence shows medium
acidic to medium alkaline (pH 5.84 to 7.93), low to high CEC (10.12 - 35.20 cmol (+)
kg -1 ), low to medium SOC (0.11 - 1.97%) and high exchangeable bases 24.45 cmol (+)
kg −1 based on the rating by Landon (1991). Using the morphological and laboratory data
the soils were classified to the subgroup level of the USDA Soil Taxonomy as Ustic
Torripsamments on sloping land, as Haplic plinthustults on midslope and as Plinthaquic
paleudalfs on low land and to Tier-2 of WRB as Rendzic Lithic Leptosols (Eutric, Dystric,
Tephric) on sloping lands, as Gleyic Plinthic Acrisols (Ferric, Humic) on midslope and as
Haplic Stagnic Gleyic Luvisols (Chromic) on low or flat areas. Incubation study was done
by incorporation of different parts of Siam weed plant with soil for 16 weeks. As a result
of mineralization after incubation, the leaves released N (0.292%) and Fe (64.15 mg
kg -1 ); bulbs released P (12.39 mg kg -1 ) and Mg (0.87Cmol (+) kg -1 ); stems released K0.22 cmol (+) kg -1 ) and Ca (5.13 cmol (+) kg -1 ) and roots released Cu (6.01 mg kg -1 ), Mn
(77.18 mg kg -1 ) and Zn (1.65 mg kg -1 ). Nutrients released were increasing from the 0 to
12 th week and started to decrease at week 16 after incubation. Therefore, from incubation
results, it is recommended that, farmers should grow their crops before the 12th week
following incorporation of Siam weed biomass into soils for plants to absorb nutrients
from the Siam weed.
AGRA.