Abstract:

Rice is a major food and cash crop under various mixed cropping systems in Uganda. Rice and
known about the causes of allelopathy, declining ecosystem productivity and the potential
benefits from the ecosystems. The main objective of this study was to determine the
compounds in Oiyza saliva, Cymbopogon nardus, Desmodium uncinatum, Mucuna pruriens
and Zea mays and their allelopathic interactive effects. Specific objectives were: (i) to identify
the compounds in rice, cymbopogon, desmodium. mucuna and maize: (ii) to determine the
allelopathic potential of compounds in rice, cymbopogon, desmodium. mucuna and maize: (iii)
to determine the effects of allelopathy on striga. crop growth, nutrient uptake and productivity
of rice based intercropping with cymbopogon, desmodium. mucuna and maize: (iv) to evaluate
the allelopathic potential of rice, cymbopogon, desmodium. mucuna and maize mixed mulches
on weeds and rice; (v) to assess the effects of plant powders and aqueous extracts from rice.
cymbopogon, desmodium. mucuna and maize on weeds. Objective (i) was implemented
between June and August 2013 at the National Crops Resources Research Institute (NaCRRI).
Namulonge, Uganda. Plants were uprooted al 45 days after emergence (DAE) and samples
analysed for organic compounds using the National institute of Science and Technology
library. In objective (ii) pot screening, equal compartments agar, germination tests and donor to
receiver plants in the same pot studies were conducted during 20I3B. In objective (iii) a screen
house experiment was done at NACRRI during 2013B and two field studies were conducted
during 20I4A. In the screen house two different crop species were planted in the same pot and
as sole crops. In the field studies, maize, mucuna. desmodium and cymbopogon were tested in
conducted during 2015A. Cymbopogon, mucuna. rice and maize species were each planted and
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sole crop and intercrop systems. In objective (iv) on-station and on-farm experiments were
some intercrops exhibit allelopathic properties and productivity is on the decline yet little is
uprooted at 55 DAE and combined in sets of three equal proportions of individual stover to
give four types of mulches that were applied under 12 treatments at planting of rice. Objective
(v) was conducted at NACRRI during 2013B and in the Held during 2015A. Leaf, stem and
root (LSR)) powders from rice, maize, cymbopogon, desmodium and mucuna were combined
in equal proportions of three to make eight powdered mixtures that w-ere applied to 72 pots in a
screen house. Field studies were conducted on station and on farm with maize, mucuna. rice
and cymbopogon mulches, Butanil herbicide, hand hoeing and rogueing of w-eeds with a weedy
cymbopogon, desmodium, rice, mucuna and maize crops. Data were also collected on
compounds in cymbopogon, desmodium. rice, mucuna and maize stover. Radicle and plumule
length were measured, germinated seeds counted and percent germination, mean germination
time (MGT) and seed germination indices (SGI) calculated for desmodium. rice, mucuna and
maize seedlings. Root lengths, plant height, dry biomass, w idth and length of leaves, number of
w'eeds and plants per pot. plant nutrient uptake and reserves in the soil at harvest were
established in polled experiments. Data were collected on maize green leaves, striga per 100
rice plants, total and Filed panicles per plant, grains per plant, filled grains per panicle and
grain yield of rice under field studies. Land equivalent ratio, competitive ratio, relative growth
rates (RGR). gross returns, net returns and returns on investments (RO1) were calculated for
different enterprises. Blank soil, cymbopogon, desmodium. rice, mucuna and maize produced
and maize predominantly produced 10. 6. 6. 6 and 9 compounds respectively from their stover.
Maize, rice and mucuna leachates reduced the root lengths, height and biomass for weeds. G’.
parviflora root and stem growth reduced on application of root exudates. Mean germination
lime for lest plants increased while the SGI reduced al 75% leachate concentrations. Growth of
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rice, mucuna and desmodium reduced when potted with mucuna and maize. Maize potted with
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24. 7. 5. 11.7 and 6 major compounds respectively. Cymbopogon, desmodium. rice, mucuna
check. Data were recorded on the compounds in blank forest soil (control), soils potted with
desmodium and cymbopogon recorded reduced RGR. NPK crop uptake and reserves in the soil
at harvest unlike rice potted with mucuna, desmodium and cymbopogon. Conversely, the
maize growth increased when potted with mucuna and desmodium and with 75% concentration
of rice/ desmodium and rice/maize leachates. Striga weed counts reduced in rice intercropped
with mucuna, desmodium and cymbopogon but increased with maize and thus, reduced rice
tillering under the latter treatment with 63% of the weeds recorded on rice plants. Sole rice and
rice intercropped with cymbopogon produced higher rice grain yields and partial land
equivalent ratio (LER) for rice. The highest combined LER were recorded under rice +
desmodium and rice + cymbopogon cropping systems. Rice + maize and rice + mucuna
intercropping systems were least productive and mucuna was the most competitive crop
followed b\ maize and cymbopogon. Butanil, hand hoeing twice or thrice and mulching rice
with maize/mucuna based mulches increased rice growth, grain yields and ROI compared to
rice/cymbopogon based mulches which most effectively controlled weeds including striga.
Increasing ESR powder concentrations reduced the number of weeds and mean weight per
weed. Rice/cymbopogon and maize/ mucuna LSR powdered mixtures and liquid bio-extracts
reduced weed densities and weight while Butanil recorded the lowest weed densities and
weight. Highest weed weight/m2 and unit weed weight were under the weedy check. The
highest striga count was recorded under Butanil, 3 and 2 hand hoeing (hh) and there were no
striga under cymbopogon mulches and weedy check. Highest ROI were under 2hh. 3hh and
utilise allelopathy as a weed management technology for increased crop productivity. Further
studies are recommended on the allelopathic potential of the compounds identified in the
current study and in use of C. nardus and M. pruriens for Striga hermonthica weed control.
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maize/mucuna based mulches given I hand rogucing of weeds. There is high potential to