PhD Thesis
The study was conducted for three seasons aimed at developing a strategy that combines
weed control with soil fertility enhancement using live and dead mulch for increased
productivity of organic sweet pepper. Synchronization experiments were set to evaluate
release patterns and availability of nutrients by leguminous green manures in soil. A
randomized complete block design (RCBD) with a plot size of 3 m x 3 m replicated four
times was used. Mucuna and greengram materials in mesh bags were buried 10 cm in soil.
Replicated bags were removed weekly and analysed to determine decomposition rates and
quantities of nutrients released into soil. The grown cover crops were slashed at the stage
of 50% flowering and used as dead mulch for weed control and their influence on weeds
dynamics evaluated when greengram and mucuna cover crops were used as live and dead
mulch. Weed density, weed biomass and crop mineral contents were analysed each season
and soil weed seed bank data were determined from different depths 0–10, 11-20 and 21-
30 cm from plots managed with hand hoe weeding, mixed grass mulch and cover crops
treatment in four replicates. Farmers assessed the efficacy of each treatment and their
preference by identifying the criteria for selecting the best treatment for weed control and
soil fertility improvement. Different treatments were ranked depending on their
effectiveness on weeds control and soil fertility improvement, its single use for the live
and dead mulch, availability and costs of the materials and the amount of labour required
for the specific treatment application. Mucuna decomposition was faster compared with
greengram, from third to twelfth week of incubation. This implies that greengram has
relatively more resistant materials to decomposition as compared with mucuna. Maximum
effect on soil nutrient content occurred in sixth and seventh weeks after application of
green manures. Total organic C in soils treated with cover crops increased by a factor of
2.3 to 3.2. Total N increased significantly from 1.28% to 2.64% at sixth week in soil with greengram and to 2.83% at seventh week in soil with mucuna. Available P content of soil
increased from 0.03 to 0.39 and 0.37 mg kg -1 in soil treated with greengram and mucuna,
respectively. Optimum microbial population was attained from fifth to seventh week after
manure application, with 2.3 x 10 8 in soil with greengram and 3.08 x 10 8 with mucuna,
significantly improved compared with original population. Plots planted with greengram
and mucuna cover crops reduced weed species to 13 and 12, respectively, from 17 weed
species identified at the beginning of the experiment. Mucuna cover crop reduced weed
biomass from 33.1 g/m 2 to 9.1 g/m 2 and weed seed bank density from 17922 to 9418 per
metre square. However, Cyperus rotundus, Cynodon dactylon and Elangia codifolia
remained to be the most observed weeds in both treatments throughout the experimental
period. Growth of sweet pepper plants planted in plots with mucuna cover crop was
improved by increasing stem branches to 22, leaves to 157 and high number of fruits per
plant (25). The highest total N and P in vegetative parts were recorded in crops planted
with mucuna having 2.81 and 1.63% and those planted with greengram 2.48 and 1.09%. In
farmers’ assessment, farmers’ criteria for selecting the best weed and soil fertility
management treatment were sweet pepper yield, fruit quality, weeds control and soil
fertility improvement. Farmers preferred the two green manure cover crops in terms of
absolutely ranking, matrix ranking and pairwise ranking. The cover crops were also
preferred due to their cost effectiveness, sustainability and availability, giving the farmers
more profit compared with other treatments. Results from this study have shown the
suitability of the cover crops on weed control and improving soil fertility. It has been
observed that the two cover crops mucuna and greengram can suppress different types of
weeds above ground and below ground in terms of weed seed bank. However, this
depends much on the type of weeds available in site, as results indicate that sedge and
grasses were not completely suppressed and few managed to grow passing the live cover
crops mulch and dead mulch. Furthermore, one year application of cover crops for weed
control did not significantly reduce weed and weed seeds population. Therefore, to obtain
sustainable benefits of using cover crops, it is important to use these cover crops
frequently in more than one season. This will help building residue effects within the field for sustainable profit