Live and dead mulch for weed and soil fertility management in organic production of sweet pepper (Capsicum annuum L.)

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