A study was conducted to determine the influence of mulches of rice (R), maize (Mz), mucuna (Mc) and cymbopogon (C) on weed growth and rice yield. Twelve mulch treatments included MzRC, RMcC, MzMC, MzRMc, MzRC + one hand rogueing of weeds (hr), RMcC + hr, MzMcC + hr, MzRMc + hr, MzRC + one hand hoeing of weeds (hh), RMcC + hh, MzMcC + hh and MzRMc + hh, 2hh, 3hh, Butanil +1hh and a weedy check in a randomised complete block design (RCBD) with three replicates. The study was conducted both on-station and on-farm (2014). CMcRMz species were each planted in 24 plots under a RCBD replicated thrice and 3 crops uprooted from the plots were combined in equal proportions of different stover into four mulches (MzRC, RMcC, MzMcC & MzRMc). The experimental site was ploughed, divided into 48 plots under RCBD replicated thrice and the mixed mulches were applied (10-12.Mt ha-1) to 12 plots at planting. Higher rice growth was recorded under MzMc than RC mulches with or without a post mulch weed control. RC based mulches most effectively reduced weed density and biomass followed by MzMc mulches. 2hh and MzRMc mulch + 1hr produced similar rice yield but lower rice yield was under RMcC and Butanil + IJPSS, 29(1): 1-14, 2019; Article no.IJPSS.50191 2 1hh. Rice growth and tiller development reduced under the weedy check giving zero yields. The highest Striga was under Butanil + 1hh (8 Striga), followed by 3hh and 2hh (3 & 2 Striga). No Striga was recorded under cymbopogon mulches and weedy check. The highest returns on investment (ROI) were under 2hh (0.52 & 0.43) at the two sites and MzRMc + hr recorded high ROI (0.47) on station, similar to 3hh on-farm. Maize, rice, cymbopogon and mucuna have high potential to produce bio-herbicides with high rice yields. Original Research Article
Crop residues and mulches release phytotoxic substances into the soil that affect plant growth. An experiment was conducted at the Uganda National Crop Resources Research Institute, Namulonge during 2016, to identify compounds in the stover of potted Cymbopogon nardus, Desmodium uncinatum, Oryza sativa, (NERICA 1), Mucuna pruriens and Zea mays (LONGE 6H) at fourty five days after germination. This marked near the average stationary phase for test crops’ growth when secondary metabolites are maximum. Organic compounds in the stover were extracted using solid phase micro-extraction. Samples were subjected to analysis using a 7890A Gas Chromatography system. Data files were transferred into a distinct folder and data was uploaded onto XCMS online platform for pair wise comparison and other related statistical analysis in the National institute of Science and Technology library. Ten terpenoids and one ester were identified in cymbopogon stover. Desmodium stover released six terpenoids and three phenols. Rice stover produced six terpenoids, three phenolic compounds and one ester. Mucuna stover released two terpenoids and four phenols. The maize stover produced five terpenoids and four phenolic compounds. Profiled compounds from cymbopogon, desmodium, rice, mucuna and maize could be responsible for the reported negative allelopathic effects such as auto-toxicity and suppression of companion crops expressed in agricultural ecosystems. Allelopathic activity of the profiled compounds should be confirmed through bioassays extracts and residues studies. The development and incorporation of the profiled metabolites into agricultural management system may lead to the production of bio-herbicides that reduce environmental degradation and increase crop productivity.
Allelochemicals cause yield differences under various ecosystems worldwide. Studies were conducted at the National Crops Resources Research Institute, Namulonge, Uganda during 2016 to investigate allelopathic properties of bioactive compounds in upland rice (NERICA 1), Desmodium uncinatum, Zea mays (LONGE 6H) and Mucuna pruriens root leachates. Studies involved pot screening, equal compartment agar experiments, germination tests and growth of potted plants. Results under the pot study indicated that maize, rice and mucuna leachates significantly (P ≤ 0.05), reduced root lengths (49%-63%), plant heights (48%-66%) and biomass (63%-75%) for Ageratum conyzoides, Bidens pilosa and Gallinsoga. parviflora weeds. G. parviflora root growth was reduced (20%-41%) and stem growth declined (19%-42%) when maize, rice and mucuna leachates were applied in the equal compartment agar study. Increased leachate concentrations (25%-75%) significantly (P ≤ 0.05), increased the mean germination time (0.4-2.8 days) for mucuna, desmodium, rice and maize as seed germination indices (SGI) were reduced (1.3%-49%). Potted mucuna, maize and desmodium reduced (1.3%-49%) rice root length. Potting mucuna with maize reduced (32%) mucuna leaf width while desmodium growth parameters were reduced (49%-64%) when potted with maize and mucuna. Potting maize with mucuna or desmodium increased the maize leaf length (18%) and SGI (25). Application of higher (25%-75%) rice/maize leachate concentrations similarly increased the maize leaf length (31%) and SGI (119). Allelopathic properties affect seed germination, crop growth and development, and characterise ecosystems age structures. Strategic management of crops under allelopathic ecosystems is critical.
Allelochemicals regulate the productivity of crop ecosystems. A screen house experiment was conducted (2016) at the National Crops Resources Research Institute, Namulonge, Uganda to determine the effects of NERICA 1 rice (an interspecific hybrid between Oryza sativa and O. glaberrima species), Cymbopogon nardus (C), Desmodium uncinatum (D), Mucuna pruriens (Mc) and LONGE 6H, Zea mays (Mz) on crop relative growth rates (RGR), nitrogen (N), phosphorus (P) and potassium (K) nutrient levels. One field study was conducted on a farm (2017) to establish the allelopathic interactive effects of RCDMcMz on Striga hermonthica (a parasitic weed), crop competition and productivity. Data was collected on striga, RMz growth, nutrient levels and yield. Potted rice reduced (30%-47%) in root length but Mz leaf length increased (31% & 15%) with Mc & D. RMc reduced (73%) striga and increased rice RGR (14-42 days). RD similarly reduced (67%) striga. RC increased (96%, 44% & 73%) rice NPK uptake, RGR (14-42 days), reduced (57%) striga and increased (1.56) the combined land equivalent ratio (CLER) and rice grain yields. RMz reduced (16%, 38% & 38%) rice NPK reserves, RGR (14-42 days), CLER (1.0), grain yields and increased (36%) striga. RD recorded higher CLER (1.56). MzMc reduced (15% & 27%) maize P uptake and NP uptake increased (42% & 9.3%) under MzC & MzD (73% & 29%). RMc increased rice RGR (14-42 days). Maize RGR (14-28 days) increased under MzD, MzMc & MzC and reduced (28-42 days) under MzD, RC & MzMc.. The ecosystems’ productivity was attributed to allelopathy.
The productivity of upland rice is highly determined by the available soil moisture and nutrients. Droughts highly influence yields especially in the second 30 days growth period. A field experiment was conducted at the Uganda National Agricultural Research Institute, Ikulwe station during 2018B and 2019B seasons to determine the productivity and economic returns of four rice varieties under two harvest modes and rainfall intensities. The treatments included NERICA 1, 4 & 6 and NAMCHE 2 given 80 kg N and 30 kg P ha-1. Treatments were replicated three times under a randomised complete block design. Data was collected on plant height, leaf number, leaf length, leaf width and number of tillers during vegetative stages in all treatments. The panicles m-2, sink size, panicle filling percentage and grain yields were determined at harvest. All the yield attributes and grain yield reduced during the droughty 2018B relative to the rainy 2019B. On the contrary, the number of tillers reduced in 2019. Correlation coefficient (r) for spikelets per m-2 were significant (>8.0) and positive (0.86) to grain yield during 2018 but were lower (0.13) in 2019. The r values were also positive, but not significant, for panicles m-2 (0.76) and for percent filled panicles (0.23) with respect to grain yield during 2018 and 2019 respectively. NERICA 4 & 6 produced higher grain yield under both moisture stress and high rainfall conditions. The results indicate that NERICA 4 and 6 varieties could be adopted and harvested at 75 days after rice emergence (DAE) for NERICA 4 and at 75 DAE and 90 DAE for NERICA 6 under low (630 mm) rainfall or harvested once at 90 DAE given high (1,500 mm) rainfall to get higher yields and Returns on Investment.
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