Md. Parvez Anwar

Efficacy, phytotoxicity and economics of different herbicides in aerobic rice

Abstract Aerobic rice is a potential water-wise rice production system, but high weed infestation has threatened its sustainability, which demands an efficient and cost-effective weed management technique. Eight commercial herbicide products were applied singly or as tank-mix or in sequence to evaluate their efficacy, rice selectivity and cost-effectiveness in aerobic rice. The study was conducted under field conditions in Malaysia during 2010/2011 following a randomized complete block design. Most of the herbicide treatments provided excellent weed control, and produced much higher net benefit than weedy or weed-free check. None of the herbicides caused significant phytotoxicity to rice plants. Among the herbicide treatments, sequential application of Cyhalofop-butyl+Bensulfuron at early growth stage followed by Bentazon/MCPA at mid growth stage provided the highest weed control efficiency, productivity and net benefit. Application of Bispyribac-sodium at early growth stage followed by Bentazon/MCPA at mid growth stage performed very close to the above-mentioned treatments. Sequential application of Pretilachlor/safener just after seeding followed by Propanil/Thiobencarb at early growth stage also provided satisfactory results in terms of efficacy and economic return. Since manual weeding was not economic, herbicide rotation using the above chemicals may be recommended for effective weed management in aerobic rice.

Seed priming influences weed competitiveness and productivity of aerobic rice

Abstract Growing rice under aerobic soil conditions is a promising water-wise technology under the context of ever-mounting water scarcity, but it is subject to poor stand establishment and high weed pressure. The present study was, therefore, designed to explore the possibility of adopting seed priming as a sustainable tool for weed management in aerobic rice. The trough experiment was established with aerobic rice line Aeron 1 considering four priming techniques: hydropriming, hardening, Zappa® priming and untreated control; and two weeding regimes: weed-free and weedy. Treatments were arranged in a randomized complete block design with four replications. Seed priming significantly improved germination attributes, weed suppressive ability and yield of rice, whilst unprimed control exhibited inconsistent germination, poor stand establishment and less weed competitiveness resulting in poor yield. Seed priming resulted in reduced mean germination time and increased germination percentage, germination index and seedling vigour index. Weed dry matter reduction by primed stand of rice ranged from 22% to 27% compared with control. A positive influence of seed priming was also evident in rice yield with an average increment of 0.4 t ha−1 over control. Weed-inflicted relative yield loss of rice was minimized by 10% as a consequence of seed priming. Zappa® solution emerged as the best priming agent, which demands its incorporation as a viable component in an integrated weed management strategy for aerobic rice.

Allelopathic Effects of Litter Axonopus compressus against Two Weedy Species and Its Persistence in Soil

This study investigated the allelopathic effect of Axonopus compressus litter on Asystasia gangetica and Pennisetum polystachion. In experiment 1 the bioassays with 0, 10, 30, and 50 g L−1 of aqueous A. compressus litter leachate were conducted. Experiment 2 was carried out by incorporating 0, 10, 20, 30, 40, and 50 g L−1 of A. compressus litter leachate into soil. In experiment 3, the fate of A. compressus litter leachate phenolics in the soil was investigated. A. compressus leachates did not affect the germination percentage of A. gangetica and P. polystachion, but delayed germination of A. gangetica seeds and decreased seed germination time of P. polystachion. A. compressus litter leachates affected weeds hypocotyl length. Hypocotyl length reductions of 18 and 31% were observed at the highest concentration (50 g L−1) compared to the control in A. gangetica and P. polystachion, respectively. When concentration of A. compressus litter leachate-amended soil increased A. gangetica and P. polystachion seedling shoot length, root length, seedling weight and chlorophyll concentration were not affected. The 5-week decomposition study of A. compressus showed that the phenolic compounds in A. compressus litter abruptly decreased about 52% after two weeks and remained steady until the end of the incubation.

Competitive ability of some cover crop species against Asystasia gangetica and Pennisetum polystachion

Abstract Asystasia gangetica and Pennisetum polystachion are the most troublesome weeds in oil palm plantations in Malaysia and establishment of cover crops under oil palms is an integral part of sustainable weed management in plantations. Replacement-series experiments were conducted to evaluate the mode and strength of competitiveness of four legume cover crop species, Calopogonium caeruleum, Centrosema pubescens, Mucuna bracteata and Pueraria javanica, and one soft grass species, Axonopus compressus, against Asystasia gangetica and Pennisetum polystachion. Relative yield, relative yield total and relative crowding coefficient were calculated with reference to shoot biomass. Asystasia gangetica was a consistently weaker competitor than Pennisetum polystachion. The legume cover crop species had higher relative yield when grown in mixtures, whereas the yield of Asystasia gangetica was lower in mixtures with legumes than in monoculture. The higher competitiveness of legumes was due to greater canopy height and leaf area index. Centrosema pubescens was a slightly weaker competitor than the other legumes. Although leaf area per plant of Centrosema pubescens did not differ from that of other three legumes, canopy height and blocking photosynthetically active radiation to the soil surface were lower. When grown with a cover crop for 12 weeks, dry weight per plant, leaf area and shoot number of Pennisetum polystachion increased as its proportion decreased in mixtures. Relative yield data indicated that Pennisetum polystachion is a strong competitor. Axonopus compressus was less susceptible to Pennisetum polystachion interference than the legumes. All cover crop species studied proved highly competitive against Asystasia gangetica, but none could compete against Pennisetum polystachion. The study confirms the feasibility of using a cover crop for management of Asystasia gangetica.

Competitive Interaction of Axonopus compressus and Asystasia gangetica under Contrasting Sunlight Intensity

Axonopus compressus is one of the native soft grass species in oil palm in Malaysia which can be used as a cover crop. The competitive ability of A. compressus to overcome A. gangetica was studied using multiple-density, multiple-proportion replacements series under a glasshouse and full sunlight conditions in a poly bag for 10 weeks. A. compressus produced more dry weight and leaf area when competing against A. gangetica than in monoculture at both densities in the full sunlight and at high density in the shade. Moreover, the relative yield and relative crowding coefficients also indicated A. compressus is a stronger competitor than A. gangetica at both densities in the full sunlight and high density in the shade. It seemed that A. gangetica plants in the shade did not compete with each other and were more competitive against A. compressus as could influence A. compressus height in the shade. It is concluded that although suppression of A. gangetica by A. compressus occurred under full sunlight, irrespective of plant density, this ability reduced under shade as A. compressus density decreased. The result suggests that A. compressus in high density could be considered as a candidate for cover crops under oil palm canopy.

Effectiveness of Integrated Weed Management in Five Varieties of Aromatic Rice in Bangladesh

Thousands of rice land races are considered to exist in Bangladesh (Haque and Miah, 1990). Each of them possesses some special characteristics. Only some of these are unique for quality traits including fineness, aroma, taste and protein contents. Bangladesh has a stock of above 8,000 rice germplasms of which nearly 100 are aromatic (Islam et al., 2016). Cultivation of this rice has been gaining popularity in the country over the recent years, because of its huge demand both for internal consumption and export (Das and Baqui, 2000). About 27% of the total rice cropped area (BBS, 2003), and 12.5% of the total monsoon rice (BBS, 2005) are occupied by aromatic fine rice varieties of Bangladesh. Moreover, the production of aromatic fine rice is profitable due to its high price over low price coarse milled rice (Raju and Reddy, 2000; Sikdar et al., 2008). Recently, some aromatic fine rice varieties being cultivated in Bangladesh are of international standard and attracting the buyers in the global markets. However, the yield of aromatic rice was lower (1.5–2.0 t ha) than the coarse rice (Islam et al., 2010). Weeding has a great influence on the performance of the associated crop (Kumar and Chopra, 2013, 2016). Thus the best weeding practice needs to be adopted by the farmers with a view to reducing weed infestation and maximizing rice yield. Mechanical and manual methods of weed controls are mainly practiced by the farmers that are very much laborious and time consuming (Kumar and Chopra, 2013, 2016). Moreover, the availability of labor is decreasing due to the out migration of agricultural labors to industries with higher wages than agriculture, increases the need of using herbicides. Use of herbicides may be an alternative method in controlling weeds more easily and effectively at low cost (Rashid et al., 2007). But no single herbicide can control all weeds effectively in all environments. To date very few studies have been conducted to find out the best weed management practices for aromatic rice. On the other hand, a suitable combination of variety and weed management practices might be helpful to increase the yield of aromatic rice. Information on the varietal performance of aromatic rice and its management practices ORIGINAL RESEARCH ARTICLE