An experiment was carried out at farmers' field to compare the effects of live mulches and herbicide on weed growth and dynamics, yield, and economic performance of direct seeded rice under humid sub-tropical condition at Phulbari, Chitwan in 2009. The experiment was conducted in Randomized Complete Block Design with eight treatments and three replications. The treatments consisted of i) control, ii) three hand weeding, iii) herbicide application (bispyribac sodium @ 80 ml/ha) + one hand weeding, iv) wheat straw mulch @ 5t/ha + one hand weeding, v) Eupatorium mulch @ 5t/ha + one hand weeding, vi) brown manuring with Sesbania aculeata @ 30 kg/ha, vii) brown manuring with Sesamum indicum @ 2kg/ha, and viii) brown manuring with Crotolaria juncea @ 30 kg/ha. Weed dry matter accumulation was significantly lower with herbicide application (1.15 g/m 2 ) than wheat straw mulch (6.75 g/m 2 ). The treatments with brown manuring and Eupatorium mulch were found to be equally effective in suppressing the weed growth by reducing both dry matter content and weed density. Application of Eupatorium mulch one day after sowing produced significantly higher grain yield (3.5 t/ha) than control (1.77 t/ha), Sesamum brown manuring (2.97 t/ha) and wheat straw mulch (2.83 t/ha). Yield attributes like effective tillers/m 2 , panicle length and panicle weight were positively correlated with grain yield (r = 0.540, 0.705, 0.531 and 0.613 respectively). The net profit (Rs. 63.17 x 1000/ha) obtained from the treatment with Eupatorium mulch was higher than other tested treatments. Eupatorium mulch and herbicide application recorded equal benefit cost ratio of 2.4. Cultivation of direct seeded rice with the application of Eupatorium mulch or brown manuring (BM) of Sesamum was found effective for increasing yield and net returns in humid subtropical condition of Chitwan. Live mulching could be an eco-friendly weed control options in DSR. The BM option also provides crop residue for the addition of organic matter. This result suggests that BM is a potential alternative of herbicide application. Either mulching with Eupatorium and wheat straw or growing of Sesbania and Crotolaria as BM with rice up to 30 DAS are advisable to increase productivity with reduced cost of production at Chitwan and similar condition.

Rice (Oryza sativa) is the major food crop in terms of production and economy and grown in all ecological regions of Nepal. Rice is cultivated traditionally through transplanting of 20-25 days old seedling in the country. Due to unavailability of suitable technology for rice cultivation, there is a huge yield gap in rice production of Nepal. Country has made target of self-sufficiency in rice production by 2020 AD. This target can be achieved through adoption of Direct seeded rice cultivation technology of rice cultivation which also helps to adapt in the climate change scenario of Nepal. Due to issues of water scarcity and expensive labour, direct seeded rice cultivation technology is adopting worldwide. Direct seeded rice is a resource conservation technology and reduces water and labor use by 50%. Productivity of DSR is 5-10% more than the yield of transplanted rice. It offers a very exhilarating opportunity to improve water and environmental sustainability. Methane gas emissions is lower in DSR than with conventionally tilled transplanted puddle rice. It involves sowing pre-germinated seeds into a puddled soil surface (wet seeding), standing water (water seeding) or dry seeding into a prepared seedbed (dry seeding). Precise water management, particularly during crop emergence phase (first 7-15 days after sowing), is crucial in direct seeded rice. Furthermore, weed infestation is the major problem, which can cause large yield losses in direct seeded rice. Weed management in DSR can be done through chemical, hand weeding or stale seed bed method.

Recent trends of a decline or stagnation in the yield of rice and wheat in rice-wheat (RW) systems of the Indo-Gangetic Plains (IGP) have raised serious concerns about the regional food security. The effect of future climate change on crop production adds to this complex problem. The validated CSM-CERES-Rice and CSM-CERES-Wheat (Ver. 4.0) data were used to test the sensitivity of the models in Punjab, India. The models were sensitive to climatic parameters (temperature, CO2 concentration, solar radiation and rainfall) on yields of both crops. Simulated rice yields were sensitive to weather as there was 13% less yield of rice in 1999 than in 2001. Similarly, simulated wheat yields were also sensitive to weather, with the highest yield in 2001, and the lowest in 2003. Increments in both maximum and minimum temperatures by 4°C, decreased rice yield by 34% and wheat yield by 4% as compared to base scenario with current weather data. By increasing 4°C for both maximum and minimum temperature along with an increase in solar radiation by 1MJ/m2/day, rice yield decreased by 32% as compared to base scenario while wheat yields were not affected. With the increase in maximum and minimum temperatures by 4°C, and also an increase in CO2 concentration by 20 ppm from the standard CO2 concentration of 335 ppm, the reduction in rice yield was 33%, but in wheat yield was only 3%. Rainfed wheat yield increased by 7%, by increasing daily rainfall by 1.5 times, and by 13%, by doubling the rainfall, both after 96 days of sowing (DAS) to maturity. Lowering rainfall to zero, for each day after 96 DAS to until maturity reduced wheat yield by 18%. The increasing maximum and minimum temperatures irrespective of whether the CO2 concentration increased or not, seemed to have more adverse effects on rice than to wheat. Simulations demonstrated that CSM-CERES-Rice and CSM-CERES- Wheat are sensitive to CO2 and climatic parameters, and can be used to study the impact of future climate change on rice and wheat productivity in RW systems in Asia. Key words: CSM-CERES-Rice, CSM-CERES-Wheat, climate change, yield, phenology J. Inst. Agric. Anim. Sci. 27:103-110 (2006)

The Institute of Agriculture and Animal Sciences (IAAS) under Tribhuvan University (TU) has been conducting various disciplinary and system research works, and publishing the findings through the IAAS Journal, IAAS Research Reports, and Nepalese Journal of Agriculture for over 25 years. A literature review was done to appraise the agronomical research works on major field crops and cropping systems at IAAS, Rampur, Chitwan, Nepal. The objectives were to summarize the results of various agronomic research works at the institute to determine the extent and causes of yield gaps of major crops, and to identify the future research priorities. The review revealed that the on-station research at IAAS in the past were conducted on 14 crops, on maize-and wheat-based systems and on 5 major themes. The main themes of research in most crops were varietal evaluation and breeding, crop management, soil management, weed management and pest management though in some crops research was conducted on other themes too. A total of 81 studies were conducted on various crops, of which 48 were on cereals, 14 on legumes, 10 on oilseed crops, and 6 on potato. There were 2 studies on wheat-based and a single study on maize-based systems. Average potential yields of rice, maize and wheat were 5.5, 4.4 and 5.0 t/ha, while research station yields and farmers' field yields of these crops were 3.4, 3.3 and 3.5 t/ha and 2.7, 1.8 and 1.9 t/ha, respectively, in Chitwan. The yield gaps between the potential and farmers' field for those crops were 2.76, 2.58 and 3.15 t/ha, while those between potential and research station yields were 2.1, 1.1 and 1.53 t/ha, respectively. The gaps between research station and farmers' field yields were much smaller in rice (0.66 t/ha) than in maize (1.48 t/ha) and wheat (1.62 t/ha). The results suggest that there is a great scope to raise yields of all cereals in farmers' fields, more so for wheat and maize than for rice. Improved agronomical research on rice varieties and crop and soil management required to reduce the yield gap for rice, while adoption of recommended technologies by farmers would help reduce yield gap in wheat. For soybean, lentil, and potato, the gap between potential and farmers' yields is much larger than the other yield gaps suggesting large scope for increase in yields in farmers' fields through both improved management and improved varieties. Innovative and new researches on eco-region suited variety identification, improved crop and soil management, improved water and N management and on agro-meteorology and crop modeling are suggested as priorities for future research to uplift the productivity and reduce yield gaps of major crops in Chitwan district of Nepal.

Accumulated heat unit and phenology of a full season open pollinated and three specialty corn (Zea mays L.) cultivars (Hybrid, QPM and Pop) were studied by growing them on three different planting dates (September 1, October 1 and November 1) in RCB design at Rampur Chitwan, Nepal during the winter season of 2009-10. The results indicated that the number of days required to attain different phenological stages were short for the early winter and gradually long for late winter plantings. For all the phenological studies, plants of normal sowing condition (September 1) recorded comparatively higher heat units than the late planting (October 1 and November 1) for all cultivars. Both early and late plantings recorded the higher helio-thermal units at advanced growth phases than at the early stages. The pheno-thermal indices at the earlier growth stages were significantly higher for early planting than the late plantings. The heat use efficiency (HUE) was found to be higher under normal planting as compared to the late plantings. Popular maize variety Rampur Composite was found to be the most suitable to produce stable HUE than the other varieties tested. The specialty corn cultivars could not show stable yield in late planting conditions suggesting their planting could be better for September sowing during early winter seasons. DOI: http://dx.doi.org/10.3126/ajn.v2i0.7526 Agronomy Journal of Nepal (Agron JN) Vol. 2: 2011 pp.111-120