Rice (Oryza sativa L.) is life for more than half of humanity. It is the most important cereal crop and is the staple diet of 70 per cent of the world’s population. About 90 per cent of the world’s rice is produced as well as consumed in Asia (Solunke et al 2006). Rice provides 30 to 75 per cent of the total calories to more than 3 billion Asians. It is the main staple food crop of India, covering 42 million hectares with a total production of 89.2 million tonnes and productivity of 21.9 q ha-1. In Punjab, rice occupied 2.8 million hectares with total production of 10.8 million tonnes and productivity of 38.3 q ha-1 (Anonymous 2012).
The developing world is facing the ramification of four inter-related problems viz; the energy crisis, food shortage, poverty and under-employment as a consequence of population explosion. To meet the global rice demand, it is estimated that about 114 million tonnes of additional milled rice need to be produced by 2035 which is equivalent to an overall increase of 26 per cent in the next 25 years (Kumar and Ladha 2011). The demand for food grains in India is increasing day by day and the requirement for the year 2025 is estimated to be increased by 40 per cent as compared with 2003-04. The possibility of expanding the area under rice in the near future is limited. To sustain present food self-sufficiency and to meet future food requirements, India has to increase its rice productivity by 3 per cent per annum (Geethalakshmi et al 2011). There has, however, been stagnation in rice productivity in recent years and long-term experiments showed a declining trend in rice yield. Further, increasing production costs lead to lowering of the benefit:cost ratio. There is dire need for change in rice production methods to improve productivity, economics and long-term sustainability.
Manual transplanting of paddy seedlings in standing water after puddling is the leading method of crop establishment in irrigated rice systems of Asia. With the advances made in rice-based cropping systems, it has been realised that repeated puddling damaged the soil structure which adversely affects the soil productivity (Singh et al 2005 b) and can negatively affect the following non-rice upland crop in rotation (Tripathi et al 2005). In Asia, irrigated agriculture accounts for 90 per cent of total diverted fresh water and more than 50 per cent of this is used to irrigate rice. The water productivity of rice in terms of evapo-transpiration is not different from other C3 cereals such as wheat. The higher water application in rice is mostly due to water requirements for puddling and losses associated with continuous flooding such as seepage and deep percolation losses to ground-water (Hafeez et al 2007). Land preparation for rice consumes about 20-40 per cent of the total water required for growing the crop (Bhuiyan et al 1995). This is the main reason for very low water productivity of traditionally grown lowland rice production system (IRRI 2001). Transplanting is labour intensive (30 person ha-1 day-1). Moreover, with decreasing arrival of migrant labourers due to Government policy (The Mahatma Gandhi National Rural Employment Guarantee Act, introduced by Indian Government in 2005, promising 100 days of paid work in people’s home village) for the last few years, timely transplanting of rice is hampered in the cereal bowl of North-West India.
Due to receding water table (Humphreys et al 2005), rising costs of labour for transplanting of paddy (Singh et al 2005 f) and the adverse effects of puddling on soil health (Timsina and Connor 2001); direct seeded rice (DSR) is gaining popularity which has been the principal method of rice establishment since the 1950s in developing countries. The farmers with differing levels of resources, land development, infrastructure and weather conditions may dictate different direct-seeding practices in the Indo-Gangetic Plains. According to Pandey and Velasco (2005) depending upon water and labour scarcity, farmers are changing either their rice establishment methods only (from transplanting to direct seeding in puddled soil Wet-DSR) or both tillage and rice establishment methods (puddled transplanting to dry direct seeding in unpuddled soil Dry-DSR).
Direct seeding is a good alternative of transplanting and yield potential of direct seeded rice is equivalent to the transplanted rice under good water management and weed control conditions (Awan et al 1989). Direct seeded rice yielded higher than traditional transplanted rice by 3-17 per cent and required 19 per cent less water with increased water productivity by 25-48 per cent (Tabbal et al 2002). De Datta (1986) reported that rice production in Asia requires 32 man days per hectare for a direct seeded crop as compared with 63 man days per hectare for a transplanted crop. Direct seeded rice requires only 34 per cent of the total labour and saves 29 per cent of the total cost of the transplanted crop.
At global level, 23 per cent rice is direct seeded. In Asia, this crop is grown as direct seeded in an area of about 29 million ha which is approximately 21 per cent of the total rice area in the region (Pandey and Velasco 2002). Rice is planted mainly through direct seeding in United States, Australia and Europe. Broadcasting and dibbling are the main methods of rice seeding in Africa. However, direct seeding on saturated soil has been widely adopted in Southern Brazil, Chile, Cuba and Caribbean countries. Direct seeded rice is also becoming popular in tropical Asian countries like Philippines, Malaysia and Myanmar primarily due to labour shortage. Direct seeding has already replaced transplanting in many parts of South-East Asia. In India, rice is direct seeded on about 42 m ha area in parts of several states, including Bihar, Uttar Pradesh, Madhya Pradesh, Gujarat, Maharashtra, Assam, Andhra Pradesh, Chattisgarh, Orissa, West Bengal, Kerala, Karnataka, Mizoram and the hill state of Uttaranchal (Patil et al 2005).
Mitchell et al (2004) reported results from comparative analysis of DSR and puddled transplanted rice in SE Asia and concluded that DSR is a cost effective alternative and lead to similar yields under good management practices. Walia et al (2009 b) reported that broadcasting dry seed in puddled field recorded the highest yield as compared with direct seeding using conventional drill and zero drill and broadcasting seeds without puddling and transplanting paddy with nursery sown at the time of direct sowing of the crop. However, the differences in grain yield were non-significant. Resource conservation technologies (RCTs) like zero tillage and bed planting are also being promoted in rice-wheat cropping systems (Gupta and Seth 2007), however, in absence of weed control, rice yields are reduced by 35-100 per cent in direct seeded/RCTs systems (Kumar et al 2008 b). The alternative tillage and crop establishment are site specific and therefore, evaluations under wide agro-ecological conditions is important to have significant adoption (Ladha et al 2009). Gopal et al (2010) discoursed the newly developed new-generation precise seeding and land leveling machinery for dry drill seeding for even and uniform crop establishment.
Proper crop establishment can be achieved by optimizing the seed rate. Inter-plant competition varies greatly with seed rate in direct seeded rice (Jones and Snyder 1987). Studies have shown that lower seed rates decreased yield drastically in direct seeded rice. With seed rate lower than optimum, the crop stands remain insufficient for high yields and there may be luxuriant weed growth (Phuong et al 2005). Optimum seed rate varies from place to place. Seed rates range from 20 kg – 60 kg ha-1 in South Asia to 200 kg ha-1 in some South-East Asian Countries (Kumar and Ladha 2011). The optimum plant density is important factor that affects crop micro-environment by influencing the degree of inter and intra-row plant competition. The conventional transplanting in puddled soil requires higher labour costs but plant population in this system is generally low (18-20 plants m-2) as compared with the recommended 35-40 plants m-2 (Malik and Yadav 2008).
Weeds are the main constraint for farmers practising direct seeding since the inherent weed control from standing water at crop establishment is lost (Rao et al 2007). High weed infestation is a major problem in DSR and causes grain yield losses up to 90 per cent (Rehman et al 2007). Manual weed control is also difficult due to difficulty in differentiating grass weeds from rice plants during early growth (Singh et al 2007). Yield losses largely depend on season, weed species, weed density, rice cultivar and its growth rate. The conversion from transplanted to direct seeded rice results in more competitive weed flora so this requires revised weed management approaches for effective weed control. DSR will only be successful provided there is good crop establishment as well as adequate weed control methods are available to provide early competitive advantage against weeds and keep the crop free from weeds (Rao and Nagamani 2007).
Presently, rice is grown as puddled transplanted crop in Punjab. The state water resources are sufficient to sustain only 1.6 m ha of rice cultivation (Bhullar et al 2012 a). It is imperative to reduce its cost of production to make rice cultivation sustainable in the state. Direct seeded rice under assured irrigation conditions has lot of scope. It may prove highly beneficial in saving lot of energy in the form of labour, time, water and capital and is conductive for mechanization. Direct seeded rice is becoming popular as it eliminates many farm operations such as nursery raising, puddling and manual transplanting and hence it reduces cost of production (Walia et al 2012). Some innovative farmers of Punjab state have started growing direct seeded rice adopting different drills with different plant densities which needs standardization. Identifying herbicides with wide-spectrum weed control ability for efficient and economical weed management is also crucial for improving the potential of direct seeding of rice in the state. This is the dire need of day to develop eco-friendly and resource sustaining techniques for the successful cultivation of crop as direct seeded rice. So keeping in view all above, the present investigation entitled, “Performance of direct seeded rice (Oryza sativa L.) in relation to establishment methods, plant densities and herbicides” was planned with following objectives:
1) To study the effect of crop establishment methods on weed dynamics, growth and yield of DSR.
2) To study the effect of plant densities on weeds, growth and yield of DSR.
3) To find out the efficacy of different herbicides on weeds, growth and yield of DSR.
4) To study the interaction effect of crop establishment methods with herbicides and seed rates with row spacings on weeds, growth and yield of DSR.