Rice (Oryza sativa), source of food and livelihood of the major population in world. Rice cultivation in puddled soil followed by execution of high dose of water for controlling weeds in the presence of water crisis lead to decreased productivity of water also shortage of labour for raising nursery and transplanting seeding are the variables of conventional rice cultivation.
However, recent technology of rice cultivation involving direct sowing of rice seeds in field without preparing nursery and labour-intensive operations including transplanting has benefits of water saving and harvesting high crop yield with high water productivity with non-puddled conditions.
Competitive weeds can cause a marked deficiency of water and plant substances by having a higher and early response to these plant growths promoting substances hence poor yield of rice. Sustainable yield in direct seeded rice, demands weed management that is the major hurdle. In this chapter different methods of weeds control along with their advantages and difficulties during their applicability are discussed in detail.
Weeds infestation not only provide stressful conditions to plants but also serve as a host for different insect pests and spores of noxious diseases. Cultural control of weeds has benefits over manual control in terms of labour and time saving, while chemical control of weeds is more efficient and provide a satisfactory control and is economical then other weeds control methods.
However, for obtaining sustainable long term most efficient and economical results to control noxious weeds in direct seeded rice technology integrated weeds control is of prime importance leading to sustainable and higher yield in DSR along with solving of water crisis. However, applicability of a weed control method should be based on the scenario of weeds infestation and available resources along with level of weeds control.
Keywords: DSR, Weeds, Integrated weeds management
Abbreviations: DSR_ Direct seeded rice
Rice, source of stable food and associated livelihood of majority of peoples worldwide. A tremendous shift in dietary habit of most of peoples in world @ 6.0 % to rice create a situation to obtain higher rice yield to meet the demand of the population. Worldwide rice is cultivated on an area of 156 Mha out of which 133 Mha area is under rice cultivation in Asia, having a production of 540 Mt per anum.
In general, most of the population of Asia consume rice, served as staple food of 92% of the lives. In Asia, India is major contributor in rice produce and is second biggest grower of rice after china, where it is cultivated on an area of 45Mha per anum and 90 Mt production. Stand establishment of rice is achieved either by raising nursery followed by transplanting or by direct seeding.
Water intensive nature and labour for transplanting leading to a shift in rice cultivation method from transplanting to either wet or dry direct seeding having increased water productivity leading to low contribution in imminent water scarcity and availability of water during critical hours of crop also solving a problem of unavailability of labour. Direct seed rice technology involves sowing of dry rice seeds in saturated soil or pre-germinated sowing of rice seed in wet/puddled soil leading to efficient water management and less contribution in decreasing of water table.
DSR devoid of labour intensification, increased water productivity and transplanting of seedlings in puddled and standing water conditions. Use of varieties having ability to better stand establishment, early and high vigour leading to cover the whole area thus creating a suppressed and stressful condition to competitive plants are of prime importance in DSR. Sowing of radicle protruded seeds in saturated or puddled soil (Wet Seeding), Dry Seeding (application of dry seeds in soil devoid of saturation) and seeding in stagnant water in field (water seeding).
Different methods of obtaining rice stand establishment in field having some advantages and disadvantages depending on the prevalent situation such as in the presence of labour scarcity situation WetDSR is practiced primarily and is more desirable in countries like Thialand, Sri lanka, Vietnam and Malaysia. Decreasing water table leading to water scarcity problem and can be overcome by using DryDSR technology hence, availability of water in critical hours of crop.
Adaptation of DryDSR technology is most suitable in areas suffering from low availability of irrigated water and prevalent dry condition as compared to areas with plenty of water for irrigating the crop and large amount of water available during critical periods of crop, wet seeding is most desirable. Lowlands and upland areas where the only source of water for irrigation is rainfall, dry seeding of rice is practiced.
The unavailability of water, cultivars having high vigour which is in direct line with high yield and noxious weeds are major hurdles in decreased yield and in some parts of world complete failure of direct seeded rice leading to shortage of rice in areas having rice as staple food. The prevalent situation in direct seeded rice can be overcome by using improved cultivars which respond to inputs by a better way and having fast early growth, adaptation of varieties in water shortage crisis and controlling weeds.
Present Scenario in DSR
A tremendous shift to Direct seeding rice technology was basically driven by acute deficiency of water and availability of expensive labour which causes a severe hindrance. By eliminating water extensive cultivation (TPR), cost of nursery development and labour shortage problems, DSR could be a better adaptive approach as it helps in water saving up to 30% and prevent transplanting shock.
In recent years, there has been a shift from TPR to DSR cultivation in several countries of Southeast Asia. This shift was principally driven by water scarcity issues and expensive labour component for transplanting under acute farm labour shortage. Direct-seeding of rice has the potential to provide several benefits to farmers and the environment over conventional practices of puddling and transplanting.
Direct seeding helps reduce water consumption by about 30% (0.9 million liters acre-1) as it eliminates raising of seedlings in a nursery, puddling, transplanting under puddled soil and maintaining 4-5 inches of water at the base of the transplanted seedlings. The farmer saves about Rs 1400 acre-1 in cultivation cost. Direct seeding (both wet and dry), on the other hand, avoids nursery raising, seedling uprooting, puddling and transplanting, and thus reduces the labour requirement.
Classification of Direct Seeded Rice System:
Table 1. Classification of Direct seeding rice systems.
Direct Seeding System | Seed Conditions | Seed Rate | Sowing method | Practice zone/environment |
Wet Bed Method | Sowing of pre-germinated seeds in saturated condition
| 80-90 kg/ha of pre-germinated seeds | Drilling, Broadcasting | Irrigated and rainfed conditions |
Dry bed Method | Under aerobic condition dry seeds were sown | 60-70 kg/ha for Broadcasting 80-90 kg/ha for drilling | Drilling, Broadcasting or Dibbling | Rainfed area |
Seeding in Stagnant water | Sowing seeds under aerobic and anaerobic condition (Dry/pre-germinated) | 80-100 kg/ha | Broadcasting | Irrigated conditions |
Constraints and solutions in DSR
Weeds
In DSR system with or without tillage seed is sown and irrigation is applied to maintain soil moisture. In this way a handsome amount of irrigation water will be conserved. This method reduces the labour, consumes less time and reduce planting cost. Moreover, soil health will be improved by DSR and it ensure higher profit.
In DSR weeds are major issue which can reduce the yield. Weed management practices can be different in DSR which may depends upon the attitude and financial conditions of the grower. Hand weeding is common method for weed eradication, but it is time consuming. Surface mulching is best method for weed management.
Weeds Management
Physical control is effective way to eradicate the weeds which is done manually or mechanically. Some physical methods are ploughing, disking, cultivating and digging. Crops demonstrate different sensitivity to disturbance, as monocotyledons like cereals are less sensitive than dicotyledons. Harrowing proved effective in direct seeded rice, particularly when weed plants are smaller than crop plants to escape harm.
Mechanical weeding is best for the rice crops which is grown in rows in this way easily the weeds can be removed by some tools or with hands it will take less time however it is very difficult to remove weeds from rice crop.
Biological method for weed control is environmentally friendly approach in which there is use of insects, nematodes, bacteria, fungi or another bio-agent that reduce weed population.
Since from last two decades herbicides have been major contributor to agriculture rather bring a revolution in agriculture. On large scale rice farming, using herbicides for weed management has become the smartest and most viable option due to scarcity and high wages of labour. Moreover, hand weeding becomes less effective at some points due to escape or regeneration of perennial weeds having many flushes.
Water Management
Agriculture sector is the biggest user of water on planet, about 70% of water withdrawals worldwide. In which More than 50% of all water used in agriculture is used to irrigate the rice crop. By adopting water conserving direct seeded rice technology, it would be possible to mitigate the problem of water crises.
Conclusion
Direct seeded rice technology (DSR) is a good adaptive approach to mitigate the waste of water hence having higher yield potential as compared to transplanted rice.
Talha Javed, Shahnawaz and Muhammad Asif
Department of Agronomy, University of Agriculture, Faisalabad, Pakistan
Corresponding author: talhajaved54321@gmail.com