In India, rice field covers an area of 43.94 million hectares (mha) with production of 106.54 mt and has the share of 21% in global rice production during 2013-14. Of the total rice area, 49.5% (22 mha) is irrigated, 13.5% (6 mha) is upland, and 32.4% (14.4 mha) is rainfed lowland.
In Asia, 90% of fresh water has been exploited by agriculture and more than 50% is utilized to irrigate rice. More than 75% of the rice supply comes from 79 mha of irrigated land. Therefore, food security is challenged and threatened by declining water availability. By the end of 2025, 2 mha of dry season rice and 13 mha of wet season rice would suffer from “physical water scarcity” in Asia. On the other hand, 22 mha of irrigated dry season rice in South and Southeast Asia already experiencing “economic water scarcity”.
Therefore, agriculture scientists looking for different approaches to reduce water use and increase the water use efficiency for rice production. An alternative approach to reduce water consumption and labour drudgery in rice cultivation is the concern.
Direct seeded rice (DSR), helps farmers to earn more carbon credits than transplanted rice (TPR) by mitigating methane emission and has higher economic returns, saves water and reduces labour requirement. DSR is the long - standing common technique practiced in many parts of the world, by broadcasting seeds directly on dry or puddled soils, dropping seeds in moist soil behind country plough or manual seeding.
Dry DSR is broadly practiced in rainfed uplands, lowlands and flood-prone areas in India. By appropriate crop managed, yield can be achieved comparable with transplanted rice(TPR) which demands more water, unwieldy, time consuming and incurs expenditure on raising nursery and transplanting. Scarcity of labour or not having access to transplanter, increasing production cost, uncertain supply of irrigation water by canal or delay in water release from reservoir and depletion of groundwater demands for an alternative approach to the conventional puddled TPR.
The productivity of water is very low in TPR system as it demands 3000 to 5000 L of water to produce 1 kg rice. Due to urbanization and increase in demand of water for intensive agriculture and industrial sector, affects the sustainability of agriculture production and in particular to rice in south Asia.
Pumping of more water from deep bore wells for intensive agriculture leads to decline in water table and poor water quality for irrigation. It is evident from states of Haryana and Punjab, where water table has declined. In central Punjab, groundwater table has fallen at about 23 cm in one year and 3-10 m over the last two decades in Haryana.
Similar situation may arise in future, in other parts of south Asia. Over exploitation of ground water may lead to depletion of water level and pollution due to arsenic contamination, as that was observed in many parts of West Bengal. Therefore, water-use efficiency must be increased in agriculture, particularly in rice cultivation.
DSR as a resource conservation technology which has several advantages over TPR system. It helps in reducing water consumption as it does away with raising of seedlings in nursery, puddling and transplanting. Thus, it reduces the labour requirement to the extent of about 40%, and saving water up to 60% from nursery raising, field preparation, seepage, percolation and evaporation loss.
Due to elimination of nursery and puddling of main field preparation, and reduction of water pumping for irrigation has saved to the tune of up to 60% energy (diesel). Under DSR, transplant injury is avoided and establishes earlier than TPR with more growth and attains physiological maturity. Therefore, exposure to late-season drought is avoided.
Possibility of early maturity (7-10 days), timely sowing of current season crop and succeeding crop are the additional advantages of DSR. Further, it helps to avoid disturbing the soil structure and reduces drudgery to farm women by eliminating transplantation. As a result, Rs 5000-6000 ha-1 could reduce in the cost of cultivation.
While, gross returns in DSR and TPR were Rs 90418 and 93564 ha-1, respectively with net return of Rs 59424 in DSR and Rs 57754 in TPR ha-1. The net income of DSR was higher than TPR due to lower cost of cultivation and it is due to substantial reduction in machineries (41.34%), irrigation (22.45%) and human labour (6.62%).
Direct seeding is done in three ways, water seeding (seeding in standing water), wet seeding (seeding pre-germinated seeds in puddled soil) and dry seeding (seeding in dry soil).
Water seeding is widely practiced in USA, principally to manage weedy rice. While, in developing countries as Philippines, Sri Lanka, Malaysia, Thailand and Vietnam are adopting wet seeding to manage labour shortage. Dry seeding is negligible in irrigated areas, but it is practiced traditionally in rainfed upland ecosystems of the Asian countries.
In Asia, South Asia and India, rice is direct-seeded around 21, 26 and 28% respectively. Rainfed uplands, lowlands, and flood-prone areas of Asia are adopting dry seeding technique.
In recent years, certain states of India like Uttar Pradesh, Punjab, Bihar, Haryana, Terai region of Uttaranchal, Odisha, Chhattisgarh and West Bengal are shifting their pattern of rice cultivation towards DSR in appropriate eco-systems. For either way of sowing (dry/wet) technique, the gain of adopting DSR technology depends on precision land leveling, that helps in uniform irrigation, uniform and better germination, controlling weed emergence and increase water use efficiency.
Other than the management, selecting varieties according to the availability of irrigation source and soil type is important to achieve desired yield. Therefore, early to medium duration varieties of 100-135 days and medium to late maturing varieties of 135-165 days are suitable for light textured sandy loam and heavy textured clay soils respectively.
However, Prerequisites for a successful crop of DSR are land leveling with water management, good crop establishment, weed and nutrient management.
Water saving in DSR
Substantial water saving is possible in DSR system. DSR trials conducted in Haryana by adopting zero or reduced till system had good grain yield comparable with TPR under less water with more water productivity and greater net profit. Moreover, it increases net return, efficiency in water and fertilizer use. Under DSR, increase in panicle number per unit area, panicle length, grain numbers panicle-1 and 1000 grain weight were observed.
A study in Philippines, reported that direct wet-seeded rice out yielded TPR by 3-17% with 19% less water and increase in water productivity by 25-48% during the crop growth period. Water management is essential, particularly during crop emergence phase of first 7-15 days after sowing with judicious moisture in the soil to avoid seedling rotting.
One hundred and fifty millimeter of water is sufficient for initial establishment of rice against 450 mm needed for transplanting. During crop establishment phase, irrigations are required at the interval of 3-5 days after initial irrigation. Subsequently, irrigation should be done at an interval of 5-7 days in DSR. Established rice plant in DSR system is more efficient in using soil moisture, requires less frequent irrigation during the growing season due to deeper roots.
On raised bed system of DSR, water use was reduced by 12-60% and increase in yield by 10% as compared to TPR. On the other hand, dry DSR saves water 35-55% when soil kept near saturation or field capacity compared with continuously flooded (~5 cm) transplanted rice. On an average, 32% of water could be saved in DSR compared to TPR without any yield penalty.
However, moisture stress should be avoided by keeping the soil wet at tillering, panicle initiation, and grain filling stages of the crop. Moisture stress at the time of anthesis will result in maximum panicle sterility. Optimum moisture should to be maintained during active tillering phase (30-45 days after sowing) and panicle emergence to grain filling stage by irrigating at 2-3 days interval to harvest optimum yield from DSR.
Labour cost and weed management in DSR
Urbanization and interest towards less drudgery work has direct effect on agriculture. Therefore, shortage of labour causes increase in transplanting cost and delay in planting. Direct seeding reduce labour cost to the tune of 40-45% by avoiding nursery raising, transplanting and saves tractor use of 50-60% in the form of labour to operate tractor, fuel, maintenance cost and time.
Apart from these possible benefits, DSR suffers from major bottleneck of high weed infestation, a potential threat for DSR that are difficult to control. In DSR, conducive condition makes weeds to germinate faster, which competes with rice for moisture, sunlight and nutrients.
To overcome this problem, four to five decades back farmers have switched over to transplanted rice with continuous flooding. Anaerobic condition, under transplanted situation enhances easy seedling establishment, suppresses weeds, and increases nutrient availability (e.g. iron, zinc, phosphorus). Several on-station experiments demonstrated effective management of weed helps in obtaining grain yield comparable to TPR.
Therefore, integration of physical, mechanical and cultural measures along with suitable herbicide are imperative to make weed management effective and economical.
Imparting knowledge on judicious use of herbicide to the farmers must be imparted to avoid development of herbicide tolerant weeds, which will have devastating impacts on production costs and yields.
Several experiments conducted at national level by agricultural universities and with IRRI collaboration, demonstrated that the use of pre-emergent herbicide of pendimethalin at 1 kg a.i. ha-1 dissolved in 500-600 L of water followed by post emergence application of metsulfuron methyl 10% + chlorimuron ethyl 10% WP herbicide at a very low dosage of 20 gm ha-1, is effective for broad leaved and sedge weed management in rice.
Paired row planting pattern by 15-30-15 cm row spacing had pressure on weeds as compared to normal row planting. The rapid growing nature of sesbania suppresses broadleaf weeds and grasses. Therefore, raising sesbania with rice and killing sesbania about 25-30 DAS with 2,4-D ester, helps to overcome weed pressure. Sesbania reduces 76–83% and 20–33% of broadleaf and grass weed density respectively and total weed biomass by 37–80% compared with a rice crop grown alone.
Field leveling for DSR
Uniform field level plays a vital role in DSR. The unevenness of land cause unequal water distribution and that leads to more yield variability within a field and poor crop establishment. Uneven land associated with water inundation in low level of soil profile and affects seed germination.
Precision land leveling is imperative practice and it facilitates uniform and good crop establishment, control over water application, limits irrigation application losses to the tune of 20-25% and reduced 35% of labour requirement for irrigation. Poorly leveled field had an average yield loss of 0.9 t ha-1.
Traditionally, leveled fields though look even but may have deviate up to ± 6 cm or more from the average elevation. Therefore, laser assisted leveling helps to maintain the field surface within ± 2 cm. Precision leveling with laser, improves water use efficiency and saves a minimum of 15 cm water in rice-wheat cropping sequence.
Laser leveling in DSR increases 2.94 and 14.43% of grain yield and water productivity respectively compared to transplanted rice. Thus, laser land-leveling is a prerequisite technology and doorway for success of DSR through improved water and crop management.
Rice varieties for DSR
As yet, no specific varieties possessing all suitable traits of DSR have been developed, but researches are involved in developing high yielding rice genotypes suitable for direct seeding condition. Genotype with good mechanical strength in the coleoptiles to make easy emergence of the seedlings under crust conditions, weed competitive genotype with early seedling vigour, efficient root system to tap soil moisture and nutrients from lower layers and yield stability are desirable traits for DSR.
Early maturing and photoperiod-insensitive rice varieties with better drought tolerance are suited for DSR. At Bulandshahr in Uttar Pradesh, under direct seeded aerobic conditions, with irrigation around field capacity rice varieties like Pusa Sugandha 3, Pusa Sugandha 4, Pusa Rice Hybrid 10, and Pusa Sugandha 5 yielded 4.75-5.75 tonnes of grains per hectare.
It was observed that, yields are on par with transplanted rice if crop is properly managed. Genotypes with anaerobic germination and early submergence tolerance are important for good crop establishment in DSR under rainfed lowland condition during heavy rainfall or uneven field condition. When seeds are placed deeper in the soil during sowing, the crop establishment is affected due to short mesocotyl in the present day high yielding varieties.
On the Other hand, cultivar suitable for DSR should possess intermediate plant height, high specific leaf area during vegetative stage and low specific leaf area during the reproductive phase with high chlorophyll content, lodging resistance and high yield. In addition, panicles should be placed within the plant’s canopy, which increases lodging tolerance.
DSR occupies a major area in eastern part of India, comprising of Eastern Madhya Pradesh, Eastern Uttar Pradesh, Bihar, Assam, Odisha, West Bengal and North-Eastern Hill region. The topography of these regions is generally unbunded and dry, henceforth direct seeding is a common practice.
Seeding is done under dry condition of May to June and harvested during September to early October. The varieties suitable for this system of rice cultivation developed by ICAR-National Rice Research Institute, Cuttack, India are listed in Table 1.
Table 1. List of varieties released from CRRI for upland and bunded upland ecosystem
|S.No.||Variety||Duration (days)||Yield potential (t/ha)|
|17||CR Dhan 40||110||3.5|
|18||CR Dhan 100 (Satyabhama)||105-110||4.7|
|19||CR Dhan 101 (Ankit)||110||4.0|
Pest and Diseases management in DSR
Similar pests and diseases were observed in DSR as that of transplanted rice with different intensity, due to high rice plant density. The increase in infection of brown spot and blast diseases and plant hoppers were reported in DSR.
In Brazil, Gaeumannomyces graminis var. graminis, a soil borne pathogenic fungus was observed in dry-seeded rice. On the other hand, population of root-knot nematode Meloidogyne graminicola increased under aerobic situation causes severe damage to rice plants.
Cultivation of resistance varieties and summer ploughing are recommended to reduce diseases and pest incidence with judicious use of nitrogenous fertilizer to avoid the incidence of blast disease and brown plant hopper.
Problems associated with DSR
Grain yield is often lower in DSR than TPR, due to increase in weed growth, poor crop stand, high percentage of panicle sterility, crop lodging, and root-knot nematode infestation.
A major constraint in broader adoption of DSR is heavy weeds and cost involved in weed control. Another major concern is prevalent of micronutrient deficiency such as Zn and Fe, due to imbalanced N fertilization and high infiltration rates in DSR. Such problems associated with DSR would change the future pattern of rice cultivation.
Nitrogen loss by denitrification, volatilization and leaching is higher in case of dry-DSR. To avoid imbalanced in N fertilization, leaf colour chart (LCC) is recommended, to adjust the dose based on the leaf colour during active tillering and panicle initiation stage.
Zinc deficiency is now becoming prevalent in most rice growing area. Therefore, zinc is recommended as basal in the form of zinc sulphate at the rate of 25-50 kg ha-1 or can be top dressed within 45 days after sowing.
Two to three foliar application spray of 0.5% zinc sulphate at an interval of 7-15 days can be done to correct deficiency. Deficiency of iron is become evident in aerobic soil, due to oxidation of available ferrous form to unavailable ferric form. To correct this deficiency, 30 kg of Fe ha-1 should be applied next to rice rows or broadcasted and has been found quite promising.
To avoid poor crop stand and overcome weed competition, farmers alternatively adopting costly practice of increasing the seeding rate by 2-3 times for DSR. Due to increase in seed rate, excessive vegetative growth before anthesis followed by a reduction in rate of dry matter production after anthesis and lower foliage N concentration at heading will lead to yield losses.
These results in higher spikelet sterility and reduces formation of grains per panicle. On the other hand, dense plant populations creates conducive conditions for diseases like sheath blight and pest as brown plant hoppers. Lower seed rate is preferable for high-tillering varieties and a slightly increased seed rate for medium-tillering types.
Placement of seeds during sowing also affects the seed germination in rice. Rice seeds placed more than 2.5 cm deep, effects crop establishment. Therefore, placement of seeds at desired depth and uniform level, multi-crop planter fitted with inclined plate seed metering system and inverted T-type tines is recommended to have good germination.
Since, the yield of Direct seeded rice (DSR) is comparable with transplanted rice, this is an alternative option to overcome the problem of labour and water shortage. Methane emissions are substantially reduced in DSR. Therefore, its gaining momentum among rice farmers as it is economical than transplanting.
However, the poorly managed field may cause partial to complete failure of DSR crop by weeds and dynamics of soil mineral nutrient. The development of early-maturing varieties with early seedling vigour and efficient nutrient management techniques along with integrated weed management would encourage farmers to switch over from TPR to DSR culture.
On the other hand, knowledge and improvement in technological approaches of direct seed rice with suitable varieties should be imparted to farmers to realize greater benefits of DSR.
A.Anandan*, S.K. Pradhan and O.N. Singh
Crop Improvement Division, National Rice Research Institute, Cuttack