Managing Drought through Direct Sowing

The main systems of rice culture are Irrigated Lowland, Rainfed Lowland, Rainfed Upland and Irrigated Upland. Irrigated rice, rainfed lowland rice, rainfed upland rice and rice from flood prone areas account for 75%, 17%, 4% and 4% respectively of global rice production.

Traditional Way of Paddy cultivation:

Seeds soaked in water for 24 to 36 hours are incubated for about 48 hours in a warm environment to facilitate  germination and the pre-germinated seeds are broadcast on the drained seedbeds of the nursery, which is kept wet for 5 days and gradually flooded thereafter. The seedlings after a nursery time, roughly equivalent to 3 and 2 weeks respectively in case of varieties of 4 to 4 ½ months and 3 months duration, are transplanted in the main field.  Prior to transplanting, the soil in the main field is puddled i.e. ploughed and harrowed and finally leveled with standing water in the field. Water from the main field is drained only towards harvest of the crop. 

Disadvantages: 

• Irrigated lowland rice requires enormous amount of water for field preparation. This process requires more water through out the crop period except pre-harvest period.
• It is a labor intensive farming method as it needs manpower to prepare nursery maintenance, pluck the seedlings from the nursery, transportation to main field, transplantation in main field.
• In main field, the seedlings experience transplantation shock. Transplantation shock delays phenological development of the crop, especially tillering. Recovery from transplantation shock and  potential yield, increase and decrease respectively with increase in age of seedlings.
• Rice production contributes to global climate change through emissions of methane and nitrous oxide and in turn suffers from the consequences. Methane is formed in soil through the metabolic activities of a small but highly specific bacterial group called methanogens. Their activity increases in submerged, anaerobic condition developed in wetland rice fields, which limit the transport of oxygen into the soil, and the microbial activities render the water-saturated soil practically devoid of oxygen. The upland, aerobic soil does not produce methane.  

 Water management:

Water management plays a major role in methane emission. Altering water management practices, particularly mid-season aeration by short-term drainage as well as alternate wetting and drying can greatly reduce methane emission in rice cultivation. Improving organic matter management by promoting aerobic degradation through composting or incorporating into soil during off-season drain period is another promising technique. 

Availability of water to raise requisite area of nurseries ahead of the normal dates of  availability of surface irrigation is a major constraint in many areas. To overcome the weather-related constraint, direct  seeding of rice is being increasingly resorted to.Due to failure of monsoon and ground water level going down makes agriculture a big question mark. Farmers are left to take decision of summer ploughing followed by repeated ploughing to make the soil to fine texture and wait till monsoon rain come and go for direct sowing. 

 Direct seeding methodology:

In this method, seeds are sown directly in the fields. It has shown a substantial reduction in water consumption and also in the production cost. This helps the crop to mature 10 to 15 days earlier than traditional method due to skipping of transplantation shock. The direct seeding also has the additional environmental benefit of reducing emission of greenhouse gases like methane apart from improving soil porosity which can increase productivity of the succeeding crop.

The methodology including paddy direct seeder can save about 30 per cent of water in the direct seeded fields and also can reduce farmers cultivation cost by '2,500 per acre, as no manual labour is needed to transplant paddy.

 

Direct seeding rice, a common practice before green revolution in India, is becoming popular once again because of its potential to save water and labour. Currently, direct seeded rice in Asia occupies about 29 Mha which is approximately 21% of the total rice area in the region. Direct seeding of rice are with profitable results as it avoids all the penalties entailed in transplanting. Direct seeded rice under no/reduced tillage is an efficient resource conserving technology (RCT) holding good promise in coming days because of the following advantages over

transplanting of rice. 

• Labour required for nursery raising, uprooting and transplanting of seedlings are saved to the extent of about 40%. 
• Saving of water (up to 60%) as nursery raising, puddling, seepage and percolation are eliminated. 
• Fertilizer use efficiency is increased because of placement/application of fertilizers in the root zone. 
• Early maturity (7-10 days) helps in timely sowing of succeeding crops. 
• Energy saving (up to 60% of diesel) because of elimination of field preparation for nursery raising, puddling and reduced water application for irrigation. 
• Reduction in methane emission and global warming potential. 
• Soil structure is not disturbed in direct seeded rice as occurs in puddled transplanted system. 
• Less drudgery to farm women labours because of elimination of transplanting. 
• System productivity is enhanced. 
• Cost of cultivation is reduced by about ‘ 5000-6000 ha-1

PRODUCTION TECHNOLOGY FOR DSR

Under the DSR technology sowing of rice seeds is done directly in the soil where they are to grow, rather than

transplanting seedlings. Direct seeding methods could be divided into wet (pre-germinated seeds) seeding and dry seeding. In wet seeding pre-germinated seeds are broadcasted into puddled and leveled field which are free from standing water. At the time of puddling basal fertilizer mixture should be added. After germination of seed, seedling desiccation due to water stress should be avoided by intermittent wetting of the field. When seedlings are of about 5 cm tall (about a week after sowing) water is impounded to prevent germination of weeds and desiccation of seedlings. The stand establishment by this method varies with the quality of land preparation, weed competition, water management and rainfall during the initial period after sowing. Following factors contribute significantly in achieving the optimum productivity of DSR under irrigated condition.

Land preparation

This is a pre-requisite for good crop husbandry. Plowing the fields during summer season helps controlling weeds. In DSR technology precision land leveling has been proved advantageous for better germination, controlling weeds emergence, uniform irrigation saving considerable amount of water and increasing water use efficiency with ultimate increase in grain yield.

 

Time of sowing

This is a critical point to achieve the success in DSR crop in the main rice growing season (kharif). The sowing of crops should be accomplished before 10-15 days of onset of monsoon. The crop should attain 2-3 leaves before rain starts. This would facilitate the early root establishment so that crop could compete with emerging weeds easily.

Seed priming

In order to enhance the seed germination, seed priming i.e., seeds soaking over night in water and then dried in shades before sowing. Seed treatment should be done with bavistin at 2.5 g kg-1 to prevent the seed-borne diseases. 

Seed rates, row spacing and seeding depth 

With zero till ferti-drill sowing, the optimum seed rates for fine grains, basmati cultivars is 15-20 kg ha-1, coarse grains 20-25 kg ha-1 and for hybrids 8-10 kg ha-1. Use of planters having inclined plate devices or a cupped metering system is very useful for proper spacing (20 cm) and reducing seed rate. For broadcasting a higher seed rate (25-30 kg ha-1) is required.Seeding depth plays key role for good germination. Depth should not be kept more than 3 cm for desired level of crop stand. Placement of seeds below 3 cm adversely affects
dynamics of seed emergence because of rapid drying of the upper layer soil moisture.

Water management

Usually a pre monsoon rain occurs during mid May to mid June in almost all the regions of the IGP. If the adequate rains are received this can be  utilized for killing the first flush of weeds through non-selective herbicides (glyphosate and paraquat) under stale seed bed technique and for sowing direct seeding rice crop through zero till  machine. In case, no rain is received during mid May to mid June, a pre-sowing surface irrigation is required. In fact, after seedling to crop emergence, no irrigation is required and soil should be moist but not saturated from sowing till emergence. During transit period of crop emergence and commencement of monsoon, one or two
irrigations are required. After commencement of rains, no further irrigation is needed unless dry spell occurs. During dry spell, irrigations may be given as life saving irrigations, particularly during the critical growth stages i.e., tillering, panicle initiation, flowering, milking and grain filling. Irrigation at alternate wetting and drying has been considered as most effective and economical in DSR as it improves rooting systems and reduces
lodging.

Nutrient management

Nutritional requirement should be met on the basis of soil analysis of the crop field. In absence of soil analysis,
following fertilizer schedule should be adopted.

• Blanket application of 120-150 kg N ha-1, 60 kg P2O5 ha-1 and 40 kg K2O ha-1 may be applied along with 25 kg  ZnSO4ha-1.
• In light textured soil, ¼ N and full amount of P2O5 and K2O should be applied basally. The remaining amount of N should be applied as top dressing into two splits at maximum tillering and panicle initiation stage.
• In clay loam soil, half N and full amount of P2O5 and K2O along with Zn and S should be given as basal dose and remaining half of N may be given into two installments i.e. at maximum tillering and at panicle initiation stages.
• In DSR, iron deficiency usually occurs especially in light textured sandy loam soils. It leads to iron chlorosis in leaves. This deficiency could be mitigated through the application of iron sulphate (FeSO4). 
• Diammonium phosphate (18 N : 46 P2O5) and NPK (12 N :32 P2O5 : 16 K2O) are applied basally through zero till fertidrill machine. Due to hygroscopic nature of urea, the drilling of fertilizer is not properly done. In this case, the remaining amount of N through urea could be applied as top dressing. 
• Leaf Colour Chart (LCC) has been proved very advantageous in economizing the nitrogen application. For hybrids and high yielding inbred rice, N application should be based on a critical LCC value of 4.  However, a critical LCC value of 3 is used for scented basmati type rice cultivars. Values of the LCC should be recorded 3 weeks after sowing and should continue till heading.

Weed management

Weeds are great menace in DSR during rainy season and inadequate weed management led to severe loss in grain yield. In puddled transplanted rice, standing water does not allow weeds to emerge. In DSR, conditions are more favorable for the germination of weeds, which competes with rice for nutrients, moisture and sun light causing large yield losses. The important weeds associated with irrigated direct seeding rice crop are
listed below -

Weed group            Weed species                                 

Grassy                     Echinochloa colona,  E. Crusgalli, Digitaria sanguinalis, Dactyloctenium aegyptium,  

                                Leptochloa chinensis, Eleusine indica, Cynodon dactylon, Paspalum distinchum, 
                                Ischaemum rugosum                  

Broad-leaved          Trianthema monogyna, Commelina benghalensis,Caesulia axillaris, Sphenoclea 

                               zeylaica, Marsila minuta, Ludwigia spp., Monochoria vaginalis

Sedges                   Cyperus rotundus, Cyperus iria, Fimbristylis littoralis, Cyperus difformis, Scirpus  

                               juncoides                             


It is very difficult rather uneconomical to keep DSR crop weed free throughout crop period. Pre-germinated weeds can be knocked down with glyphosate/grammoxone (at 0.5% two days before seeding) or by 1-2 very shallow ploughing (stale seed bed method). Second flush of weeds can be removed manually It has been proved that weed free conditions provided during 2-6 weeks after sowing gave optimum grain yield of DSR. Based on several trials conducted under different SAUs and IRRI collaborated projects, following herbicides have been
found effective against annual and perennial weed species in DSR.



Herbicide                          Dose (kg a.i. ha-1)     Time of application        Target weed
Paraquat                             0.5                             1-2 DBS                          All types of weeds
Glyphosate                        1.2 -1.6                        7-15 DBS                        All types of weeds
Pendimethalin                    1.0                               1-2 DAS                         Grasses, broad leaved
Pretilachlor + safener z       1.5                               1-2 DAS                         All types of weeds
Ethoxysulfuron                   15                                10-15 DAS                     Sedges, broadleaved
2,4-D                                 0.5                               20 -25 DAS                    Sedges, broadleaved

Use of herbicides

Paraquat: It is a contact and non-selective foliar herbicide, which can be applied on emerged weeds before
sowing. Weed mortality takes place within 6-8 hours of application. The DSR crop may be sown after 1-2 days following the application of the herbicide.
Glyphosate: It is non-selective highly translocated herbicide, very effective against perennial grasses reproducing
through underground rhizomes, tubers and stolons. This herbicide may be applied on the foliage of emerged weeds prior to sowing of DSR. It is inhibitor of acetolactate synthesis. A rain free period of 6-8 hours is necessary following the application of herbicide. The DSR crop may be sown 15-20 days after application of this herbicide as it takes 2-3 weeks time for complete mortality especially perennial grasses.
Pretilachlor with safener: It is selective herbicide absorbed by hypocotyls and coleoptiles and roots of
germinating weeds. It is applied as pre-emergence for controlling annual grasses, broadleaved and sedges. Pretilachlor causes phyto-toxicity in rice and hence is always used with safener.
Pendimethalin: It is soil applied herbicide and usually applied as pre-emergence to control seasonal grasses and broadleaved weeds. It is absorbed by roots and coleoptiles and acts by inhibiting cell division and cell elongation. 
2,4-D: It may be applied  at 30-35 days after sowing in DSR crop to knock down the broadleaved weeds. It is available in sodium, amine and ester forms. The amine and ester forms are comparatively more effective than sodium salts. 
Chlorimuron ethyl + metsulfuron methyl ready mix: It is applied as post-emergence to control broadleaved weeds and sedges.
Ethoxysulfuron: It is used as early post emergence and mainly taken by roots and leaves and translocated within the plants. This could be used successfully in DSR for controlling broadleaved weeds and sedges.
Azimsulfuron: This is a post-emergence herbicide and could be used 15-20 days after sowing or 2-3 leaf stage to
check the grasses, broadleaved weeds and sedges. This herbicide is absorbed by roots and leaves and inhibits
acetolactate synthase in susceptible weed plants. 

Integrated weed management

There is hardly any herbicide which could control the menace of all types of weeds in a single application. Integration of preventive, physical, mechanical, cropping and cultural measures along with low doses of herbicides is imperative to make weed management effective, economical and eco-friendly.