|Production Know How
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1. Sprinkler irrigation system conveys water from the source through pipes under pressure to the field and distributes over the field in the form of spray of 'rain like' droplets. It is also known as over head irrigation.
2. Different types of sprinkler systems namely portable, semi-portable, semi-permanent and permanent are in vogue. But due to increased labour costs and energy costs, different types of sprinklers are developed. Centre-pivot system is largest sprinkler system with a single machine can irrigate up to 100 ha. A centre - pivot sprinkler consists of a series of sprinklers mounted on a lateral pipe, 50 - 800 m long, mounted or carried by a row of five or more mobile towers.
3. One end of the lateral is fixed on a pivot pad. The unit rotates around a centre pivot where water is pumped into the pipe, and water is distributed through sprinkler fitted on lateral.
4. The limitations of this system are,
• 10 - 20 % of area is not irrigated at the corners of square or rectangular plot.
• High energy requirement and Huge cost of the equipment. Now lateral - move systems are developed to overcome the draw backs in centre-pivot system for irrigating square or rectangular plots.
• This irrigation system consists of lateral - move systems which move up and down the field. 5. Sprinkler irrigation can be advantageously chosen in the following situations: a. When the soil is too shallow eliminating the possibility of levelling of lands. b. When the land is too steep (> 1% slope).
1. Drip irrigation is defined as the precise, slow application of water in the form of discrete or continuous or tiny streams of miniature sprays through mechanical devices called emitters or applicators located at selected points along water delivery lines.
2. Drip irrigation is also called trickle irrigation. Drip irrigation is adopted extensively in areas of acute water scarcity and especially for crops such as Coconut, Grape, Banana, Ber, Citrus, Sugarcane, Cotton, Maize, Tomato, Brinjal and plantation crops.
3. The advantages of drip irrigation are :
• No fertilizer nutrient loss due to localized application.
• High water distribution efficiency.
• Levelling of the field not necessary.
• Only root zone is saturated.
• Moisture always at field capacity in the root zone.
• Soil factor plays less important role in frequency of irrigation.
• No soil erosion.
• Highly uniform distribution of water i.e., controlled by each nozzle.
• Low labour cost. • Variation in supply can be regulated by regulating the valves and drippers.
• Fertigation can be adopted with drip irrigation.
• The disadvantages of drip irrigation is expensive i,e., initial cost is more in installing drip method.
1. Water inputs to lowland rice fields are needed to match the outflows by seepage, percolation, evaporation, and transpiration.
2. Seepage is the lateral subsurface flow of water and percolation is the down flow of water below the root zone. Typical combined values for seepage and percolation vary from 1-5 mm d-1 in heavy clay soils to 25-30 mm d-1 in sandy and sandy loam soils.
3. Evaporation occurs from the pond, coping-with-water-scarcity-in-rice-production water layer and transpiration is water loss from the leaves of the plants. Typical combined evapo-transpiration rates of rice fields are 4-5 mm d-1 in the wet season and 6-7 mm d-1 in the dry season, but can be as high as 10-11 mm d-1 in subtropical regions before the onset of the monsoon.
4. Total seasonal water input to rice fields (rainfall plus irrigation) varies from as little as 400 mm in heavy clay soils with shallow groundwater tables to more than 2000 mm in coarse-textured (sandy or loamy) soils with deep groundwater tables.
5. Around 1300-1500 mm is a typical value for irrigated rice in Asia. Outflows of water by seepage and percolation account for about 25-50% of all water inputs in heavy soils with shallow water tables of 20-50 cm depth, and for 50-85% in coarse-textured soils with deep water tables of 150 cm depth or more.
1. Aerobic rice is a production system in which especially developed “aerobic rice” varieties are grown in well-drained, non-puddled, and non-saturated soils.
2. With appropriate management, the system aims for yields of at least 4-6 tons per hectare. Compared with flooded lowland rice, aerobic rice requires 30-50% less water.
3. Aerobic rice can be found, or can be a suitable technology, in the following areas:
a. “Favourable uplands”: areas where the land is flat, where rainfall with or without supplemental irrigation is sufficient to frequently bring the soil water content close to field capacity, and where farmers have access to external inputs such as fertilizers.
b. Fields on upper slopes or terraces in undulating, rainfed lowlands. Quite often, soils in these areas are relatively coarse-textured and well-drained, so that ponding of water occurs only briefly or not at all during the growing season.
c. Water-short irrigated lowlands: areas where farmers do not have access to sufficient water anymore to keep rice fields flooded for a substantial period of time.
1. In the system of raised beds, rice is grown on beds that are separated by furrows through which the irrigation water is coursed.
2. In irrigation engineering terms, the system of raised beds is comparable to “furrow irrigation”. Irrigation is intermittent and the soil of the beds is dominantly in aerobic conditions; hence the system can be considered an aerobic rice system.
3. In general, furrow irrigation is more water efficient than flash-flooding, and furrow irrigation should hold promise for aerobic rice. Though dimensions may vary, beds are usually around 35 cm wide, separated by furrows that are 30 cm wide and 25 cm deep.
4. Rice can be transplanted or direct seeded on the beds.
5. Among the potential benefits of raised beds are improved water and nutrient use efficiency, improved water management, higher yields, and – when the operations are mechanized – reduced labour requirements and improved seeding and weeding practices.
6. However, raised beds for rice are still in the experimental phase and a number of problems still need to be overcome.
1. Plastic film with its moisture barrier properties does not allow the soil moisture to escape. Water that evaporates from the soil surface under mulch film, condenses on the lower surface of the film and falls back as droplets.
2. Thus moisture is preserved for several days and increases the period between two irrigations.
3. The irrigation water or rainfall either moves into the soil through holes on the mulch around the plant area or through the un-mulched area.
4. Water erosion is completely averted since soil is completely covered form bearing action of rain drops.
1. AWD is also called ‘intermittent irrigation’ or ‘controlled irrigation’.
2. In alternate wetting and drying (AWD), irrigation water is applied to obtain flooded conditions after a certain number of days have passed after the disappearance of ponded water.
3. The number of days of non-flooded soil in AWD before irrigation is applied can vary from 1 day to more than 10 days.
4. AWD increased water productivity (WPIR) with respect to total water input because the reductions in water inputs were larger than the reductions in yield.
5. More water can be saved and water productivity further increased by prolonging the periods of dry soil and imposing a slight drought stress on the plants, but this usually comes at the expense of a slight yield loss.
6. AWD is a mature technology that has been widely adopted in China, India and Philippines. Very little research has been done in Guyana to quantify the impact of AWD on the different water outflows of rice fields: evaporation, seepage, and percolation.
1. In saturated soil culture (SSC), the soil is kept as close to saturation as possible, thereby reducing the hydraulic head of the ponded water, which decreases the seepage and percolation flows.
2. SSC in practice means that a shallow irrigation is given to obtain about 1 cm of ponded water depth a day or so after the disappearance of ponded water.
3. Although conceptually sound, SSC will be difficult to implement practically since it requires frequent (daily or once every two days) applications of small amounts of irrigation water to just keep a standing water depth of 1 cm on flat land, or to keep furrows filled just to the top in raised beds. But can be an alternative if the situation become worsens.
Different ways of managing the water scarcity include
1. Saturated soil culture.
2. Alternate wetting and drying.
4. Raised beds.
5. Aerobic rice.
6. Managing water in low laying areas.
1. Ripening is the last phase of the growing period includes the milk, dough, yellowing and full ripening grain stages.
2. Very little water is needed at this period and after the yellowing ripening stage no standing water is required.
3. This allows draining of a field about 10 days before harvest and facilitates harvesting by machine.
4. Rodent damage may increase on drained fields.