Methods to improve economic use of water for irrigation

Methods to improve economic use of water for irrigation

    1. Unlimited water supply conditions
    a. Conservation of water
    1. Reduce conveyance losses by lining channels or preferably by using closed conduits.
    2. Reduce direct evaporation during irrigation by avoiding midday sprinkling and minimize foliar interception by under canopy by overhead sprinkling.
    3. Reduce run-off and percolation losses due to over irrigation.
    4. Reduce evaporation from bare soil by mulching and by keeping inter -row strips dry.
    5. Reduce transpiration by weeds, keeping the inter-row strips dry and applying weed control measures where ever needed.
    b. Enhancement of crop growth
    1. Select most suitable and marketable crops for the region.
    2. Use optimal timing for tillage, planting and harvesting
    3. Use appropriate insect, parasite and disease control
    4. Effective fertilization
    5. Conserving soil and avoiding progressive salinization for long-term sustainability
    6. Irrigating at high frequency and at amount required
    • Irrigation is practiced to achieve maximum yield per unit of land and ultimately the profit. When water is becoming scarce maximum yield per unit of water utilized is the concern. A grower is usually concerned about maximizing profit. When water is plentiful and inexpensive this is nearly the same as irrigation for maximum yield. However as irrigation rates approach those needed for maximum yields, water use efficiency declines. If water is scarce or very expensive the interest shifts toward obtaining maximum yield per unit of water applied. This shift usually involves deficit irrigations and the duration of stress, the marketable plant product and the stage of growth when stress occurs. One must consider the economics of deficit irrigation by comparing the savings that result from reducing deficit irrigation to achieve the reductions and the value of crop yield lost that may accompany reduced irrigation.
    2. Limited water supply conditions
    The following points may be considered for managing limited or deficit water supply for getting maximum yield and profit.
    a. Deep soils that have moderately high water holding capacities are suited to deficit irrigation.
    b. Drought resistant crops
    c. Crop growth stage at which irrigation deficits are imposed
    d. Pre-plant irrigation is needed or not, conveyance and application efficiency, water infiltration rates and runoff, thus
    reducing required application amounts

    e. Precipitation need to be considered for crop water requirements
    f. Cultural practices need to be modified to reduce the ET.
    a. Deep soils that have moderately high water holding capacities
    • The amount of water stored in the soil profile and available to a crop to supplement low irrigation rates during high water use periods is an important factor in limited irrigation. Moderate to high amounts of stored water allow water deficits to develop gradually and thus improve the plants’ ability to stand water stress. Small amounts of water allow rapid development of stress within the plant and increase the risk of yield reduction. Low storage may be due to shallow root restricting layers, coarse-textures or subsoil depleted of available water. A soil with a coarse surface texture but underlaid by fine material may store enough profile water to be productive under deficit irrigation.
    b. Use of drought resistant crops
    • Drought resistance is the ability of a crop to grow satisfactorily in areas subject to deficit water. Mechanisms or adaptations have evolved in higher plants that favour survival and growth with inadequate or irregular water supplies. These mechanisms have been classified as drought escape, avoidance and tolerance.
    c. Growth stages of the crop
    • Water is essential for the growth of plants from germination through physiological maturity but the sensitivity to water deficit changes during the growing season.
    • Increased water-use efficiency can be achieved though selection of the crops to be grown according to the expected water supplies (rain and irrigation) and by consideration of the stage of plant growth at which water stress is imposed. Crop production should be timed so that the most sensitive stages of plant development will be completed when deficient water is least likely. A major factor is the marketable plant product, whether vegetative growth, a seed, or a fruit. Because of the great variation among species in the harvested plant part and in the sensitivity to water stress at various growth stages, it is appropriate to discuss crops in general groups.
    i)Crops grown for seed or grain
    • Growth stages for this group can be classified roughly as early vegetative, reproductive and seed fill. The decrease in yield and quality of seed due to water stress is markedly influenced by the growth stage at which the stress occurs. It is generally accepted that water stress causes the most crop injury and yield reduction when it occurs during reproduction, especially during pollination. Excess water stress at this time can irreversibly damage crops to such an extent that yields are reduced, regardless of later water regimes. Flowering and pollination are usually associated with high rates of water-use so internal water stress can develop rapidly if soil water is deficient. The early vegetative and seed maturation stages of development are only slightly sensitive to water stress.
    ii) Vegetable crops
    • Vegetable crops are sensitive to water stress because the marketable product is usually a fresh fruit, tuber or vegetative growth. In these crop products the water content at harvest is an important quality item. They are more sensitive to water deficits than crops grown for dry matter. These crops can tolerate mild stress and then resume near normal growth when the stress is alleviated.
    • Potatoes are considered to be high water users and the marketable product is the tubers. Deficit irrigation during tuber development will cause small tubers and reduce yields. Both total yield and quality (marketable yield) are affected by water stress and this effect varies greatly with the cultivar.
    • Tomato production is sensitive to water deficits in the flowering stage. Stress at this time can cause shedding of young fruits.
    iii) Fruit trees
    • Irrigation requirements for fruit trees differ from those of field crops in several important aspects: (1) several years usually are required from planting until a marketable yield is produced (2) water is major component of the commercial product, the fleshy part of the reproductive organ (3) there is a long-term cumulative response of fruit trees to water regime and (4) the crop is relatively high-valued compared to the cost of irrigation. Proper irrigation according to specific requirements of the tree under specific climatic and soil conditions will have a marked effect on the yield and quality of product.
    • When an orchard is first established, transpiration is very low because of the small crop canopy. Most water is lost from the soil by evaporation and the transpiration is minimum from the trees. Considerable savings in irrigation water can be achieved by eliminating this superfluous ET. One way to do this is by using drip irrigation. With drip irrigation only a small volume of soil near the tree is kept wet, eliminating any application between trees. Roots are effectively restricted to the wetted volume and this has caused apple trees to set fruit one or two years earlier than when sprinkler irrigation was used. After a full canopy had developed, differences in irrigation water requirements due to the method of application were small.
    • A successful flowering and pollination period is essential to a fruit crop. With deciduous trees, this stage of growth occurs before leaf development, while ET is low and there usually is soil water available from winter precipitation. Water stress during blossoming and fruit setting is less likely than during fruit development and maturation.
    • A recent development in fruit production is the manipulation of the root/shoot ratio through use of regulated deficit irrigation. By withholding or reducing irrigation during the early season, when fruit growth is slow, excessive vegetative growth is controlled. Resumption of full irrigation when the fruit grows rapidly assures a high quality fruit. The period of deficit irrigation stimulates later fruit growth with the result of more fruit on a smaller tree, compared with full season irrigation.
    • It is essential that soil water be easily available during the time of rapid fruit growth and maturation. Fruits that mature under a water deficit are small with low water content and high soluble solids. This negative effect of water stress on fruit size and water content may be more important in the market place than the total yield.
    • An evergreen fruit crop such as citrus requires water throughout the year. They are also grown widely in arid and semiarid regions so that more consideration must be given to an adequate soil water supply during blossoming and fruit setting than with deciduous trees. Water requirements for citrus vary widely both among species and with differences among locations. The cumulative response of citrus to wet and dry irrigation regimes was demonstrated in Israel for a young grove. Yields at all irrigation levels increased each year but the rate of increase was much higher with adequate than with inadequate irrigation.
    d. Preplant irrigation
    • Pre-plant irrigation accomplishes several objectives.
    • Three are important (i) Storing water in the soil profile for later crop use (ii) Germinating weed seeds so the seedlings are killed in the preparatory tillage before planting and (iii) Providing adequate seed zone water for germination, emergence and early crop development.
    e. Precipitation need to be considered for crop water requirements
    • The precipitation is to be taken into account in working out water needs of crops. The contribution of precipitation in reducing the irrigation requirement is achieved by using it for stand establishment, partial wetting of the profile for intake of rain water, reducing runoff due to precipitation and withholding irrigation at the time of precipitation and timely withdrawal of irrigation at the end of growing season.
    f. Cultural practices need to be modified to reduce the ET
    • Conservation tillage, residue management, moderate plant densities, flexible planting dates, short duration crops and use of fallow are some of the cultural practices considered under limiting irrigated situations to reduce the ET.

Last modified: Saturday, 23 June 2012, 4:36 AM