Implementing Efficient Water Use Technologies

Irrigation

Irrigation is the artificial application of water to the crop field at needed intervals. Irrigation helps to grow agricultural crops, maintain landscapes, and increase the productivity where rainfall is not sufficient to meet the crop demands.

Importance of Irrigation

Irrigation is necessary for agriculture and farming due to the following reasons:

• Plants absorb minerals and nutrients from the soil via their roots. These minerals are dissolved in the water present in the soil. Then the water transports these nutrients to all parts of the plant, enabling growth and photosynthesis.
• Irrigation provides the moisture that is crucial during the germination phase of the plant’s life cycle.
• Irrigation also makes the soil more fertile (by adding moisture to it) and easier to plough
• Proper irrigation also increases yield from the farm.

Surface Irrigation

• In all the surface methods of irrigation, water is either ponded on the soil or allowed to flow continuously over the soil surface for the duration of irrigation.
• It does not result in high levels of performance.
• This is mainly because of uncertain infiltration rates which are affected by year-to-year changes in the cropping pattern, cultivation practices, climatic factors, and many other factors

Uncontrolled Flooding

• When water is applied to the cropland without any preparation of land and without any levees to guide flow of water on the field, the method is called ‘uncontrolled’, wild or ‘free’ flooding.
• Uncontrolled flooding generally results in excess irrigation at the inlet region of the field and insufficient irrigation at the outlet end.
• Efficiency is reduced because of either deep percolation or flowing away of water from the field.
• The advantage of this method is the low initial cost of land preparation.

Controlled Flooding

Border strip method

• Border strip irrigation (or simply ‘border irrigation’) is a controlled surface flooding method of applying irrigation water. In this method, the farm is divided into a number of strips. These strips are separated by low levees (or borders).
• The border strip method is suited to soils of moderately low to moderately high intake rates and low erodibility.
• This method, however, requires preparation of land involving high initial cost. 

Check Method

• The check method of irrigation is based on rapid application of irrigation water to a level or nearly level area completely enclosed by dikes as shown in below figure.
• In this method, the entire field is divided into a number of almost levelled plots (compartments or ‘Kiaries’) surrounded by levees.
• This method is suitable for a wide range of soils ranging from very permeable to heavy soils.
• Loss of water through deep percolation (near the supply ditch) and surface runoff can be minimized and adequate irrigation of the entire farm can be achieved. Thus, application efficiency is higher for this method.
• There is some loss of cultivable area which is occupied by the levees. 
• An alternative to flooding the entire land surface is to construct small channels along the primary direction of the movement of water and letting the water flow through these channels which are termed ‘furrows’, ‘creases’ or ‘corrugation’ as shown in below figure.
• Furrows necessitate the wetting of only about half to one-fifth of the field surface. This reduces the evaporation loss considerably.
• Furrows provide better on-farm water management capabilities for most of the surface irrigation conditions, under variable and severe topographical conditions.
• Possibility of increased erosion
• Furrow irrigation requires more labour than any other surface irrigation method. This methods application is limited to row crop like potato, groundnut 

Sprinkler Irrigation

This system mimics the phenomenon of rain. Water is carried by pipes to central locations on the farm. Sprinklers placed here distribute the water across the fields. This is the most efficient method to irrigate the uneven land. Sprinkler system also provides the best coverage regardless of the size of the farm. Schematic diagram and field application of sprinkler irrigation method is shown in below figure.

Sprinkling is the method of applying water to the soil surface in the form of a spray which is somewhat similar to rain. Rotating sprinkler-head systems are commonly used for sprinkler irrigation. Each rotating sprinkler head applies water to a given area, size of which is governed by the nozzle size and the water pressure.

Alternatively, perforated pipe can also be used to deliver water through very small holes which are drilled at close intervals along a segment of the circumference of a pipe. Sprinklers have been used on all types of soils on lands of different topography and slopes, and for many crops. The following conditions are favourable for sprinkler irrigation:

• Very previous soils which do not permit good distribution of water by surface methods,
• Lands which have steep slopes, easily erodible, and difficult to levelling and also not cost effective.
• Irrigation channels which are too small to distribute water efficiently by surface irrigation, and
• Lands with shallow soils and undulating lands which prevent proper levelling required for surface methods of irrigation

Advantages:

• Low water loss and hence saves water (Irrigation efficiency is about 75 to 85%)
• Enhances plant growth and crop yield 
• Saves labour and energy
• Control weed growth
• No soil erosion
• Improves fertilizer application efficiency
• Suitable for any topography
• Uniform application of water

Disadvantages:

• High skill in design, installation, and subsequent operation.
• High initial cost, cannot adopt by ordinary farmers
• Clogging of small conduits and openings due to sand, clay particles, debris, chemical precipitates and organic growth.
• Not suitable for closely planted crops such as wheat and other cereal grains.
• Poor application efficiency in windy weather and high temperature
• High evaporation losses
• Water should be free of debris Physical damage to crops by application of high intensity spray

Drip Irrigation

The most commonly used method of irrigation these days is the drip method. They lay the pipes in rows near the crops or plants. These plastic pipes have holes in them. Water seeps from these holes drop by drop, hence the name drip irrigation. This is an extremely efficient method of irrigation as it reduces water wastage.

• Trickle irrigation system comprises main line, sub-mains, laterals, valves (to control the flow), drippers emitters, pressure gauges, water meters, filters, pumps, fertilizer tanks, vacuum breakers, and pressure regulators.

The drippers are designed to supply water at the desired rate (1 to 10 litters per hour) directly to the soil. Low pressure heads at the emitters are considered adequate as the soil capillary forces causes the emitted water to spread laterally and vertically.

Quality of Irrigation Water

• Irrigation water must not have direct or indirect undesirable effects on the health of human beings, animals, and plants.
• The irrigation water must not damage the soil and not endanger the quality of surface and ground waters with which it comes into contact.
• The presence of toxic substances in irrigation water may threaten the vegetation besides degrading the suitability of soil for future cultivation.
• Surface water, ground water, and suitably treated waste waters are generally used for irrigation purposes. The various types of impurities, which make the water unfit for irrigation, are classified as:
• Sediment concentration in water
• Total concentration of soluble salts in water
• Proportion of sodium ions to other ions
• Concentration of potentially toxic elements present in water
• Bacterial contamination

Soil Moisture Conservation Techniques

The main objective of soil moisture conservation is to minimize the amount of water lost from the soils through evaporation (water loss directly from the soil) and transpiration (water loss occurring through the plants) – or combined, the evapotranspiration. Preserving soil moisture is important means to maintain the necessary water for agricultural production, and also helps minimize irrigation needs of the crops. This is especially important in areas where rainwater and/or ground water resources for irrigation are scarce or decreasing due to climate change or other causes.

Natural mulch consists of dead leaves, twigs, fallen branches and other plant debris which accumulate on the earth's surface. It also called the organic mulch. It will be adding more nutrients to the soil and improves the soil health and increased the crop productivity. Organic mulching technique is given in below figure.

Inorganic materials used for mulches do not add nutrients or humus to soil and do not decompose except after long exposure to weathering. Otherwise these materials are effective mulches, and several are permanent and quite attractive.

Implementation

There is a variety of methods that can be used to conserve soil moisture. Most of these are relatively low cost and complexity approaches, primarily relying on the presence of required materials and technical capacity locally. Many of the methods rely on providing some kind of cover for the soil to minimize evapotranspiration and direct soil exposure to heat and sun. Generally, most methods used for soil quality improvement and conservation, will also yield benefits to soil moisture conservation. Examples of methods for reducing excess soil moisture loss include following:

• Spreading manure or compost over the soil – this minimizes evapotranspiration and also provides valuable nutrients to the soil through processes of decomposition
• Mulching – mulch is a layer of organic (or inorganic) material that is placed on the root zone of the plants. Examples of mulch materials include straw, wood chips, peat. Inorganic mulch in form of plastic sheeting is also used. Mulching is most suited for low to medium rainfall areas, and less suited for areas with very wet conditions.

Conservation tillage – reducing or, in extreme cases, completely eliminating the tillage to maintain healthy soil organic levels which increases the soils capacity to absorb and retain water. Conservation tillage is a specific type of such approach where crop residue is left on the soil to reduce evapotranspiration, and protect soil surface from wind, sun and heavy rain impacts.

• Crop rotation – growing different types of crops every season helps improve soil structure and thus water holding capacity. Examples include rotating deep-rooted and shallow rooted crops that make use of previously unused soil moisture, as plants draw water from different depth levels within the soil. Crop rotation may also improve soil fertility and help control pests and diseases.
• Green manuring – growing of plant materials with the sole purpose of adding to the soil for improved organic matter and nutrients. The improved soil quality then also improves water retention capacity.
• Deep tillage – suited for some areas and soils, deep tillage can help increase porosity and permeability of the soil to increase its water absorption capacity.
• Mixed cropping and inter-planting - cultivating a combination of crops with different planting times and different length of growth periods.
• Contour ploughing – by ploughing the soil along the contour instead of up- and downward slopes, the velocity of runoff is reduced, creating even barriers, and more water is retained in the soils and distributed more equally across the cropland.
• Strip cropping - growing erosion permitting crops and erosion resisting crops in alternate strips. Other soil moisture conservation techniques may include rainwater harvesting to minimize runoff and collect water for use on site. For more technologies on this see technology sheet Rainwater harvesting for infiltration.

Source : Jaldoot Resource Book