It can be classified into: 1.
Crop water use efficiency: It is the ratio of crop yield to the amount of water used by the crop for evapotranspiration. 2. Field water use efficiency: It is ratio of crop yield to the total amount of water used in the field. 3. Physiological water use efficiency: It is calculated in terms of the amount of fixed per unit of water transpired. Types of Efficiency of water: 1. Application efficiency = Water directly available to the crop / water received at field inlet x 100 2.
Conveyance Efficiency = Water received at inlet to a block of fields / water released at project head works x 100 3. Project Efficiency = Water made directly available to the crop / water released at head works
Scheduling of Irrigation:
Definition It’s the process of determining when to irrigate and how much water to apply or frequency with which water is to be applied based on needs of the crop and nature of the soil. Objectives: i. Proper scheduling is essential for efficient use of irrigation water. ii. It leads to saving water and energy. iii. Higher crop yield, efficient use of inputs and lower production costs.
Approaches to Divide when to Irrigate — I. Soil approach: Methods involve determination of water content of the soil and finding the deficit in available at which it’s proposed to irrigate. (a) Gravimetric approach (b) Feel and appearance (c) Tensiometers (d) Electrical resistance (e) Water budget technology (ET, Effective Precipitation and soil water contents). II. Plant approach: Monitoring plants is the most direct method of determining when to irrigate. (a) Appearance and growth: Indicators which include leaf and shoot wilting, leaf colour, drooping of leaves, rolling of leaves etc., not often these are very effective and confusing. (b) Leaf temperature: When partial or full stomatal closure occurs due to reduced transpiration, because of reduced availability of water and increase in heat temperature.
(c) Leaf water potential: Which indicates the plants need for water. Here the pressure used to measure the leaf moisture potential. This method is not extensively used since considerable time, care and training are required, no obtain reliable results.
(d) Stomatal resistance: Leaf resistance to vapour diffusion into the atmosphere is primarily governed by the degrees of stomatal closure. Its therefore an index to the need for water. III. Meteorological Approach: (a) IW/Epan ratio: Ratio between a fixed amount of irrigation water and cumulative pan evaporation (EPan) from an open pan evaporimeter minus effective rainfall since previous irrigation is used as a basis for scheduling irrigation to crops.
i. Smaller IW/CPE ratio – Irrigation @ large intervals. ii. Larger ratio – Irrigation @ shorter intervals.
IV. Rough Methods for Farmers: (a) Soil-cum-sand miniplot technique: Based on plant as an indicator of water need. It’s to reduce artificially available water holding capacity, of the soil in root zone depth in the miniplot by mixing sand with it.
The field is irrigated when the plants in the mini-plot show moisture deficiency symptoms by wilting. (b) Can Evaporometer method: Evaporation from one litre can has a correlation with evopo transpiration from a crop. When the water level in the can has dropped to an amount equal to the amount of water to be applied in each irrigation, its time to irrigate. How much Water to Apply? The amount of water to be applied to the plants can be determined by the following methods: Net Irrigation Requirement: It’s the depth of irrigation water, required to bring the soil moisture in the effective root zone depth to field capacity.
NIR = (MFC – MbU) / 100 x DbD Where, MFC – Moisture content @ field capacity (%) Mbi – Moisture content before irrigation (%) Db – Bulk density of the soil (g/cc) D – Depth of soil (cm) Gross Irrigation Requirement: GIR= Net irrigation requirement /Field efficiency of System Irrigation Interval: It refers to the number of days between two irrigations in the period of highest consumptive use of the crop growth without rain fall. It’s the function of soil, crop and water. Design interval= MFC – Mbi / Pco Pw = peak period moisture use rate of the crop (cm). Irrigation Period: It’s the number of days that can be allowed for applying the irrigation to a given design area during the peak consumptive use period of the crop being irrigated. Ip= In / ET (crop) Peak In = net amount of moisture (cm) ET = peak period water use rate of the crop.
Irrigation requirement = crop water requirement – Effective rain fall. It can be expressed in mm/day or mm/month. Methods of Irrigation: Definition: Application of irrigation water to cropped field by different types of lay outs are called Methods of Irrigation. Objectives: i. Necessary to save the water by proper methods to arrest run-off loss, perculation loss and evaporation losses etc. ii. To optimise the crop water need.
Factors Influencing Irrigation Methods: 1. Soil Type: Physical properties such as texture, structure, porosity, infiltration rate influence the selection of method. 2. Soil Depth: If the soil is shallow, holds less water, needs levelling and forming bunds to hold maximum water to increase irrigation interval.
If soil is deep, holds more water and needs longer irrigation interval. 3. Topography of Land: Topography decides the method of irrigation. If the land is more slopy, basin method can’t be used. Instead strip method can be used. In undulating topography, sprinkler/ Drip irrigation method can be used. 4.
Climate: Rainfall, temperature, humidity, wind velocity, radiation etc., influence the irrigation methods. For e.
g. heavy wind affects sprinkler irrigation and temperature affects surface method of irrigation by high evaporation loss. 5.
Water source: Flow velocity, quantity, quality of available water, decide the methods of irrigation methods. 6. Crops to be grown: Value of the plant and geometry of the crop to be cultivated are main criteria. For e.g.
, for high value/cash crop or wide spaced crop, sprinkler/drip can be used. Classification of Irrigation Methods The methods can be classified as— 1. Surface method or gravity method 2.
Sub-surface/sub-irrigation 3. Pressurized or micro irrigation (a) Drip-irrigation (b) Sprinkler irrigation I. Surface/Gravity Irrigation: Common method of irrigation practiced all over the world. Water is applied directly to the surface by providing some checks so the water flow. 1. Border Strip Method: Field is divided in two long parallel strips by providing small parallel earthen bunds or levees or dykes along both the side of the strips. The end of the strip may or may not be closed, based on the length of the strips.
The application efficiency of this system is 75-85%. a. Suitable to soils with moderately low to moderately high infiltration rate, fields with 0-5% slope and not suited to very sandy soil and very clayey soil as they have too high and low infiltration rate.
b. For closely spaced crops like pulses, wheat, barley, alfalfa, and ragi. It can be divided into — (i) Graded Borders, with slope 0.1 to 0.5% in the longitudinal directions and there are very little slope across the strip. (ii) Level border, where there is no slope.
2. Check basin method: Adopted for levelled land surfaces. Also known as basin method.
Land is divided into small basins. Area of basin surrounded by earthen bunds or levees or dykes. a. Suitable in fine textured soil. b. Suitable for crops like cereals, millets, pulses and oil seeds.
Disadvantages — a. Needs high degree of levelling. b.
Not suitable for coarse textured soil. It can be further classified into, (i) Rectangular or square or irregular basin. (ii) Ring basis – mostly for orchard crop. These are circular basins formed around individual trees.
3. Furrow method of Irrigation: Small, evenly spaced shallow furrows or channels are formed in beds. Suitable for crops like, cotton, maize, sugar cane, potato, beet root, onion and vegetable crops It can be classified into — (a) Corrugated furrow (b) Graded furrow (c) Level furrow (d) Contour furrow (a) Corrugated furrow: Small furrow made by plough. 60 mm of bottom width and a depth of 100-150 mm. (b) Graded: Open ended which facilitate more time for infiltration and uniform distribution along the furrows. This is adopted in the land having more slope.
(c) Level furrow: Adopted for land having no or little slope or levelled lands. (d) Contour furrow: Furrows formed along the contours. 4. Surge Irrigation: It’s the application of water into the furrows intermittently in a series of relatively short on and off times of irrigation cycle. This method gives more uniform soil moisture distribution and storage in the crop root zone. The irrigation efficiency is 85-90%. II.
Sub-surface Irrigation: Water is applied below the ground surface through net work of pipes or some devices. Main aim is to reduce evaporation loss and to maintain an artificial water table near the root zone of the crop. Mainly suitable for high temperature area, where ET losses are very high. III. Pressurized Irrigation Methods: Under this method we have both sprinkler as well as drip irrigation methods, where water is applied thro network of pipelines by means of pressure services. (A) Sprinkler Irrigation System: This is the method of applying irrigation water above the soil surface in the form of spray or droplets, similar to natural rainfall. It’s made by pumping water under pressure through network of pipelines and allowing to eject out by means of small orifices or nozzles or holes. It can be classified into — 1.
Rotating head system: Special device to sprinkle the water called sprinkler head. Which consists of small nozzles and metal ring or water ejected through the nozzle strike the metal ring which changes its direction by the help of the spring attached to it. 2. Perforated pipe system: Lateral pipes, small holes are made, based on the nature of the crops to distribute water uniformly. Suitability and advantages: i. Highly suitable for sandy soil, where infiltration rate is more. ii. Lands having undulating topography or steep slopes where levelling is economically not advisable.
iii. Stream size is very small, where surface flow is low. iv. Controls canopy temperature. v.
Wastage of land or basin, ridges and furrows and irrigation channels are reduced. vi. Almost suitable for all crops except rice which needs stagnation of water.
Disadvantages: i. Distribution efficiency decrease in heavy windy areas. ii. With saline water, causes clogging of pores. iii. Continuous power supply required to operate system to maintain pressure.
iv. Costly to install and maintain. v. Uniformity of application is difficult.
Drip or Trickle Irrigation:
Water is applied through network of pipelines and allowed to fall drop by drop at crop root zone by a special device called emitters or drippers. The main principle is to apply the water at crop root zone based on the daily ET demand of the crop without any stress.
Components Advantages: i. Application of water in slow rate, facilitates the easy infiltration into the soil. ii. Root zone is always maintains with field capacity level.
iii. No seepage or percolation/evaporation losses. iv. Restricted weed growth due to limited wetting zone. v. Fertigation, chemigation and herbigation possible. vi. Salt content near the root zone is reduced.
vii. Saline water can also be used. viii. Adopted for any type of topography. ix. More area can be maintained with little quantity of water. x. Used for widely spaced crops like cotton, sugar cane, tomato, brinjal, coconut and orchard crops.
Disadvantages: i. Clogging in emitters due to salt content of water and other impurities like, dust, etc. ii. Damage of pipelines by rodents.
iii. Not economical for closely spaced crops which require more number of pipes and drippers per unit area. iv. Proper maintenance and periodical cleaning of drippers and pipelines (with 1% HC1) are very important to maintain the system efficiently.
Definition: It’s the process of removal of excess water or gravitational water from the surface and the sub surface of farm lands with a view to avoid water logging and creates favourable soil conditions for optimum plant growth. Need or Objectives: i.
It raises the soil temperature, that is, keeps the soil relatively warm. ii. To have optimum soil water balance. iii. It has greater necessity due to heavy precipitation. iv.
Excess salts are leached down. Areas of salinity and alkalinity where annual evaporation exceeds rain fall and capillary rise of ground water occurs. v. Low lying flat areas surrounded by hills. Characteristics of Good Drainage i. Should be permanent.
ii. Must have adequate capacity to drain the area completely. iii. Should have minimum interference with cultural operations.
iv. Should have minimum loss of cultivable area. v. Should intercept or collect water and remove it quickly with in shorter period.
Methods of Drainage: 1. Surface method 2. Sub-surface method 1. Surface Method: It’s to remove the excess water from the surface of the soil profile.
It can be done by developing slope in the land. It’s suitable for, slowly permeable clay and shallow soil and for regions of high intensity rainfall. The land with less than 1.5% slope is also needed a good drainage. It can be made by land smoothing, making field ditches.
The Method can be further classified into, (a) Lift drainage (b) Gravity drainage (c) Field surface drainage (d) Ditch drainage (a) Lift drainage: It’s to drain the excess water from low lying area or areas having water due to embankment. It can be achieved by the use of scoops or pump. (b) Gravity drainage: Water is allowed to drain from the areas of higher elevation to lower reaches through, the regulated gravity flow through, the outlet of various types. (c) Field surface drainage: Excess water received from the rain or irrigation is drained through this method. Irrigated basins or furrows are connected with the drainage under lower elevation, which is connected to the main out let to the form pond used for water harvesting. (d) Ditch drainage: Ditches of different dimension are constructed at distances inside the soil up to the depth of ditch. Such ditches are interceptors or relief drains. This method can be adopted for nurseries, seed beds and rainfed crops.
2. Sub-surface Drainage System: Sub surface drains are underground artificial channels through which excess water may flow to a suitable outlet. The main purpose is to lower the ground water level below the root zone of the crop. It’s mostly needed to medium textures soil, high value crop and high soil productivity. Types of Sub-surface drainage — (a) Tile drainage (b) Vertical drainage (c) Well drainage/Drainage wells (a) Tile drainage: Continuous fine of tiles laid at a specific depth and grade so that the excess water enters through the tiles and flow out by gravity. The tile drains are made up of clay and concrete. (b) Vertical drainage: Disposal through well into porous layers of earth. Such a layer must be capable of taking large volume of water rapidly.
These layers found in river bed. (c) Drainage wells: These wells are used for the drainage of agricultural lands especially in irrigated areas. Systems of Drainage: 1. Random 2. Parallel 3. Herringbone 4. Grid iron 5.
Interceptor 1. Random: Lines are laid more or less @ random to drain these wet areas. This is used where the wet areas are scattered and isolated from each other. 2. Parallel: Poorly drained soils of homogenous texture and mild slopes are drained through this system. It consists of the drains laid out in long parallel laterals which discharge into a common main drain. 3. Herring bone: Here, the mains are in a narrow depression and the laterals enter the main from both sides @ an angle of 45°, like the bones of a fish.
4. Grid Iron: Similar to herring bone, but the laterals enter the main only from one side @ right angles. This is adopted in flat regularly shaped fields. This is an efficient drainage system. 5. Interceptor: Ditches of different dimensions are constructed at distances to drain the excess water accumulated on the surface and inside the soil upto the depth of ditch. Such ditches are interceptors or relief drains. Its an effective and efficient method, which is adopted for nurseries, seed beds and rain fed crops.
Quality of Irrigation Water:
I. Suitability mainly depends on i. Amount of type of salts present in the water II. Main constituents are, i.
Calcium, Magnesium, Sodium as cations. ii. Chloride, Sulphate and Bicarbonate iii. Other ion > like Bo, Mo III. Parameters which divide the quality of Irrigation water i.
Total salt concentration (Salinity) ii. Sodium adsorption ratio (Sodicity) iii. Bicarbonate and Boron content 1. Total concentration of Soluble Salts i. Total dissolved solids ii.
Electrical Conductivity 2. Concentration of Na i. SAR: ii. SSP: IV.
Quality parameters for irrigation water: ClassEC (dsm-I)SARRSC (me q/l)Good<2.0<10<2.5Normal2-4<10<2.5Sodic<4>10>2.5Poor>4>10>2.
5V. Management of Saline water for Irrigation: (a) Irrigation practices: 1. Salt tolerant crops – Barley, Sugarbeet, Cotton, Mustard. 2. Semi-tolerant – Sorghum, rice, Castor. 3. FYM/green manure.
4. Application of fertilizer 5. Planting seed on the side of a ridge. (b) Irrigation management: 1.
Giving heavy – Pre-sowing Irrigation 2. Frequent shallow Irrigation 3. Drip Irrigation 4. Furrow Irrigation (c) Improving Water Quality: 1. Adding chemical to precipitate harmful constituents 2. Good water + Saline water (d) Soil Management: 1. Irrigation and drainage 2. Mulching 3.
Gypsum application Drainage coefficient: Rate of water removal which is used in drainage design to obtain the desired protection of crops from excess surface and sub-surface water. It can either be expressed as the depth of water in centimeteres (inches) to be removed in a specific time or flow rate per unit of area or flow rate per unit time varying with the size of the area.