Agriculture for Engineers 4 (3+1)

Lesson 43. Irrigation Methods

43.2 WHY TO IRRIGATE?

• To meet the requirement of the crop by adding water to the soil
• To cool the soil environment around these root zone thereby making more favorable environment for plant growth.
• To wash out or dilute the salts in the soil and thus help in maintaining the salt balance.
• To reduce the hazards of soil piping.
• To soften the tillage pans.
• To put the land and labor into an economic use.
• To increase production, productivity and potentiality of crops.

43.3 FACTORS AFFECTING WATER REQUIREMENT OF HORTICULTURAL CROPS

• The irrigation efficiency
• The nature of the crop
• The climatic conditions
• The character of soil
• The method of irrigation and
• The insect-pests and disease havoc.

43.4 HOW TO IRRIGATE?

Much attention is required to the efficient use of water. As water becomes a rare commodity and the need becomes more pressing for maximum economic returns, new and more efficient methods of measuring and evaluation technique of handling irrigation water are necessary. For optimum production, timely application of water in proper quantity at proper intervals is absolutely essential.

43.5 METHODS OF IRRIGATION

43.5.1 Surface Irrigation

Surface irrigation is one of the simplest and widely adopted methods all over the world, especially in India. The water is made to flow on the soil surface or in the furrow. This method is advantageous one own to less investment. The disadvantages are this method requires more attention; soil becomes more puddle and bake; more losses of water through seepage and over irrigation; uneven distribution of water and farm machinery cannot conveniently cross at different point.

This includes flooding and furrow irrigation

(1) Flooding includes (a) free wild flooding (b) border flooding (c) check flooding and (d) basin method (Single and double)

(2) Furrow irrigation includes

(a) deep furrow method and (b)  corrugation  method.

43.5.2 Sub-Surface Irrigation

This system includes two methods viz., natural and artificial. Artificially porous pipes are laid underground below the root zone and water is allowed to move in pipes. The water moves freely upward by capillary movement. In this method, the maintenance is very cheap; there is no soil cracking in this method and little to no wastage of water. At the same time, this method requires adequate drainage, involves high initial cost in purchasing the tile pipes; and also not suitable in all types of soils. In certain parts of the USA this method is adopted conveniently for irrigation potato crop.

43.5.3 Sprinkler Irrigation

This method is followed where topography is uneven and the soil is porous, shallow or highly arable. Irrigation by this method at the seedling stage has proved very beneficial. In this method the water is conveyed to the field under pressure through pipes having several nozzles, which spray the water on the crop plants. The advantages are this method insures uniform distribution of water economy of water; may be adopted in various types of soil; no fear of soil erosion; no hindrance in the use of farm implements; and water soluble fertilizers can also be applied through sprinkler. This method is also not free from disadvantages like very high initial cost; more loss of water under very hot days through increased evaporation; and strong winds ay also cause uneven distribution of water.

43.5.4 Drip Irrigation

In this method, thin non-corrosive perforated plastic tubes are placed on the soil surface or in furrows, and in some cases buried in the soil, and connected to a controlled water supply source. The water and/or fertilizer is distributed evenly in a continuous slow flow directly to the plant roots in upward as well as downward directions. In drip irrigation system, almost all water is applied directly to the root zone and surface area remain almost dry, and hence it requires about 25 per cent less quantity of water than that of surface irrigation; the tendency of weed growth and leaf shedding is minimized.; further, drip irrigation is fair, suitable under saline soil conditions, it saves extra labour, and it makes possible the localized fertilizer application. Drip irrigation hastens the maturity and overcomes the erosion and seepage problems and does not interfere with cultural practices. Similarly, pitcher irrigation has proved very advantageous in case of cucurbits.

The production, productivity and potentiality of crops may be obtained up to a desired level with an efficient use of irrigation water in combination with other several agricultural inputs in right amounts, in right time through right method of applications.

43.6  HOW TO INCREASE WATER USE EFFICIENCY?

• Proper selection of crop and varieties according to local agro climatic condition.
• Short growth duration.
• By changing cropping pattern of farm.
• Use of chemicals, which shorten the life cycle of the plant and reduce transpiration.
• Selection of high yielding varieties.
• Use of fertilizers.
• Reasonable control of inhibitors.
• Proper cultural and environmental manipulation.
• Characterize the stages of plant growth, which are most and least critical during life cycle of plants.

43.7 WATER MANAGEMENT IN NURSERY

These methods are not suitable for nursery growing due to their several ill effects. Carbonate (RSC) and boron content are also used to find out suitability of irrigation water. Irrigation water, which contain more than 3 ppm boron is harmful to the nursery plants. The classification of water on the basis of E.C. and boron content and its suitability for different soils have been given in Table 43.1 and Table 43.2, respectively.

 Table 43.1: Classification of irrigation water based on electric conductivity

Class	EC (m mhos/cm)	Quality characterization	Soils for which suitable
C1	<1.5	Normal water	All soils
C2	1.5-3	Low salinity water	Light and medium textured soils
C3	3-5	Medium saline water	Light and medium textured soils for semi-tolerant crops
C4	5-10	Saline water	Light and medium textured soils for tolerant crops
C5	>10	High saline water	Not suitable

 

Table 43.2: Classification of water on the basis of boron content

Class	Boron (ppm)	Quality characterization	Soils for which suitable
B1	<3	Normal water	All soils
B2	3-4	Low boron water	Clayey soil and medium textured soils
B3	4-5	Medium boron water	heavy textured soils
B4	5-10	Boron water	heavy textured soils
B5	>10	High boron water	Not suitable