Water Management in Horticultural Crops

1. Surface irrigation

Surface irrigation

• Surface irrigation method is most widely practiced.
  
• In this method water is conveyed to the point of infiltration directly the soil surface in channels that vary in shape, size and hydraulic characteristics.
  
• The channels may vary from corrugation to long narrow strips or large fields where water is impounded.
On the basis of their conveyance size and shape, surface irrigation may be of following types.
A. Methods involving complete flooding of the soil surface
a. Wild flooding

• In this method water flows from the ditch directly to the field without much control on either side of the flow. It covers the entire field and moves almost unguided.
  
• The rate of advancing front is controlled by the topography of the field.
  
• Land leveling is not precisely followed.
  
• The depth of water sheet at different points may not be same, somewhere deep causing water logging and somewhere very shallow leading to water scarcity a few days after drying.
  
• Uneven distribution of water and low water application efficiency are the common drawbacks of this method. But the method is easy and inexpensive.
  
• Close growing crops are generally irrigated by this method.
b. Border Irrigation

• Borders are usually long, uniformly graded strips of land, separated by earthen bunds. The bunds so formed are not to contain the water from ponding but to guide it as it flows down the field.
• Border irrigation is generally best suited to the larger mechanized farms as it is designed to produce long uninterrupted field lengths for ease of machine operations. Borders can be upto 800 m or more in length and 3-30 m wide depending on a variety of factors. It is less suited to small-scale farms involving hand labour or animal powered cultivation methods.
• Border slopes should be uniform, with minimum slope of 0.05% to provide adequate drainage and a maximum slope of 2% to limit problems of soil erosion. Deep homogenous loam or clay soil with medium infiltration rates is preferred. Close growing crops such as pasture, alfalfa are preferred. Borders may be either laid along the slope (straight) or across the slope(contour)
c. Check or Check Basin Irrigation

• Check method consists of dividing the field into several relatively level plots called checks surrounded by low bunds. They are irrigated with comparatively large flow of water. Small checks are levelled while bigger ones are slightly sloping along the length. A check is also termed as check basin. There are two methods of check irrigation, rectangular check method and contour method
i. Rectangular check irrigation

• In a relatively uniform land with a gentle slope, checks may be rectangular and sometimes square. They may be a few square meters in size for vegetable crops. The size of a check is a function of the water intake rate of soil, land slope and the available stream size. In lighter soils the size of a check may necessarily be small to achieve uniform wetting and in heavier soils the size may be large.
• Water is conveyed to checks by a system of supply channel, laterals and field channels. Laterals or field channels are laid out in such a way that a channel passes through a set of two rows of checks. Such a channel
• is used to irrigate checks on both the sides. A supply channel is constructed on the upper reach of the field and laterals usually follow the slope, if there is any.
• Check method is adopted for irrigating row crops as well as closely spaced grain crops, fodder and vegetables in a wide range of soils having moderate to slow infiltration rates.



Advantages and limitations
• Advantages of the method are that
  
(i)variable size of streams can be effectively used
(ii) it can be adopted for wide range of soils
(iii)water application efficiency is high

 
Principal limitations are

1. Precise land leveling is necessary,
2. Considerable land is wasted by bunds and channels,
3. Labour requirement is high for preparing the land for irrigation
4. Movements of farm animals, implements and machinery are often restricted by bunds and channels.
ii. Contour check irrigation

• In slopping and rolling lands contour checks are constructed by rising bunds or ridges along contours having vertical intervals of 15 to 30 cm.
  
• Checks at the end of the adjoining contours may sometimes be joined at suitable places to make them continuous.
  
• They are almost uniformly level or gently sloping and are often small.
  
• A contour checks is also termed contour check basin. Contour checks are suitable for growing vegetables.
B. Methods involving partial flooding of the soil surface
a.Furrow Irrigation Methods

• Furrow irrigation refers to irrigating land by constructing furrows between two rows of crops or alternately after every two rows of crops. It wets the land surface only partly and water in the furrow moves laterally by capillarity to the unwetted areas below the ridge and also downward to wet the root zone of soil. Furrow irrigation is adopted to irrigate all row crop such as potato and vegetable crops on ridges. Plantation and fruit crops are also irrigated by furrow method.


Principal limitations of the method are:

(i) land requires precise grading to a uniform slope
(ii) labour is necessary to control water in furrows
(iii) this method is unsuitable for light irrigation.

Classification of furrow irrigation methods

• Furrow irrigation methods may be classified based on the types of furrows employed and the pattern of irrigation adopted. The methods are: (a) straight graded furrow irrigation (b) straight level furrow irrigation (c) contour furrow irrigation (d) alternate furrow irrigation and (e) raised bed and furrow irrigation.
  
• The first two types are formed as explained earlier (Furrow methods), with or without slopes for easy flow of water. The other types are as follows.
i.Contour furrow irrigation

• Contour furrow method of irrigation is adopted in an uneven and rolling topography. When the longitudinal slope exceeds the safe limits for graded furrow, furrows are constructed along the contour.
ii. Alternate furrow irrigation

• When the supply of water is limited, irrigation is applied through alternate furrows. Besides, this alternate furrow method is adopted where salt is a problem. Water is discharged in alternate furrows keeping the in-between furrow dry. In the subsequent irrigation, water is allowed to flow through the alternate furrows that had been kept dry on the previous occasion. This method saves quite a good amount of water and is very useful and crucial in areas of water scarcity and salt problems.
iii. Raised bed and furrow irrigation

• Raised beds of 1 to 1.5m width alternating with furrows are often constructed for growing vegetables crops, particularly those vegetable crops that creep on soil surface. Fruits of such vegetables get damaged on coming in contact with the moist soil. Two rows of plants are usually raised on two sides of a bed or ridge. A furrow runs between two rows of the adjacent ridges of beds and supplies water to the plant rows. The method assures saving of a large amount of water. The surface soil of beds or ridges remains dry and the creeping plants and their fruits are not damaged. Water from furrow moves laterally into the soil below the bed or ridge to meet the crop need.
• It prevents accumulation of salts at the base of plants and reduces the salt injury to crop in areas where salt is a problem.


iv. Corrugation irrigation

• Corrugations are miniature furrow adopted for irrigating close growing crops such as grain, forage and pasture crops. Crops may be line sown or broadcast and corrugations may bear any definite relation to crop rows. This method is used for fine to moderately coarse soils, especially soils that forms crust. Corrugations reduce crusting as they wet only a part of the land surface. They are not suitable for sandy soils as corrugations get smooth quickly due to collapse of ridges, particularly in moderate to high rainfall areas. The method is advantageous when the available stream is small.
• Principal advantages of the methods are that (i) it saves quite a good amount of water (ii) small supply stream is used (iii) used for soils with crusting problems and (iv) high water application efficiency.
b.) Basin and ring irrigation

• Fruit crops in orchards are irrigated by constructing basins or rings around trees. Basins are usually used for small trees, while rings are used in bigger trees which are widely spaced.
Basin irrigation

• A basin is usually made for one tree sapling but it may include more than one tree sapling when they are not spaced very wide. Basins may be square, circular or rectangular.
• Basins are made longer and wider as saplings grow in size. The land inside basins is flat with the base area of trees kept little raised so that the sapling stems do not come in direct contact with water. Only a part of the total land surface is flooded. Water is supplied through laterals and each basin may be connected with another one by a small furrow to get the water supply. A lateral or field channel passes between two rows of trees alternately supplying water to individual basins on both sides. A basin usually covers the complete area under the tree canopy. Desired quantity of water is allowed into a basin for complete infiltration.



Advantages and limitations

• Advantages are that (i) a considerable amount of irrigation water is saved (ii)water application efficiency is very high (iii) entire area excepting the basin area does not require precise land leveling, (iv) the labour requirement and the cost of making basins are low and (v) no land is wasted. This method is adaptable for fruit trees or shrubs in orchards and plantations. The principal disadvantage is that working with implements and machineries is prevented.
Ring irrigation

• Ring method consists of irrigating fruit trees in orchards by constructing circular trenches around trees. Ring trenches are smaller in both depth and width around small trees and are larger around bigger trees. Usually a ring is laid out at the periphery of the tree canopy. The ring trenches are usually made 30 to 50 cm wide and narrow furrows. Laterals pass through a set of two rows of trees supplying water into rings on both sides. Water supply process is essentially the same as with the basin irrigation. Water in desired quantity is allowed to stand in the trenches for infiltration.
c.) Surge Irrigation

• Surge irrigation is defined as the intermittent application of water to field surface under gravity flow which results in a series of “on and off” modes of constant or variable time spans. Large intermittent flows rather than continuous ones are used in two sets of furrows and gated pipes laid in the “Tee” configuration. Water is switched alternatively from one set of furrows to the other by a valve and automatic time controller until irrigation is completed. The cycle time (irrigation period plus the rest period) can be made to vary from 30 minute to several hours.