Soil Study

Irrigation methods Irrigation water may be applied to crops by spreading it on the field   surface, by applying it beneath the soil surface, by spraying it under pressure or by applying it drop by drop. Each of these activity can be accomplished by using different irrigation techniques. Surface Irrigation Subsurface Irrigation Sprinkler Irrigation Drip or Trickle Irrigation

Drip or Trickle Irrigation Drip trickle irrigation in one of the latest methods of irrigation that is becoming popular in areas with water scarcity and coarse soils having high infiltration rate. It minimizes conveyance and other conventional losses such as deep percolation, runoff and soil water through dippers. In this method, irrigation is accomplished by using small diameter plastic lateral lines with devices called emitters or drippers at selected spacing to deliver water drop by drop to the soil surface near the base of the plants. The system applies water slowly to keep the soil moist within the desired range of plant root system. The system operates at less pressure 10 to 15 psi. the emitters dissipate pressure energy from the distribution system by means of orifices, vortexes and tortuous or long flow paths thus allowing a limited volume of water to discharge. Most emitters are placed on ground but they can also be buried. The emitted water moves within sol system largely...

Classification of Sprinkler System It is classified whether the sprinkler heads are operated individually or as group along laterals or how they are moved or cycled to irrigate the entire field. According to mobility, the sprinkler system may be classified as portable, semi portable and permanent. Portable System                 It has portable main lines, lateral and pumping plant, risers and sprinkler heads. It can be moved from field to field in different settings. This type of system is placed on the field for irrigation application. After completion of irrigation it can be completely moved from the field and therefore do not provide any hindrance to farm operation. However, labor requirement increases. Semi- Portable System                 Water course, pumping plant, main and sub mains are fixed only laterals a...

Sprinkler Irrigation In this method water is sprayed into the air and allowed to fall on the ground surface somewhat resembling rainfall. The spray is developed by flow of water under high pressure through small orifices or nozzles. The pressure is usually obtained by pumping. With careful selection of nozzle sizes, operating pressure and sprinkler spacing, the amount of irrigation water required to refill the crop rootzone can be applied nearly uniformly at a rate to suit the infiltration rate of the soil, obtaining efficient irrigation. Suitability                 Sprinkler irrigation can be used for almost all crops except rice and on most soils except very fine textured soils where the infiltration rates are less than 4 mm/hr. It is well suited to sandy soils and small streams. Shallow soils and soils involving extensive land preparation (undulating topography) can be irrigated efficiently....

Subsurface Irrigation In this method of irrigation, water is applied below the ground surface by maintaining an artificial water table at some depth depending upon the soil texture and the depth of the plant roots. Water reaches the plant roots through capillary action. Water may be introduces through open ditches or underground pipe lines such as tile drains or mole drains. The depth of open ditches or tranches varies from 30 to 100 cm and are spread about 15 to 30 cm apart. Suitability                 It is suited to soils having reasonably uniform texture and permeable enough for water to move rapidly both horizontally and vertically within and for some distance below the crop rootzone. The soil profile must also contain barrier against excessive losses through deep percolation, either a nearly impermeable layer in the substratum when artificial water table can be maintained throughout ...

Surface Irrigation (gravity irrigation) In the surface methods of irrigation, water is applied directly to the soil surface from a channel located at the upper reach of the field. The driving force in such irrigation system is gravity and hence alternate name is gravity irrigation or gravity flooding. Two general requirements of prime importance are to obtain high efficiency and uniform distribution of water over the field. Once distributed over the field, water enters the soil and is redistributed by the forces of gravity and capillary to be available for plant use through root system. The surface irrigation is further subdivided into a number of techniques depending on the shape, slope and surface shaping of the field as summarized below. Basin Irrigation Border Irrigation Furrow Irrigation Corrugation Irrigation

Furrow Irrigation This method of irrigation is used in the irrigation of row crops with furrows developed between the crop rows in the planting and cultivating processes. The size and slope of the furrow depends upon the crop grown, equipment used and spacing between crop rows. Water infiltrates into the soil and spread laterally to irrigate the areas between the furrows. The length of time, the water to flow in the furrows depends on the amount of water required to replenish to rootzone and the infiltration rate of the soil and rate of lateral spread of water in the soil. Both large and small irrigation stream can be used by adjusting the number areas where surface drainage is necessary, the furrows can be used to dispose of the runoff from rainfall rapidly. Suitability                 Furrow irrigation can be used to irrigate all crops planted in rows, including orchard and vegetables. This method ...

Corrugation Irrigation It consists of running water in small furrows called corrugations which directs the flow down the slope. In this method, more and smaller furrows are made for water control. This method minimize the crusting effect and used for seed germination sometimes, which have been broadcast.

Border Irrigation This method makes use of parallel ridges to guide a sheet of flowing water as it moves down the slope. A border may be level or graded depending on the provision of no. of some scope in longitudinal direction. The slope in transverse direction is zero in both the cases. In graded border, the land is divided into a number of long parallel uniformly graded strips of land called borders that are separated by low ridges. It has no cross slope but uniform gentle in the direction of irrigation. The essential feature is to provide such a surface that water can flow down with uniform depth. Each strip is irrigated independently by a sheet of water confined by the border ridges. The width of border strip depends on the size of irrigation stream, amount of cross slope, kind and width of farm machinery and the desired accuracy of land leveling. Length of border strips should be limited to 400 meters. Longer strips are advantageous as they reduce the cost of wate...

Basin Irrigation This is the most common simplest and oldest method of controlled irrigation in Pakistan. There are many variations in its use. However, in general, it involves dividing the field into smaller unit areas so that each has a nearly level surface. Ridges are constructed around the field farming basin within which are constructed around the field forming basin filled to the desired depth can be controlled. The basins are filled to the desire depth and the water is retained until it infiltrates into the soil. When irrigating rice the depth of water may be maintained for considerable period of time by allowing water to continue to flow into the basins. Suitability                 Basin irrigation is used on many different soils. The prime important soil character influencing the design of basin is the water infiltration rate. This and the size of the available stream determine the a...