Irrigation Management

Agriculture and Rural Development (Phase-I/II) Water Resource

Irrigation management aims at increasing food production, contributing to economic development, and reducing poverty through improvements in performance, productivity, and sustainability of irrigated agriculture and irrigation systems.

Irrigation is the artificial exploitation and distribution of water at the project level aiming at the application of water at field level to agricultural crops in dry areas or in periods of scarce rainfall to assure or improve crop production.

History

Scholars such as Julian H. Steward and Karl August Wittfogel have seen the management of irrigation as a crucial factor in the development of many early states (hydraulic empires).

Understanding the context

The last 60 years have seen remarkable developments in water resources use in agriculture in response to population growth and increased demand for food. While the world population grew from 2.5 billion in 1950 to 7 billion today, the irrigated area doubled and water withdrawals tripled through massive developments in hydraulic infrastructure.

Irrigation is the major water user on a global scale, accounting for about 70 percent of the total water withdrawal. The irrigated area at the global level represents around 20 percent of the total agricultural land and contributes 40 percent of the total food production. However, the performance of the majority of existing irrigation systems remains low.

With increasing competition from other sectors, irrigation is under pressure to reduce its share of water use. At the same time irrigation is regarded as one of the main means for increasing food production and rural incomes. This is why it is imperative to modernize irrigation systems and improve irrigation governance in order to achieve high water productivity and sustain the resources base.

Water management

The most important physical elements of an irrigation project are land and water. In accordance with the propriety relations of these elements there may be different types of water management:

the communal type
the enterprise type
the utility type

Communal type

Until the end of the 19th century the development of irrigation projects occurred at a mild pace, reaching a total area of some 50 million ha worldwide, which is about 1/5 of the present area (see Irrigation statistics). The land was often private ha "privates" property or assigned by the village authorities to male or female farmers, but the water resources were in the hands of clans or communities who managed the water resources cooperatively.

Enterprise type

The enterprise type of water management occurred under large landowners or agricultural corporations, but also in centrally controlled societies. Both the land and water resources are in one hand.

Large plantations were found in colonised countries in Asia, Africa, and Latin America, but also in countries employing slave labor. It concerned mostly the large scale cultivation of commercial crops such as bananas, sugarcane and cotton. As a result of land reforms, in many countries the estates were reformed into a cooperatives in which the previous employers became members and exercised a cooperative form of land and water management.

Utility type

The utility type of water management occurs in areas where the land is owned by many, but the exploitation and distribution of the water resources are managed by (government) organizations.

After 1900 governments assumed more influence over irrigation because:

water was increasingly considered government property owing to the increasing demand for good quality water and the reducing availability
governments embarked on large scale irrigation projects as they were considered more efficient
the development of new irrigation schemes became technically, financially and organizationally so complicated that they fell outside the capabilities of the smaller communities
the import and export policies of governments required the cultivation of commercial cash crops whilst, by controlling the water management, the farmers could be more easily guided to plant these kind of crops.

Types of irrigation

Furrow systems

This system comprises a series of small, shallow channels used to guide water down a slope across a paddock. Furrows are generally straight, but may also be curved to follow the contour of the land, especially on steeply sloping land.

Row crops are typically grown on the ridge or bed between the furrows, spaced from 1 meter apart.

Flood or border check systems

These systems divide the paddock into bays, separated by parallel ridges or border checks. Water flows down the paddock's slope as a sheet guided by ridges. On steeply sloping lands, ridges are more closely spaced and may be curved to follow the contour of the land.

Border systems are suited to orchards and vineyards, and for pastures and grain crops.

Level basin systems

These systems differ from traditional border check or flood systems in that slope of the land is level and area's ends are closed.

Water is applied at high volumes to achieve an even, rapid ponding of the desired application depth within basins.

Center-pivot sprinkler systems

A center-pivot sprinkler is a self-propelled system in which a single pipeline supported by a row of mobile towers is suspended 2 to 4 meters above the ground. Water is pumped into the central pipe. As the towers rotate slowly around the pivot point, a large circular area is irrigated. Sprinkler nozzles mounted on — or suspended from — the pipeline distributes water under pressure as the pipeline rotates. The nozzles are graduated small to large so that the faster moving outer circle receives the same amount of water as the slower moving inside.

Hand move sprinkler systems

Hand move sprinkler systems are a series of lightweight pipeline sections that are moved manually for successive irrigations. Lateral pipelines are connected to a mainline, which may be portable or buried. Hand move systems are often used for small, irregular areas. Hand move systems are not suited to tall-growing field crops due to difficulty in repositioning laterals. Labor requirements are higher than for all other sprinklers.

Solid set and fixed sprinkler systems

Solid set or fixed refer to a stationary sprinkler system. Water-supply pipelines are generally fixed (usually below the soil surface) and sprinkler nozzles are elevated above the surface. Solid-set systems are commonly used in orchards and vineyards for frost protection and crop cooling. Solid-set systems are also widely used on turf and in landscaping.

Travelling gun sprinkler systems

Travelling gun systems use a large sprinkler mounted on a wheel or trailer, fed by a flexible rubber hose. The sprinkler is self-propelled while applying water — travelling in a lane guided by a cable. The system requires high operating pressures, 100psi is not uncommon.

Side-roll wheel-move systems

Side-roll wheel-move systems have large-diameter wheels mounted on a pipeline. This enables the line to be rolled as a unit to successive positions across the field. Crop type is an important consideration for this system since the pipeline is roughly 1 metre above the ground.

Linear or lateral-move systems

Linear or lateral-move systems are similar to center-pivot systems, except that the lateral line and towers move in a continuous straight path across a rectangular field. Water may be supplied by a flexible hose or pressurized from a concrete-lined ditch along the field's edge.

Low-flow irrigation systems

Low-flow irrigation systems (including drip and trickle) use small-diameter tubes placed above or below the soil's surface. Frequent, slow applications of water are applied to the soil through small holes or emitters. The emitters are supplied by a network of main, sub-main, and lateral lines. Water is dispensed directly to the root zone, avoiding runoff or deep percolation and minimizing evaporation. These systems are generally used in orchards, vineyards, or high-valued vegetable crops.

Irrigation scheduling

Irrigation scheduling is the process by which an irrigator determines the timing and quantity of water to be applied to the crop or pasture. The challenge is to estimate crop water requirements for different growth stages and climatic conditions.

To avoid over or under watering, it is important to know how much water is available to the plant, and how efficiently the plant can use it. The methods available to measure this include: