Water in agriculture
Some of the best agricultural lands can be found in the Netherlands due to the abundant water availability and fertile soil. As modernized water systems are so extensively organized (as polders, ditches, etc.), water availability can be regulated very precisely. In winter the water levels are usually quite high, while in spring the water levels can be lowered to make tillage possible. In the case of a dry summer extra water can be allowed in the ditches from the river. In the lower parts of the Netherlands water levels are sometimes dammed up to overcome dry periods. In the higher parts of the Netherlands, water is sometimes pumped from ditches and used with sprinkling systems. Since water from rainfall and groundwater is normally enough, hardly any supplemental water is needed to cultivate crops.
This abundance of water however, is a rare phenomenon worldwide. In most areas supplemental water is used in agriculture and this is called irrigation. Irrigation is the movement of water, by people, to plants, and to vary crops and crop productivity. The importance of irrigation can be clearly seen in the following figures: irrigation makes up 20% of the total arable area in developing countries, but produces 40% of all crops. In general the yield of most crops can be increased 100-400% with the help of irrigation.
Other mind-boggling figures:
Irrigation supports the production of:
- 30% of all food crops (grains, pulses, root crops, oilseeds, fruit, vegetables, narcotics, beverages, medical supplies…)
- 45% of all food grains (rice, wheat, maize, sorghum)
- 55% of rice and wheat (soon 65%)
Although the Dutch don’t irrigate that much in their own country, several Dutch NGOs have a strong interest in irrigation. This is perhaps a colonial legacy from the excessive irrigation systems in Indonesia. Examples of Dutch NGOs working with irrigation are: the International Institute for Land Reclamation and Improvement (ILRI), whose stated mission is to facilitate sustainable land and water management in developing countries through applied research, training, and technical support; and SNV, a Dutch organization that finances development projects and sends professionals to work with local NGOs.
How does irrigation work?
As we have seen irrigation is:
…the movement of water -> water has to move from one place to another to accommodate agricultural production. The water source for irrigation may be a nearby or distant body of liquid or frozen water such as a river, spring, lake, aquifer, well, or snowpack. Depending on the distance of the source and the seasonality of rainfall, the water may be channeled directly to the agricultural fields or stored in reservoirs or cisterns for later use. An irrigation system is usually made up of canals, which require control technologies to ensure that the right amount of water arrives at the right place at the right time. The methods of delivering water to the land can vary widely.
…by people -> irrigation involves people — usually there farmers, system operators, engineers, decision makers and managers, all of whom have distinct interests in the distribution of water. The way people are involved in irrigation shapes their property rights, all of which control access to water sources.
…to plants -> different types of crops require different amounts of water at different intervals.
…to vary crops and crop productivity -> farmers can adjust their cultivation pattern and get higher economic returns when their water supplies are reliable.
Various types of irrigation are differentiated in the way water is obtained from its source and is distributed throughout a field and among farmers. In general, the goal is to supply every field uniformly with water so that each plant has the precise amount of water it needs—no more and no less. A few examples:
- Ditch (furrow) irrigation The plants are grown in somewhat raised beds or listed rows and the water is distributed throughout the field via unlined ditches, or furrows, between the rows or beds. This is a popular method because not much extra equipment is needed to irrigate. However it is not the most efficient method. Depending on heat, wind, and soil permeability, much water may be lost before it can benefit the crop.
- Terracing Large steps are cut into hillsides to achieve the leveling of land. The leveled sections are used as garden plots or small fields, most commonly rice fields. As water flows down the hillside it is channeled to each plot. Terracing is often very labor-intensive, since the fields are small and difficult to access thus presenting great challenge to mechanizing the work. In addition, the step walls need constant maintenance, especially in rainy climates to prevent landslides. However, terracing does allow steep mountainsides to be used to raise crops.
- Overhead (sprinkler) irrigation With overhead irrigation, water is piped to one or more centralized locations within the field and is distributed by high-pressure sprinklers, guns, or lower-pressure sprays overhead. This type of system mounted overhead on permanently installed risers is often referred to as a solid-set irrigation system. A drawback of overhead irrigation is that much water can be lost because of high winds or evaporation, and irrigating the field uniformly can be a problem if the system is not properly designed. Also, water remaining on the leaves of plants may promote fungal growth and other crop diseases.
- Center pivot irrigation This is a form of overhead irrigation consisting of several segments of pipe joined together and supported by trusses, mounted on wheeled towers with sprinklers positioned along its length. The system moves in a circular pattern and is fed with water from the pivot point at the center of the arc. These systems are common in parts of the United States where terrain is flat. Center pivot equipment can also be configured to move in a straight line, where the water is pulled from a central ditch. In this case, the system is called a linear move irrigation system.
- Drip, or trickle, irrigation Drip irrigation is delivered at or near the root zone of plants, drop by drop. This type of system can be the most water-efficient method of irrigation if managed properly, since evaporation and runoff are minimized. Drip irrigation methods range from very high-tech and computerized to low-tech and relatively labor-intensive systems.
- Sub-irrigation In sub-irrigation systems, water is delivered from below, absorbed upwards, and the excess is collected for recycling. This method is most often used in commercial greenhouse production, usually with potted plants. Sub-irrigation requires fairly sophisticated, expensive equipment and management. Advantages of sub-irrigation include the conservation of water and nutrients; and even more importantly, because it is automated and requires less system maintenance, it involves less labor. It is similar in principle and operation to subsurface drip irrigation.