Modern Management of Centennial Furrow Irrigation
There are many ways how crops can be irrigated by applying artificial water—drop by drop, sprinkling or applying the water on the entire field surface. Each type has its own irrigation system which mainly differs in the way how water is applied to crops and their overall efficiency.
Maybe not the most efficient but certainly one of the oldest types of artificial water application is furrow irrigation. Furrow irrigation is actually surface irrigation in which water is applied to the field from open ditches or pipes through small channels or furrows. The entire field is divided into furrows, small and parallel channels, which carry water through the field. The crop is usually grown on the ridges between the furrows.
How Is Furrow Irrigation Suitable for Farming?
Furrow irrigation can be used to irrigate many different crops, like vegetables and fruit trees, but it is most convenient for growing row crops (corn, sunflower, potato, soybean, wheat). Actually, it is suitable for all crops that would be damaged if water covered their stem or crown.
Besides crop type, additional factors affect the efficiency of furrow irrigation system. These are as follows:
Soil type; soil type determines the amount of applied water due to its water holding capacity. The most suitable soil for furrow irrigation is medium to moderately fine-textured soil with high water holding capacity
Slope; uniform flat or gentle slopes are preferred, less than 0.5%
Climate; wind, precipitation intensity, as well as volume, determine the furrow efficiency in order to prevent surface runoff and excessive soil erosion
Water; furrow suitability may be affected by water quantity and quality
Types of Furrow Irrigation
There are four types or furrow irrigation systems. They are level furrows, graded straight furrows, graded contour furrows, and corrugations.
1. Level furrows
Level furrows are small irrigation channels, with blocked ends laid out with little or no grade. Water is applied using a large stream until the furrow capacity is filled. Level furrows are best suited for crops grown in rows on beds between the furrows, as well as for all climatic areas, except the humid, due to possible crop damage or soil waterlogging. This type requires very extensive land preparation and careful water management for successful operation.
The main advantages are easily adjustable water amount according to the crop needs, reduced runoff and easy system automatization. This type also has some disadvantages, such as inefficiency of the system in areas of high wind, lodging water may damage some crops, and furrow capacity can’t hold rainfall water.
2. Graded straight furrows
Graded straight furrows are small irrigation channels in a straight line, parallel to a field boundary, used to irrigate all row crops. They are used on all soils except sandy, which has very high intake rate and provides poor lateral spread of water between furrows.
This furrow type also requires a well-leveled field with little or no slope and high human labor.
3. Graded contour furrows
Graded contour furrows are small graded irrigation channels with uneven or warped surfaces. They are mainly used on surfaces where it is not practical to use straight furrows. The furrows are curved to fit the field contour. This type can be used on all slopes and soil types except sandy, and soils which crack easily when dry.
The disadvantage of this type is constant furrow management and rodent control to prevent furrow damage.
Corrugations are small, closely spaced irrigation channels used to irrigate close-growing crops on moderately steep land. Irrigation water is applied through small channels or corrugations evenly spaced across the field. Due to their small capacity, channels need to conform to the field slope.
Corrugations are best suited for areas with low rainfall, on soils that tend to crust, and for the growth of high-density crops. Although this type provides good water management for crops, its main flaw is high labor requirements and farm equipment operation.
How to Create Furrows?
The goal of every successful irrigation is uniform water application over the field in order to avoid leaching and overlogging. Although simple and technology free, furrow irrigation is certainly not an easy irrigation system type. Prior irrigation, farmers have to consider many different factors to achieve good water management results.
Before a farmer starts with furrow irrigation establishment, first he needs to construct furrows. Rural farmers with usually small plots use animal and hand-drawn ridgers. On the other hand, farmers in developed countries preferably use a ridger plow attached to a tractor. The plow can vary in size, depending on the field surface.
Another thing to consider is furrow layout—length, shape, and spacing. Although they are determined by the field properties such as slope and soil type, furrow design is also affected by crop type and farmer’s practice in overall crop production management.
1. Furrow length
In an ideal case, furrow length is equal to field length. But since the farmer’s job is never so easy, he needs to consider several factors when determining the furrow length. It’s affected by slope, soil type, stream size, rainfall intensity, and irrigation depth.
2. Furrow shape
Furrow shape is influenced by the soil type and the stream size. Light (sandy) soil requires deep and narrow furrows to prevent vertical water flow. Additionally, in heavier (clay) soil, furrows are much wider and shallower.
3. Furrow spacing
Soil type plays a major role in determining furrow space. In sandy soils, furrows are spaced 30-60 cm (11-22 in), while in clay soils much wider, 75-150 cm (30-59 in). In clay soils double-ridged furrows can be made, thus creating beds with more plant rows.
The System of Water Distribution to the Furrows
The last step in furrow management is delivering water to the furrows across the field. Water distribution system needs to be located in such a way that all farm operations can be maintained properly. Additionally, the water conveyance system has to meet the following properties:
Uniform water distribution over the field
Low operational costs
Rational and efficient water conveyance
Every water distribution system includes farm ditches or pipelines with related structures for application of artificial water over the field.
1. Farm ditches
Farm ditches for irrigation are open channels used to carry irrigation water to the field where crops are grown. In order to prevent ditch erosion, ditches have to have concrete linings. Otherwise, they can be difficult to maintain and disturb proper water conveyance. Although concrete farm ditches are not always the best solution, because they can obstruct the use of farm equipment.
Farm ditch system includes the following structures that deliver water directly to the furrows:
Flumes—artificial channels for water delivery used where ditches are not practical
Inverted siphons—closed conduits that carry water under depressions, roads, or other obstructions
Culverts—closed conduits installed at ditch grade commonly used to carry water under farm roads
Siphon tubes—aluminum or plastic pipes used for controlling the flow of water into each furrow
Spiles—pipes used to distribute water from a ditch into furrows, permanently set on the bank of the head ditch
2. Irrigation pipelines
Besides open farm ditches, water can be delivered to the furrow by pipelines. Irrigation pipelines can be placed on the surface, underground or like a combination of both. Both types have their advantages and disadvantages, and their usage depends on the farmer itself. To some farmers, surface pipes are better because they can be moved to another location, but their relocation requires labor and pipes can be damaged.
Furrow Irrigation in Line with Modern Farming
Alongside drip and pivot irrigation systems, furrow irrigation has also become modernized. All processes are now automatized—time for irrigation, turning the water on and off, and irrigation of field by portion. Though, farmers mainly practice semi-automatic systems, where the irrigator decides when irrigation is needed and delivers the irrigation water to the field.
Automation of furrow irrigation system requires specific field and water properties as well as proper design, installation, and maintenance of the distribution system.
Until recently, furrow irrigation was just a low-cost irrigation system type but due to modernization, its establishment and maintenance require additional cost and effort. These improvements have certainly placed centennial furrow irrigation to a completely new level. However, in order to become the farmer’s first solution, there is only one thing left to change—its water efficiency.
Text sources: FAO || NRCS
Image sources: Sustainable Cotton Project || ACSESS || Monterey County || MicroFarm || AgriExpo || The U.S. Climate Resilience Toolkit