Rain Fed Farming
Rain fed farming is the most natural form of farming, where water is introduced to the soil through rain, snow, or other types of precipitation. Thus, making it the simplest and cheapest way to raise crops. Still, any product that relies on these means is vulnerable to water shortages during extended dry seasons or sustained drought, and yields are strictly limited by variations in the local climate.
Irrigation
Irrigation is an artificial method of dispersing water to crops through use of implements ranging from individual buckets of water to computerized micro-irrigation systems. Irrigation systems have existed for thousands of years and are credited with permitting the growth of cities and the birth of civilization as we know it today.
Historically, irrigation has been employed in situations where rainfall is seasonal or unreliable. In times of extended dry weather or drought, irrigation is often used to maintain crop yields or salvage a season’s harvest. Even where rainfall is relatively reliable, supplemental irrigation has been used to boost productivity by supporting additional plantings per year.
Irrigation systems themselves have varied considerably over time and technology. Flood irrigation usually involved diverting surface water from nearby rivers into channels that could be directed between rows of crops or that could even cover entire fields. Other types of irrigation involve sending water uniformly across fields using an arsenal of sprinkler setups which draw from wells or springs and surface water such as rivers and lakes, or more recently, constructed reservoirs and treated wastewater.
Flood or Furrow Irrigation
Traditional flood irrigation has always been a simple matter of using water from a surface source and diverting it onto a field. In this method, the entire surface of the soil is covered by water. The mechanism for flooding the field has varied over human history, from hand-carried buckets to powered pumps and modern vehicles. Surge flooding is slightly more strategic variation, as it involves releasing water on a prescribed schedule, which reduces runoff and associated erosion. It also permits farmers to concentrate the supply of water to those periods when moisture is most valuable to the crops.
These low-tech solutions are still in use across the world, including in the US. They’re very inexpensive to install and maintain, although grading is often necessary to ensure water is equally distributed. Lower quality water, with moderate amounts of sediment can be used, but this irrigation method makes it difficult to apply small amounts of water through entire fields.
Spray or Sprinkler Irrigation
Spray and Sprinkler irrigation methods imitate natural rainfall, as water is dispersed through the air, running over leaves and stems to the soil beneath. This is the most common type of irrigation in the US, with systems available for residential, industrial, and agricultural usage.
This type of system requires machinery which can be fairly complex, particularly when it’s automated and geared to cover 100 acres or more. In center-pivot systems, that goal is achieved by rotating a boom that can be 1200 feet or more from a central point. Engines power individual connected sections as they pivot around that point in a giant circle. Along that rotating boom is a water tube with nozzles. A high-pressure system can spray enormous volumes of water high into the air using large water guns, while low pressure systems spray gently downward, directly onto the plants. Both systems are widely used in the US, although low pressure systems are becoming more popular due to their improved efficiency.
Sprinkler irrigation systems are popular because they are only moderately expensive and allow for even distribution of water across large fields, even at very low rates. Many systems are programmable to accommodate customized schedules and watering rates. Fertilizer or pesticides can be easily delivered, by injecting them into the water as it is dispersed. On the other hand, high pressure systems can lose as much as 30% of water through evaporation, and water applied to foliage on sunny days can lead to damage from scalding.
Drip or Micro-irrigation
Micro-irrigation is a modern technique, which involves a system of porous tubing, perforated pipes, or other types of applicators that apply small amounts of water directly to the roots of plants. The pipes and tubes themselves can be buried or lay on top of the ground. This is a low-pressure, targeted method of irrigation that ensures the water is provided exactly where it is needed. This means that, aside from using less water, it can reduce weeds, minimize fertilizer requirements, and eliminate runoff with associated erosion. It’s also easily adaptable to irregularly shaped fields. Still, micro irrigation is relatively expensive to install, and it can require significant maintenance to ensure tubes do not degrade or clog, which causes problems in moisture distribution. There is also a risk of damage to tubing by mowers and trimmers.
Subirrigation
Subirrigation systems are best suited to areas where the water table is fairly high since it raises and maintains local water levels to a specific depth, commonly just below the root line. The entire structure may consist of a series of ditches and pipes and is generally a permanent installation. This model minimizes water loss and is less labor-intensive than other methods. It also has the considerable advantage of doubling as a drainage system. However, it should be used with uniform soils, and isn’t suitable for water with high salt content. Most importantly, it is relatively vulnerable to drought since it requires a steady, adequate water supply throughout the growing season.
Conclusion
Agricultural activities account for the largest expenditure of water on farms around the world. Many irrigation methods have been developed over millennia, nearly all of which still are in use today. The best irrigation system for any one case differs according to the size of the farm, the location, available infrastructure, the type and specific needs of the crop, and the relative costs of installation, maintenance, and water. In the following chapters, we’ll explore the challenges of today’s changing weather patterns and climate norms, availability of water and its efficient use, how farms can manage and recover from droughts, and how they can prepare for increasing challenges in the future.
