At this point, you’ve hopefully discovered a few alternate sources of water, created plans for an irrigation reservoir or two to capture and store it, and set up a system to capture and reuse tailwater. You’ve examined your crop choices and growing calendar with an eye towards avoiding undue strain on your resources. The final piece to consider is how efficiently your irrigation water is delivered to your thirsty crops.
Modern irrigation systems are leaps and bounds beyond what was popular even 50 years ago and it’s now possible to install a system that can monitor the state of your crops, the soil, the air temperature, determine how much water to apply directly to the soil, and to do so remotely with a few touches on your phone screen. The newest systems have capabilities that can help farmers optimize crop production even while saving them time and labor. When it comes to saving water, the irrigation system is a key part of the equation, and fortunately, a lot can be accomplished without the full spectrum of bells and whistles.
It’s possible to divide irrigation methods into two general categories: gravity systems and pressurized systems. The oldest methods of irrigation used gravity and included flood and furrow methods. Water is directed to the fields from nearby ditches or a stream and allowed to flow between rows of plants or to completely cover the ground. The field may remain inundated or be drained off. This is a simple system, but it tends to lose a lot of water with evaporation, runoff, and deep percolation into the soil. In the US, flood and furrow methods are used infrequently except for crops like rice, which require flood conditions to thrive.
Gravity Systems
Although gravity systems might be considered primitive, there are modern tools that substantially improve their efficiency. Surge flooding systems, for example, release water along crop furrows at specified intervals. The on/off surge effect allows water to travel to the end of the field more quickly than if it was applied continuously. Since water reaches all corners of the fields uniformly in a relatively short span of time, less water needs to be applied and less is lost in runoff. Today, even newer methods of surge irrigation are still being developed, which is important in states like Mississippi, where rice is widely grown. Multiple Inlet Rice Irrigation (MIRI) uses perforated pipes to distribute water simultaneously across all paddies, instead of starting at one end and allowing the water to flow across the field until it is entirely flooded. Based on field experience, moving from surge flooding to MIRI can realize up to 25% in water savings while reducing labor costs and increasing yields.
Pressurized Systems
Pressurized systems are generally more efficient than gravity systems, but there is still wide variation among the specific methods. Sprinkler irrigation, particularly center-pivot setups, have been popular for decades and remain one of the most common irrigation methods used in the US. High pressure systems use options like impact sprinklers, which pivot around the central mechanism, shooting water high into the air to irrigate a large circular pattern. High pressure sprinkler systems tend to lose a lot of water, whether from evaporation or winds, and the delivery is imprecise, meaning that some areas might be overwatered while others remain dry.
Low pressure systems are designed to deliver water more directly along the rows and can be installed on center-pivot or laterally moving structures. In these examples, pipes or hoses fitted with sprinkler nozzles extend along a moving structure. Various systems can be configured to deliver water anywhere from high overhead to close to soil level, underneath the leaf canopy. These systems deliver water with more precision than high pressure sprinklers, but sprinklers high off the ground are also subject to waste in windy conditions. The closer to the ground the water is released, the more efficiently it operates, from a water-usage standpoint.
Root Zone Systems
Moving along to more recent and more efficient options bring us to drip or micro irrigation systems, which deliver water under low pressure directly to the root zone of plants with perforated pipes or a variety of specialized emitters. Emitters can be placed at regular intervals either above or below ground or can be precisely spaced to match a specific plant, a technique that’s especially useful with perennials. Water delivered using a root zone system is highly targeted, so distribution is very uniform and water waste through runoff, wind, or other disruptions is eliminated. In an ideal setup, adding mulch to a micro irrigation system would allow the soil to retain even more moisture while reducing weeds and crop diseases. Orchards are often fitted with drip irrigation systems.
Bells and Whistles
We’ve covered the basics of delivering water to crops, but that’s not all that’s involved in avoiding waste. When water is delivered unevenly, or when differences in microclimates mean the windward side of a slope dries more quickly than the rest of the fields, it’s understandable that farmers might choose to irrigate just a little bit more to make sure that everyone gets their share. But this isn’t an ideal response. Not only does it expend more water, much of which isn’t needed, but over-watering can negatively affect crop growth too.
Today, it’s common practice to employ moisture sensors to help detect which sectors might need a bit more water and others that could tolerate a bit less or even be skipped entirely. Connecting this data with a Variable Rate Irrigation (VRI) system opens the opportunity to establish a dynamic irrigation plan that adjusts watering throughout the season as conditions and needs change. This kind of system, coupled with zone and nozzle controls, would allow managers highly targeted and precise control over how much water is applied, not only spatially, but over the course of a growing season. Some systems even connect with smartphones, offering decision support tools and remote control of irrigation equipment.
