A brief history of agricultural drainage
The primary purpose of agricultural drainage is to remove excess water from the landscape in order to improve crop productivity. Technically, according to the International Committee of Irrigation and Drainage, drainage is the “removal of excess surface or groundwater from any area, naturally or by virtue of man-made surface or sub-surface conduits, [and] has four main functions: creating well drained arable lands, preventing salinization of the soils, lowering of groundwater table and removal of accumulated salts or toxic elements.”
The earliest evidence we have of the creation of artificial drainage systems for agriculture is from around 4,000 B.C. in Iran. There is also evidence of drainage systems used in Egypt, China and India around 2,000 B.C. The complexity of these irrigation methods grew alongside the development of agriculture.
The anthropogenic salinization of cropland is a big issue in arid regions. To understand why, it is helpful to remember that the saline content of the world’s oceans is contributed in part by millions of years of stream erosion. This erosion contributed toward the accumulation and deposition of minerals and salts eroded from river rocks by collected rainwater (which is slightly acidic), carried along by the river in solution as ions. These ions mostly consist of sodium and chloride, which together make sodium chloride, or table salt.
The accumulation of these ions in floodplains or fields can lead to salinization of the soil. In climates where there are high annual evaporation rates and low annual precipitation rates (as well as restricted soil drainage), lowland fields accumulate these salts. This is a common occurrence in Colorado and California. For example, an estimated 250,000 acres have been removed from production because of high salinity soils in the San Joaquin valley of California, along with a further 1.5 million acres that are potentially salt impaired. It is thought that the downfall of the ancient Sumerian culture is attributable to the widespread salinization of farmlands and poor drainage management.
Moving water from one place to another has evolved into a critical activity in modern civilizations. Sometimes that means moving water away from croplands, and sometimes that means moving water onto them.
- The Right Amount of Water
Those who work in the field of sustainable agriculture often hear the mantra “Slow It, Spread It, Sink It.” In contrast, conventional farming generally regards removing surface and soil water, in order to increase crop yield, as a primary goal.
Is there an ideal soil moisture for growing crops? It depends on your soil type and the crop that you are growing. Over the years, a farmer can grow to understand their soil moisture needs according to the weather, the field and the crop they are growing. Understanding the soil moisture in a field on a day-to-day basis can help a farmer reduce soil compaction when doing field operation. A simple hand-feel and soil-appearance test can be helpful, but taking consistent measurements using a moisture meter tends to create more useful data and benchmarks that can be used to track trends.
In general, clay soils are critically low in soil moisture when they are below 60 percent moisture and need to be irrigated when they are at 60-80 percent moisture; loamy soils are dangerously low below 70 percent and need to be irrigated at 70-88 percent; and sandy soils are dangerously low below 80 percent and need irrigation at 80-90 percent moisture. The physical characteristics of your soils and the needs of your crops require day-to-day analysis.
In regions that lack sufficient surface water for irrigation, groundwater is pumped from aquifers, at ever-increasing depths as the years go by. This common practice has the potential to increase salt concentration in soils and aquifers.
The importance of providing the right amount of water for any specific crop can’t be over-emphasized. A study of crop yields over the last 65 years shows that the gap between crops grown using precipitation versus irrigation is widening. Research tells us that wet or flooded field conditions can reduce row crops like corn by 7 to 30 bushels in the Midwest. While this may not seem like a high amount of lost production on a per-acre basis, the accumulative loss over hundreds of acres can be significant.
- Engineering for a Change
In the 1930s, the U.S. Soil Conservation Service (SCS) began to develop national policies and strategies to address soil conservation and erosion reduction. This agency was formed in part as a response to the Dust Bowl. This period of severe dust storms was caused by the conversion of grasslands on the Great Plains into croplands after World War I and the subsequent mechanical tillage and mismanagement of the soil.
The United States Department of Agriculture (USDA) was the governing body of the SCS, which became the Natural Resources Conservation Service (NRCS) in later years. The NRCS produced scientific research and materials, in cooperation with county extension agencies, focused on how to reduce erosion and improve soil. Much of these materials involved the management of wind and water erosion. The NRCS outlined specific and scientifically proven practices to reduce erosion such as grassed waterways and grade stabilization structures. These vegetated landscape systems helped maintain the soil in the field, as opposed to washing away in heavy rains. Even though the dehydration of the landscape was a major contributor to the Dust Bowl, many of these practices were intended to direct water away from the crop fields and into ditches — in order to improve crop yields.
- What Line Is Key?
While farmers in the U.S. were busy building waterways and ditches to direct water away from their fields, in Australia a former miner named P. A. Yeomans who ran a thriving earth-moving business had purchased a thousand acres in the bush and developed a new drainage system. He based his system on the practical understanding of land form that he had developed while pursuing earthmoving and mining. He called his system the Keyline Plan.
The Keyline Plan was a system of cultivating landscapes so that surface water was absorbed or stored in the soil rather than running off into a ditch or stream. Yeomans had noted that a key aspect of mining was routing water to a specific place on the landscape, and he surmised that within the field of agriculture this may also be the case. The revolutionary aspect of his system was that, instead of running a cultivation pattern down slope to facilitate drainage — or on contour, to facilitate retention of water in place — he patterned his landscapes slightly off-contour, directing surface water from the valley onto the ridge.
This seems impossible when you first hear about it — like moving water uphill without a pump — but the idea is simple enough. Yeomans thought that this slight change in cultivation patterning could have tremendous results on the landscape. The Keyline pattern starts from a point on the landscape, called the Keypoint, where the slope changes from convex to concave, and is repeated at a set interval down from that point into the valley. The ridges are also patterned in a similar manner, but this pattern is based on a lower ridge contour line and patterned uphill.
These two sets of lines are joined in a manner that makes logical sense to the designer. The line that crosses the Keypoint is called the Keyline, and water storage “dams” (or “ponds,” as they are called in the U.S.) are typically placed along a Keyline. In landscapes other than the typical geomorphology of Yeoman’s property, the keyline patterning must be adapted to the geomorphology of the region in order to function properly.
It is important to note that the Keyline modality was developed in the relatively arid climate of Australia, with an average rainfall of under 30 inches. It was an early form of what we now call sustainable agriculture.
The Keyline modality is very different than the NRCS modalities, which are more concerned with drainage and its resulting sluices, dams and retaining ponds. The purpose of the Keyline System was to retain as much water in or on the soil as possible, in order to facilitate crop growth and landscape hydration. The NRCS is tasked by the federal government to develop methods to increase production of annual crops such as corn, wheat, soy and other grains, while also decreasing erosion. The two modalities are driven by two different sets of goals.
- Watering a Permanent Agriculture
In the 1970s, a professor and his graduate student (Bill Mollison and David Holmgren) would come to develop a system of sustainable agriculture and social design that they called permaculture. This new modality, which was based on present-day scientific understanding of ecological systems but was also heavily reliant on a storehouse of indigenous knowledge, drew heavily on the Keyline modality.
The idea of swales and berms were promoted around this time as well in permaculture materials, especially The Permaculture Designer’s Manual. Swales were just another name for ditches until permaculture used the term to indicate ditches on contour; this is similar to the NRCS conservation practice of terracing. The Designer’s Manual outlined several methodologies of earthmoving, drawing on Mollison’s personal research and observations of earthmoving techniques around the world. It included a section on Keyline methods, introducing the Australian concept to many of today’s permaculture designers and practitioners, as well as curious land planners and landscape architects.
In more recent years, Mark Shepard has developed his own methods of rainwater management, using permaculture, Keyline planning and his own hands-on experimentation. Shepard introduced the concept of using swales slightly off-contour to direct surface water runoff into pocket ponds on a landscape planted in perennial and annual crops. He also ran livestock through this production landscape. His methodology involved using equipment many farms already have, such as a two-bottom moldboard plow to shape a swale and berm in one or two passes with a tractor.
Shepard’s methodologies are outlined in his books Restoration Agriculture and Water for Any Farm.
- The Use of Drain Tile
Drain tile is a semi-permanent installation of plastic tubing buried 3 to 5 feet underground. These lateral networks of tubes collect the water that percolates through the upper soil horizons of a field and directs the water into a main line, which then drains out into ditches and ultimately into streams and rivers.
The larger the field that is drain-tiled, the more environmental impact this “waste” water has on the surface water quality in the watershed. Drain-tile-collected water concentrates fertilizer residue as nitrate and releases this concentrate into the environment. The closer the tiles are spaced, the faster the field drains, but this also means that there is more nitrate concentrated in the water. Faster drainage doesn’t necessarily mean a substantial improvement in crop growth, so farmers are beginning to install drain tile at wider spacings of about 20 feet. Some farmers also use controlled drainage, or drainage water management, as well as reducing their fertilizer use in order to facilitate a positive impact on the surface water quality in their townships and watersheds.
While woody plant roots, such as trees and shrubs, will definitely clog these drainage lines, a recent study from Iowa State University indicates that crop roots, and even long, fibrous prairie plant roots, will not impact drain tile when the system is installed at a regular depth of 3 to 4 feet. On the other hand, drain tile installers in Canada, who regularly install drain tile at depths of 2.5 to 3 feet, have found instances where crop roots from wheat and alfalfa have blocked tile drainage. Proper installation seems to be a key factor in avoiding this issue.
- The Nature of Ditches
Regardless of how or why water is spread, the humble ditch is generally the low-tech method of dispersal.
The landscape is full of naturally formed “ditches” that we call creeks, streams and rivers. The hydrological cycle creates these channels that drain regions and ultimately continents. Gravity plays a large role in this cycle, and water sculpts valleys and ravines drop by drop. This large-scale manipulation of the continental landscape occurs over millennia without human intervention. With our intervention — with a shovel or fossil-fueled heavy machinery — we create artificial ponds and streams within hours and days. In nature, water is only engineered by one other animal: the beaver. Without the beaver, millions of acres of lowland would be barren and dehydrated. Using appropriate methods, perhaps we can also play a role in rehydrating the landscape while also growing crops and livestock.
The ditch slows the process of erosion through the use of vegetation. Roots and fungus create a matrix of life that extends through the network of soil openings. When these roots and fungi die, the carbon captured by the roots, and consumed by the fungi, is deposited into the soil. The crust of the earth, including the soil horizons, is the Earth’s primary depository of carbon. Roots and fungi, and their associated microorganism herds, can only grow as long as they have access to water, and thus water plays an essential role in carbon capture and the creation of organic matter within the soil.
- Using the Right Methods
It is important to utilize the methodologies that help you as a producer reach your own personal farming or ranching goals, regardless of well-meaning advice from extension agents or permaculture gurus.
Digging a trench in the ground is a powerful way to exert control over our environment, and sometimes that can be detrimental to the ecosystem if it is not designed and managed correctly. In the semi-arid regions of Colorado and other states, where surface water rights are essential to agriculture, farmer- and rancher-led organizations manage the drainage ditches that branch from streams and riverways. These are legal organizations that dictate how and why a farmer can use a ditch, as well as ditch upkeep and maintenance. Ditches, where water is scarce, are taken very seriously — as seriously as roadways and electrical lines.
- Conclusion
With a shovel and a plan, we can redirect surface water to create an abundant backyard ecosystem, with raingardens, ponds, and dry stream beds. With more powerful equipment, we can do the same in our fields.
At whatever scale we are working in, we should always design and plan our systems using the best science available, as well as the wisdom of our elders and those who lived on this land for thousands of years, in order to make the right choices necessary to benefit our production landscapes and the ecosystem in which we farm.
The acres that we steward are interconnected with the rest of the planet, and when we provide pathways for water to slow down, spread out and sink in, we foster life and regeneration on our production landscapes.
Andrew French is a land planner and GIS analyst for the NRCS and for Midwest landowners. He owns and operates Full Boar Farm in Boyceville, Wisconsin.
