Photo by Scott Powell, Montana State University
IRRIGATED AGRICULTURE IN MONTANA
resulted in a diversity of irrigation methods, including both gravity-based flood and sprinkler irrigation and more mechanized pump systems. A variety of irrigation management systems have also been developed, and today irrigation water is managed by individuals, groups of individuals, private irrigation companies, state and federal agencies, and federal or state-designated irrigation districts, all with varying levels of oversight, measurement, and cooperation. These activities have resulted in a productive and vibrant farm economy that is an essential part of Montana’s $4.4 billion agricultural industry.³ The land area allocated to irrigated agriculture is a small portion of the total cropland but accounts for a disproportionate share of the total agricultural production and farm revenues.
Irrigated agriculture has been an important component of the culture and livelihoods of Montana residents since the mid-19th century. The earliest documented irrigation was associated with the first homesteaders in the state wanting to take advantage of fertile river-valley soils and abundant surface water. The expansion and growth of irrigated agriculture was linked to mining opportunities in the region, as well as the Homestead Act of 1862 and the Desert Land Act (Carey Act) of 1894, which incentivized homesteaders to settle the land by farming. Irrigators gradually settled Montana’s alluvial river valleys, and new methods of water delivery, governance, and field application led to the nearly 7,500 irrigated farms and more than 20,000 miles of conveyance e ditches and canals that exist today. Variation in irrigation development has
Figure 2 | Statewide Irrigation Consumption by 8-digit Hydrological Unit. (Montana State Water Plan¹)
Irrigation and crop type
A large variety of crops is grown on irrigated lands across Montana, but the dominant crops include alfalfa, hay, barley, wheat, corn, safflower, and sugar beets (Table 1). Crop type plays an important role in determining the timing and amount of irrigation water applied to fields because of variation in plant water demand, rooting depth, life cycle characteristics, and susceptibility to water stress.⁴ These differences also influence irrigator decisions about method and timing of water application and whether it is feasible or worthwhile to change or modify their infrastructure.
Top crops in Montana
| CROP | % OF TOTAL IRRIGATED CROPS IN MT | % GROWN WITH FLOOD IRRIGATION | % GROWN WITH SPRINKLER IRRIGATION |
|---|---|---|---|
| Alfalfa | 40% | 42% | 58% |
| Grassland/pasture | 15% | 73% |
27% |
| Other hay/non-alfalfa | 13% | 67% | 33% |
| Barley |
10% |
35% | 65% |
| Spring Wheat | 8% | 32% | 68% |
| Corn | 4% | 57% | 43% |
| Winter wheat | 3% | 44% | 56% |
| Sugar Beets | 2% | 68% | 32% |
| Canola | 1% | 5% | 95% |
| Potatoes | 1% | 2% | 98% |
Table 1 | Top Crops in Montana. The top ten irrigated agriculture crops in Montana by percent land area, and the proportion of each crop grown with flood and sprinkler irrigation.⁵⁴
Figure 3 | Conversion to sprinkler irrigation in Montana by major watershed. A comparison of the Department of Natural Resources and Conservation Water Resource Survey (DNRC-WRS) mapping and the Department of Revenue Final Land Unit (DORFLU) classification in 2019 provides an estimate of the amount and geographic location of conversion from flood to sprinkler irrigation in Montana.⁵⁴ This comparison is limited to the land area included in the mid-20th century DNRC-WRS. The analysis therefore captures proportional changes in irrigation method across Montana but may underestimate actual acreage converted to sprinkler.
Irrigation methods and changes over time
irrigation efficiency, have allowed producers to more carefully match crop demands with applied water, increase their crop yields, improve water and soil quality, and significantly reduce farm labor. In addition, some individuals and irrigation districts have begun to line and seal the bottom of canals and ditches to prevent the seepage of water during its conveyance to farms.
Comparison of historic and 2019 surveys of irrigated land (Figure 3) shows that between the mid-20th century and 2019, about 21% (or 420,000 acres) of mapped flood-irrigated land in Montana was converted to sprinkler irrigation; 70% was converted to center pivot (290,000 acres) and 30% was converted to other types of sprinkler irrigation (130,000 acres; Figures 3 and 4). Most of the conversion (80%) has taken place in the headwater valleys of western Montana. About 2% (30,000 acres) of flood irrigated land has been converted to urban and suburban uses—primarily housing, industrial, subdivision—near population centers. In 2019, of the nearly 2 million acres of irrigated agricultural land in Montana, 50% was flood irrigated, 36% was irrigated by center pivot, and 14% was irrigated by other sprinkler methods. In addition to development of new sprinkler irrigation since the mid-20th century, roughly 250,000 acres of land were developed for new flood irrigation.
The early settlers relied on flood irrigation, which diverts water from the source (stream) through a canal to the farm, with a series of lateral canals to encourage the water to flow in sheets across a field, temporarily saturating everything along the way. This method of irrigation requires gravity, significant labor and hands-on management, and a large volume of diverted water to travel to the fields and beyond. Farm fields were typically uneven and water delivery was varied, with some spots getting saturated and others less so. After the turn of the century, the Pick Sloan Act of 1944 launched the development of large water projects and the establishment of cooperative irrigation districts. This era was marked by notable growth in the agricultural industry in Montana through the building of many federal dams and canal systems to supply irrigation water and provide downstream flood control.
Over time, increasing demands for water, concerns for water quality, and challenges in labor availability and cost compelled many irrigators to seek out ways to modernize their farm operations. In recent decades, one of the most widespread changes to irrigation methodology has been the conversion from gravity-based flood irrigation to more time- and labor-efficient mechanized and electric pump-based sprinkler irrigation (Box 2).ᶠ Such conversions, often in the context of increasing
Conversions from flood to sprinkler irrigation near Hamilton and Bozeman, Montana.
Figure 4 | Flood irrigated fields in Hamilton and Bozeman areas that were converted to sprinkler irrigation between the mid-20th century and 2019. Also shown are flood irrigated parcels not converted or converted to urban uses. Based on comparison of Montana Department of Natural Resources and Conservation Water Resources Surveys (1946-1971) and Montana Department of Revenue Final Land Unit Classification 2019.⁵⁴
INCREASED IRRIGATION EFFICIENCY AND PERCEIVED WATER SAVINGS A significant motivator for agencies in supporting the shift from flood to sprinkler irrigation has been to increase irrigation efficiency, i.e. to prevent seepage and runoff, and to maximize the proportion of diverted and applied water that is consumed by crops. The switch to sprinkler irrigation has meant that producers tend to divert less water from the source during times of active irrigation, potentially free-ing up water for alternative uses. Thus, increased irrigation efficiency has often been equated with water conservation. However, while more water is left in-stream at the time and place of diversion, overall water consumption may actually increase due to the new sprinkler technologies and additional consumption by downstream users.
AGRICULTURAL ECONOMICS The structural economics of the U.S. and world agricultural markets have created a persistent push toward ever-increasing mechanization and the consolidation of smaller farms into larger operations. These changes have made it more difficult to maintain the viability of farms and ranches with traditional, non-mechanized irrigation methods.
Motivating factors for converting to flood irrigation
Many producers choose to maintain flood irrigation, and there are a variety of factors influencing this decision.5 Although flood irrigation requires a greater investment of time and labor relative to sprinkler irrigation, it involves significantly lower financial and technological inputs, even for the more precisely managed forms of flood irrigation such as gated pipe over leveled fields. Sprinklers, particularly center pivots, represent a large financial investment even if cost-share is available, and also require electricity to operate, adding additional cost and technical upkeep. Therefore, a producer must be confident in his or her ability to recover investment costs and power costs in order to view conversion as a viable option. Year-to-year water availability, general land productivity, and crop markets may all influence whether cost recovery seems feasible. In some cases, topographic and soil characteristics may influence choices in irrigation method. For instance, in areas with high salinity, it can be important to flush a certain amount of water through the soil to keep soil salinity low and producers may maintain flood irrigation to support this process. Finally, the desire to preserve traditional ranching methods and lifestyle may also factor into decisions to maintain flood irrigation.
Motivating factors for converting to sprinkler irrigation
The physical characteristics of a field or farm, such as slope, soil type, and water availability, can dictate decisions around irrigation methodology and may necessitate the use of one particular method over another. Yet in many cases, multiple irrigation options exist, and the decision to change methods is driven by a combination of motivators, each with varying influence on the producers, canal companies, and government agencies involved.
REDUCED LABOR Most flood irrigation is time and labor intensive, requiring producers and hired workers to be in the fields several times a day for weeks at a time. Gradual adoption of wheel line sprinklers and center pivots has steadily reduced time and labor costs. The benefits of this technology extend beyond the current generation of producers, as increased time and labor efficiency may make it more appealing and feasible for younger generations to stay in, or enter, the field of agri-culture. More automated irrigation can also allow sufficient time to pursue off-farm employment opportunities to supplement household income
INCREASED CROP PRODUCTION Sprinkler irrigation technologies allow producers to apply water more accurately and precisely to crops, better matching crop water demand, and often leading to higher crop density or yield. Sprinklers may also allow producers to diversify and grow higher value products.
ECONOMIC INCENTIVES Economic incentives provided to producers by state and federal agencies have supported the conversion to sprinkler irrigation across the West. In Montana, conversion was relatively slow to take hold, likely resulting from limited funding and few cost share opportunities. In recent years, the Farm Bill has enabled the Natural Resources Conservation Service (NRCS) to provide increased cost sharing and funding opportunities to producers for irrigation related projects.
IMPROVED WATER QUALITY With the increasing use of agricultural chemicals and fertilizers in the 1960s, there was growing concern that ex-cess water applied in flood irrigation provided a conduit for chemicals and nutrients to seep into groundwater or flow overland to surface water, leading to contamination. There are a number of physical and irrigation management-related factors that influence the degree of water quality impacts. However, with sprinkler systems, and even more so with center pivots, water, fertilizer and other agri-cultural chemicals can be applied more precisely,
generally reducing the risk of contamination.
box 2 - Irrigation Methods
Wheel line irrigation– Wheel line (or wheel move) sprinklers are portable irrigation systems consisting of a lateral pipe attached to large wheels, with sprinklers placed at set intervals along the pipe; a power mover at the center of the pipe moves the line across a field.
Center pivot irrigation– Invented in 1948, center pivots are irrigation pipes supported by trusses and mounted on wheeled towers that make a mechanized circuit around a field. Sprinkler nozzles are placed at set intervals and can be placed at varying heights from the ground. Modern versions are highly automated and can also be used to apply fertilizer and other agrochemicals.
FLOOD IRRIGATION– Water is applied and distributed over the soil surface through the use of gravity. Flood irrigation practices range from uncontrolled to highly controlled, with the use of dams, ditches, furrows, and/or gated pipe to regulate the flow of water over lands that range from uneven pasture to carefully leveled fields.
SPRINKLER IRRIGATION– Method of providing rainfall-like irrigation to crops. Water is distributed through a system of pipes, often by pumping, and then sprayed into the air through sprinklers.
Hand line irrigation– Developed in the 1930s, hand line systems were the first move away from flood irrigation. Hand lines consist of irrigation pipe laid along the ground with sprinklers placed at set intervals. Lines must be moved by hand across a field.
Table of Contents | Key Messages | Water and Irrigated Agriculture | Irrigated Agriculture in Montana | The Paradox of Irrigation Efficiency | Hydrology of Irrigated Agriculture | Assessing Consequences of Changing Irrigation Methods | Water Policy and Irrigated Agriculture | Adapting to Change | Conclusion | List of Contributors | Glossary | Footnotes | References