Agronomy news March 2000

Water Relocation In The Arkansas Valley?

CSU faculty proposes feasibility study of a possible solution to “Silent Killer”.

A “silent killer” stalks the Arkansas River Valley in the form of salinity. Seventy percent of the irrigated fields in the Arkansas Valley are affected by increased salinity, resulting in an estimated 10-50% yield reduction for alfalfa and corn. Some 25,000 to 30,000 acres of the roughly 250,000 farmable acres in the Arkansas Valley have been lost to agricultural production because of this increased salinity. As a result, farmers in the Valley are seeking ways to maintain a viable agricultural economy, including the innovative alternative of moving water from highly saline soils to potentially high yielding soils within the basin that are not presently being irrigated.

Water relocation involves identifying those soils that are heavily damaged by salinity inside the present irrigation canal systems boundaries. Land outside the present canal systems boundaries that has not been irrigated and is not saline must also be identified. The soils damaged by salt will normally be located in the areas that have been irrigated for many years (since the late 1800’s) inside the area of the supply canals. Relocating the water above and below the present canal systems to land that has been determined to be good land for irrigation would offer multiple benefits.

The first potential benefit is significantly increased irrigation efficiency from the use of center pivot or drip irrigation systems on the “new” land. Additionally, production costs could be reduced because of larger fields and fewer, if any, field ditches to maintain. Yields would be substantially increased on non-saline soils. Seepage could be reduced by using pipelines to carry the reduced amounts of water needed by the more efficient irrigation systems. These systems would also reduce runoff carrying salts back to the river. The present saline fields could be planted to salt-tolerant grasses to provide better wildlife habitat and/or grazing land, and eventually be reclaimed. Finally, since the water would still be used in an area close to the present communities, the economy of the area could be improved due to the higher yields and lower production costs.

Analysis of the relocation concept is needed to examine its feasibility. A proposed study could be conducted under the direction of several university faculty already doing research in the Valley. The tasks envisioned are to survey the native vegetation and soils using existing data in both the old irrigated lands and those that might become newly irrigated under a water relocation plan. The spatial variability of soil salinity, and water salinity, in both surface water and groundwater needs to be understood and mapped. Some of this work has already been conducted. Where feasible, return flow patterns need to be examined under current and proposed irrigation patterns. The economics and legalities of moving the water also must be analyzed. Options for actually carrying out such a water relocation program need to be examined.

Reclaiming the saline soils in the Arkansas Valley will cost millions — to lower the river, install drainage systems, line the canals and leach the salts out of the soils. Instead of spending that money to reclaim saline soil, relocating the water to non-saline areas with good drainage may be a better and cheaper option. Jim Valliant (Regional Irrigation Specialist for southeast Colorado) and Tom Pointon (a director of the Southeast Colorado Water Conservancy District and a member of the Arkansas River Compact Commission) are optimistic about the possibilities of this potential solution. Hopefully, funding will become available to study this concept’s merits.

by Jim Valliant
Regional Irrigation Specialist
Robert Ward
Director, Colorado Water Center

Weld County Soil Conservation District Examines Salinity Problem

More than 2000 acres of South Platte Basin are mapped.

Beginning in the mid 1990’s, Weld County producers noticed increasing salinity problems. The soil surface of some fields appeared white where it never had before, dry edible beans could no longer be grown in places where they had previously produced well, and vegetable growers saw yields start to decrease. The West Greeley Soil Conservation District (WGSCD), with assistance from the Natural Resources Conservation Service, decided to examine the increasing salinity problem. The District received a matching grant from the Colorado Natural Resources Matching Grant Program to buy equipment necessary to start a salinity testing program.
The first tool purchased was a Geonics EM-38, which is an electromagnetic instrument that measures the apparent conductivity (EM readings) of the soil. A GPS unit was purchased to record the location of each measurement taken. A laptop computer and GIS software were also purchased to produce 2-D and 3-D maps of salinity levels. The District also hired a technician to do the testing, bought an all-terrain vehicle to quickly cover more acreage, and the program was underway.
A problem was found when using software to convert EM readings to the actual electrical conductivity of a saturated extract (EC_e). There was a correlation between the methods, but after sending samples to a lab for salinity analysis, computer generated EC_e values were lower or higher than the measured values. Laboratory analysis of several samples from each field was cost prohibitive. Therefore, WGSCD bought a Hach Salinity Appraisal Laboratory for in-house EC_e testing. Concurrently, the US Salinity Laboratory in Riverside, California released their free ESAP software. The ESAP software uses geo-statistics to choose the best places in a field to correlate EM readings to EC_e. After testing the selected samples using the Hach Lab, the EM readings can be correlated to EC_e automatically using ESAP. ESAP also predicts yield loss for most crops and has map-making capabilities.
So far WGSCD has tested over 2000 acres. The District has provided testing for a diverse group of producers including: corn, bean, alfalfa, and beet growers. Vegetable growers use the service most, because of both the low salinity threshold and high dollar value of vegetable crops. Most acres tested in Weld County have an EC_e value between 1.0 dS/m and 3.0 dS/m. However, some areas with poor irrigation and/or a high water table have EC_e values greater than 5.0 dS/m. On average, ditch irrigation water has an EC_e of about 0.6 dS/m, and well irrigation water of about 1.5 dS/m. The district has also found high sodium levels in water from some irrigation wells.
The salinity program is considered a success at WGSCD and will continue as long as cooperators need it. If any district cooperator in WGSCD would like their farm tested, please call us at (970) 365-8097 ext. 3. A complete salinity analysis costs $50 per field. If time permits, we will test outside WGSCD. The fee for testing outside WGSCD is $2.50 per acre with a $100 minimum charge.
by Nick Hoban
West Greeley Soil Conservation District

Investigating Salinity Issues On The Lower South Platte

Northern Colorado Water Conservancy District teams with the Bureau of Reclamation to collect and analyze data.

Irrigating farmers in the lower South Platte River basin are becoming aware of a growing salinity problem. Many growers have asked why their historically productive ground has become less productive without major changes in their farming practices. Salinity is causing growers to abandon certain crops from their operations because of low yields. Growers are searching for answers to their concerns. While the adverse effects of salinity on crop yields have been well documented, additional cooperative efforts must be made to study the scope of the problem and provide information on how to best manage salinity to preserve productive farm ground.
Irrigation Management Service (IMS) of the Northern Colorado Water Conservancy District (NCWCD) and the U.S. Bureau of Reclamation have united to study and research salinity issues throughout the District’s boundaries, which includes most of the lower South Platte region. Information gathered from other institutions such as Colorado State University, the Natural Resource Conservation Service and the West Greeley Soil Conservation District have generated concerns regarding salinity levels throughout the lower South Platte. This information and their ongoing work in the area has encouraged the NCWCD to become more involved and investigate the problem further.
Starting in spring 2001, the IMS will begin investigating and monitoring salinity levels in irrigation water and soils throughout the District. The IMS plans to monitor salt mass balances throughout the lower South Platte River and its tributaries including the St. Vrain, Little Thompson, Big Thompson and the Cache la Poudre rivers. The IMS will monitor these rivers by utilizing flow data from the current U.S. Geological Service stream gauging stations. IMS will also install up to twenty additional observation wells, intensifying the observations along the river/delivery system. Many of the new data collection sites will be automated and transmit data via cellular phone. The IMS will also collect soil salinity readings throughout the District with a salinity vehicle to take soil readings in the field easily and quickly. To avoid duplication of data already being collected, the IMS also hopes to work closely with other institutions and agencies already conducting salinity studies. The IMS would like to process this information and make it readily available to the general public via the web.
This salinity study is expected to continue for seven years. The first couple of years will be devoted to collecting data concerning salinity levels throughout the Lower South Platte River. While continuing to take readings from the instrumentation installed during the initial two years, the succeeding years will study salinity with a more site-specific approach. This site-specific plan includes more direct work with growers on managing salinity issues. Salinity is one more problem facing Colorado farmers, and the District hopes the information and findings gathered from this study will help farmers maintain productive operations for many years to come.
by Alan A. Halley
Agricultural Resource Specialist
Northern Colorado Water Conservancy District


Investigating Salinity Issues On The Lower South Platte
Northern Colorado Water Conservancy District teams with the Bureau of Reclamation to collect and analyze data.
Irrigating farmers in the lower South Platte River basin are becoming aware of a growing salinity problem. Many growers have asked why their historically productive ground has become less productive without major changes in their farming practices. Salinity is causing growers to abandon certain crops from their operations because of low yields. Growers are searching for answers to their concerns. While the adverse effects of salinity on crop yields have been well documented, additional cooperative efforts must be made to study the scope of the problem and provide information on how to best manage salinity to preserve productive farm ground. Irrigation Management Service (IMS) of the Northern Colorado Water Conservancy District (NCWCD) and the U.S. Bureau of Reclamation have united to study and research salinity issues throughout the District’s boundaries, which includes most of the lower South Platte region. Information gathered from other institutions such as Colorado State University, the Natural Resource Conservation Service and the West Greeley Soil Conservation District have generated concerns regarding salinity levels throughout the lower South Platte. This information and their ongoing work in the area has encouraged the NCWCD to become more involved and investigate the problem further. Starting in spring 2001, the IMS will begin investigating and monitoring salinity levels in irrigation water and soils throughout the District. The IMS plans to monitor salt mass balances throughout the lower South Platte River and its tributaries including the St. Vrain, Little Thompson, Big Thompson and the Cache la Poudre rivers. The IMS will monitor these rivers by utilizing flow data from the current U.S. Geological Service stream gauging stations. IMS will also install up to twenty additional observation wells, intensifying the observations along the river/delivery system. Many of the new data collection sites will be automated and transmit data via cellular phone. The IMS will also collect soil salinity readings throughout the District with a salinity vehicle to take soil readings in the field easily and quickly. To avoid duplication of data already being collected, the IMS also hopes to work closely with other institutions and agencies already conducting salinity studies. The IMS would like to process this information and make it readily available to the general public via the web. This salinity study is expected to continue for seven years. The first couple of years will be devoted to collecting data concerning salinity levels throughout the Lower South Platte River. While continuing to take readings from the instrumentation installed during the initial two years, the succeeding years will study salinity with a more site-specific approach. This site-specific plan includes more direct work with growers on managing salinity issues. Salinity is one more problem facing Colorado farmers, and the District hopes the information and findings gathered from this study will help farmers maintain productive operations for many years to come. by Alan A. Halley Agricultural Resource Specialist Northern Colorado Water Conservancy District