LAND MANAGEMENT FOR DRYLAND SALINITY CONTROL IN MONTANA,
NORTHERN GREAT PLAINS. Jane M. Holzer, Scott K. Brown and Tera O. Ryan. Montana
Salinity Control Association, Conrad, MT 59425.
Salinization of soil, shallow ground water and surface water resources has occurred over
portions of the U.S./Northern Great Plains (NGP) during the past +60 years. Saline conditions are
manifested in degraded water resources and salt-encrusted soil that reduces or prevents
vegetative growth. Over one million hectares (ha) (several million acres) of formerly productive
land in the NGP, including 121,500 ha (300,000 acres) in Montana, have been adversely affected by
dryland salinity. The soluble salt is sulfate-dominated with calcium, magnesium and sodium.
Degradation, for the most part, is attributed to the semi-arid crop-fallow dryland farming
practices that replaced native rangeland conditions. Crop-fallow systems (summer-fallow) produce
a cash crop every other field season and the land in the intervening field season is left idle to store
soil moisture. However, the inefficient use of annual precipitation allows deep percolation of soil
moisture and the downward migration of soluble salts. The deep percolation creates a non-natural
buildup of shallow saline ground water that, combined with certain geologic conditions, leads to the
development of low volume saline springs called saline seeps.
The saline seep reclamation process in Montana is an excellent example of a locally led
conservation program that coordinates the technical and financial resources from the private,
county, state and federal level for individuals and groups.
The Montana Salinity Control
Association (MSCA) multidisciplinary technical field team addresses saline seep problems on an
individual farm and/or watershed basis. A soil and hydrogeologic assessment of each site is
conducted to locate the key recharge areas. Land-use changes focus on the upland recharge area to
lower the perched water table with the evolution away from crop-fallow systems to intensive
cropping and perennial forage rotations over a broad landscape. In Montana, water quality laws
restrict drainage of saline areas to protect the state-owned surface and ground water; as a result,
drainage is rarely used. Drainage of saline seeps has not been economical for landowners either.
The assessment begins with the installation of a grid of shallow ground water monitoring
wells across the landscape to evaluate the flow patterns and isolate the recharge area extent for
specific saline discharge areas. The key to lowering the water table in the saline discharge area
is the land management conversion from crop-fallow to perennial vegetation in the designated
recharge area. Perennial forage uses the annual precipitation and utilizes the deep subsoil
moisture to reduce the leaching into the shallow ground water table. In Montana, alfalfa
(Medicago sativa) is the predominant perennial species chosen for the economic return and
winter-hardiness. Perennial forage rotation requires a minimum of five years to lower the water
table in the recharge-discharge area, but may require longer before returning to an annual
cropping rotation.
No amendments or drainage measures are necessary in Montana’s saline discharge areas
since natural precipitation leaches the soluble salts downward as the water table drops. Salttolerant forage can be established in the discharge area as conditions improve to reduce
evaporation and utilize soil moisture.
Water table monitoring is a key component of determining reclamation success. Along
with the visual improvements of the discharge area, well hydrographs show the long-term water
table trends in response to surface land management. Land managers use the water table trends
to rotate between perennial forage and annual cropping to maintain the shallow water table at
213 cm (7 feet) Below Ground Surface (BGS), without waiting for visible saline conditions to
return.
In an example case study in Hill County, Montana, the saline ground water at 61 cm (2
feet) BGS caused a surface salt crust that prevented crop production.
The ground water
assessment defined the recharge area which had two separate ownerships, and both owners
initially managed with the crop-fallow rotation. The owner with the saline seep changed to
alfalfa production in the recharge area he owned
and planted salt-tolerant forage in the saline area.
Hydrograph: Land Use Effects on Water Levels
0
(Ft) Below Ground Surface
-2
-6
Perennial
Forage
Established
-61
-122
-183
-244
-8
-10
Saline Discharge Area
-12
-305
-366
-427
-14
-488
-16
Alfalfa
Established
Recharge area
-549
-20
-610
-22
-671
-24
-732
(cm) Below Ground Surface
(ft) Below Ground Surface
-4
-18
The water table trend changed from 183 cm (6
0
Crop/Fallow
86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10
19 19 19 19 19 19 19 19 19 19 19 19 19 19 20 20 20 20 20 20 20 20 20 20 20
feet) BGS to 549 cm (18 feet) BGS in six years.
In the discharge area well, approximately 800
meters (0.5 miles) away, the saline water table
simultaneously dropped from 61 cm (2 feet) BGS
to 305 cm (10 feet) BGS in the same 6-year
period and salts were leached below the rooting
zone. Across a property boundary, the water table in the adjoining recharge area showed no
change for the same 6-year time period (1987-1992). In 1998, the land-use changed to perennial
vegetation and the water table dropped from 213 cm (7 feet) BGS to 671 cm (22 feet) BGS in
seven years.
Special/Papers/Abstract 2014 3rd Internatl Salinity Forum-Montana