No. 164, September1997
http://www.ext.nodak.edu/extnews/snouts
North Dakota Irrigation Districts
Maintaining the Quality of Irrigated Soils
Tech Tip: Steel wool and fabric softener hinders rodents
Tech Tip: Seal control panels and boxes
Tech Tip: Record critical water data on site
Nitrates in Groundwater – Is There More to the Story?
North Dakota has had a group of irrigation districts in place for many years, but only recently have irrigation districts taken on a renewed interest. With the cooperative movement in North Dakota we see the benefits of working together for benefit to all. As the new irrigated crops are flourishing, we see the benefit of working together for financing, purchasing inputs, and working for the environment together.
There are at least five new districts in the state within the last year, and many other areas are looking to form. We are working through the High Value Irrigated Crops Task Force and the Central Dakota Irrigation district to hold an update for irrigation districts in early October. The program will include, financing, research updates, energy information and a report on a statewide specialty crop association.
If you are interested in attending or wish to learn more about irrigation districts, give me a call or send me an email message.
Rudy Radke, (701) 845-8528
NDSU Extension Ag Diversification Specialist
barnes@ndsuext.nodak.edu
A recent broad definition of soil quality states that it is "the capacity of the soil to function within ecosystem boundaries to sustain biological productivity, maintain environmental quality and promote plant and animal health." In irrigated agriculture, the ecological boundaries of a field are primarily impacted by the soil type present and the quality of irrigation water available. Soil productivity or more specifically crop growth are closely related to salts and associated dissolved minerals in the soil and irrigation water. Generally, fields irrigated with water containing salts and sodium will tend to accumulate these salts and sodium and may reach levels at which crop growth (i.e., productivity) are reduced. Only the coarser textured (sandier) soils are likely to have high enough internal drainage to leach salts out of the crop rooting zone.
Most waters suitable for irrigation drawn from subsurface North Dakota aquifers are classified as C3 (high-salinity) water by the USDA Salinity Laboratory system and range in electrical conductivity (E.C.) from 750 to 2250 micromhos/cm. These are waters that cannot be used on soils with restricted drainage and require careful management even on soils with good drainage. North Dakota soils have been classified according to their suitability to be irrigated and categorized as unsuitable, conditional or irrigable soils.
Non-irrigable soils are categorized because of their slope, salinity, sodicity, slow permeability, wetness or restrictive layers in the subsoil. Conditional soils usually are classified because of slow permeability and internal drainage. Their capacity for irrigation is limited because of their sensitivity to degradation due to water quality with a maximum allowable E.C. levels less than 1000 micromhos/cm and sodium absorption ratios (SAR) of less than 6. Sodium adsorption ratio is the ratio of dissolved sodium to the dissolved calcium and magnesium in the water. The greater the SAR value, the greater the potential for soils to become sodic and for the soil particles to disperse and cause a decrease in water infiltration and internal drainage. Irrigable soils on the other hand, can tolerate water up to an E.C. of 3000 and an SAR of 12.
To maintain a handle on potential changes in water and soil quality, both the irrigation water and soil should be sampled at least every five years when the water E.C. is less than 1800 micromhos/cm and SAR is less than 6 and more frequently if the E.C. or SAR are greater than these values.
Water quality within an aquifer can be highly variable, and long term pumping of water can cause changes in the quality of the water. Usually water will become more saline or sodic, but sometimes the quality of the water can improve because of recharge by less saline surface water nearby. Changes in water salinity or sodicity can impact soils and crop management, and adjustment in management is often difficult if the salinity or sodicity of the soil is increased. It is much easier to add salt or sodium to a soil than to remove them.
Along with the periodic water sampling, soils should also be sampled at least every 5 years to determine if irrigation has changed its potential for productivity. Each major soil type should be sampled at two sites: one within the field receiving irrigation water and another nearby that is dry land. The soil should be sampled by genetic horizon or 12-inch depth increments at both sites to a depth of at least 4 feet and preferably to a depth of 6 feet. For best results, the sampling should be done by or under the supervision of a professional soil scientist. Sampling of the two sites allows for evaluation in soil changes due to the irrigation.
Both soil and water samples should be analyzed for pH, electrical conductivity and SAR as a minimum. The Soil and Water Environmental Characterization Laboratory at NDSU has the capability to process the samples and evaluate the results. Contact the Soil Science Department for a fee schedule.
Additional information on soil and water compatibility can be found in the NDSU Extension Service publications:
These publications are available through county extension offices or from the Agriculture Communication Distribution Center on the NDSU Campus.
Larry J. Cihacek, (701) 231-8572
Associate Professor, NDSU Soil Science Dept.
cihacek@badlands.nodak.edu
The large snowfall received last winter forced many rodents to find shelter in irrigation control panels. With fall approaching, rodents will again be looking for a winter home. Don't let them use your electrical panels or motors. Stuffing steel wool into electrical conduits, holes and other entrances will stop rodents from entering, nesting and feeding on your wires.
BE CAREFUL. Before opening any electrical boxes to inspect wires for damaged insulation, make sure the power has been disconnected.
DON'T use steel wool if you have exposed wires. Steel wool will short any exposed wires and you will have fireworks, equipment damage and possible personal injury, the same things we are trying to prevent the rodents from doing.
Fabric softener strips have been reported to prevent rodents from entering enclosed areas. This information has not been verified, but it might be worth trying.
Dirt and moisture eventually find their way into most electrical panels and control boxes. Using compressed air to blow out all dirt and moisture out of contactors and panels will prevent corrosion and failed contactors. Reseal boxes at the first sign of weather seal damage. Pickup topper seal will work well and has adhesive to make installation a snap.
To prevent misplacing information on your well and pump, record it on the inside of the electrical panel with a permanent marker (ear tag marker works well). BE CAREFUL. Disconnect all power, at the meter, before opening any electrical boxes.
Record annual pressure, flow, static and pumping water levels for future comparison and monitoring. Record well depth, depth of pump, screen type, and well capacity. It will make trouble shooting future problems much easier with recorded data.
Tom Scherer, (701) 231-7239
NDSU Extension Agricultural Engineer
tscherer@ndsuext.nodak.edu
Nitrate contamination of groundwater is a subject with truth and myth intertwined so tightly that reasonable decisions regarding management is often difficult. It's too easy to take one of two extreme views: 1) inputs of nitrate into the environment are an innocuous consequence of human activities that warrants little or no attention because of the benefits; or 2) presence of nitrates are a portent of environmental doom that must be dealt with regardless of the economic carnage or loss of personal freedom.
Proponents of these extremes are similar in that they both distill a complex environmental problem into a simple one that requires little thought in regard to consequences of actions. We use this process of problem simplification as a method of saving time and allocating it to other problems, supposedly of greater importance. This is very effective if the problem can indeed be simplified. However, if problem simplification merely ignores complexity for the sake of expediency, then we've created an additional problem of unfulfilled expectations. Public policy that addresses complex environmental problems with unrealistically simple solutions is predestined to failure.
An illustration of my point is the case of nitrate contamination of groundwater in North Dakota. We've known for many years that elevated concentrations of nitrates occur in samples of groundwater from some wells. Historical well water data from North Dakota Department of Health indicate that about 10 percent of the wells tested have nitrate concentrations above the EPA standard of 10 ppm. Studies in other states such as Nebraska have found a relatively strong link between elevated nitrate concentrations in certain aquifers and nitrogen fertilizer applications.
Through simple extrapolation of Nebraska data to North Dakota, one would assume the presence of high nitrates in North Dakota to be related to fertilizer applications. The simple answer to the simple problem is public policy that results in nitrogen fertilizer reductions throughout the state. Would this policy be based on good science?
North Dakota is not Nebraska, and to assume that geologic materials, soils, climate, and crop management are the same in these two states is an enormous error. Water quality research has shown conclusively that variation in natural factors that affect pollution levels is often significant within a single field, let alone between states. Monitoring results from drinking water wells is not necessarily a reflection of impacts from field activities. In fact, most studies that have attempted to determine relationships between well contamination and human activities have found no strong connection between specific field practices and nitrate contamination. Animal waste, septic tank filtration fields, and fertilizer spills have also been identified as sources of nitrate contamination in groundwater. Data from the U.S. Geological Survey and North Dakota Water Commission monitoring wells reveal no general deterioration of aquifers of the state with respect to nitrates except for sporadic incidences of high concentrations in solitary wells. These high concentrations often are proven to be only temporary.
Groundwater pollution is affected by factors that influence local infiltration and movement of water. In the 1980s research from the NDSU Department of Soil Science established the importance of depression focused water flow on landscapes in North Dakota. These studies not only verified the contributions of certain types of wetlands to groundwater recharge, but they also showed that hydrologic relationships between soils and groundwater are extremely variable along hill-slopes within a single field. Research at sites near Carrington and Oakes have helped further identify relationships between depression focused recharge and groundwater contamination.
The study at Carrington showed that most recharge to the aquifer occurred in micro-depressional areas that could hardly be discerned from non-depressional areas except during periods of overland flow. Although groundwater recharge occurred from the area studied, significantly elevated levels of nitrates were not found in the aquifer. The Carrington study also showed that natural topographic conditions had a much greater influence on groundwater recharge and contaminant movement compared to differences in inputs and management systems.
Both the Carrington and Oakes studies found that during certain periods saturated water flow by-passed portions of the soil matrix via preferential flow through large channels and pores. This type of water flow was identified as a cause of increased concentrations of nitrates for short durations in some of the monitoring wells. However, most of the movement of recharge water and dissolved nitrate was associated with much slower bulk flow through smaller pores that dominate the soil matrix. Several studies at Oakes have shown that a lag of about 12 to 14 months exists between nitrogen applications and nitrate movement to the top of the aquifer. However, the actual contribution of nitrate from different parts of the field is highly variable and dependent on focused flow and the presence or absence of tile drainage. As research from Cornbelt states with significant tile drainage has shown, the drains at the Oakes site protected groundwater by shunting water and nitrates to surface outlets. A surface water research study in the Oakes area found that nitrate concentration of tile drainage was significantly reduced after it moved through a wetland downstream from the tile outlet.
Evidence of denitrification in the upper part of certain aquifers in North Dakota has been found in recent years. Studies done in the Elk River Valley aquifer by the Environment and Energy Research Institute at the University of North Dakota and the North Dakota Water Commission confirm that this process protects the aquifer from excessive concentration of nitrates. Work on the Oakes aquifer also determined that denitrification was occurring, but with a slightly different twist. Apparently the process is not as effective in protecting areas of the aquifer with greater thicknesses of overlying materials. In other words, we may have to reassess the theory of decreasing vulnerability with increasing depths to the water table, at least with respect to nitrate contamination.
The results of groundwater studies in North Dakota lead us to the conclusion that nitrate contamination is a locally controlled phenomenon that does occur, but it is extremely variable. Under some circumstances it may be due to poor handling practices of nitrogen sources. In the field, nitrate contamination is related to groundwater recharge, which is strongly influenced by the hydraulics of focused flow in depressions. The process of preferential flow contributes to the movement of a relatively small percentage of the mass of water and contaminants to groundwater. However, this process does contribute to a sporadic pattern of high concentrations of nitrates for short durations in monitoring wells. It appears that management systems that reduce overland flow to depressional areas would have an impact on nitrate movement to groundwater. It also appears that sporadic spikes in nitrate concentrations in monitoring wells are not particularly worrisome, because they do not reflect the bulk flow of nitrate through the system. Denitrification is a process that helps protect aquifers in North Dakota. Continued research is needed in this area to establish the limits of this protection within different aquifers under various management systems.
From an agronomic point of view, we know that application of nitrogen fertilizer has had a significant role in increasing crop yields and economic returns for producers in North Dakota. We also know that despite educational efforts many producers in the state still do not apply enough nitrogen to meet the yield potential of the crops they produce. Conservationists have demonstrated the value of improved soil and water protection from increased residue from well fertilized crops compared to unfertilized crops. We have to be careful that our natural resource policies don't just substitute one problem for another.
The evidence from groundwater studies in North Dakota does not support an environmental policy that would blanket the state with nitrogen fertilizer reductions. Further, this policy would be counter-productive to good agronomic and conservation practices.
The Nebraska studies are based on good science. There's no reason to suspect the accuracy of the well water monitoring results from the North Dakota Department of Health. However, using only this information leads to simplification of a complex problem by way of inappropriate assumptions.
How do we avoid the "oversimplification trap"? Although it runs contrary to the demand for immediate solutions to both real and perceived problems, the application of patience and resolve to scientific study will serve our need to understand the environment. The good sense of public policy based on scientific study will prevail if we allow it. Environmental problems rarely, if ever, can be labeled as simple. They require careful and critical analyses founded in good science. Research has revealed that characterization of many environmental problems, particularly non-point source pollution, is site-specific. Management schemes that realistically address environmental problems must first characterize natural variability. Research projects that determine the processes that influence variability, such as those just described, will eventually help address these problems in the most appropriate way.
Bruce Seelig, (701) 231-8690
NDSU Extension Water Quality Specialist
bseelig@ndsuext.nodak.edu
Water Spouts, No. 164, September 1997.
NDSU Extension Service, North Dakota State University of
Agriculture and Applied Science, and U.S. Department of
Agriculture cooperating. Sharon D. Anderson, Director, Fargo,
North Dakota. Distributed in furtherance of the Acts of Congress
of May 8 and June 30, 1914. We offer our programs and facilities
to all persons regardless of race, color, national origin,
religion, sex, disability, age, Vietnam era veterans status, or
sexual orientation; and are an equal opportunity employer.
This publication will be made available in alternative
formats for people with disabilities upon request, 701/231-7881.
North Dakota State University
NDSU Extension Service