Interactive Effects of Tillage and Rotational Cropping Systems on Nitrate Leaching

Elevated levels of nutrients and pesticides have been widespread in nation's surface and ground waters for several decades. Nearly one half of the U.S. drinking water supply comes from groundwater and the majority of rural households rely on groundwater for their drinking water supplies. Some occurrences of high nitrate nitrogen (NO₃-N) concentrations in groundwater supplies have been attributed to agricultural irrigation and fertilization practices.

Much of the agricultural land in NGP non-irrigated (dryland crops and range lands) and is not subject to high rates of N fertilization, and any leaching can be largely controlled by continuous (every year) cropping systems. However, shallow groundwater pollution with nitrate and other agrochemicals can be a major environmental concern in eastern Montana and western North Dakota under irrigated crops.

Ground water contaminants such as NO₃-N and other agricultural chemicals may persist for long periods of time because they degrade slowly, if at all, in saturated conditions. As a result, it often takes years to flush aquifers. The cost and time required to remove non-point ground water contaminants make direct cleanup highly impractical. We believe that controlling surface applications and minimizing loss below the crop root zone are the most cost-effective methods of ground water protection.

However, one of the greatest restraints in managing water quality is the inability of agricultural producers to control irrigation inputs in ways that account for the variability in growing conditions across a field. Thus, it is obvious that current technologies and management practices need to be improved to ensure the efficient use of water, as well as nutrients, to optimize production levels throughout fields and minimize groundwater degradation.

In order to quantify leaching, twelve passive wick-type lysimeters were installed at 3 ft below the soil surface with TDR soil water probes in the soil above to monitor water flux and quantify the amount of drainage below the root zone of sugar beets and potatoes under various tillage and irrigation management systems. We will also measure the concentration of nitrate in the leachate caught below the root zone of these irrigated crops. Further, we will also assess the suitability of some water quality simulation models for testing and evaluation under NPA conditions using these data.

Contributing Scientists: Jay Jabro (Soil Scientist), Robert Evans (Agricultural Engineer), Jed Waddell (Soil Scientist), James Kim (Post Doctoral Research Associate) and Bill Iversen (Physical Scientist)