ESTABLISHING A LYSIMETER NETWORK IN SOUTHEASTERN MINNESOTA TO ASSESS NITRATE TRANSPORT THROUGH THE ROOT ZONE OF AGRICULTURAL AND NON-AGRICULTURAL SOILS

The Driftless Area of southeastern Minnesota includes a variety of competing land uses spanning agriculture, recreation and tourism, and high-value cold water trout streams. The Driftless Area includes the largest karst terrain in the upper Midwest. Agriculture is a long-standing foundation of the economy within the region. Understanding and managing the impacts of agricultural practices on sediment transport and water quality is a primary focus of local resource managers. This challenge is made more urgent and critical by the rapid growth of recreation and tourism focused on the trout stream resources of the Driftless Area.

Agricultural nutrient management is recognized as a critical water quality concern in southeastern Minnesota. An important question centers on the flux of nitrate through the soil and beyond the root zone. Nitrates leaching past the root zone represent a dual-edged problem. Once below the root zone the nitrogen is no longer available to the crop and represents a wasted agricultural resource. Furthermore, the nitrate is fated to become a contaminant delivered to the trout streams by shallow subsurface throughflow and groundwater movements expedited by the karst hydrology.

To quantify the flux of nitrate through the root zone a lysimeter network has been established in southeastern Minnesota. The lysimeters are primarily deployed in various agricultural cropping and management systems, but as a point of comparison sites representing prairie, forest, residential, and golf courses have also been instrumented. The lysimeters were installed in spring and summer 2011 and are being sampled weekly. The nitrate levels in the preliminary water samples from the lysimeter network range from 0 mg/L to 32 mg/L. Generally, the highest values derive from row crop agricultural land uses and lower concentrations are associated with pasture and non-agricultural land uses. .

As sufficient data is collected it will be possible to understand the relationship between nitrate flux through the root zone and various land uses and agricultural management practices. This will guide recommendations regarding BMP implementation. The preliminary data also suggest that much of the excess nitrate reaching the groundwater, and eventually trout streams, is agriculturally-derived.