| What it is: The North Platte Natural Resources District has established
the Lisco-Oshkosh-Lewellen Groundwater Quality Sub-Area in parts
of Garden and Morrill Counties where groundwater is contaminated
by nitrate, a colorless and odorless chemical compound that is harmful
to human health. The sub-area consists of a strip of land along
the north side of the North Platte River ranging in width from about
2 miles to about five miles. The west boundary of the sub-area is
about 3 miles west of Lisco and the east boundary is at the Garden-Keith
county lines east of Lewellen.
Map of the sub-area
Many farmers in the sub-area are required to comply with Level
2 regulatory controls adopted by the North Platte NRD. The controls
are listed in detail below.
Why it was formed: The U.S. Environmental Protection Agency
has established a maximum contaminant level (MCL) of 10 parts
per million for nitrate as nitrogen in drinking water. In the
Lisco-Oshkosh-Lewellen Sub-Area, about one-third of the wells
tested periodically by the NRD exceed this concentration. In some
areas, nitrate concentrations exceed 80 parts per million. A study
conducted for the NRD by the University of Nebraska-Lincoln Conservation
and Survey Division identified the source of the nitrate as fertilizer
that had leached from corn fields overlying the shallow groundwater
aquifer.
What it means: Farmers in the Lisco-Oshkosh-Lewellen Groundwater
Management Sub-Area are required to comply with Level 2 regulatory
controls, which are intended to improve the management of fertilizer
and irrigation water in the area. These controls include:
1. Each farm operator must obtain certification by meeting district-approved
educational requirements on various topics including nutrient
management and irrigation management. Certification Must be renewed
every four years.
2. Beginning May 1, 2001, approved water-measuring devices will
be required for all irrigators, including groundwater (well) irrigators
and surface water (ditch) irrigators. Measuring devices must meet
specifications and be kept in working order. The North Platte
NRD will provide cost-share to reimburse farmers 65 percent of
the cost of installing water-measuring devices.
3. Annual analysis of water from each irrigation well for nitrate-nitrogen
levels.
4. Annual deep soils analysis of residual nitrate-nitrogen content
on each field.
5. Fields that are smaller than 5 acres and are planted to a
crop other than corn are exempt from 2, 3 and 4.
6. Annual reports must be submitted by operators for each field,
including results of soil and irrigation water rests; crop grown
and yield goal used as basis for determining nitrogen needs; recommended
nitrogen fertilizer rate recommendation; amounts and dates of
fertilizer applications; amount of manure applied; flow meter
readings from beginning and end of irrigation season and total
amount of water applied; dates and amount of water applied each
irrigation and method of irrigation scheduling used; actual yield
of present year's crop and planned crop rotation for following
year.
7. Ban on fall and winter applications of commercial fertilizer
(after September 1; wheat and other small grains exempted.)
Complete text of the controls
The regulatory controls include practices that will help farmers
determine how much fertilizer they need and thus avoid overfertilizing.
But the controls also include practices aimed at allowing farmers
in the sub-area to improve irrigation management. This is because
water, especially irrigation water, is the means by which nitrate
is carried from the corn crop's root zone to the underlying groundwater.
Thus, to avoid nitrate leaching, both nutrient (fertilizer) management
and irrigation management are necessary.
Garden County is susceptible to groundwater contamination because
of the presence of irrigated agriculture, the shallow depth to
groundwater, and the presence of sandy soils.
These links lead to several extension publications on the importance
of managing both nitrogen and irrigation water to avoid nitrate
contamination:
Irrigation
Scheduling Using Crop Water Use Data (Nebr)
Irrigation
Management in Sandy Soils (Minn)
Nitrogen
movement (ND)
Groundwater Page
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