NU Water-Related Research in Franklin County

This study examines the water use of winter annual weeds. More winter annual weeds grow now than 20 years ago because of the adoption of reduced tillage systems, where the soil is not disturbed between harvest and planting. Winter annuals typically germinate in the fall, overwinter as small plants, and grow rapidly as temperatures warm in the spring; these weeds are especially well adapted to limited summer rainfall. Common winter annuals in Nebraska are downy brome, henbit, field pennycress, wild mustard, marestail (horseweed), foxtail barley, shepherdspurse, speedwell, and prickly lettuce. This project is investigating whether allowing winter annual weeds to grow too long in the spring depletes the soil of moisture that would benefit the crop later in the summer.

Estimated potential nitrogen immobilization by winter annual weeds may be calculated as:

• 500 lbs/ac of winter annual biomass growth at planting time (this would be a relatively dense, uniform stand of weeds).
• As a general statement, nitrogen composes approximately 3% of plant biomass.
• $0.58/lb of nitrogen fertilizer (based on $950/ton of anhydrous ammonia)

Based on these assumptions, a dense, uniform stand of winter annuals could tie up approximately 15 lb of nitrogen per acre (500 x 0.03), or $8.70 per acre (15 x 0.58) of nitrogen intended for a corn crop.

Estimating the irrigation cost to replace water used by the same 500 lbs/A of winter annual biomass by assuming:

• 500 lbs/A of winter annual weed biomass at planting time,
• 800 lbs of water is required to produce 1 lb of winter annual weed biomass.
• At $2.50 diesel fuel, applying 1 inch of irrigation water per acre would cost $9.66.

The 500 lbs of winter annual biomass would use 400,000 lbs of water per acre (500 x 800), or 47,920 gallons of water (400,000 lb x 0.1198 gal/lb). This equals 1.75 acre inches of soil water (47,920 gal /{27,158 gal/acre in}) used by these weeds. Based on a cost of $9.66 to apply 1 inch of irrigation water, it would cost approximately $17.00 per acre to replenish the water used by winter annual weeds in this scenario.

It is important to learn how to grow crops with limited amounts of water and to determine crop water use with SDI. In 2007 a field study with corn was initiated that will be continued in 2008 and 2009. The treatments are:

• Rainfed (no irrigation)
• 0.50 ET (meet 50% of evapotranspiration requirements) throughout the season
• 0.75 ET throughout the season
• 1.00 ET throughout the season
• no irrigation at first, 1.00 ET during 2 weeks around tasseling, then no more irrigation after that
• 0.50 ET at first, 1.00 ET during 2 weeks around tasseling, then 0.50 ET after that
• 0.50 ET at first, 1.00 ET during 3 weeks around tasseling, then 0.50 ET after that
• 0.50 ET at first, 1.00 ET during 4 weeks around tasseling, then 0.50 ET after that
• 0.75 ET at first, 1.00 ET during 4 weeks around tasseling, then 0.75 ET after that

Using SDI may not only increase water use efficiency, but also nutrient use efficiency when applying nutrients through the SDI system. This study was conducted at WCREC to assess the effect of different in-season nitrogen (N) application (via SDI) timings on corn production and residual soil nitrate-nitrogen (NO3-N). We evaluated the effect of three N application timing methods at two N application rates (UNL recommended rate and the UNL rate minus 20%) on corn grain, biomass yield, and end-of-study distribution of residual soil NO3-N.

In 2006, there were no significant differences in corn grain yields between the two N application rates. In 2007, the grain yield under the UNL recommended N rate was significantly higher (3.0 bu/ac) than under the UNL-minus-20% N rate. In both years, grain yield and biomass production for the N application timing treatments were not significantly different. The lack of response to different N application timing treatments indicates that there is flexibility in N application timing for corn production under SDI. This two-year field study was published in Soil Science.

Impact: This study helps us better understand the most appropriate times to apply N with SDI (underground fertigation). If applied at inappropriate times, nitrates are not used by the crop and may leach into groundwater. If N use is minimized, the producer's cost can be minimized.

The goals of a recently funded project to measure the potential benefits of developing a groundwater trading market in Nebraska is discussed in this Cornhusker Economics article. Groundwater is a major component of agricultural water use. In extensive regions of the Western United States, rural agricultural economies rely entirely on groundwater. At the same time as providing water for human needs, groundwater is also an input to streams, wetlands and riparian areas that provide important ecosystem services. Ongoing groundwater pumping will deplete flows in adjacent streams, leading to potential conflict between human and environmental uses of water. In the last decades, many conflicts over transboundary allocations of water, endangered species and instream and riparian habitat have been driven by surface water-groundwater interaction. For example, claims have been filed with the United States Supreme Court over the impacts of groundwater use on flows of transboundary rivers for the Pecos River (Texas vs. New Mexico), the Arkansas River (Kansas vs. Colorado) and the Republican River (Kansas vs. Nebraska and Colorado). Groundwater has typically been viewed as private property, and its use in agriculture is generally neither regulated nor quantified precisely. However, there is growing interest in moving to systems that regulate groundwater use. The ability to trade groundwater allocations is often a part of such conversations.

The South Central Agricultural Laboratory is a University of Nebraska research farm located about 15 miles east of Hastings immediately south of Highway 6. The primary focus of this farm is the development and refinement of irrigated crop production practices for Nebraska agriculture and beyond. A number of research projects are currently underway on site and in conjunction with producers in the region.

1. Crop water use efficiency, nitrogen use efficiency, and best irrigation and fertigation management practices for subsurface-irrigated corn and soybeans.
2. Measurement of soil evaporation under no-till, conventional (disk) till, and ridge till practices for corn using frequency-domain reflectometers under three irrigation frequencies and five irrigation levels for corn.
3. Development of best deficit irrigation management strategies for soybeans.
4. Center pivot irrigation engineering and evapotranspiration research: measurement of crop coefficients, evapotranspiration, and yield of corn under deficit irrigation settings.
5. Measurement of crop water use and crop water use efficiency of eight corn hybrids under full and deficit irrigation and dryland settings.
6. Measurement of maximum allowable crop water stress that can be imposed on corn, stress versus crop growth-yield- and available soil water relationships.
7. Crop canopy temperature measurements to quantify crop water stress index for corn and soybeans.
8. Measurements of hydraulics and uniformity coefficients, crop water use efficiency of a new low pressure irrigation system for soybeans.
9. Measurement of energy fluxes and crop coefficients using high frequency techniques such as Bowen ratio energy balance system and Eddy covariance system to provide improved evapotranspiration data for corn, soybeans, and natural grassland.
10. Measurement of non-growing (dormant season) evaporative losses to quantify annual evaporation and other water balance components.
11. Operational characteristics of atmometers (ETgage) to measure reference evapotranspiration and Watermark granular matrix sensors to monitor soil water status and their practical applications and demonstrations for effective irrigation management.
12. Rootworm pressure effect on crop water uptake under center pivot irrigation.
13. On-farm demonstration of limited irrigation strategies for making maximum use of water resources. The project is being conducted in partnership with the NRCS and Nebraska Corn Board in Hordville, Geneva, York, Edgar, Ord, West Point, Schuyler, and Mead in grower fields.

The University of Nebraska West Central Research and Extension Center is a research and extension facility of the University of Nebraska Institute of Agriculture and Natural Resources (IANR). It serves as the site for field-based research and extension involving faculty and graduate students in eight IANR departments. West Central consists of approximately 1,800 acres of which 1,100 acres are in pasture with the remaining in dryland and irrigated cropping systems. West Central delivers research-based education and information to citizens throughout the state. Extension specialists and educators are committed to excellence, conducting educational programs customized to meet the needs of Nebraskans. These educational programs, delivered via a variety of methods, are offered through federal, state and county partnership arrangements and provide research-based information and other educational resources to the 20-county West Central district and beyond.

The Gudmundsen Sandhills Laboratory (GSL), a 13,000 acre working ranch in the Nebraska Sandhills, is also part of West Central. GSL is situated over a relatively small portion of the High Plains Aquifer where saturated thickness exceeds 1000 feet. GSL also features a valley with a live stream, a drained valley with wet meadows, an adjacent lake, dry valleys, and many dune types so that literally all the surface and groundwater locales in the Sandhills are represented and available for research. In 2004 a U.S. Climate Reference Network station was established at GSL to provide future long-term observations of temperature and precipitation accurate enough to detect present and future climate change.

Terraces in the Republican River Basin total about 2 million acres; about 15% of the basin above Hardy, Nebraska is terraced. The goal of this project is to better understand how on-farm conservation practices, specifically terraces and small ponds, affect the basin's water supplies. Data has been collected at five dryland fields near Culbertson, Curtis, and Stamford, Nebraska and Colby and Norton, Kansas. The Kansas sites are in areas where three main tributaries of the Republican River - Beaver, Sappa, and Prairie Dog creeks - flow toward Harlan County Reservoir. The field data collected will be used to determine if computer models created for the Republican River Basin accurately measure the impact of conservation terraces and small reservoirs on the basin.

Initial research results show:

• About 16% of land in the Republican Basin is protected by terraces, and an equal number by small reservoirs
• About 45% of runoff into a terrace channel goes to evapotranspiration (ET), 45% goes to groundwater recharge, and 10% overtops the terraces
• Small reservoirs retain about 90% of inflow, most of which goes to groundwater recharge - little evaporation
• Much overland flow is loss in transmission as recharge or ET from plants in the creek

Integrated values for the basin be completed by the end of 2010. For more information, see the following slides presented at the 2010 Greater Platte Basins Symposium:

• Derrel Martin, Field-Scale Hydrologic Impacts of Conservation Terraces and Small Reservoirs in the Republican River Basin
• Dean Eisenhauer, Water Storage Capacity and Overland Runoff Impacts of Conservation Terraces in the Republican River Basin

As part of this project, Harvey and his students are conducting research to unravel the hydrology of central Nebraska's Rainwater Basin wetlands. These wetlands are of international importance as habitat for millions of migratory water birds. In addition, these playa wetlands may contribute to groundwater recharge and water quality improvement. However, many of the wetlands have been drained, and those remaining suffer functional impairment due to sedimentation and pesticide and fertilizer runoff.

Most of the remaining Rainwater Basin wetlands are geographically isolated. Currently research is underway to investigate the role of these wetlands in providing groundwater recharge and water quality improvement. This is a significant environmental issue of concern because groundwater in this region is of vital importance, providing drinking and irrigation water. Moreover, groundwater levels are declining throughout much of the region. Levels of nitrate and atrazine exceed drinking water standards in some parts of the basin. Most of the remaining playa wetlands are impaired by sediment and there is an active program to restore the wetlands by removing this sediment. Study sites are located in Phelps, Kearney, Clay, Fillmore, and York counties (see map below).

Three components need to be measured when establishing a hydrologic budget for these closed basin wetlands which are surface storage, evapotranspiration (ET), and groundwater recharge. ET is calculated by the Bowen-Ratio Energy Budget (BREB) Method with the aid of a Bower Tower. Surface storage and recharge data will be aided by stilling wells and drive-point wells, respectively. Hydroperiods and plant community diversity are being determined before and after sediment removal to evaluate the impact of in-washed sediments on recharge and underlying groundwater quality. Chloride concentrations obtained from upland runoff collectors will be incorporated into the Chloride Mass-Balance Method along with precipitation and sediment chloride concentrations to obtain recharge fluxes for a wetland site.

Two Master's theses and one Bachelor's thesis have been completed as part of this project:

• Wilson, Richard D. (2010), Evaluating Hydroperiod Response in the Rainwater Basin Wetlands of South-Central Nebraska, MS Thesis, UNL School of Natural Resources, 163 p.
• Foster, Sarah E., (2010), Temporal and Spatial Variations of Ions, Isotopes and Agricultural Contaminants in Surface Waters and Groundwater of Nebraska’s Rainwater Basin Wetland Region, MS Thesis, UNL Department of Earth and Atmospheric Sciences, 185 p.

This study examines how much water trees use in different forests. In riparian forests, invasive plants affect the quantity of water infiltrating and running off land by intercepting water and transpiring water. Sap flow sensors are being used to monitor how removal of invasive tree species affects tree-level and stand-level evapotranspiration. In addition, vegetation transects will reveal how understory plants respond to invasive tree removal. Researchers are gathering data using eddy covariance towers and satellite images. Study results will be used to test whether removing eastern Red Cedar and Russian Olive Trees can significantly improve water yields.

In regards to the understory response following the removal of invasive woody species from a cottonwood riparian forest, this research shows that:

• Removing invasive species increased the frequency of invasive form and warm season grasses.
• Species diversity increased when invasive tree species were removed.
• Changes in understory species following thinning were most pronounced where eastern redcedars were removed.
• Light level differences observed under different canopy types likely explain differences in understory species response to thinning. This will be examined in future studies.

The terms of the Cooperative Agreement for the Platte Basin and the Supreme Court settlement decision for the Republican Basin both require that Nebraska reduce its consumptive use of irrigation water. This analysis evaluated the economic and the budgetary costs of meeting these requirements. Both the on-farm and off-farm costs were evaluated for both land retirement and water allocation programs, implemented in several different ways, over three alternative time periods, 10, 25 and 50 years.

The on-farm economic costs were defined as the change in net farm income associated with less irrigation. Off-farm economic costs were defined as the statewide change in household income resulting from changes in irrigation, as the effects ripple through the Nebraska economy. Budgetary costs were defined as the cost to the state budget (taxpayers) of policies which compensate irrigators for reducing consumptive use are implemented. Statewide economic costs were found to be lower for land retirement than for allocation programs, assuming the same total change in consumptive use. Total budgetary costs depended primarily on: where the irrigation reductions occurred (proximity to river); on how long the program was continued (number of years), and on whether irrigation was reduced voluntarily with incentives, or by regulation, or by some combination of regulation and incentives. It was found that policy makers could minimize the cost of reducing consumptive use from irrigation and augmenting stream flow by purchasing rather than leasing irrigation rights, by using a regulatory rather than a willing seller incentive approach, and by reducing irrigation at locations close to the river.

Hedonic (mass appraisal) land valuation models were estimated in the Republican and Platte watersheds of Central and Western Nebraska. These models are based on assumption that the buyers and sellers of agricultural land are able to accurately assess the value of irrigation when negotiating sale contract prices, and that irrigation equipment can be distinguished from land and irrigation values. Alternative models were estimated using various combinations of explanatory variables (all measured at the parcel level of analysis). These include: soil productivity measures, topography precipitation, parcel size, cropping patterns, topography, aquifer thickness, well pumping capacity, distances to elevators and towns, and irrigation systems.

The location of all agricultural land sales statewide (2000-2007) and estimated irrigation values in the Platte and Republican Watersheds were identified. Preliminary mass appraisal model results were summarized in tables and the locations of retired irrigation parcels in the Republican Watershed (as part of a 2006 NE DNR and USDA Pilot Program) were identified. The value of irrigated cropland is on average $615/acre (this is the value of irrigated cropland only and does not include the value dryland corners within pivot systems). As well, there are numerous areas and site-specific parcels within the watershed with both lower and higher irrigation values. In fact, we have calculated irrigation values for all of the natural resource districts in the Republican watershed: they range from $488/acre to $948/acre. These estimates are still considered 'preliminary' and may be subject to revision. These irrigation values also do not account for premiums above and beyond marginal market values that farmers and landowners will likely require to willingly participate in future irrigation retirement programs.

The State of Nebraska is attempting to aggressively manage invasive species along the riparian corridors of the Platte River and the Republican River. Although the impetus for the removal is different, in both basins state agencies and weed management districts are using herbicides and mechanical removal to control a combination of invasive species led by Phragmites australis (common reed), Tamarix ramosissima Ledeb. (saltcedar), and Elaeagnus angustifolia L. (Russian olive).

Along the central stretch of the Platte River, invasive species have overtaken sandbars and side channels which are invaluable wildlife habitat. In an attempt to reclaim this habitat for bird species such as the Piping Plover and Whooping Crane, the state is removing large stretches of common reed. Along the Republican River, the state is removing all invasive species to reduce riparian evapotranspiration. By reducing evapotranspiration the hope is to increase stream flow along the Republican River. Since 2007 invasive species along the mainstem of the river and along the banks of the Harlan Reservoir have been sprayed with herbicide or mechanically removed.

In order to understand the impacts of removing invasive species along riparian corridors researchers at the University of Nebraska-Lincoln and collaborators at other universities have developed a multi-faceted research project.

On the Republican River basin researchers are directly measuring evapotranspiration rates from native and invasive plants. Researchers are also using a regional water balance model to estimate the water savings that could be achieved by removing all invasive species within the basin.

On the Platte River researchers are monitoring water quality changes associated with a controlled herbicide treatment of common reed. Using a combination of in situ instruments and grab samplers researchers are determining the impacts of species removal. Other experiments are being conducted to measure how invasive species alter biogeochemical processes and sediment characterization.

Visit the project website for more information, including real-time meteorological data from a riparian wetland near the Republican River, real-time water quality data at a stream site on the Platte River, and quarterly project reports.

Final Report on Riparian Vegetation Impacts on Water Quantity, Quality, and Stream Ecology

This study is using a combination of techniques including remote sensing, to develop reliable estimates of evapotranspiration from riparian zones and determine varying water use rates for typical and invasive species in the Republican River Basin. The project will provide datasets of evapotranspiration and the annual water balance for a range of conditions in the riparian areas along the Republican River. Specific deliverables of the project include:

• Map of surface energy fluxes, including evapotranspiration, across three watersheds in the Lower, Middle and Upper Republican Natural Resources Districts for different spatial and temporal (i.e. daily, seasonal and annual) scales.
• Map of riparian vegetation classification across three watersheds using high resolution remote-sensing and ground truth observations.
• Comparison of water use and water availability on riparian vegetation and adjacent treated research area by measuring evapotranspiration rates, using various methods.
• Data for planners and decision-makers to develop water management policies.
• Extension and education materials to inform and communicate results to stakeholders.

The Rainwater Basin is one of the most endangered wetland ecosystems in North America. This ecosystem is critical to many species including migratory waterfowl. Land use and runnoff from agriculture and cattle confinement operations are likely to be reducing the basin's health and diversity, however little information exists concerning macroinvertebrates. Twenty-two locations were assessed for water quality parameters, vegetation composition, and macroinvertebrates identified to genus. Samples were collected biweekly starting in April through July for three years. Macroinvertebrate diversity was impacted in areas with little buffer although the effects were not pronounced. Institution of a more effective vegetative buffers strip may reverse this trend to improve ecosystem quality and provide for invertebrate resources for migratory birds.

Click here to see a poster about this research

The extent of exogenous hormone use in beef cattle production, in addition to endogenous hormones, increases the risk of hormone residues entering the environment when manure is applied to soil. This research will provide key information on the environmental fate of hormones commonly found in feedlot cattle manure. This information is critical in developing management practices for concentrated animal feeding operations and farms that will reduce environmental risks associated with land application of manure.

This research will be conducted using the specialized percolation lysimeters research site at the West Central Research and Extension Center during 2008 and 2009. The site contains fourteen percolation lysimeters installed at the center of each of fourteen field plots. Each plot is 40 ft m by 40 ft. Each lysimeter contains an undisturbed soil core with a diameter of 3 ft and a depth of 8 ft and has porous extractors at the bottom, which allows the extraction of leachate from unsaturated soil using a vacuum pump. These lysimeters have been used successfully for several nitrate-leaching experiments. Water samples, which represent the water that is leached from the crop root zone, can be collected at the bottom of these lysimeters and will be used to determine the amounts and types of hormones leaching below the crop root zone. Treatments will consist of treated stockpiled manure, treated compost manure, and a check (no manure application). The manures will be applied to the lysimeters and field areas adjacent to the lysimeters in the spring of 2008 at application rates to satisfy the nitrogen needs of corn based on University of Nebraska recommendations. The check plots will receive commercial nitrogen fertilizer to match the manure N availability. Three treatments and three replications (nine lysimeters in nine plots) will be used for this study.

Wheat will be planted in the lysimeters and adjacent plots during both years. Soil moisture from each plot will be measured weekly at 1 ft depth increments to a depth of 7 ft, using the neutron probe method. Water samples will be collected every three weeks from the lysimeters from April to November in both years. Soil samples will be collected at six depth increments down to a depth of 8 ft, four times between application and October in 2008, and three times from April to August in 2009. To reduce sampling errors created by spatial variability within each plot, five sub-samples will be taken from each depth. The sub-samples will then be mixed to create one composite sample. Background soil profile samples will be taken before the manure is applied. Sampling depths will be increased as needed, based on the confirmed movement of hormones of interest through the soil profile. Soil and leachate samples will only be taken during the periods when the ground is not frozen (April to November), when movement of water is expected.