David G. Hopkins

Phyto (In)Stabilization of Elements

The effects of plants (corn, soybean, and sunflower) and fertilizer on mobility of more than 60 elements were assessed in a greenhouse experiment. Unplanted columns with the same soil served as controls. Half the columns received fertilizer and all columns were watered at the same rate. At the end of the experiment, the columns were watered to mimic a rainstorm event such that water drained from the bases of the columns, which was collected and analyzed for element content. Soil from between the roots of the plants was also collected and the water-extractable fraction determined. It was expected that (1) more mobile elements, as measured by water extraction, would be leached from the soils at a higher rate compared to less mobile elements, (2) plants would immobilize most elements, but that some would be immobilized, and (3) that this would depend on plant species. The results led to the following conclusions: plants cause metal mobility to vary over a wide range for a specific soil and do mobilize some elements (e.g., Th) while immobilizing others (e.g., U). The effects depended on plant species for some elements. Water-extractable fractions of elements do not predict mobility.

Rapid Shifts in Soil Organic Carbon Mineralization within Sodic Landscapes

Sodic soils have poor plant growth and thus carbon (C) inputs are reduced compared to nonsodic soils. Soil samples were taken from three sodic zones: 1) patch-center, 2) transition, and 3) adjacent at three sites located in southwest North Dakota. Soil sodium adsorption ratio (SAR) was highest at patch centers (mean of three sites, SAR = 306), and then declined to transition (SAR = 29.5) and was lowest at adjacent (SAR = 9.21). The labile C pool showed an inverse relationship with SAR. In the northern Great Plains, C dynamics is highly variable and can be strongly controlled by the development and persistence of sodic soils.

Hourly Reference Evapotranspiration Estimates for Alfalfa in North Dakota

When many places in the world are facing water scarcities, the Devils Lake basin in northeastern North Dakota has received above normal inflow due to excess rainfall since 1993. A research project is being conducted to determine the extent to which irrigation can utilize some of the excess surface waters in the basin without impairing the productivity of soils, many of which are classified as only conditionally irrigable. Understanding of the evapotranspiration (ET) process is critical for irrigation application, but ET research is generally lacking in this region. The sub-humid continental climate in North Dakota has high variations in hourly, daily, seasonal, and annual ET rates. The soil normally stays wet in the early growing season. Irrigation is needed in the mid-growing season when crops are also in a critical stage for supplemental water. In this study, hourly reference evapotranspiration rates for alfalfa were examined by the ASCE EWRI Penman-Monteith method. The weather data used in the calculations were collected from a 42-ha alfalfa field located in Benson County, North Dakota. Thirty minutes values, including air temperature, relative humidity, solar radiation, and wind speed were measured and average hourly values were used in the reference ET calculations. The evaluation and comparison among the daily and sum of 24 hour reference ET provided a good assessment on the highest amount of water that could be potentially used by agricultural crops in the Devils Lake area.

Soil property distribution following oil well access road removal in North Dakota, USA

Abstract: Increases in oil extraction on public lands in the US northern Great Plains has created an extensive network of access roads that must be removed upon well abandonment. However, the effects of road removal on soil properties are largely unknown. The objective of this study was to determine whether soil properties were altered on removed roadbeds and whether time since road removal has improved soil properties. Soils were sampled (n = 208) on perpendicular transects across removed roadbeds and extending into undisturbed areas on 16 restored roads located on two ecological site classifications such as (i) thin loamy and (ii) sandy. A Bayesian hierarchical mixed model was used to determine posterior predictive distributions and means of measured particle size distribution, gravel content, infiltration rate, pH, electrical conductivity, sodium adsorption ratio, CaCO3 content, and organic matter. Alterations in the predicted distribution of particle size, pH, CaCO3 content, and sodium adsorption ratio were attributed to mixing topsoil with subsoil during the road removal process. Soil organic matter decreased on roads. Most importantly, measured soil properties on removed roads did not improve with time since road removal. The alterations in soil properties can have lasting effects on nutrient availability, vegetation dynamics, and ecological resiliency of the native prairie.

Evaporation Estimates for the Devil’s Lake Basin

Water levels in the Devil’s Lake basin of northeastern North Dakota have risen substantially since 1993 causing flooding and damage to agricultural land and infrastructure. A proposed flood mitigation method is to remove water from the basin through irrigation and evapotranspiration (ET). Constraints on the project include predominantly clay-loam surface textures, many of which are imperfectly drained, and the inability to use subsurface drainage to remove excess water. Objectives of this paper are to estimate ET for selected crops using a soil water balance approach and compare these ET values to those from a locally-developed irrigation scheduling algorithm, a remote sensing algorithm, and eddy covariance methods. Data were collected during the 2006 to 2008 growing seasons from 25 data collection stations spread across 10 field sites. Rain and irrigation were measured with manual rain gauges, deep percolation with fluxmeters, soil water contents with neutron attenuation, and water table depths with ground water monitoring wells installed at 18 stations. The ET values will be compared using correlation and nonparametric tests. With unbiased data for ET water loss, managers can assess whether gains in ET for irrigated vs. nonirrigated crops warrant the use of large-scale irrigation in the basin for flood mitigation. This paper represents analyses completed to date and outlines procedures for comparison of ET estimates.

Assessment of SEBAL model for estimating evapotranspiration in the Devils Lake basin

Above-average rainfall in the last twelve years has led to rising water levels in the Devils Lake basin in northeastern North Dakota. An irrigation test project has been started at ten farmercooperator field sites within the basin to estimate how much additional water can be utilized via irrigation of agricultural crops. Comprehensive soil/water compatibility investigations coupled with GIS analysis of detailed soil survey data (SSURGO) will be utilized to assess the potential for sustainable irrigation development and potentially extend the results to the entire basin. The installation and monitoring phase of the test project will be described in this paper. Water balance monitoring at the sites will include measurements of rainfall and irrigation, soil water content, deep percolation, and ground water level. The surface energy balance algorithm for land (SEBAL) model will be developed in Erdas Imagine/Arc Map interface for estimating evapotranspiration (ET) in the basin. Correlations will be developed between ET and soil physical and chemical properties affecting sustainability as well as other factors, such as crop types, soil map units, and landscape position in order to assess the feasibility, impact, and sustainability of the larger scale irrigation in this mostly non-irrigated basin.