Gary R. Sands

Effects of Agricultural Drainage on Aquatic Ecosystems: A Review

The extensive development of surface and subsurface drainage systems to facilitate agricultural production throughout North America has significantly altered the hydrology of landscapes compared to historical conditions. Drainage has transformed nutrient and hydrologic dynamics, structure, function, quantity, and configuration of stream and wetland ecosystems. In many agricultural regions, more than 80% of some catchment basins may be drained by surface ditches and subsurface drain pipes (tiles). Natural channels have been straightened and deepened for surface drainage ditches with significant effects on channel morphology, instream habitats for aquatic organisms, floodplain and riparian connectivity, sediment dynamics, and nutrient cycling. The connection of formerly isolated wetland basins to extensive networks of surface drainage and the construction of main channel ditches through millions of acres of formerly low-lying marsh or wet prairie, where no defined channel may have previously existed, have resulted in large-scale conversion of aquatic habitat types, from wetland mosaics to linear systems. Reduced surface storage, increased conveyance, and increased effective drainage area have altered the dynamics of and generally increased flows in larger streams and rivers. Cumulatively, these changes in hydrology, geomorphology, nutrient cycling, and sediment dynamics have had profound implications for aquatic ecosystems and biodiversity.

A generalized environmental sustainability index for agricultural systems.

Abstract This paper presents the design and development of an Environmental Sustainability Index (ESI) and describes a case study used to evaluate the performance of the index. The objective of the index was to provide a modelling-based, quantitative measure of sustainability from an environmental perspective, comprising both on- and off-site environmental effects associated with agricultural systems. A performance approach was utilized for the ESI, having inputs that were derived from long-term simulations of crop management systems with the EPIC model (Erosion Productivity Impact Calculator). 15 sub-indices for representing sustainability were chosen employing a dual framework for characterizing environmental sustainability, embodying the agricultural system’s: (i) inherent soil productivity and groundwater availability; and (ii) potential to degrade the surrounding environment. A case study was developed based on prevalent corn and wheat agricultural production systems in Baca County, located in southeastern Colorado. Principal components analysis was employed to assess the information content of the 15 sustainability sub-indices. Sensitivity analysis was performed to evaluate the effects of model input uncertainty on the index. The effect of the time frame over which the index is computed was also examined for time frames ranging from 50 to 300 years. Results show that the ESI is capable of demonstrating clear differences among crop management systems with respect to sustainability.

Water quality modeling of fertilizer management impacts on nitrate losses in tile drains at the field scale

Nitrate losses from subsurface tile drained row cropland in the Upper Midwest U.S. contribute to hypoxia in the Gulf of Mexico. Strategies are needed to reduce nitrate losses to the Mississippi River. This paper evaluates the effect of fertilizer rate and timing on nitrate losses in two (East and West) commercial row crop fields located in south-central Minnesota. The Agricultural Drainage and Pesticide Transport (ADAPT) model was calibrated and validated for monthly subsurface tile drain flow and nitrate losses for a period of 1999-2003. Good agreement was found between observed and predicted tile drain flow and nitrate losses during the calibration period, with Nash-Sutcliffe modeling efficiencies of 0.75 and 0.56, respectively. Better agreements were observed for the validation period. The calibrated model was then used to evaluate the effects of rate and timing of fertilizer application on nitrate losses with a 50-yr climatic record (1954-2003). Significant reductions in nitrate losses were predicted by reducing fertilizer application rates and changing timing. A 13% reduction in nitrate losses was predicted when fall fertilizer application rate was reduced from 180 to 123 kg/ha. A further 9% reduction in nitrate losses can be achieved when switching from fall to spring application. Larger reductions in nitrate losses would require changes in fertilizer rate and timing, as well as other practices such as changing tile drain spacings and/or depths, fall cover cropping, or conversion of crop land to pasture.

The Long-term Field-scale Hydrology of Subsurface Drainage Systems in a Cold Climate

Subsurface drainage is a common practice in the agricultural regions of the northern Midwest. Concerns about the impact of subsurface drainage on surface water quality and hydrology have increased over the past decade, spawning continued research on artificial drainage. Annual and decadal climatic variability necessitates a long–term perspective to fully evaluate these impacts. In addition, less is known about the hydrology of artificially drained lands in cold regions, where soil freezing and snowmelt routinely occur. A field–scale hydrologic analysis of subsurface drainage was performed using DRAINMOD v5.1 for an 85–year climatic period (1915 to 1999) for south–central Minnesota. This version of DRAINMOD included modifications for soil freeze/thaw and snowmelt processes. The results give insight into the long–term variations of subsurface drainage and other precipitation abstractions in a cold climate. Seasonal hydrology was characterized by well defined drainage and evapotranspiration (ET) “seasons” from March to June and from July to October, respectively. On average, 74% of infiltrated water was removed by subsurface drainage during the drainage season (March to June), representing 27% of annual precipitation. Significant increases in the 28–year average precipitation and drainage depths were apparent over the 85–year simulation period. Frequency and extreme value analysis revealed that annual drainage represented approximately 40% of annual precipitation at the 2–year return interval. Simulated annual drainage volumes were distributed normally, wherein the predicted 100–year annual drainage depth was 532 mm. Decreased drain spacing was found to significantly affect infiltration and drainage over the 85–year period. The results have potential uses for drainage practitioners, water management decision makers, and environmental and agricultural scientists and may pose significant challenges for addressing water quality issues on artificially drained lands.

Comparing the Subsurface Drainage Flow Prediction of the DRAINMOD and ADAPT Models for a Cold Climate

The DRAINMOD computer model has been widely used for simulating the performance of subsurface drainage systems. The ADAPT model was created by merging components of DRAINMOD and GLEAMS and has evolved for over ten years, including the recent addition of soil freeze/thaw processes. DRAINMOD was also recently modified for soil freeze/thaw processes for application in cold climates. Computational time step, method of ET estimation, and soil freeze/thaw processes are examples of ways in which current versions of these models differ from one another. Previous comparisons of these models were made for warmer climates, before the addition of cold–climate hydrology to both models. The performances of DRAINMOD and ADAPT were compared for cold–climate conditions, calibrated using two years of observed data from a 23–ha farm field in southern Minnesota. Model performance was evaluated and compared for seasonal, monthly, daily, and event–based time scales and during snowmelt runoff periods. Observed data showed that 60% and 20% of annual subsurface drainage runoff occurred during the transition period between winter and spring (snowmelt period) in 1998 and 1999, respectively. DRAINMOD overpredicted drainage by 11% and 25% for these periods, and ADAPT’s results were within 10% of observed values for the snowmelt periods. Both models performed well at simulating the number and timing of drainage events in both snowmelt and later–season periods. The models performed best on a cumulative basis over the 2–year simulation period, where DRAINMOD overpredicted cumulative subsurface drainage by 1.7%, and ADAPT underestimated cumulative drainage by 0.2%. The models diverged in their abilities to predict the largest daily drainage events: DRAINMOD overpredicted and ADAPT underpredicted these events. Substantially more effort was required to calibrate ADAPT because of the increased complexity of the model.

Plant Growth Component of a Simple Rye Growth Model

Cover cropping practices are being researched to reduce artificial subsurface drainage nitrate-nitrogen (nitrate-N) losses from agricultural lands in the upper Mississippi watershed. A soil-plant-atmosphere simulation model, RyeGro, was developed to quantify the probabilities that a winter rye cover crop will reduce artificial subsurface drainage nitrate-N losses given climatic variability in the region. This article describes the plant growth submodel of RyeGro, Grosub, which estimates biomass production with a radiation use efficiency-based approach for converting intercepted photosynthetically active radiation to biomass. Estimates of nitrogen (N) uptake are based on an empirical plant N concentration curve. The model was calibrated with data from a three-year field study conducted on a Normania clay loam (fine-loamy, mixed, mesic Aquic Haplustoll) soil at Lamberton, Minnesota. The model was validated with data measured from a field trial in St. Paul, Minnesota. The cumulative rye aboveground biomass predictions for the calibration years differed by -0.45, 0.09, and 0.16 Mg ha-1 (-17%, 9%, and 32%), and the plant N uptake predictions differed by -10.5, 8.0, and 4.0 kg N ha-1 (-16%, 30%, and 21%) from the observed values. The predictions of biomass production and N uptake for the validation year varied by -1.4 Mg ha-1 and 16 kg N ha-1 (-27% and 24%) from the values observed in the field study, respectively. A local sensitivity analysis of eight input parameters indicated that model output is most sensitive to the maximum leaf area index and radiation use efficiency parameters. Grosub demonstrated the capability to predict seasonal aboveground biomass production of fall-planted rye in southwestern Minnesota within an accuracy of ±30% in years when production exceeds 1 Mg ha-1 by mid-May, and to predict seasonal rye N uptake within ±25% of observed values.

Controlled drainage to improve edge-of-field water quality in Southwest minnesota, USA

Wet, poorly drained soils throughout the northern Cornbelt are often artificially drained to improve field conditions for timely field operations, decrease crop damage resulting from excess water conditions, and improve crop yields. Drainage has also been identified as a contributing factor to water quality impairments in surface waters. Our objective was to quantify drain flow volume, nitrogen and phosphorus loss, and grain yield from a conventional free-drainage (FD) compared to a controlled drainage (CD) system in Minnesota, USA. A field study was conducted from 2006-2009 on a tile-drained Millington loam soil (fine-loamy, mixed, calcareous, mesic Cumulic Haplaquoll). The field site consisted of two independently drained management zones, 15 and 22ha, respectively. The project used a paired design approach to statistically evaluate treatment effects. During the calibration period (2006-2007) each zone was managed the same. The treatment phase of the experiment began in 2008 with one zone managed in FD mode and the other managed in CD mode. During the two year treatment period (2008-2009) drain flow volume was reduced on average 63%, 141 to 52 mm. There was also evidence that annual nitrate-nitrogen, total phosphorus, and ortho-phosphorus loads were reduced by 61, 50, and 63%, respectively. However, the reasons for a 33% increase in flow weighted mean total phosphorus concentration under controlled drainage are unclear. The use of CD showed environmental benefits compared to FD but has not resulted in a consistent yield benefit at this site to date.

Meta-Analysis as a Statistical Tool for Evaluating the Hydrologic Effects of Water Table Management

Controlled drainage is a water table management practice used to reduce drainage volumes and environmental impact of subsurface drainage. Meta-analysis was conducted with fifty-three controlled drainage volume reduction results selected from twenty papers published between 1979 and 2008 to study the underlining factors influencing controlled drainage responses. The observations showed a wide variation in effectiveness of controlled drainage across different soils, crops and locations: drainage volumes reductions from -8% to 95% have been reported in literature. To investigate the potential causes for this wide variation, we performed a meta-analysis to aggregate the controlled drainage results using the log-response ratio effect size. The results of the meta-analysis showed that the effectiveness of controlled drainage depends on a combination factors: soil texture, crop type, and varies by hardiness zones. A chronologic, cumulative meta-analysis of fifty-three controlled drainage studies demonstrated that controlled drainage is effective and with a mean effect of 47%. A categorical meta-analysis suggested that soil types, crop types and differences in seasonality affect the effectiveness of controlled drainage to reduce drainage volumes.

Modeling Nitrate-Nitrogen Losses in Response to Tile Drain Depth and Spacing in a Cold Climate

The Agricultural Drainage and Pesticide Transport (ADAPT) model was used to evaluate the effects of tile drain spacing and depth on NO3-N losses in southeastern Minnesota. The model was calibrated and validated using 4 years of monthly flow and nitrate loss data from two tile drained fields (11 and 9.3 ha) in Nicollet County. Half the monitoring data from the 11 ha field were used for calibration and half for validation of the model. The model was also validated using independent monitoring data from the 9.3 ha field. For the calibration period on the 11 ha field, the model predicted mean monthly tile drainage and NO3-N losses of 141.5 m3/day and 5.2 kg/ha, respectively, against measured tile drainage (126.2 m3/day) and NO3-N losses (4.5 kg/ha). For validation, the predicted mean monthly tile drainage and NO3-N losses were 131.7 m3/day and 4.4 kg/ha, respectively, against measured tile drainage and NO3-N losses of 80.4 m3/day and 3.0 kg/ha, respectively. Similar validation results were found with 9.3 ha field. Long-term simulations were made for a wide range of climatic conditions (1954-2003) to evaluate the effects of drain spacing and drain depth on tile drainage and NO3-N losses. Simulations results indicate that increasing spacing and decreasing depth of tile drains reduces the tile drainage and NO3-N losses, and can serve as a remedy to the excess NO3-N losses.

The Impact of Drainage Depth on Water Quality in a Cold Climate

The impact of drainage depth on hydrology and water quality in southern Minnesota was investigated through a field experiment. Subsurface drainage systems were installed on nine field-sized watersheds ranging in size from 0.8 to 2.5 ha. The nine systems comprised two drainage depths (90 and 120 cm) and conventional (13 mm/day design drainage rate) and narrow (one-half the conventional) drain spacings. Surface and subsurface drainage runoff and nitrate-nitrogen were monitored with automated equipment for 2001 and 2002. Results from the two years show that for the conventional drain spacing, annual drainage runoff and nitrate-nitrogen were reduced for the shallow drains by up to 40 and 47 percent, respectively. The results for the narrowly spaced drainage systems were more ambiguous, however. Reductions in nitratenitrogen were attributed primarily to reductions in drainage runoff volume because only minor differences in nitrate-nitrogen concentrations were observed among watersheds. It is hypothesized that the reduced drainage volume in the shallow systems was accompanied by an increase in deep seepage below the drainage systems. Data from 2003 are still be analyzed and modeling research is underway to predict the impacts of shallow drainage over long climatic records and for other soil types.