Mark Dougherty

A simple Landsat–MODIS fusion approach for monitoring seasonal evapotranspiration at 30 m spatial resolution

Persistent cloud-cover in the humid southeastern USA and the low temporal resolution of Landsat sensors limit the derivation of seasonal evapotranspiration (ET) maps at moderate spatial resolution. This article introduces a Landsat Moderate Resolution Imaging Spectroradiometer (Landsat–MODIS) ET fusion model that uses simple linear regression to integrate Landsat-derived reference ET fraction (ETrF) from mapping ET at high resolution with internalized calibration (METRIC) model and the vegetation temperature condition index (VTCI) derived from MODIS images. For a study site in Florida, model-estimated ET and ET estimated using energy budget eddy covariance at a US Geological Survey (USGS) station in Ferris Farm, Florida, were found to be in a good agreement with a root mean squared error of 0.44 mm day–1, coefficient of determination (R2) of 0.80, Nash–Sutcliffe efficiency of 0.79 for daily ET (ETd), and 2% relative error for cumulative seasonal ET during the growing season of 2001. At another study site in Alabama, the model underestimated 2008 annual water balance ET for the Fish River Watershed by 39 mm or 4%. Comparisons of model-estimated ET with that obtained using a non-fusion Landsat-only approach at both sites indicated that the fusion of Landsat and MODIS ET values reduces potential errors in ET estimation that would otherwise arise due to insufficient availability of cloud-free Landsat images for METRIC processing. Validation results and application of the model in deriving seasonal/annual ET for different land-cover classes in the Fish River Watershed suggested that the fusion model has the potential to be used in continuously monitoring ET for field- to watershed-level agricultural and hydrological applications in the southeastern USA.

Validation of evaporation estimates from a modified surface energy balance algorithm for land (SEBAL) model in the south-eastern United States

A modified surface energy balance algorithm for land (SEBAL) model, which has been widely used in the western United States since its development in 1998, was validated in the humid south-eastern United States using daily and monthly evapotranspiration (ET) estimates. Sixteen Landsat 5 Thematic Mapper (TM) images from April 2000 to September 2006 were processed, and the results were compared with energy-budget eddy covariance (EBEC) ET estimates from four US Geological Survey (USGS) stations. The model performed well in terms of Nash–Sutcliffe efficiency (NSE) coefficients (daily = 0.82, monthly = 0.77) and coefficients of determination (R 2, daily = 0.83, monthly = 0.77). Root mean square errors (RMSEs, daily = 0.48 mm/day, monthly = 16 mm/month), mean absolute errors (MAEs, daily = 0.32 ± 0.36 mm/day, monthly = 12 ± 10 mm/month), mean relative errors (MREs, daily = 7 ± 8%, monthly = 11 ± 12%) and mean bias errors (MBEs, daily = 0.05 mm/day, monthly = −2 mm/month) were comparable to the results from similar studies in the western United States. Results from the study support the applicability of the modified SEBAL model in the rapidly growing south-eastern United States as a tool for estimating consumptive water use via remotely sensed methods.

Municipal wastewater treatment through an aerobic biofilm SBR integrated with a submerged filtration bed

A biofilm reactor and a gravitational filtration bed were integrated as a sequencing batch reactor (SBR) to aerobically treat a municipal wastewater. Polyacrylonitrile balls (50 mm diameter, 90% porosity) were filled into the upper part of the SBR as biofilm attaching materials and anthracite coal (particle size approximately 1.17 mm) was placed into the lower part as filter media. The SBR was aerated during filling and reaction phases, followed by a 10 min discharge phase during which the wastewater went through the filtration bed without aeration. The SBR was tested with raw wastewater from a municipal WWTP in Wuhan, China from July 2006 to January 2007, during both a warm season and a cold season. The SBR showed a capability to accept COD and turbidity fluctuations in the receiving wastewater. Seasonal influence on COD and nitrogen removal by the biofilm reactor was significant. Nitrogen and phosphorus removals were limited by COD levels in the wastewater. The filtration process removed considerable COD, nitrogen, phosphorus, and turbidity. The overall SBR effluent quality consistently satisfied the national secondary effluent discharge standard of China, except for total phosphorus. An anaerobic phase before the aerobic reaction is proposed to improve phosphorus and nitrogen removal. The filter normally required a backwash every seven days and the water needed for backwash was less than 4% of the wastewater treated by the SBR. This experiment provides information needed for further investigation to improve performance of the SBR.

Calibration and use of plate meter regressions for pasture mass estimation in an Appalachian silvopasture

A plate meter for measuring pasture mass was calibrated at Agroforestry Research Site in Blacksburg, Virginia, USA, using six ungrazed plots of established tall fescue overseeded with orchardgrass. Each plot was interplanted with bare root honey locust and black walnut seedlings spaced along a gradient ranging from 1.8 to 11.0 m. Plate height (PH) of forage between trees was measured by placing a 46 mm × 46 mm × 5.6-mm-thick acrylic plastic plate meter on pasture canopy at six locations four times a season. PH was measured between ground and plate as it rested on pasture canopy. To calibrate the plate meter against a known dry matter yield, 50 × 50-cm clip plots followed each PH measurement. The resulting regression slope was 421 kg ha−1 cm−1, with an r 2 value of 0.86. Unique research investigating the response of forage mass to site elevation is presented using the developed equation. The field-calibrated regression slope of ruler height (RH) to PH was 1.71 cm cm−1, with an r 2 value of 0.87, showing good correlation between RH and PH. A comparable regional regression equation was found to adequately predict independent calibration clip plot data reported at this site. The results support the application of regression equations for estimating pasture mass in areas having similar climates and pasture composition.

Hydraulic management of a soil moisture controlled SDI wastewater dispersal system in an Alabama Black Belt soil

Rural areas represent approximately 95% of the 14000 km(2) Alabama Black Belt, an area of widespread Vertisols dominated by clayey, smectitic, shrink-swell soils. These soils are unsuitable for conventional onsite wastewater treatment systems (OWTS) which are nevertheless widely used in this region. In order to provide an alternative wastewater dosing system, an experimental field moisture controlled subsurface drip irrigation (SDI) system was designed and installed as a field trial. The experimental system that integrates a seasonal cropping system was evaluated for two years on a 500-m(2) Houston clay site in west central Alabama from August 2006 to June 2008. The SDI system was designed to start hydraulic dosing only when field moisture was below field capacity. Hydraulic dosing rates fluctuated as expected with higher dosing rates during warm seasons with near zero or zero dosing rates during cold seasons. Lower hydraulic dosing in winter creates the need for at least a two-month waste storage structure which is an insurmountable challenge for rural homeowners. An estimated 30% of dosed water percolated below 45-cm depth during the first summer which included a 30-year historic drought. This massive volume of percolation was presumably the result of preferential flow stimulated by dry weather clay soil cracking. Although water percolation is necessary for OWTS, this massive water percolation loss indicated that this experimental system is not able to effective control soil moisture within its monitoring zone as designed. Overall findings of this study indicated that soil moisture controlled SDI wastewater dosing is not suitable as a standalone system in these Vertisols. However, the experimental soil moisture control system functioned as designed, demonstrating that soil moisture controlled SDI wastewater dosing may find application as a supplement to other wastewater disposal methods that can function during cold seasons.

Subsurface Drip Irrigation Placement and Cotton Irrigation Water Requirement in the Tennessee Valley

Fluctuations in dryland cotton yield in the Tennessee Valley region of northern Alabama are common and are usually related to irregular drought periods during the growing season. Subsurface drip irrigation (SDI) has gained popularity as a water delivery system for small, irregular-shaped cotton fields. A seven-year study was conducted with the objective to determine the response of seed cotton yield to SDI tape orientation relative to crop row direction and different irrigation rates under dryland conditions of the Tennessee Valley. Seven treatments were tested in a randomized incomplete block design which consisted of three irrigation treatments (33%, 66%, and 99% pan evaporation), two SDI tape orientations (parallel and perpendicular), and a dryland control. All SDI treatments produced yields significantly higher than non-irrigated, dryland cotton in four out of seven years. Maximum yield was obtained at a median pan evaporation water replacement value of 74%. No statistical differences were observed between SDI tape orientations on seed cotton yield in all years except in 1999 when parallel out yielded perpendicular at lower irrigation rates. Results confirm the long-term efficacy of supplemental irrigation to increase seed cotton yield irrespective of SDI tape placement during sporadic periods of drought. These results are applicable only for fields with the same soil type or with similar water movement characteristics.

Precision Fertilization Using Sub-Surface Drip Irrigation (SDI) for Site-Specific Management of Cotton

Results are presented for a first year study that investigates different fertigation treatments for cotton produced using precision agriculture in the Tennessee Valley of Alabama. The study evaluates the timing and placement of soluble nitrogen and potassium (K2O) fertilizer on cotton using four different fertigation treatments and a non-fertigated control irrigated with sub-surface drip irrigation (SDI) tape. The pressure-compensating SDI product was installed in 2005 using an auto-guidance system to ensure all tape runs are precisely located parallel and 80 inches apart. The experimental plots consist of four replications of five eight-row treatments that compare four fertigation management scenarios and one conventional side-dress treatment. Each of the resulting twenty treatment plots has eight 360-foot rows of cotton on 40-inch row spacing, with SDI tape buried approximately 15 inches between every other row of cotton. The response to treatments is quantified by measuring yield, quality, and nutrient uptake of the cotton. Results show that fertigated cotton yields were higher than the non-fertigated control, with higher yields observed in the three treatments receiving fertigation within 50 days of square. The two highest yielding treatments also received 20 and 40 pounds, respectively, of pre-plant surface nitrogen and potassium. Fertigated cotton yields averaged 3.0 bales per acre compared with 2.6 bales per acre for the non-fertigated control and 2.2 bales per acre in a nearby sprinkler-irrigated study.

Impact of a real-time controlled wastewater subsurface drip disposal system on the selected chemical properties of a vertisol

The operation of onsite septic effluent disposal without considering seasonal moisture changes in drain field conditions can be a major cause of the failure of conventional septic systems. This study addressed this issue from a soil hydraulic perspective by using real-time drain field soil moisture levels to limit septic effluent disposal in a vertisol via subsurface drip irrigation. A prototype system was field-tested in a Houston clay soil and results describe the subsequent impact on selected soil chemical properties. After one year of hydraulic dosing with a synthetic wastewater, soil total carbon and nitrogen concentrations increased, but no increase in soil total phosphorus concentration was observed. Soil NO3-N leaching potential was noted, but soil NH4-N concentrations decreased, which could be ascribed to NH4-N nitrification, fixation within clay sheets and NH3 volatilization. Soil K+, Mg2+ and Na+ concentrations increased in soil layers above the drip lines, but decreased in soil layers below drip lines. Soil electrical conductivity accordingly increased in soil layers above drip lines, but the range was significantly lower than the threshold for soil salinity. Although the moisture-controlled effluent disposal strategy successfully avoided hydraulic dosing during unfavourable wet drain field conditions and prevented accumulation of soil salts in the soil profile beneath the drip lines, soil salts tended to accumulate in top soil layers. These adverse effects warrant system corrections before large-scale implementation of subsurface drip irrigation of effluent in similar vertisols.

In-Field Application Uniformity Evaluation of Pressure-Compensating Subsurface-Drip Irrigation Products

In the southeast United States, Subsurface Drip Irrigation (SDI) is an available agricultural irrigation practice. Research performed at the Tennessee Valley Research and Extension Center (TVREC), Belle Mina, Alabama indicated poor irrigation uniformity in an active experimental plot equipped with pressure-compensated SDI. The need therefore existed to quantify the performance of the SDI without disrupting ongoing crop research. A study was conducted to develop and validate an in-situ testing technique to assess the application uniformity of SDI, and to evaluate if variable operating pressure or slope was a significant response variable. Laboratory investigations indicated that new pressure-compensated SDI dripline of the type used at TVREC had an emitter discharge of 1.04 L h-1 (0.275 gal h-1) at 5% coefficient of variation (CV) above the manufacturers specification of 0.98 L h-1 (0.26 gal h-1) at 2.5% CV. A trailer mounted field testing apparatus was fabricated to interface with the in-situ SDI dripline in order to deliver water over a range of operating pressures while measuring sample discharge from a predetermined number of emitters. This apparatus was tested under laboratory conditions to compare emitter discharge equivalent values with per-emitter discharge; measurements from the apparatus agreed to within a half percent of per-emitter discharge values. Field evaluations indicated that the lowest discharge occurred for the irrigated SDI dripline operating at 48-kPa (7-psi) pressure. Discharges from non-irrigated and irrigated driplines operating at 83 and 117 kPa (12 and 17 psi) were not significantly different (a = 0.05). Emitter discharge estimates were within ±5% of the baseline discharge rate determined from laboratory evaluations (1.04 L h-1; 0.275 gal h-1) regardless of operating pressure or system activity, except for irrigated driplines operating at 48 kpa (7 psi) (-7%). Three sample driplines exhibited flows exceeding ±5% of the baseline discharge; flows that may prompt a system manager to investigate this discharge anomaly more closely. Spatial yield estimates indicated that cotton lint yield may have been adversely affected by poor SDI uniformity. Techniques and equipment developed in this study provide SDI researchers and users a field method to evaluate in-situ SDI application uniformity and emitter discharge performance.

Small-scale biodiesel production: a case study of on-farm economics

In an attempt to reduce input costs, farmers have become interested in growing alternative crops for the production of biofuels such as biodiesel. Using small-scale cold presses and conversion systems to offset variable diesel fuel prices, biodiesel could be produced on-farm. For example, a farmer could grow oilseed crops such as soybeans, canola, sunflower, or peanuts (grown in the southeastern US) and either sell through traditional commodity marketing or choose to produce his/her own biodiesel. In another scenario, farmers could acquire waste vegetable oil (WVO) for biodiesel production. However, research is limited on the economics of such processes, given the variability that could occur. As has been observed in the past several years, fluctuations in commodity and petroleum fuel markets may drastically influence the economics of a small-scale, on-farm biodiesel production process. Likewise, other variables such as crop yield, seed oil content, capacity of the biodiesel production system, mechanical pressing efficiency, vegetable oil price, chemical costs for biodiesel production, and value added utilization of co-products will ultimately define the bottom line of this process. Therefore, this project was conducted with the following objectives; 1) Assess economics of a current small scale biodiesel production system in Auburn University’s Biosystems Engineering department and 2) use the data collected to develop a prediction model for a small-scale, on-farm biodiesel production system scenario. Auburn University Biosystems Engineering Department’s biodiesel production system utilizes all WVO from dining facilities on campus, totaling 3,300 gal/yr. Biodiesel is produced for approximately