Dana Sullivan

EVALUATING THE SENSITIVITY OF AN UNMANNED THERMAL INFRARED AERIAL SYSTEM TO DETECT WATER STRESS IN A COTTON CANOPY

Airborne thermal infrared (TIR) imagery is a promising and innovative tool for assessing canopy response to a range of stressors. However, the expense associated with acquiring imagery for agricultural management is often cost-prohibitive. The objective of this study was to evaluate a less expensive system, an unmanned airvehicle (UAV) equipped with a TIR sensor, for detecting cotton (Gossypium hirsutum L.) response to irrigation and crop residue management. The experimental site was located on a 6.1 ha field in the Tennessee Valley Research and Extension Center located in Belle Mina, Alabama, where landscapes are gently rolling and soils are highly weathered Rhodic Paleudults. Treatments consisted of irrigation (dryland or subsurface drip irrigation) and crop residue cover (no cover or winter wheat (Triticum aestivum L.)). TIR (7 to 14 µm) imagery was acquired on 18 July 2006 at an altitude of 90 m and spatial resolution of 0.5 m. Coincident with image acquisition, ground truth data consisting of soil water content (0-25 cm), stomatal conductance, and canopy cover were measured within a 1 m radius of each sample location. All sample locations were georeferenced using a real-time kinematic (RTK) GPS survey unit. Analysis of sample locations acquired in multiple flight lines was used to assess the stability and repeatability of the UAV system during an acquisition. Compared to field measurements of stomatal conductance with CVs ranging from 2% to 75%, variability in TIR emittance (CV < 40%) was within the observed tolerance of ground truth measurements of stomatal conductance. Significant differences in canopy cover and stomatal conductance across irrigation treatments allowed testing of the sensitivity of the UAV system. A negative correlation was observed between TIR emittance and stomatal conductance (r = -0.48) and canopy closure (r = -0.44), indicating increasing canopy stress as stomatal conductance and canopy closure decreased. TIR emittance exhibited greater sensitivity to canopy response compared to ground truth measurements, differentiating between irrigation and crop residue cover treatments. TIR imagery acquired with a low-altitude UAV can be used as a tool to manage within-season canopy stress.

Thrips (Thysanoptera: Thripidae) mitigation in seedling cotton using strip tillage and winter cover crops

BACKGROUND Thrips are the most consistent insect pests of seedling cotton in the southeastern United States, where symptoms can range from leaf curling to stand loss. In a 2 year study, thrips adults and immatures were sampled at 14, 21 and 28 days after planting on cotton planted with a thiamethoxam seed treatment in concert with crimson clover, wheat or rye winter cover crops and conventional or strip tillage to investigate potential differences in thrips infestations. RESULTS Densities of adult thrips, primarily Frankliniella fusca (Hinds), peaked on the first sampling date, whereas immature densities peaked on the second sampling date. Regardless of winter cover crop, plots that received strip tillage experienced significantly fewer thrips at each sampling interval. In addition, assessment of percentage ground cover 42 days after planting showed that there was more than twice as much ground cover in the strip-tilled plots compared with conventionally tilled plots. Correlation analyses showed that increased ground cover was inversely related to thrips densities that occurred on all three sampling dates in 2008 and the final sampling date in 2009. CONCLUSIONS Growers who utilize strip tillage and a winter cover crop can utilize seed treatments for mitigation of early-season thrips infestation.

Satellite mapping of conservation tillage adoption in the Little River experimental watershed, Georgia

Conservation tillage is a commonly adopted best management practice for improving soil quality and reducing erosion. However, there are currently no methods in place to monitor conservation tillage adoption at the watershed scale. The primary objective of this study was to evaluate the usefulness of Landsat TM data as a tool to depict conservation tillage in a small Coastal Plain watershed. Satellite imagery was used to calculate four commonly used indices: Normalized Difference Vegetation Index, Crop Residue Cover Index, Normalized Difference Tillage Index, and the Simple Tillage Index. Ground truth data consisted of a windshield survey, assigning each site a tillage regime (conventional or conservation tillage) at 138 locations throughout the watershed and surrounding areas. A logistical regression approach was used on two subsets of the data set (n = 20 or n = 44) to determine the influence of the number of ground control points on the success of modeling the occurrence of conservation tillage. The most accurate model was re-applied to the satellite image and evaluated using an independent sample of 94 survey sites. Results indicate that the normalized difference tillage and simple tillage indices performed best, with an overall accuracy of 71% and 78% for models developed using n = 20 and n = 44 sample locations, respectively. Errors were typically in the form of commission. Results are encouraging and suggest that currently available satellite imagery can be used for rapid assessment of conservation tillage adoption using minimal a priori information.

Using Remote Sensing Data to Evaluate Surface Soil Properties in Alabama Ultisols

Evaluation of surface soil properties via remote sensing could facilitate soil survey mapping, erosion prediction, and allocation of agrochemicals for precision management. The objective of this study was to evaluate the relationship between soil spectral signature and surface soil properties in conventionally managed row crop systems. High-resolution remote sensing data were acquired over bare fields in the Coastal Plain, Appalachian Plateau, and Ridge and Valley provinces of Alabama using the Airborne Terrestrial Applications Sensor multispectral scanner. Soils ranged from sandy Kandiudults to fine textured Rhodudults. Surface soil samples (0 to 1 cm) were collected from 161 sampling points for gravimetric soil water content, soil organic carbon, particle size distribution, and citrate dithionite extractable iron content. Surface roughness and crusting were also measured during sampling. Two methods of analysis were evaluated: (1)multiple linear regression using common spectral band ratios and (2)partial least-squares regression. Our data show that thermal infrared spectra are highly, linearly related to soil organic carbon, sand and clay content. Soil organic carbon content was the most difficult to quantify in these highly weathered systems, where soil organic carbon was generally <1.2%. Estimates of sand and clay content were best using partial least-squares regression at the Valley site, explaining 42 to 59% of the variability. In the Coastal Plain, sandy surfaces prone to crusting limited estimates of sand and clay content via partial least-squares and regression with common band ratios. Estimates of iron oxide content were a function of mineralogy and best accomplished using specific band ratios, with regression explaining 36 to 65% of the variability at the Valley and Coastal Plain sites, respectively.

RESEARCH FROM THE COASTAL PLAIN EXPERIMENT STATION, TIFTON, GEORGIA, TO MINIMIZE AFLATOXIN CONTAMINATION IN PEANUT

Scientists with the U.S. Department of Agriculture–Agricultural Research Service (USDA-ARS) and scientists with the University of Georgia located at the Coastal Plain Experiment Station in Tifton, Georgia, have been conducting research on aflatoxin contamination of peanut since the early 1960s. Early efforts were focused on identifying the risk factors for increased aflatoxin contamination and helped to document the importance of drought, high soil temperatures, and pod damage. Later efforts were focused on the development of screening techniques and the identification of sources of resistance to Aspergillus colonization and/or aflatoxin contamination. This laid the foundation for a conventional resistance breeding program and has resulted in the development of peanut breeding lines that have high yield and low aflatoxin contamination relative to standard control cultivars. Recent research efforts include studies on the use of molecular genetic approaches to reduce aflatoxin contamination. This includes the evaluation of genetically engineered peanut and the development of molecular markers.

The evaluation of conservation practice placement in the Little River Experimental Watershed using geographic information systems

The Conservation Effects Assessment Program Watershed Assessment Study is a joint effort between the USDA Natural Resources Conservation Service (NRCS) and the USDA Agricultural Research Service to evaluate the effectiveness of federally funded conservation programs. In response to this initiative, a 26-year history of NRCS conservation practice placement (1980 to 2006) was evaluated for the Little River Experimental Watershed (LREW) in the southeastern coastal plain of Georgia. To accomplish this task, currently available geographic databases were integrated and queried to assess levels of commonly adopted practices and to evaluate factors affecting practice placement. Databases included (1) USDA NRCS Conservation Practice Database for the LREW, (2) USDA NRCS Soil Survey Geographic Database (SSURGO), and (3) 30 m (98 ft) digital elevation maps. Nearly 50% of all cropland fields in the LREW were delineated as having participated in conservation programs. Practices were predominantly used for water quality and erosion control. Sixty to 65% of the fields (77% of land area) implemented soil erosion and/or water quality control practices in high resource concern areas. Results showed that hydrologic group and proximity to a water body, rather than slope class, were the predominant factors in conservation practice placement. Using a subwatershed database having complete field coverage of four LREW subwatersheds (with and without USDA NRCS assistance), geographic information system databases were queried to evaluate the adoption and placement of erosion control practices that were visible in a 2005 digital orthoquad. Forty-seven percent of all fields in the subwatershed database had implemented visible erosion control–specific conservation practices. and implementation was linearly related to slope class (r2 = 0.64, p < 0.10). Fields identified as having participated in federally funded conservation programs coincided with high resource concern areas 35% of the time.

Evaluating a crop residue cover index for determining tillage regime in a cotton-corn-peanut rotation

Conservation tillage is a well known best management practice that improves soil quality, reduces runoff and erosion, and increases infiltration. However, a rapid assessment strategy for quantifying the rate and spatial distribution of conservation tillage practices is lacking. This study was designed to evaluate the sensitivity of a remotely derived crop residue cover index for depicting conventional tillage (CT), strip tillage (ST), and no-tillage (NT) systems in a cotton-corn-peanut rotation in the southeastern Coastal Plain. Treatments consisted of CT (rip and bed operation), NT, NT with subsoiling, and ST. Remotely sensed data were acquired three times prior to canopy closure, using a handheld multispectral radiometer (485 to 1,650 nm) and thermal imager (7,000 to 14,000 nm). Using a combination of visible and near-infrared spectra, a crop residue cover index was calculated and evaluated. Results showed that crop residue cover is greatest in years planted with peanut or cotton—likely due to the later winter cover crop termination date compared to years when corn is planted. The crop residue cover index outperformed the thermal infrared, accurately separating conventional from conservation tillage treatments in four out of six data acquisitions in 2004 and 2006. Differentiation among conservation tillage treatments was inconsistent. Regression analyses showed that a strong linear relationship existed between the crop residue cover index and measured crop residue cover (r2 = 0.51 to 0.86, alpha = 0.10). These data suggest that remotely sensed data may be used as a rapid, field-scale indicator of conservation tillage adoption. Rapid assessment methodologies are necessary to quantify the impact of conservation practice adoption on water quality/quantity, assess adoption rates, and improve the placement of conservation tillage practices at local, watershed and regional scales.

Long-Term Nitrogen Load from the Little River Experimental Watershed on the Coastal Plain of Southwest Georgia

The USDA-Agricultural Research Service, Southeast Watershed Research Laboratory initiated flow measurement of the Little River in a 334 km2 area near Tifton, Georgia in the late 1960’s. Monitoring of stream nitrogen concentrations began in 1974 for seven of the eight nested subwatersheds in the area, known as the Little River Experimental Watershed. This paper summarizes the first 30 years of the stream nitrogen record, from 1974-2003. The calculated nitrogen loading data provides insight into the effects of changing land use and agricultural practices, stream-side riparian zones, and climate cycles on nitrogen cycling over the long term in the Southeast Coastal Plain.

Adapting Radio Control (RC) Models for Research Roles

Small Unmanned Aircraft Systems (sUAS) are useful for numerous observations that can be helpful in Earth science research and related applications. The benefits of small, instrumented platforms operated within line -of -sight include high spatial resolution, quick response, minimum environmental impact, and affordability. Experiments with radio control models have proven to be an efficient method for testing instrumentation and development of mission scenarios, with significan tly less labor than custom designing and fabricating entirely new vehicles . Three examples of successful prototypes are outlined.

Conservation tillage : Monitoring adoption with satellite imagery

The term conservation tillage is used to refer to any method of tillage that minimally disturbs the surface, leaving at least 30% residue cover after planting. As such, conservation tillage is one of the most widely adopted conservation practices. Conservation tillage is oftentimes coupled with a crop residue management program, which in the southeastern United States typically includes a winter cover crop for biomass production. Conservation tillage has been attributed with improving soil quality, reducing runoff, and reducing fuel costs. In the southeastern United States, conservation tillage has also been hailed with increasing plant available water and reducing the total number of irrigations necessary to produce a crop. Because many states in this region of the nation are facing water restrictions and severe drought conditions, conservation tillage shows promise as a sustainable, water saving practice. In 2004, the Conservation Technology Information Center estimated that 4.55 × 107 ha (1.13 × 108 ac) of the nations cropland has adopted some form of conservation tillage, an overall increase of 4.0 × 106 ha (1.0 × 107 ac) since 2002. However, at the present time, no national monitoring system is in place to continue these efforts on a regular basis. Natural resource inventory