Assessing corn recovery from early season nutrient stress under different soil moisture regimes.

Corn (Zea mays) biomass accumulation and nutrient uptake by the six-leaf collar (V6) growth stage are low, and therefore, synchronizing nutrient supply with crop demand could potentially minimize nutrient loss and improve nutrient use efficiency. Knowledge of corn's response to nutrient stress in the early growth stages could inform such nutrient management. Field studies were conducted to assess corn recovery from when no fertilizer application is made until the V6 growth stage, and thereafter, applying fertilizer rates as those in non-stressed conditions. The early season nutrient stress and non-stress conditions received the same amount of nutrients. As the availability of nutrients for plant uptake is largely dependent on soil moisture, corn recovery from the early season nutrient stress was assessed under different soil moisture regimes induced via irrigation scheduling at 50% and 80% field capacity under overhead and subsurface drip irrigation (SSDI) systems. Peanut (Arachis hypogaea) was the previous crop under all conditions, and the fields were under cereal rye (Secale cereale) cover crop prior to planting corn. At the V6 growth stage, the nutrient concentrations of the early season-stressed crops, except for copper, were above the minimum threshold of sufficiency ranges reported for corn. However, the crops showed poor growth, with biomass accumulation being reduced by over 50% compared to non-stressed crops. Also, the uptake of all nutrients was significantly lower under the early season nutrient stress conditions. The recovery of corn from the early season nutrient stress was low. Compared to non-stress conditions, the early season nutrient stress caused 1.58 Mg ha-1 to 3.4 Mg ha-1 yield reduction. The percent yield reduction under the SSDI system was 37.6-38.2% and that under the overhead irrigation system was 11.7-13%. The high yield reduction from the early season nutrient stress under the SSDI system was because of water stress conditions in the topsoil soil layer. The findings of the study suggest ample nutrient supply in the early season growth stage is critical for corn production, and thus, further studies are recommended to determine the optimum nutrient supply for corn at the initial growth stages.

Estimating yield-contributing physiological parameters of cotton using UAV-based imagery.

Lint yield in cotton is governed by light intercepted by the canopy (IPAR), radiation use efficiency (RUE), and harvest index (HI). However, the conventional methods of measuring these yield-governing physiological parameters are labor-intensive, time-consuming and requires destructive sampling. This study aimed to explore the use of low-cost and high-resolution UAV-based RGB and multispectral imagery 1) to estimate fraction of IPAR (IPARf), RUE, and biomass throughout the season, 2) to estimate lint yield using the cotton fiber index (CFI), and 3) to determine the potential use of biomass and lint yield models for estimating cotton HI. An experiment was conducted during the 2021 and 2022 growing seasons in Tifton, Georgia, USA in randomized complete block design with five different nitrogen treatments. Different nitrogen treatments were applied to generate substantial variability in canopy development and yield. UAV imagery was collected bi-weekly along with light interception and biomass measurements throughout the season, and 20 different vegetation indices (VIs) were computed from the imagery. Generalized linear regression was performed to develop models using VIs and growing degree days (GDDs). The IPARf models had R2 values ranging from 0.66 to 0.90, and models based on RVI and RECI explained the highest variation (93%) in IPARf during cross-validation. Similarly, cotton above-ground biomass was best estimated by models from MSAVI and OSAVI. Estimation of RUE using actual biomass measurement and RVI-based IPARf model was able to explain 84% of variation in RUE. CFI from UAV-based RGB imagery had strong relationship (R2 = 0.69) with machine harvested lint yield. The estimated HI from CFI-based lint yield and MSAVI-based biomass models was able to explain 40 to 49% of variation in measured HI for the 2022 growing season. The models developed to estimate the yield-contributing physiological parameters in cotton showed low to strong performance, with IPARf and above-ground biomass having greater prediction accuracy. Future studies on accurate estimation of lint yield is suggested for precise cotton HI prediction. This study is the first attempt of its kind and the results can be used to expand and improve research on predicting functional yield drivers of cotton.

Salmonella Survival in Soil and Transfer onto Produce via Splash Events.

Nearly one-half of foodborne illnesses in the United States can be attributed to fresh produce consumption. The preharvest stage of production presents a critical opportunity to prevent produce contamination in the field from contaminating postharvest operations and exposing consumers to foodborne pathogens. One produce-contamination route that is not often explored is the transfer of pathogens in the soil to edible portions of crops via splash water. We report here on the results from multiple field and microcosm experiments examining the potential for Salmonella contamination of produce crops via splash water, and the effect of soil moisture content on Salmonella survival in soil and concentration in splash water. In field and microcosm experiments, we detected Salmonella for up to 8 to 10 days after inoculation in soil and on produce. Salmonella and suspended solids were detected in splash water at heights of up to 80 cm from the soil surface. Soil-moisture conditions before the splash event influenced the detection of Salmonella on crops after the splash events-Salmonella concentrations on produce after rainfall were significantly higher in wet plots than in dry plots (geometric mean difference = 0.43 CFU/g; P = 0.03). Similarly, concentrations of Salmonella in splash water in wet plots trended higher than concentrations from dry plots (geometric mean difference = 0.67 CFU/100 mL; P = 0.04). These results indicate that splash transfer of Salmonella from soil onto crops can occur and that antecedent soil-moisture content may mediate the efficiency of microbial transfer. Splash transfer of Salmonella may, therefore, pose a hazard to produce safety. The potential for the risk of splash should be further explored in agricultural regions in which Salmonella and other pathogens are present in soil. These results will help inform the assessment of produce safety risk and the development of management practices for the mitigation of produce contamination.

Evaluation of Grower-Friendly, Science-Based Sampling Approaches for the Detection of Salmonella in Ponds Used for Irrigation of Fresh Produce.

The recognition that irrigation water sources contribute to preharvest contamination of produce has led to new regulations on testing microbial water quality. To best identify contamination problems, growers who depend on irrigation ponds need guidance on how and where to collect water samples for testing. In this study, we evaluated several sampling strategies to identify Salmonella and Escherichia coli contamination in five ponds used for irrigation on produce farms in southern Georgia. Both Salmonella and E. coli were detected regularly in all the ponds over the 19-month study period, with overall prevalence and concentrations increasing in late summer and early fall. Of 507 water samples, 217 (42.8%) were positive for Salmonella, with a very low geometric mean (GM) concentration of 0.06 most probable number (MPN)/100 mL, and 442 (87.1%) tested positive for E. coli, with a GM of 6.40 MPN/100 mL. We found no significant differences in Salmonella or E. coli detection rates or concentrations between sampling at the bank closest to the pump intake versus sampling from the bank around the pond perimeter, when comparing with results from the pump intake, which we considered our gold standard. However, samples collected from the bank closest to the intake had a greater level of agreement with the intake (Cohen's kappa statistic = 0.53; p < 0.001) than the samples collected around the pond perimeter (kappa = 0.34; p = 0.009). E. coli concentrations were associated with increased odds of Salmonella detection (odds ratio = 1.31; 95% confidence interval = 1.10-1.56). All the ponds would have met the Produce Safety Rule standards for E. coli, although Salmonella was also detected. Results from this study provide important information to growers and regulators about pathogen detection in irrigation ponds and inform best practices for surface water sampling.

RNA Sequencing of Contaminated Seeds Reveals the State of the Seed Permissive for Pre-Harvest Aflatoxin Contamination and Points to a Potential Susceptibility Factor.

Pre-harvest aflatoxin contamination (PAC) is a major problem facing peanut production worldwide. Produced by the ubiquitous soil fungus, Aspergillus flavus, aflatoxin is the most naturally occurring known carcinogen. The interaction between fungus and host resulting in PAC is complex, and breeding for PAC resistance has been slow. It has been shown that aflatoxin production can be induced by applying drought stress as peanut seeds mature. We have implemented an automated rainout shelter that controls temperature and moisture in the root and peg zone to induce aflatoxin production. Using polymerase chain reaction (PCR) and high performance liquid chromatography (HPLC), seeds meeting the following conditions were selected: infected with Aspergillus flavus and contaminated with aflatoxin; and not contaminated with aflatoxin. RNA sequencing analysis revealed groups of genes that describe the transcriptional state of contaminated vs. uncontaminated seed. These data suggest that fatty acid biosynthesis and abscisic acid (ABA) signaling are altered in contaminated seeds and point to a potential susceptibility factor, ABR1, as a repressor of ABA signaling that may play a role in permitting PAC.

Low Concentration of Salmonella enterica and Generic Escherichia coli in Farm Ponds and Irrigation Distribution Systems Used for Mixed Produce Production in Southern Georgia.

Studies have shown that irrigation water can be a vector for pathogenic bacteria. Due to this, the Food Safety Modernization Act's (FSMA) produce safety rule requires that agricultural water directly applied to produce be safe and of adequate sanitary quality for use, which may pose a challenge for some farmers. The purpose of this research was to assess the presence and concentration of Salmonella and generic Escherichia coli in irrigation water from distribution systems in a mixed produce production region of southern Georgia. Water samples were collected during three growing seasons at three farms irrigating crops with surface water (Pond 1, Pond 2) or groundwater (Well) during 2012-2013. Salmonella and generic E. coli populations were monitored by culture and Most Probable Number (MPN). Confirmed isolates were characterized by pulsed-field gel electrophoresis and serotyping. In Pond 1, Salmonella was detected in 2/21 surface, 5/26 subsurface, 10/50 center pivot, and 0/16 solid set sprinkler head water samples. In Pond 2, Salmonella was detected in 2/18 surface, 1/18 subsurface, 6/36 drip line start, and 8/36 drip line end water samples. Twenty-six well pumps and 64 associated drip line water samples were negative. The overall mean Salmonella concentration for positive water samples was 0.03 MPN/100 mL (range <0.0011-1.8 MPN/100 mL). Nine Salmonella serovars comprising 22 pulsotypes were identified. Identical serovars and subtypes were found three times on the same day and location: Pond 1-Pivot-Cantaloupe (serovar Rubislaw), Pond 1-Pivot-Peanut (serovar Saintpaul), and Pond 2-Drip Line Start-Drip Line End-Yellow Squash (serovar III_16z10:e,n,x,z15). Generic E. coli was detected in water from both farm ponds and irrigation distribution systems, but the concentrations met FSMA microbial water quality criteria. The results from this study will allow producers in southern Georgia to better understand how potential pathogens move through irrigation distribution systems.

Genomic evidence reveals numerous Salmonella enterica serovar Newport reintroduction events in Suwannee watershed irrigation ponds.

Our previous work indicated a predominance (56.8%) of Salmonella enterica serovar Newport among isolates recovered from irrigation ponds used in produce farms over a 2-year period (B. Li et al., Appl Environ Microbiol 80:6355-6365, http://dx.doi.org/10.1128/AEM.02063-14). This observation provided a valuable set of metrics to explore an underaddressed issue of environmental survival of Salmonella by DNA microarray. Microarray analysis correctly identified all the isolates (n = 53) and differentiated the S. Newport isolates into two phylogenetic lineages (S. Newport II and S. Newport III). Serovar distribution analysis showed no instances where the same serovar was recovered from a pond for more than a month. Furthermore, during the study, numerous isolates with an indistinguishable genotype were recovered from different ponds as far as 180 km apart for time intervals as long as 2 years. Although isolates within either lineage were phylogenetically related as determined by microarray analysis, subtle genotypic differences were detected within the lineages, suggesting that isolates in either lineage could have come from several unique hosts. For example, strains in four different subgroups (A, B, C, and D) possessed an indistinguishable genotype within their subgroups as measured by gene differences, suggesting that strains in each subgroup shared a common host. Based on this comparative genomic evidence and the spatial and temporal factors, we speculated that the presence of Salmonella in the ponds was likely due to numerous punctuated reintroduction events associated with several different but common hosts in the environment. These findings may have implications for the development of strategies for efficient and safe irrigation to minimize the risk of Salmonella outbreaks associated with fresh produce.

Distribution and Characterization of Salmonella enterica Isolates from Irrigation Ponds in the Southeastern United States.

Irrigation water has been implicated as a likely source of produce contamination by Salmonella enterica. Therefore, the distribution of S. enterica was surveyed monthly in irrigation ponds (n = 10) located within a prime agricultural region in southern Georgia and northern Florida. All ponds and 28.2% of all samples (n = 635) were positive for Salmonella, with an overall geometric mean concentration (0.26 most probable number [MPN]/liter) that was relatively low compared to prior reports for rivers in this region. Salmonella peaks were seasonal; the levels correlated with increased temperature and rainfall (P < 0.05). The numbers and occurrence were significantly higher in water (0.32 MPN/liter and 37% of samples) than in sediment (0.22 MPN/liter and 17% of samples) but did not vary with depth. Representative isolates (n = 185) from different ponds, sample types, and seasons were examined for resistance to 15 different antibiotics; most strains were resistant to streptomycin (98.9%), while 20% were multidrug resistant (MDR) for 2 to 6 antibiotics. DiversiLab repetitive extragenic palindromic-element sequence-based PCR (rep-PCR) revealed genetic diversity and showed 43 genotypes among 191 isolates, as defined by >95% similarity. The genotypes did not partition by pond, season, or sample type. Genetic similarity to known serotypes indicated Hadar, Montevideo, and Newport as the most prevalent. All ponds achieved the current safety standards for generic Escherichia coli in agricultural water, and regression modeling showed that the E. coli level was a significant predictor for the probability of Salmonella occurrence. However, persistent populations of Salmonella were widely distributed in irrigation ponds, and the associated risks for produce contamination and subsequent human exposure are unknown, supporting continued surveillance of this pathogen in agricultural settings.

Prioritizing watersheds for conservation actions in the southeastern coastal plain ecoregion.

The aim of this study was to apply and evaluate a recently developed prioritization model which uses the synoptic approach to geographically prioritize watersheds in which Best Management Practices (BMPs) can be implemented to reduce water quality problems resulting from erosion and sedimentation. The model uses a benefit-cost framework to rank candidate watersheds within an ecoregion or river basin so that BMP implementation within the highest ranked watersheds will result in the most water quality improvement per conservation dollar invested. The model was developed to prioritize BMP implementation efforts in ecoregions containing watersheds associated with the USDA-NRCS Conservation Effects Assessment Project (CEAP). We applied the model to HUC-8 watersheds within the southeastern Coastal Plain ecoregion (USA) because not only is it an important agricultural area but also because it contains a well-studied medium-sized CEAP watershed which is thought to be representative of the ecoregion. The results showed that the three HUC-8 watersheds with the highest rankings (most water quality improvement expected per conservation dollar invested) were located in the southern Alabama, northern Florida, and eastern Virginia. Within these watersheds, measures of community attitudes toward conservation practices were highly ranked, and these indicators seemed to push the watersheds to the top of the rankings above other similar watersheds. The results, visualized as maps, can be used to screen and reduce the number of watersheds that need further assessment by managers and decision-makers within the study area. We anticipate that this model will allow agencies like USDA-NRCS to geographically prioritize BMP implementation efforts.

Diversity and antimicrobial resistance of Salmonella enterica isolates from surface water in Southeastern United States.

A study of prevalence, diversity, and antimicrobial resistance of Salmonella enterica in surface water in the southeastern United States was conducted. A new scheme was developed for recovery of Salmonella from irrigation pond water and compared with the FDA's Bacteriological Analytical Manual (8th ed., 2014) (BAM) method. Fifty-one isolates were recovered from 10 irrigation ponds in produce farms over a 2-year period; nine Salmonella serovars were identified by pulsed-field gel electrophoresis analysis, and the major serovar was Salmonella enterica serovar Newport (S. Newport, n = 29), followed by S. enterica serovar Enteritidis (n = 6), S. enterica serovar Muenchen (n = 4), S. enterica serovar Javiana (n = 3), S. enterica serovar Thompson (n = 2), and other serovars. It is noteworthy that the PulseNet patterns of some of the isolates were identical to those of the strains that were associated with the S. Thompson outbreaks in 2010, 2012, and 2013, S. Enteritidis outbreaks in 2011 and 2013, and an S. Javiana outbreak in 2012. Antimicrobial susceptibility testing confirmed 16 S. Newport isolates of the multidrug resistant-AmpC (MDR-AmpC) phenotype, which exhibited resistance to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline (ACSSuT), and to the 1st, 2nd, and 3rd generations of cephalosporins (cephalothin, amoxicillin-clavulanic acid, and ceftriaxone). Moreover, the S. Newport MDR-AmpC isolates had a PFGE pattern indistinguishable from the patterns of the isolates from clinical settings. These findings suggest that the irrigation water may be a potential source of contamination of Salmonella in fresh produce. The new Salmonella isolation scheme significantly increased recovery efficiency from 21.2 (36/170) to 29.4% (50/170) (P = 0.0002) and streamlined the turnaround time from 5 to 9 days with the BAM method to 4 days and thus may facilitate microbiological analysis of environmental water.

Development of a novel cross-streaking method for isolation, confirmation, and enumeration of Salmonella from irrigation ponds.

The 2013 Produce Safety Rules in Food Safety Modernization Act (FSMA) require regular testing for generic Escherichia coli in agricultural water intended for pre-harvest contact with the edible portion of fresh produce. However, the use of fecal contamination indicators frequently does not correctly reflect distribution of foodborne pathogens such as Salmonella enterica, and ensuring food safety may require direct detection and enumeration of pathogens in agricultural settings. Herein we report the evaluation of different cost-effective methods for quantification, isolation, and confirmation of Salmonella in irrigation pond water and sediment samples. A most probably number (MPN) dual enrichment culture method was used in combination with differential and selective agars, XLT4 and CHROMagar™ Salmonella plus (CSP). The necessity for PCR confirmation was evaluated, and methods were compared by cost and performance measures (i.e., sensitivity, specificity, positive predictive value, and negative predictive value). Statistical analyses showed that using XLT4 as the initial selective agar to isolate Salmonella colonies improved recovery compared to CSP agar; however, PCR confirmation was required to avoid false positive results on either agar. Therefore, a novel cross-streaking method utilizing CHROMagar™ agar for individual colony confirmation of Salmonella presence/absence on XLT4 was developed. This method classifies the colony as positive if typical Salmonella appearance is observed on both agars. Statistical analysis showed that this method was as effective as PCR for species confirmation of pure individual strains isolated from enrichment cultures (sensitivity=0.99, specificity=1.00, relative to PCR). This method offers a cost-effective alternative to PCR that would increase the capacity and sensitivity of Salmonella evaluation.

Occurrence and population density of Campylobacter jejuni in irrigation ponds on produce farms in the Suwannee River Watershed.

Campylobacter spp., especially Campylobacter jejuni, are common causal agents of gastroenteritis globally. Poultry, contaminated water, and fresh produce are considered to be the main sources for infection by this pathogen. In this study, occurrence and population density of C. jejuni from vegetable irrigation ponds in the Suwannee River watershed were investigated and the relationship to environmental factors was analyzed. Two water samples were collected from each of 10 ponds every month from January 2011 to February 2012. Campylobacter jejuni was detected by quantitative real-time PCR. Nine of the 10 ponds were positive for C. jejuni some of the time with an overall prevalence of 19.3%. The highest counts were obtained in spring 2011. Oxidation-reduction potential and total nitrogen concentration were positively correlated (P < 0.05) with mean population and occurrence of C. jejuni, while temperature and dissolved oxygen percent saturation (DO%) were negatively correlated with mean population (P < 0.05). Presence of this pathogen was related to bacterial community composition. No correlations were found between C. jejuni and fecal indicators. Increasing DO% of irrigation water and limiting nitrogen pollution in the ponds are suggested to reduce the contamination risk of C. jejuni in a major fruit and vegetable growing area.

Factors affecting the occurrence of Escherichia coli O157 contamination in irrigation ponds on produce farms in the Suwannee River Watershed.

Outbreaks of enteritis caused by Escherichia coli O157 associated with fresh produce have resulted in questions about the safety of irrigation water; however, associated risks have not been systematically evaluated. In this study, the occurrence and distribution of the human pathogen E. coli O157 from vegetable irrigation ponds within the Suwannee River Watershed in Georgia were investigated, and the relationship to environmental factors was analyzed. Surface and subsurface water samples were collected monthly from 10 vegetable irrigation ponds from March 2011 to February 2012. Escherichia coli O157 was isolated from enriched filtrates on CHROMagar and sorbitol MacConkey agar media and confirmed by an agglutination test. Presence of virulence genes stx1, stx2 , and eae was tested by polymerase chain reaction. In addition, 27 environmental variables of the sampled ponds were measured. Denaturing gradient gel electrophoresis was conducted for the analysis of bacterial communities in the water samples. Biserial correlation coefficients were calculated to evaluate the log10 colony-forming unit per millilitre correlations between the environmental factors and the occurrence of E. coli O157. Stepwise and canonical discriminant analyses were used to determine the factors that were associated with the presence and absence of E. coli O157 in water samples. All 10 ponds were positive for E. coli O157 some of the time, mainly in summer and fall of 2011. The temporal distribution of this bacterium differed among the 10 ponds. Temperature, rainfall, populations of fecal coliform, and culturable bacteria were positively correlated with the occurrence of E. coli O157 (P < 0.05), while the total nitrogen concentration, oxidation-reduction potential, and dissolved oxygen concentration were negatively correlated with the occurrence of this pathogen (P < 0.05). Temperature and rainfall were the most important factors contributing to the discrimination between samples with and without E. coli O157, followed by bacterial diversity and culturable bacteria population density. Bacterial numbers and diversity, including fecal coliforms and E. coli O157, increased after rainfall (and possibly runoff from pond margins) in periods with relatively high temperatures, suggesting that prevention of runoff may be important to minimize the risk of enteric pathogens in irrigation ponds.

Model for prioritizing best management practice implementation: sediment load reduction.

Understanding the best way to allocate limited resources is a constant challenge for water quality improvement efforts. The synoptic approach is a tool for geographic prioritization of these efforts. It uses a benefit-cost framework to calculate indices for functional criteria in subunits (watersheds, counties) of a region and then rank the subunits. The synoptic approach was specifically designed to incorporate best professional judgment in cases where information and resources are limited. To date, the synoptic approach has been applied primarily to local or regional wetland restoration prioritization projects. The goal of this work was to develop a synoptic model for prioritizing watersheds within which suites of agricultural best management practices (BMPs) can be implemented to reduce sediment load at the watershed outlets. The model ranks candidate watersheds within an ecoregion or river basin so that BMP implementation within the highest ranked watersheds will result in the most sediment load reduction per conservation dollar invested. The model can be applied anywhere and at many scales provided that the selected suite of BMPs is appropriate for the evaluation area's biophysical and climatic conditions. The model was specifically developed as a tool for prioritizing BMP implementation efforts in ecoregions containing watersheds associated with the USDA-NRCS conservation effects assessment project (CEAP). This paper presents the testing of the model in the little river experimental watershed (LREW) which is located near Tifton, Georgia, USA and is the CEAP watershed representing the southeastern coastal plain. The application of the model to the LREW demonstrated that the model represents the physical drivers of erosion and sediment loading well. The application also showed that the model is quite responsive to social and economic drivers and is, therefore, best applied at a scale large enough to ensure differences in social and economic drivers across the candidate watersheds. The prioritization model will be used for planning purposes. Its results are visualized as maps which enable resource managers to identify watersheds within which BMP implementation would result in the most water quality improvement per conservation dollar invested.

Survival dynamics of fecal bacteria in ponds in agricultural watersheds of the Piedmont and Coastal Plain of Georgia.

Animal agriculture in watersheds produces manure bacteria that may contaminate surface waters and put public health at risk. We measured fecal indicator bacteria (commensal Escherichia coli and fecal enterococci) and manure pathogens (Salmonella and E. coli 0157:H7), and physical-chemical parameters in pond inflow, within pond, pond outflow, and pond sediments in three ponds in agricultural watersheds. Bishop Pond with perennial inflow and outflow is located in the Piedmont, and Ponds A and C with ephemeral inflow and outflow in the Coastal Plain of Georgia. Bromide and chloride tracer experiments at Bishop Pond reflected a residence time much greater than that estimated by two models, and indicated that complete mixing within Bishop Pond was never obtained. The long residence time meant that fecal bacteria were exposed to solar UV-radiation and microbial predation. At Bishop Pond outflow concentrations of fecal indicator bacteria were significantly less than inflow concentrations; such was not observed at Ponds A and C. Both Salmonella and E. coli 0157:H7 were measured when concomitant concentrations of commensal E. coli were below the criterion for surface water impairment indicating problems with the effectiveness of indicator organisms. Bishop Pond improved down stream water quality; whereas, Ponds A and C with ephemeral inflow and outflow and possibly greater nutrient concentrations within the two ponds appeared to be less effective in improving down stream water quality.

Variable rate application of nematicides on cotton fields: a promising site-specific management strategy.

Field tests were conducted to determine if differences in response to nematicide application (i.e., root-knot nematode (RKN) populations, cotton yield, and profitability) occurred among RKN management zones (MZ). The MZ were delineated using fuzzy clustering of five terrain (TR) and edaphic (ED) field features related to soil texture: apparent soil electrical conductivity shallow (ECa-shallow) and deep (ECa-deep), elevation (EL), slope (SL), and changes in bare soil reflectance. Zones with lowest mean values of ECa- shallow, ECa- deep, NDVI, and SL were designated as at greater risk for high RKN levels. Nematicide-treated plots (4 rows wide and 30 m long) were established in a randomized complete block design within each zone, but the number of replications in each zone varied from four to six depending on the size of the zone.The nematicides aldicarb (Temik 15 G) and 1,3-dichloropropene (1,3-D,Telone II) were applied at two rates (0.51 and 1.0 kg a.i./ha for aldicarb, and 33.1 and 66.2 kg a.i./ha for 1,3-D) to RKN MZ in commercial fields between 2007 and 2009. A consolidated analysis over the entire season showed that regardless of the zone, there were not differences between aldicarb rates and 1,3-D rates. The result across zones showed that 1,3-D provided better RKN control than did aldicarb in zones with low ECa values (high RKN risk zones exhibiting more coarse-textured sandy soils). In contrast, in low risk zones with relatively higher ECa values (heavier textured soil), the effects of 1,3-D and aldicarb were equal and application of any of the treatments provided sufficient control. In low RKN risk zones, a farmer would often have lost money if a high rate of 1,3-D was applied. This study showed that the effect of nematicide type and rate on RKN control and cotton yield varied across management zones (MZ) with the most expensive treatment likely to provide economic benefit only in zones with coarser soil texture. This study demonstrates the value of site specific application of nematicides based on management zones, although this approach might not be economically beneficial in fields with little variability in soil texture.

Geostatistical modeling of the spatial distribution of sediment oxygen demand within a Coastal Plain blackwater watershed.

Blackwater streams are found throughout the Coastal Plain of the southeastern United States and are characterized by a series of instream floodplain swamps that play a critical role in determining the water quality of these systems. Within the state of Georgia, many of these streams are listed in violation of the state's dissolved oxygen (DO) standard. Previous work has shown that sediment oxygen demand (SOD) is elevated in instream floodplain swamps and due to these areas of intense oxygen demand, these locations play a major role in determining the oxygen balance of the watershed as a whole. This work also showed SOD rates to be positively correlated with the concentration of total organic carbon. This study builds on previous work by using geostatistics and Sequential Gaussian Simulation to investigate the patchiness and distribution of total organic carbon (TOC) at the reach scale. This was achieved by interpolating TOC observations and simulated SOD rates based on a linear regression. Additionally, this study identifies areas within the stream system prone to high SOD at representative 3rd and 5th order locations. Results show that SOD was spatially correlated with the differences in distribution of TOC at both locations and that these differences in distribution are likely a result of the differing hydrologic regime and watershed position. Mapping of floodplain soils at the watershed scale shows that areas of organic sediment are widespread and become more prevalent in higher order streams. DO dynamics within blackwater systems are a complicated mix of natural and anthropogenic influences, but this paper illustrates the importance of instream swamps in enhancing SOD at the watershed scale. Moreover, our study illustrates the influence of instream swamps on oxygen demand while providing support that many of these systems are naturally low in DO.

Stream buffer effectiveness in an agriculturally influenced area, southwestern Georgia: responses of water quality, macroinvertebrates, and amphibians.

To determine useful metrics for assessing stream water quality in the Southeastern Coastal Plain, we examined differences among two buffered and three unbuffered streams in an agricultural landscape in southwestern Georgia. Potential indicators included amphibian diversity and abundance, aquatic macroinvertebrate populations, riparian vegetative structure, water quality, and stream physical parameters. Variability among sites and treatments (buffered vs. unbuffered) existed, with sites in the same treatment as most similar, and disturbances from a nearby eroding gully strongly affecting one unbuffered site. Of the invertebrate metrics examined, percentages of clingers, Ephemeroptera-Plecoptera-Trichoptera (EPT), Elmidae (Coleoptera), Crustacea (Decapoda and Amphipoda), and dipterans were found to be possible indicators of stream health for perennial streams within this region. Overall, buffered sites showed higher percentages of sensitive invertebrate groups and showed lower and more stable concentrations of nitrate N, suspended solids, and fecal coliforms (FCs). Percent canopy cover was similar among sites; however, riparian vegetative coverage and percent leaf litter were greatest at buffered sites. No differences in amphibian abundance, presence, and absence within the riparian area were apparent between sites; however, instream larval salamanders were more abundant at buffered streams. In this study, stream buffers appeared to decrease nutrient and sediment loads to adjacent streams, enhancing overall water quality. Selected benthic macroinvertebrate metrics and amphibian abundance also appeared sensitive to agricultural influences. Amphibians show potential as indicator candidates, however further information is needed on their responses and tolerances to disturbances from the microhabitat to landscape levels.

Macroinvertebrate biomonitoring in intermittent coastal plain streams impacted by animal agriculture.

Little attention has been given to the ecology of intermittent coastal plain streams in the southeastern United States, and it is not known whether available macroinvertebrate biomonitoring methods reliably detect degradation in these streams. This study compared differences in biomonitoring metrics between reference and agricultural streams, and between the flow period (January-April) and the intermittent flow period (May-December). Percentages of crustaceans, isopods, and Ephemeroptera-Plecoptera-Trichoptera (EPT) were significantly higher at the reference site than the two most impacted sites during the flow period, probably resulting from the abundance of leaf litter and lower temperatures. During this same period, the agriculturally impacted sites had a significantly higher percentage of dipterans--a group that thrives in the silty, nutrient-rich waters. Four metrics (percent Crustacea, Isopoda, Diptera, and EPT) had no overlap between values for the most impacted and the least impacted sites during the flow period, but no metrics were able to detect more discrete differences among sites. Sites were physically and biologically similar during the intermittent period when natural stresses (i.e., stagnant water, high temperatures, low dissolved oxygen) were high, with many metrics, such as percentages of dominant family, burrowers, chironomids, and dipterans becoming similar at all sites. Our findings indicate that development of a better understanding of invertebrate fauna in reference conditions and of the natural variation in intermittent streams is necessary to develop effective biomonitoring programs for these systems.

Prioritizing wetland restoration for sediment yield reduction: a conceptual model.

In a climate of limited resources, it is often necessary to prioritize restoration efforts geographically. The synoptic approach is an ecologically based tool for geographic prioritization of wetland protection and restoration efforts. The approach was specifically designed to incorporate best professional judgment in cases where information and resources are otherwise limited. Synoptic assessments calculate indices for functional criteria in subunits (watersheds, counties, etc.) of a region and then rank the subunits. Ranks can be visualized in region-scale maps which enable managers to identify areas where efforts optimize functional performance on a regional scale. In this paper, we develop a conceptual model for prioritizing watersheds whose wetlands can be restored to reduce total sediment yield at the watershed outlet. The conceptual model is designed to rank watersheds but not individual wetlands within a watershed. The synoptic approach is valid for applying the sediment yield reduction model because there is high demand for prioritizing disturbed wetlands for restoration, but there is limited, quantitative, accurate information available with which to make decisions. Furthermore, the cost of creating a comprehensive database is prohibitively high. Finally, because the model will be used for planning purposes, and, specifically, for prioritizing based on multiple decisions rather than optimizing a single decision, the consequence of prioritization errors is low. Model results cannot be treated as scientific findings. The conclusions of an assessment are based on judgement, but this judgement is guided by scientific principles and a general understanding of relevant ecological processes. The conceptual model was developed as the first step towards prioritizing of wetland restoration for sediment yield reduction in US EPA Region 4.