Heavy metal contamination is a major concern for soil and water quality. To quantify their potential hazard, it is crucial to understand their mobility and retention in soils. The source of the problem is anthropogenic activities such as mining, smelting, usage of sewage sludge and fertilizers. The objective of this study was to quantify Cd, Cu and Pb transport and retention in three soils having different properties, and evaluate their competitive influence on the mobility of individual heavy metal. The second objective was to quantify Cd, Cu and Pb retention kinetics in the different soils. This study also investigates the extent and distribution of retained Cd, Cu and Pb with depth in soil columns. In the study, batch experiments were carried out for different range of concentrations in time. The results indicated that retention of Cd, Cu and Pb in Windsor, Mahan and Webster soil is nonlinear. Lead exhibited highest retention among all three metals. Moreover, all three metals exhibited highest affinity in Webster soil, which has a higher clay content (mostly smectite), organic material and cation exchange capacity. Sorption of all metals was also observed to be kinetic when retention time increased from one day to seven days. Miscible displacement experiments in saturated soil columns were also carried out in two ways. In the first type, consecutive pulses of Cd, Cu and Pb were sequentially introduced to each soil column followed by an extended period of leaching with the background solution (KNO3, 0.005M). In the second type, two consecutive pulses of mixed solution (Cd, Cu and Pb), each followed by leaching with the background solution, were introduced to soil columns. Results indicate that Cd was the most mobile with the highest recovery the effluent solution, whereas Pb was the least mobile with the lowest recovery among all elements and soils. It was also observed that Pb resulted in enhanced mobility of both Cd and Cu . Efforts to describe results from the column experiments based on a multirection and transport model (MRTM) showed varied degrees of success. Although the models accounts for several sorption mechanisms including nonlinear equilibrium, kinetics, and irreversible reactions, the model was not successful in predicting the competitive behavior of heavy metals in the soil columns.

Field studies were conducted in 2011, 2012, and 2013 near Alexandria, LA to determine glufosinate rates and timings for control of rhizome johnsongrass [Sorghum halepense (L.) Pers.] in glufosinate-resistant soybean [Glycine max (L.)Merr.]. Johnsongrass control (75%) and height reduction (63%) throughout the season were greatest when glufosinate was applied at 0.7 kg ai ha-1 followed by (fb) 0.6 kg ha-1. Furthermore, following initial applications of glufosinate at 0.7 kg ha-1 (2670 kg ha-1) increased soybean yields were observed compared to 0.5 kg ha-1 (2400 kg ha-1), and soybean yields were greater following sequential glufosinate applications of 0.6 kg ha-1 followed by 0.5 kg ha-1. These data suggest that sequential applications of glufosinate is an option to control rhizomatous johnsongrass in glufosinate-resistant soybean. Additionally, field trials were conducted in 2011 and 2012 to assess control of johnsongrass in soybean with sequences of chlorimuron, clethodim, and fomesafen applied at early-post-emergence (EPOST), mid-postemergence (MPOST), and late-postemergence (LPOST). Sequential applications of glufosinate was added as a comparison treatment at all three timings. Clethodim applied EPOST was similar in johnsongrass control to sequentially applied glufosinate 35 days after LPOST. Johnsongrass control at harvest following sequential glufosinate applications (90%) or clethodim fb chlorimuron fb fomesafen (82%) did not differ. At harvest, differences in johnsongrass heights were not observed between treatments. Following sequentially applied glufosinate soybean yields were similar where clethodim was applied LPOST. Furthermore, trials were conducted to assess johnsongrass control in cotton [Gossypium hirsutum L.] in 2011, 2012, and 2013 following glufosinate applied two or three times sequentially, initiated 2, 3, or 4 wk after planting and sequential applications timed 2 or 3 wk apart. Johnsongrass control was maximized when three applications were applied at least 3 wk apart. However, johnsongrass control and reduction in heights was greatest when timing the initial application 4 WAP. Additionally, cotton yield was comparable to three total applications when two applications were made initiated 4 WAP.

The potential usage and benefits of native perennial grasses (NPG) in urban plantings may be severely hindered during establishment by high weed pressure. Two studies were conducted with the objectives of examining the tolerance of several NPG to commonly available herbicides during vegetative establishment; and comparison of establishment vigor of NPG in Louisiana when weed control is implemented. The first study was conducted in greenhouse conditions to evaluate tolerance of broomsedge (Andropogon virginicus L.); blue grama (Bouteloua gracilis (Willd. ex Kunth) Lag. ex Griffiths); Virginia wildrye (Elymus virginicus L.); switchgrass (Panicum virgatum L.); little bluestem (Schizachyrium scoparium (Michx.) Nash); and Indiangrass (Sorghastrum nutans (L.) Nash) established 6 weeks from plugs to applications of pendimethalin; sulfosulfuron; imazapic; triclopyr; or fenoxaprop. Overall, fenoxaprop was the most injurious to NPG and slowed tillering on affected species compared to controls. Plants treated with imazapic, triclopyr, or sulfosulfuron varied in tolerance among species as well as timing of application relative to temperature. Pendimethalin was consistently the least injurious to NPG. In the second study, the same NPG species were evaluated for establishment vigor in Baton Rouge, Louisiana and Fort Polk near Leesville, Louisiana over a 12-month period with pendimethalin applied at initial planting in October 2011 and again in March 2012. At the Baton Rouge site, little bluestem and broomsedge had the highest canopy coverages of 97.7% and 100% and corresponding biomasses 156.8 and 244.8 g at the conclusion of the 12-month establishment period along with the lowest weed encroachment of 1.7%. Little bluestem and broomsedge also achieved the highest canopy coverages and biomasses at the Fort Polk site, but overall NPG establishment was slower compared to NPG establishment in Baton Rouge. Environmental factors such as soil texture, fertility, and rainfall between the two locations affected NPG establishment. Results indicate herbicide applications at least during the first year of NPG vegetative establishment may be necessary to reduce weed competition in order to establish NPG in disturbed urban sites. Species selection, herbicide selection and application, and site characteristics must be accounted for when establishing NPG in urban areas.

Field experiments in 2013 evaluated residual herbicide effects on ball (Trifolium nigrescens viv.) and white (Trifolium repens L.) clover. For the October planting, averaged across clovers, ground cover for 2,4-D plus aminopyralid and 2,4-D plus picloram averaged 4.4 and was less than for the nontreated (7.0). For the November and March plantings, ground cover for all herbicides was equivalent to the nontreated. Averaged across clover species and planting date, herbicide treatments except 2,4-D plus aminopyralid (4) resulted in ground cover 49/112 days after planting (DAP) equal to the non-treated (5.7). Lowest plant population 4 to 6 wk after Oct/Nov planting was observed for 2,4-D plus aminopyralid (6.3) and 2,4-D plus picloram (7.3). Only 2,4-D plus aminopyralid resulted in yield reduction from the nontreated (29.8%). Field experiments also evaluated simulated residual effects of fluroxypyr plus triclopyr and 2, 4-D plus picloram on ball (Trifolium nigrescens viv.), white (Trifolium repens L.), crimson (Trifolium incarnatum L.) and red (Trifolium pretense L.) clover. For all clovers, when averaged across herbicide rates, plant population 214/217 and ground cover 86/87 DAP was equivalent for fluroxypyr plus triclopyr and the non-treated and greater than 2,4-D plus picloram. Averaged across herbicide rates, clover height was equivalent for fluroxypyr plus triclopyr and the non-treated. 2,4-D plus picloram reduced clover height 67 to 88% from the non-treated. Ground cover 161/196 DAP, when averaged across clovers, for all rates of fluroxypyr plus triclopyr was equivalent to the non-treated. All rates of 2,4-D plus picloram were reduced compared to the non-treated (1.4 to 4.0 vs 7.9). Averaged across clovers, plant height following all rates of fluroxypyr plus triclopyr was equivalent to the non-treated (14.2 to 14.3 vs 15.3 cm) and greater than 2,4-D plus picloram. Compared with the non-treated, 2,4-D plus picloram at 25, 38, and 50% x rates reduced height 58, 76, and 85% respectively. Averaged across clover species, yield for fluroxypyr plus triclopyr at all rates was equivalent to the non-treated (2624.0 to 2839.7 vs 2811.9 kg/ha). Compared with the non-treated, 2,4-D plus picloram at 25, 38, and 50% x rate reduced yield 65,89, and 99%, respectively.

Burgeoning demand for sweetpotato [Ipomoea batatas (L.) Lam] is being driven by strong consumer consumption of fries and robust fresh market sales. Acreage has rebounded to meet needs, but increased supply has weighed negatively on fresh market prices, and processing sweetpotato is generally at a low price point. Growers are challenged with increasing production costs and labor is the most expensive input; reducing labor costs through mechanized harvest is critical. Many popular varieties of sweetpotato are highly susceptible to skinning damage and the problems that are associated with exposed root flesh such as rotting, weight loss, and sunken areas. The present study compared methods to assess skinning damage and determine if it is possible to breed for a more skinning resistant variety to aid in further mechanization. A torque wrench was found best at quantifying the amount of force required to cause skinning damage. A two year study of a parent and offspring population using the torque wrench found a heritability estimate of 0.10 on an individual plant basis and a 0.63 heritability on a family basis. It is assumed that an estimate above 0.50 is sufficient to improve a trait and data showed utility using families in breeding scheme, albeit this brings complications. The research also examined genes differentially expressed at skinning injury sites in 2 different environments. Over expression of genes involved in healing may decrease damage that does occur after skinning damage and complement a more durable skin. Consequences of skinning are lessened by curing roots (32° C; 85% relative humidity for 5 days); wound sites are rapidly healed with nominal desiccation. Cyt P450 and Ext, genes associated with periderm formation and wound healing, were found up-regulated in a curing environment compared to skinned sites at ambient outside conditions (conditions varied from approximately 26-30°C, with 50-70% RH ) over multiple time points (2 h, 4 h, and 24 h after skinning). Multiple genes associated with stress were found up-regulated in the ambient conditions. It is hypothesized that selection of genotypes with a more durable skin and enhanced repair mechanisms may further the quest towards mechanized harvest.

Cotton is sold by weight, but a bales lint price per pound is determined by its fiber quality profile. Cotton quality is defined by a set of standardized properties (length, strength, elongation, uniformity, color, trash, and micronaire) collected on every United States bale. Each cotton fiber is the remnant of a single cell which upon harvest exists as a dry, hollow tube of crystalline cellulose. The length, perimeter, and thickness are a fibers physical dimensions. These dimensions influence both the mechanics involved in yarn spinning and the quality of the yarn produced. Genetic and environmental factors affect the development and consequently, the final properties of cotton crops. However, information is lacking about the degree of influence they impart, especially on fiber perimeter (fineness) and cell wall thickness (maturity), both components of micronaire. The goals of this dissertation were to: 1) Summarize and review the techniques available to industry to measure fiber perimeter and maturity in order to discuss their advantages and limitations, 2) Validate the use Cottonscope to measure fiber quality variation, 3) Determine the significance of within-plant yield variation, and 4) Determine the significance of within-plant quality variation. Small differences in micronaire are often indistinguishable, making breeding efforts difficult. With new instruments, selecting for the components of micronaire may increase selection efficiency and genetic gain compared to breeding for micronaire directly. In addition, these results show that yield and quality within genotypes are highly variable, and a significant amount of the variation is attributable to a bolls fruiting site. Substantial bias can be introduced if boll sampling does not consider fruiting position. The results show that plot sampling techniques can greatly influence fiber quality testing results and as a result the effectiveness of genetic selection. The Cottonscope is a very accurate and precise tool for measuring fiber fineness and maturity ratio and improving the interpretation of micronaire. Micronaire had strong correlation with fiber fineness data. Breeding for lower micronaire would be a useful strategy to improve fiber fineness in environments where low fiber maturity is not a problem.

A glasshouse study was conducted on the Louisiana State University campus in Baton Rouge to evaluate herbicide activity on Nealley's sprangletop. Herbicides were applied to Nealleys sprangletop plants in the one-two tiller stage with height of 20-30 cm. Nealley's sprangletop control, leaf number, height, tiller number, and fresh weight biomass were evaluated. Nealley's sprangletop treated with glyphosate, quizalofop, fenoxaprop, and clethodim was controlled 89 to 99%. A field study was conducted at the LSU AgCenter Rice Research Station (RRS) and a grower location (GL) to evaluate herbicide rates and timings for control of Nealley's sprangletop in drill-seeded rice. Herbicide treatments were cyhalofop at 271, 314, and 417 g ai ha-1 and fenoxaprop at 66, 86, and 122 g ai ha-1 applied pre- or post-flood, propanil at 3360 g ai ha-1 applied pre-flood, and propanil plus thiobencarb at 5040 g ai ha-1 applied pre-flood. Cyhalofop increased control of Nealley's sprangletop compared with control observed with propanil plus thiobencarb. Nealley's sprangletop treated with fenoxaprop at 86 or 122 g ha-1 pre-flood resulted in increased control of Nealley's sprangletop over propanil or propanil plus thiobencarb. Field studies were conducted at the RRS and a GL on drill-seeded rice to evaluate removal timings of Nealley's sprangletop and the impact on rice yield. Fenoxaprop was applied at 122 g ha-1 at 7, 14, 21, 28, 35, and 42 days after emergence (DAE). Rice from the 7 DAE removal yielded 1910 kg ha-1 more than the nontreated. Delaying the initial herbicide application from 7 to 42 DAE caused a rice yield loss of 1790 kg ha-1 with a net loss of $460 ha-1, or $13 ha-1 loss per day. Field studies were conducted at the RRS and a GL in drill-seeded rice to evaluate Nealley's sprangletop infestation densities in rice and the impact on rice yield. Analysis indicated significance for Nealley's sprangletop density on rice yield where the linear effects of density were significant (P < 0.0064). Based on economic evaluations, Nealley's sprangletop at densities of 5 to 10 plants m2 are sufficient threshold levels for treatment.

Proper nitrogen (N) management is essential to optimize crop production. This study was conducted to evaluate different N fertilizer management strategies to improve N use efficiency and yield in sugarcane production in Louisiana. This research was initiated in 2013 at the Sugar Research Station in St. Gabriel, LA and was arranged in a randomized complete block design with four replications consisting of different N rates (0, 45, 90, and 135 kg N ha-1) and sources (urea-46% N, ammonium nitrate [AN]-34% N, and urea-ammonium-nitrate solution [UAN]-32% N dribbled and knifed-in) as treatments. Sensor readings were taken from different N response trials to validate the sugarcane yield potential prediction and N response index (RI) models based on normalized difference vegetation index (NDVI). Soil nitrate (NO3-) and ammonium (NH4+) at 0-15 and 15-30 cm depths were also measured at different dates after N fertilization. At the grand growth stage, plots which were knifed-in with UAN showed a more even distribution of NO3- and NH4+ compared to urea- and AN-treated plots for both depths. Among the treatments, the highest sugarcane yield was achieved from plots treated with 90 kg N ha-1 as UAN knife-in and 135 kg N ha-1 as AN. Yield potential prediction models established in 2012 and 2015 could be used to estimate sugar and cane yield using NDVI readings collected at 21 (r2=0.30 and r2=0.51) and 60 (r2=0.41 and r2=0.52) days after N fertilization (DANF), respectively. Both RI and modified RI models demonstrated a better level of precision when RI was predicted at 60 DANF (r2=0.30) for both cane and sugar yield compared to 21 DANF (r2=0.15). The outcomes of this study demonstrated the effectivity of UAN knife-in as N source and the current N recommendation, but there were indications that application of higher N rate may further maximize yield. This study also revealed some limitations of the models used for predicting the components of remote sensor-based N recommendations for Louisiana sugarcane production. Apart from strengthening the yield and sensor readings database, areas of focus for future research include the use of different vegetation indices and reflectance readings from different wavebands.

Loss of phosphorus (P) from soil may degrade water quality. The problem exists where soil has been heavily fertilized with P, including use of poultry litter as fertilizer for pastures on the Coastal Plain. This research proposed that amending a P-enriched soil with a material that has a relatively high capacity to sorb P would decrease such loss in runoff or subsurface drainage. The P sorption behavior of two adsorbent materials, naturally occurring soil ironstone and bauxite refining residue (red mud), was examined in laboratory studies, with results guiding the design of a greenhouse experiment using these materials mixed with P-enriched Ruston soil (fine-loamy, siliceous, semiactive, thermic Typic Paleudults) used to grow common bermudagrass (Cynodon dactylon). The Langmuir P sorption maxima of ironstone and red mud were about five-times greater than that of Ruston but sorption was affected by kinetics. Miscible displacement studies confirmed reduced P mobility in these materials compared to Ruston, and reduced mobility of P in Ruston when mixed at a 9 to 1 ratio, with red mud being more effective than ironstone. The greenhouse experiment compared Ruston mixed with the P adsorbents at 0, 5, 10 and 20% with 4 replicates in a completely randomized design. Bermudagrass yield was greatest in the red mud treatments but variability among replicates led to no significant treatment effect in mass of P leached. Decreased infiltration with red mud led to ponding lasting longer than one day, which therefore represented potential loss of desorbed soil P in runoff. However, under simulated rainfall later in the experiment losses of P were numerically least from the red mud treatments, suggesting that the shorter-term results reflected transient behavior and that red mud may have potential as a soil amendment to reduce P losses.

A field study was conducted in 2015 and 2016 at the H. Rouse Caffey Rice Research Station (RRS) to evaluate mixture interactions of quizalofop and ALS-inhibiting herbicides. Quizalofop was applied at 120 g ai ha-1. Mixture herbicides included penoxsulam at 40 g ha-1, penoxsulam plus triclopyr at 352 g ha-1, halosulfuron at 53 g ha-1, bispyribac at 34 g ha-1, orthosulfamuron plus halosulfuron at 94 g ha-1, orthosulfamuron plus quinclorac at 491 g ha-1, imazosulfuron at 211 g ha-1, and bensulfuron at 43 g ha-1. All ALS herbicides mixed with quizalofop indicated antagonistic responses for weedy rice or barnyardgrass control at either 14 or 28 days after treatment (DAT). At 28 DAT, quizalofop mixed with penoxsulam or bispyribac controlled barnyardgrass 33 to 38%, compared with an expected control of 91 to 92%. A study was conducted at the RRS to evaluate interactions of quizalofop applied in mixtures with contact herbicides. Quizalofop was applied at 120 g ha-1. Mixture herbicides included carfentrazone at 18 g ha-1, propanil at 3360 g ha-1, saflufenacil at 25 g ha-1, or thiobencarb at 3360 g ha-1. Propanil severely antagonized quizalofop activity on weedy rice and barnyardgrass at all evaluations. At 28 DAT, barnyardgrass treated with quizalofop mixed propanil indicated an observed control of 16%, compared with an expected control of 93%. A study was conducted at the RRS evaluating sequential applications of quizalofop at 120 g ha-1 and propanil plus thiobencarb at 672 g ai ha-1. A prepackage mixture of propanil plus thiobencarb was applied for each timing treatment when ACCase-R rice was at the 2- to 3-leaf growth stage (day 0). Application timing treatments consisted of quizalofop applied at 7, 3, and 1 days before (DBPT) and after (DAPT) the propanil plus thiobencarb application at day 0. Additionally, quizalofop was applied alone and in a mixture with propanil plus thiobencarb at day 0. Quizalofop activity was reduced on weedy rice and barnyardgrass when applied at 1 and 3 DAPT or mixed with propanil plus thiobencarb at day 0; however, quizalofop activity was not reduced when applied before propanil plus thiobencarb.