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Imidacloprid (IDP) is an active ingredient of the Admire brand pesticide used to control the vector (Asian citrus psyllid) that transmits the causative organism Candidatus Liberibacter asiaticus (CLas) for citrus greening or huanglongbing disease. Imidacloprid products are applied via soil drench where citrus roots are mostly concentrated which is between 0 and 60 cm depth. These soil depths exhibit different characteristics that may affect IDP leaching beyond the rooting zone. Representative soil samples were collected from Entisols and Ultisols, which are the dominant soil orders under citrus production in central Florida, at 15 cm increments up to 60 cm to estimate and understand the batch sorption, kinetics, equilibria, and degradation of IDP. Results showed that the equilibrium time for IDP at 0-15 cm depth (10 hours) was 2 times faster than at 15-60 cm (20 hours) for the Entisol. Nevertheless, all depths reached equilibrium within 24 hours for the Entisol. The 0-30 cm depth adsorbed 2 times more IDP than the 30-60 cm depth for both soils. Nevertheless, the adsorption coefficient was approximately ≤ 1 mL g-1 for both soils. The half-life of IDP in both soils ranged from 10 to 17 days. The Entisol showed higher adsorption than the Ultisol at both depths, probably due to relatively lower organic carbon (OC) content in the Ultisol compared to the Entisol. Thus, the Ultisol showed high IDP leaching vulnerability compared to the Entisol. Movement of IDP is affected by the amount of OC in the citrus critical zone.

Citrus greening (huanglonbing (HLB)) disease has drastically reduced citrus fruit production in Florida over the last two decades. Scientists have developed sustainable nutrient management practices to live with the disease and continue fruit production. Best pesticide management practices have been devised to reduce the spread of HLB by Asian citrus psyllid (ACP). However, soil application of excessive nutrients and the use of soil drench application of pesticides to huanglongbing-infected citrus groves have been a serious environmental concern since the recent development of resistance to some pesticides. It is important to understand the consequences of applying pesticides and nutrients beyond the recommended application rates with an inappropriate method for citrus growth and development. Alternatively, foliar sprays of some nutrients proved effective to meet plants’ requirements, and foliar sprays of effective insecticide products could provide an adequate mode of action for group rotation to minimize insecticide resistance by ACP and other pests. Sustainability in citrus production systems should include best management practices that improve pesticide and nutrient efficiency by including the total maximum daily load exiting the grove to reduce pesticide and nutrient exports into waterbodies.

Abstract Manganese deficiencies have been observed in shallow soils with high water tables and in well‐drained sandy soils of Florida. This study investigated Mn leaf uptake in citrus trees on a Florida sandy soil through modified Mn fertilization methods and rates. Tree rows were supplied with three N rates and Mn at single and double the recommended rates (recommended rate: 10.08 kg ha−1) using foliar and soil application methods. The double foliar application rate increased leaf Mn by 20% over the single application rate. The leaf concentration of Mn was within the optimum concentration, according to the IFAS guidelines for optimal leaf Mn concentration, for summer 2018 and winter 2019. The Mn sorption coefficient was 22 times higher at the 0‐ to 15‐cm depth compared with the 15‐ to 60‐cm soil depths. Thus, Mn would be retained in the top 0‐ to 15‐cm soil depth. An increase in the foliar application improved Mn concentration in leaves, whereas soil application limited Mn availability in the root zone for plant uptake.

Solute fate in soil-plant continuum could either be soil or leaf uptake or leaching beyond the rooting zone. An adsorption coefficient (KD) is an important chemical property to describe the interaction between the solute and soil, affecting the solute movement in soils from one point to another. Boron (B), manganese (Mn), and zinc (Zn) uptake are evident in the leaves as a constituent of photosynthesis and other plant body-building mechanisms for growth and development. This study investigates the availability of micronutrients (B, Mn, and Zn) to citrus trees through modified application methods and rates. Leaf samples were collected from experimental plots arranged in a randomized complete block design, with 4 micronutrient treatments: control, foliar ×1, foliar ×2, and soil ×1. Boron, Mn, and Zn rates were 1.12, 10.08, and 5.60 kg ha−1, respectively. Composite soil samples were randomly collected at 5 points, and a 1-point adsorption study was conducted in 4 soil depths at an increment of 15 cm from the soil surface. Adsorption coefficient (KD) for Mn and B was 22 and 3 times higher at 0–15 cm than at soil depth of 15–60 cm. The adsorption coefficient (KD) for Zn was 2.5 times greater at 0–15 cm than 15–30 cm soil depth, while there was little or no sorption at 30–60 cm. Leaf Mn and Zn concentrations showed that foliar spray was 2 times higher than the soil application method, while B showed that the soil application method was 2 times higher than foliar application method for 2 seasons sampling events. Thus, the behavior of B, Mn, and Zn in the soil via adsorption coefficient (KD) reflects the availability of B, Mn, and Zn in the citrus leaves.

Nitrogen and micronutrients have a key role in many citrus plant enzyme reactions. Although enough micronutrients may be present in the soil, deficiency can develop due to soil depletion or the formation of insoluble compounds. The objectives of this study were to (1) determine the adsorption, distribution, and availability of Zn in a sandy soil; (2) compare the effectiveness of foliar and soil application methods of Zn on Huanglongbing [HLB] affected trees; (3) compare foliar application rates of Zn for HLB-affected trees; (4) determine the effect of N rates on yield, soil inorganic N distribution patterns, and tree growth parameters. Tree rows were supplied with three N rates of 168, 224 and 280 kg·N·ha−1 and Zn at single and double recommended rates (recommended rate = 5.6 kg·Zn·ha−1) using foliar and soil application methods, in a split-plot experimental design. The results show that Zn concentration in the 0–15 cm soil depth was three times higher than the 30–45 and 45–60 cm soil depths during the study. An adsorption study revealed high Zn (KD = 6.5) sorption coefficients at 0–15 cm soil depth, while 30–45 and 45–60 cm depths showed little sorption. Leaf Zn concentration for foliar spray was two times higher than the soil application method. A nitrogen level of 224 kg N ha−1 improved canopy volume when compared to other N levels at the expense of reduced fruit weight. Foliar Zn application at 5.6 or 11.2 kg ha−1 and N rate at 224 kg ha−1 appear to be adequate for improving the performance of HLB-affected citrus trees.

Imidacloprid (IM) is used to control the Asian Citrus Psyllid (ACP) and citrus leafminer (CLM), which are related to the spread of huanglongbing (HLB or citrus greening) and citrus canker diseases, respectively. In Florida citrus, imidacloprid is mainly soil-drenched around the trees for proper root uptake and translocation into plant canopy to impact ACP and CLM. The objective of this study was to determine the effect of imidacloprid rate, and irrigate amount on concentration of imidacloprid in the soil following drench application to citrus trees in three age classes. The plots were established at the Southwest Florida Research and Education Center, Immokalee, using a randomized complete-block design for three age classes of trees: one-year-old trees (B1), three to five-year-old trees (B2), and eight-year-old trees (B3). The treatments were a combination of two rates each of imidacloprid (1D, 2D) and micro-sprinkling irrigation (1I, 2I). Imidacloprid and bromide (Br-) used as tracer were applied simultaneously. Soil moisture and concentrations of imidacloprid and Br were monitored using soil cores from hand held augers. Soil moisture content (θV) did not differ under two irrigation rates at any given observation day or depth, except following heavy rainfall events. Br- was lost from the observation depths (0-45 cm) about two weeks after soil-drench. Contrarily, imidacloprid persisted for a much longer time (4-8 weeks) at all soil depths, regardless of treatment combinations. The higher retardation of imidacloprid was related to the predominantly unsaturated conditions of the soil (which in turn reduced soil hydraulic conductivities by orders of magnitude), the imidacloprid sorption on soil organic matter, and the citrus root uptake. Findings of this study are important for citrus growers coping with the citrus greening and citrus canker diseases because they suggest that imidacloprid soil drenches can still be an effective control measure of ACP and CLM, and the potential for imidacloprid leaching to groundwater is minimal.

Imidacloprid (IMD) is a neonicotinoid pesticide soil-drenched to many crops to control piercing-sucking insects such as the Asian citrus psyllid (ACP). Neonicotinoids are persistent in the environment and transport analyses are helpful estimate leaching potential from soils that could result in groundwater pollution. The objective of this study was to analyze IMD breakthrough under saturated water flow in soil columns packed with three horizons (A, E, Bh) of Immokalee Fine Sand (IFS). Also, we used the dimensionless form of the convective-dispersive model (CD-Model) to compare the optimized transport parameters from each column experiment (retardation factor, R; fraction of instantaneous-to-total retardation, β; and mass transfer coefficient, ω) with the parameters obtained from sorption batch equilibria and sorption kinetics. The tracer (Cl-) breakthrough curves (BTCs) were symmetrical and properly described by the CD-Model. IMD BTCs from A, Bh, and multilayered [A+E+Bh] soil columns showed steep fronts and tailing that were well described by the one-site nonequilibrium (OSNE) model, which was an evidence of non-ideal transport due to IMD mass transfer into the soil organic matter. In general, IMD was weakly-sorbed in the A and Bh horizons (R values of 3.72 ± 0.04 and 3.08 ± 0.07, respectively), and almost no retardation was observed in the E horizon (R = 1.20 ± 0.02) due to its low organic matter content (0.3%). Using the HYDRUS-1D package, optimized parameters (R, β, ω) from the individual columns successfully simulated IMD transport in a multilayered column mimicking an IFS soil profile. These column studies and corresponding simulations agreed with previous findings from batch sorption equilibria and kinetics experiments, where IMD showed one-site kinetic mass transfer between soil surfaces and soil solution. Ideally, sandy soils should be maintained unsaturated by crop irrigation systems and rainfall monitoring during and after soil-drench application. The unsaturated soil will increase IMD retardation factors and residence time for plant uptake, lowering leaching potential from soil layers with low sorption capacity, such as the E horizon.

Soil organic carbon (OC) content is often estimated by determining organic matter (OM) content via mass loss on ignition (LOI) and assuming that there are 580 g OC [kg.sup.-1] OM. We utilized thermogravimetry (TG), oven-determined mass LOI, and the Walkley-Black (WB) wet oxidation method to evaluate the relationship between OC and OM contents of carbonatic and organic soils from Florida and Puerto Rico and Spodosols from Florida. These soils have contrasting components and formed under different ecological settings. The OC content of OM, based on TG-determined OM mass LOI (TG OM) and WB OC, was higher for Histosols and Spodosols than for carbonatic soils. Regression coefficients between WB OC and TG OM were high for all soils. The factor to convert OM to OC, based on TG OM and WB OC, was 0.56 [+ or -] 0.04 ([+ or -] 0.04 is the 95% confidence interval) ([R.sup.2] = 0.93) for carbonatic soils, 0.67 [+ or -] 0.06 ([R.sup.2] = 0.94) for Spodosols, and 0.69 [+ or -] 0.04 ([R.sup.2] = 0.99) for Histosols. Results show that accuracy in estimating OC from OM content may be improved if the conversion equation is developed from soils within limited compositional and/or biogeochemical ranges. As such, there is no universal conversion factor between OM and OC for all soils. Loss on ignition is not a reliable OM measure if there are mass losses below 200[degrees]C that are mistakenly attributed to OM combustion, as in the case of reversible dehydration for Histosols of this study. However, TG enables detection of and accounting for such mass losses. Isothermal TG also confirmed that reversible mass loss between 105 and 200[degrees]C was energy--rather than time dependent. Abbreviations: CI, confidence interval; LOI, Loss on ignition; OC, Organic carbon; OM, Organic matter; PR, Puerto Rico; TG, Thermogravimetry; TOC, Total organic carbon; WB, Walkley and Black.

Sorbent-sorbate interactions heavily retard the movement of P during water flow in most soils. The effect of sou/solution rado on sorption [k.sub.i]netics and movement of P during unsteady unsaturated water flow were investigated. A series of batch experiments with soil/ solution ratios ranging from 0.1 to 6.4 Mg [m.sup.-3] were conducted to obtain sorption rate coefficients. Aqueous P solutions (100-800 g [m.sup.-3]) were applied at two constant fluxes (1.4 x [10.sup.-6] and 6.9 x [10.sup.-6]m [s.sup.-1]) to columns of an air-dry spodic soil. The experimental data were simulated with a parallel two-site nonlinear, nonequilibrium transport model during unsteady, unsaturated water flow. Phosphorous sorption followed Freundlich-type reversible [k.sub.i]netics with a very fast reaction occurring in Type I sites and a slow reaction occurring in Type R sites. The sorption reaction of P in batch experiments was satisfactorily described by the model but the rate coefficients varied with the soil/ solution ratio. Experimentally determined rate coeffecients described P movement in column experiments at an influx rate of 6.9 x [10.sup.-6]m [s.sup.-1], but not for the slower influx rate of 1.4 x [10.sup.-6]m [s.sup.-1], hence calibration of rate coefficients was necessary for describing P movement during the slower water influx. We developed a technique for determining rate coefficients under water saturated-unsaturated conditions that provides a way to validate P transport models during transient, unsaturated water flow.

Models help to describe and predict complex processes and scenarios that are difficult to understand or measure in environmental management systems. Thus, model simulations were performed (i) to calibrate HYDRUS-2D for water and solute movement as a possible decision support system for Candler and Immokalee fine sand using data from microsprinkler and drip irrigation methods, (ii) to validate the performance of HYDRUS- 2D using field data of microsprinkler and drip irrigation methods, and (iii) to investigate Br-, NO3-, and water movement using annual or seasonal weather data and variable fertigation scenarios. The model showed reasonably good agreement between measured and simulated values for soil water content (R² = 0.87-1.00), Br (R² = 0.63--0.96), NO3--N (R² = 0.66-0.98), P (R² = 0.25-0.78), and K (R² = 0.44-0.99) movement. The model could be successfully used for scheduling irrigation and predicting nutrient leaching for both microsprinkler and drip irrigation systems on Florida's sandy soils. [ABSTRACT FROM AUTHOR]

United States Golf Association putting greens are susceptible to nitrogen (N) and phosphorus (P) leaching. Inorganic soil amendments are used to increase moisture and nutrient retention and may influence N and P leaching. This study was conducted to determine whether N and P leaching could be reduced using soil amendments and surfactant-modified soil amendments. Treatments included a control (sand), sand-peat, zeolite, calcined clay, hexadecyltrimethylammonium-zeolite, and hexadecyltrimethylammonium-calcined clay. Lysimeters were filled with a 30-cm rootzone layer of sand-peat (85:15 by volume), below which a 5-cm treatment layer of amendments was placed. A solution of NO3-N, NH4-N, and orthophosphate-P (2300, 2480, and 4400 μg mL-1, respectively) was injected at the top of each lysimeter, and leachate was collected using an autocollector set to collect a 10-mL sample every min until four pore volumes were collected. Uncoated amendments, sand, and peat had no influence on NO3-N retention, whereas hexadecyltrimethylammonium-coated amendments reduced NO3-N leaching to below detectable limits. Both coated and uncoated amendments reduced NH4-N leaching, with zeolite reducing NH4-N leached to near zero regardless of hexadecyltrimethylammonium coating. Pure sand resulted in a 13% reduction of applied orthophosphate-P leaching, whereas peat contributed to orthophosphate-P leaching. Surfactant-modified amendments reduced orthophosphate-P leaching by as much as 97%. Surfactant-modified soil amendments can reduce NO3-N, NH4-N, and orthophosphate-P leaching and, thus, may be a viable option for removing leached N and P before they enter surface or ground waters. [ABSTRACT FROM AUTHOR]

The article presents a study on the impact tomato packinghouse wastewater compositions on the Spodosol leaching of phosphorus (P) and relative cations, such as calcium (Ca), magnesium (Mg), and potassium (K). It notes the use of polyvinyl chloride soils columns in the experimentation process and states the sequential leaching events conducted through wastewater irrigation. It indicates that wastewater-treated columns were greater in leachate concentrations of Na, Ca, Mg, and K than in the control treatment. It suggests the possibility of tomato packinghouse wastewater to be beneficial in land application in Spodosols in Florida without significant P and cation leaching.

The article discusses the use of mixed solvent systems to measure sorption isotherms of strongly hydrophobic organic chemicals (SHOCs), thereby avoiding the overestimation of the normalized sorption coefficient that sometimes results from adsorption of SHOCs on container walls. The sorption coefficient and percent recovery of anthracene, dichlorodiphenyltrichloroethane (DDT), and dieldrin during sorption on centrifuge tubes made of polytetrafluoroethylene (PTFE), polycarbonate (PC), polypropylene copolymer (PPCO), and glass high pressure liquid chromatography vials were obtained in volume ratio-varied methanol-water mixtures. Data analysis finds that sorption on container walls is a source of error that may be one cause of the large variability in literature on SHOCs.