Gilbert C. Sigua

Watershed scale assessment of nitrogen and phosphorus loadings in the Indian River Lagoon basin, Florida

There is a growing evidence that the ecological and biological integrity of the lagoon has declined during the last 50 years, probably due to the decline in water quality. Establishment of a watershed scale seagrass-based nutrient load assessment is the major aim of water quality management in the Indian River Lagoon (IRL). Best estimate loadings incorporate wet and dry deposition, surface water, groundwater, sediment nutrient flux, and point source effluent discharge data. On the average, the IRL is receiving annual external loadings of 832, 645 and 94,476kg of total nitrogen (TN) and total phosphorus (TP), respectively, from stormwater discharges and agricultural runoff. The average internal cycling of TN and TP from sediment deposits in the IRL was about 42,640kg TN and 1050kg TPyr(-1). Indirect evidence suggests that atmospheric deposition has played a role in the ongoing nutrient enrichment in the IRL. The estimated total atmospheric deposition of TN and TP was about 32,940 and 824kgyr(-1), while groundwater contribution was about 84,920 and 24,275kgyr(-1), respectively, to the surface waters of the IRL. The estimated annual contribution of point effluent discharge was about 60,408kg TN and 7248kg TP. In total, the IRL basin is receiving an annual loading of about 1,053,553kg TN and 127,873kg TP. With these results, it is clear that the current rate of nutrient loadings is causing a shift in the primary producers of the IRL from macrophyte to phytoplankton- or algal-based system. The goal is to reverse that shift, to attain and maintain a macrophyte-based estuarine system in the IRL.

INFLUENCE OF RAINFALL INTENSITY AND CROP RESIDUE ON LEACHING OF ATRAZINE THROUGH INTACT NO-TILL SOIL CORES

Pesticide leaching may be affected by rainfall parameters and the amount and type of vegetation on the soil surface. This study was conducted to determine the effect of rainfall intensity and crop residue on the movement of [ring-14C]atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and bromide (Br) through no-till (NT) cores. Undisturbed soil cores (10 cm diameter by 8 cm depth) were taken from the surface horizon of a NT corn (Zea mays L.) field. The cores were surface treated with 1.3 kg ai ha−1 atrazine and 150 kg ha−1 of Br and subjected to simulated rainfall at 3, 6, 9, or 12 mm h−1. The amount of crop residue on the surface of another set of soil cores was adjusted to 0, 2000, 4000, and 8000 kg ha−1, then treated with atrazine and subjected to 9 mm h−1 of simulated rain. Overall, the transport of atrazine and Br were significantly (P < 0.01) affected by rainfall intensity. An average of 92% (Br) and 52% (atrazine) of the total amount applied was leached through the soil cores by 2 pore volumes (520 ml) of simulated rain applied at 12 mm h−1 compared with 61% for Br and 33% for atrazine at the 3-mm h−1 rate. Covering soil cores with 2000 or 8000 kg ha−1 of crop residue reduced atrazine leaching by 26 to 37%, respectively, compared with soil cores without crop residue. Soil cores covered with recently harvested vegetation reduced atrazine leaching by 39% compared with cores covered with aged crop residue.

Carbon mineralization in two ultisols amended with different sources and particle sizes of pyrolyzed biochar.

Biochar produced during pyrolysis has the potential to enhance soil fertility and reduce greenhouse gas emissions. The influence of biochar properties (e.g., particle size) on both short- and long-term carbon (C) mineralization of biochar remains unclear. There is minimal information on the potential effects of biochar particle sizes on their breakdowns by soil microorganism, so it is unknown if the particle size of biochar influences C mineralization rate and/or stability in soils. In order to evaluate the effect of different sources (BS) and particle sizes (BF) of biochar on C loss and/or stability in soils, an incubation study on C mineralization of different biochar sources and particle sizes was established using two soils (ST): Norfolk soil (fine loamy, kaolinitic, thermic, typic Kandiudults) and Coxville soil (fine loamy kaolinitic, thermic, Paleaquults). In separate incubation vessels, these soils were amended with one of two manure-based biochars (poultry litters, PL; swine solids, SS) or one of two lignocellulosic-based biochars (switchgrass, SG; pine chips, PC) which were processed into two particle sizes (dust, <0.42 mm; pellet, >2 mm). The amount of CO2 evolved varied significantly between soils (p≤0.0001); particle sizes (p≤0.0001) and the interactions of biochar source (p≤0.001) and forms of biochars (p≤0.0001) with soil types. Averaged across soils and sources of biochar, CO2-C evolved from dust-sized biochar (281 mg kg(-1)) was significantly higher than pellet-sized biochar (226 mg kg(-1)). Coxville soils with SS biochar produced the greatest average CO2-C of 428 mg kg(-1) and Norfolk soils with PC had the lowest CO2-C production (93 mg kg(-1)). Measured rates of carbon mineralization also varied with soils and sources of biochar (Norfolk: PL>SS>SG≥PC; Coxville: PC>SG>SS>PL). The average net CO2-C evolved from the Coxville soils (385 mg kg(-1)) was about threefold more than the CO2-C evolved from the Norfolk soils (123 mg kg(-1)). Our results suggest different particle sizes and sources of biochar as well as soil type influence biochar stability.

Genetic Diversity and Geographical Distribution of Indigenous Soybean-Nodulating Bradyrhizobia in the United States

ABSTRACT We investigated the relationship between the genetic diversity of indigenous soybean-nodulating bradyrhizobia and their geographical distribution in the United States using nine soil isolates from eight states. The bradyrhizobia were inoculated on three soybean Rj genotypes (non-Rj, Rj 2 Rj 3, and Rj 4). We analyzed their genetic diversity and community structure by means of restriction fragment length polymorphisms of PCR amplicons to target the 16S-23S rRNA gene internal transcribed spacer region, using 11 USDA Bradyrhizobium strains as reference strains. We also performed diversity analysis, multidimensional scaling analysis based on the Bray-Curtis index, and polar ordination analysis to describe the structure and geographical distribution of the soybean-nodulating bradyrhizobial community. The major clusters were Bradyrhizobium japonicum Bj123, in the northern United States, and Bradyrhizobium elkanii, in the middle to southern regions. Dominance of bradyrhizobia in a community was generally larger for the cluster belonging to B. elkanii than for the cluster belonging to B. japonicum. The indigenous American soybean-nodulating bradyrhizobial community structure was strongly correlated with latitude. Our results suggest that this community varies geographically.

Recycling biosolids and lake-dredged materials to pasture-based animal agriculture: alternative nutrient sources for forage productivity and sustainability. A review

Domestic sewage sludge or biosolids and lake-dredged materials are examples of materials that can be used to cut fertilizer costs in pasture-based animal agriculture. Sustainable biosolids and lake-dredged materials management is based upon controlling and influencing the quantity, quality and characteristics of these materials in such a way that negative impacts to the environment are avoided and beneficial uses are optimized. This article examines the following two key questions. Is the use of these materials in an agricultural setting harmless and sensible? Is the use of biosolids secure in all climates, in all soils and is it sustainable over the long term? Recycling biosolids and lake-dredged materials to pasture-based animal production is quite productive as alternative nutrient sources for forage production. Perennial grass can be a good choice for repeated applications of biosolids and lake-dredged materials. Although biosolids and lake-dredged materials supply some essential plant nutrients and provide soil property-enhancing organic matter, land-application programs still generate some concerns because of possible health and environmental risks involved. Repeated applications of biosolids and lake-dredged materials indicate no harmful effects on soil quality and forage quality. Beneficial uses of biosolids and lake-dredged materials are both economical and environmental. The concentrations of soil nitrogen and phosphorus following repeated application of biosolids were far below the contamination risk in the environment. The residual effect of biosolids over the long term can be especially significant in many forage-based pastures where only 50% of the million hectares of pastures are given inorganic nitrogen yearly. Long-term studies have demonstrated the favorable and beneficial effects of added lake-dredged materials on the early establishment of bahiagrass in sandy pasture fields. Often these materials can be obtained at little or no cost to the farmers or landowners. Lake-dredged materials can be used as soil amendments (lime and fertilizer) for early establishment of bahiagrass in beef cattle pastures. Bahiagrass in plots that were treated with biosolids and lake-dredge materials had significantly higher forage yield and crude protein content when compared with those bahiagrass in the control plots or untreated plants.

Assessing the efficacy of dredged materials from lake panasoffkee, florida: Implication to environment and agriculture part 1: Soil and environmental quality aspect

Background, Aims and ScopeDredged materials because of its variable but unique physical and chemical properties are often viewed by society and regulators as pollutants, but many have used these materials in coastal nourishment, land or wetland creation, construction materials, and for soil improvement as a soil amendment. Environmental impact assessment is an important pre-requisite to many dredging initiatives. The ability to reuse lake-dredge materials (LDM) for agricultural purposes is important because it reduces the need for offshore disposal and provides an alternative to disposal of the materials in landfills. Additional research on disposal options of dredged materials are much needed to supply information on criteria testing and evaluation of the physical and chemical impacts of dredged materials at a disposal site, as well as information on many other aspects of dredging and dredged material disposal. While preliminary efforts are underway to provide information to establish criteria for land disposal, testing procedures for possible land disposal of contaminated sediments are still in their developing stage. The objective of this study (Part 1) was to quantify the effect of applied LDM from Lake Panasoffkee (LP), Florida on soil physico-chemical properties (soil quality) at the disposal site. This series of two papers aims at providing assessment of the efficacy of lake-dredged materials from LP especially its implication to environment (soil quality, Pan 1) and agriculture (forage quality and pasture establishment, Part 2).MethodsThe experimental treatments that were evaluated consisted of different ratios of natural soil (NS) to LDM: LDMO (100% NS:0% LDM); LDM25 (75% NS:25% LDM); LDM50 (50% NS:50% LDM); LDM75 (25% NS:75% LDM); and LDM100 (0% NS:100% LDM). Field layout was based on the principle of a completely randomized block design with four replications. The Mehlich 1 method (0.05N HCl in 0.025N H2SO4) was used for chemical extraction of soil. Soil P and other exchangeable cations (Ca, Mg, K, Al, and Fe) were analyzed using an Inductively Coupled Plasma (ICP) Spectroscopy. The effects of dredged materials addition on soil quality and compaction were analyzed statistically following the PROC ANOVA procedures.Results and DiscussionSediments that were dredged from LP have high CaCO3 content (82%) and when these materials were incorporated into existing topsoil they would have the same favorable effects as liming the field. Thus, sediments with high CaCO3 may improve the physical and chemical conditions of subtropical sandy pastures. The heavy and trace metal contents of LDM were below the probable effect levels (PEL) and threshold effect levels (TEL). Average values for Pb, Zn, As, Cu, Hg, Se, Cd, and Ni of 5.2 ± 1.3, 7.0 ± 0.6,4.4 ± 0.1, 8.7 s= 1.2, 0.01 ± 0.02,0.02 ± 0.02,2.5 s 0.1, and 14.6 = 6.4 mg kg-1, respectively, were below the TEL and the PEL. TEL represents the concentrations of sediment-associated contaminants that are considered to cause significant hazards to aquatic organisms, while, PEL represents the lower limit of the range of the contaminant concentrations that are usually or always associated with adverse biological effects. As such, the agricultural or livestock industry could utilize these LDM to produce forages. LDM should be regarded as a bénéficiai resource, as a part of the ecological system. Addition of LDM had significant (p ≤ 0.001) effects on soil physico-chemical properties and soil quality. Compared with the control plots, the soils in plots amended with LDM exhibited: (1) lower degree of soil compaction; (2) an increase in soil pH, Ca, and Mg; (3) decrease in the levels of soil Mn, Cu, Fe, Zn, and Si; and (4) no significant change in the level of Na in the soil. Results have shown the favorable influence that LDM had on soil compaction. The treatment x year interaction effect was not significant, but the average soil compaction varied widely (p ≤ 0.001) with LDM application. In 2002 and 2003, soil compaction of plots was lowered significantly as a result of LDM additions. The least compacted soils in 2002 and 2003 were observed from plots with LDM75 with mean soil compaction of 300 × 103 and 350 × 103 Pa, respectively.ConclusionBeneficial uses of dredged materials from LP, Florida are both economical and environmental. Often these materials can be obtained at little or no cost to the farmers or landowners in south Florida. Environmentally, dredging of sediments that are rich in CaCO3 should restore the 19.4-sq km LP by removing natural sediments from the lake bottom to improve the fishery, water quality, and navigation of the lake. The bottom sediment materials from lakes, river, and navigational channels usually are composed of upland soil enriched with nutrients and organic matter. These materials should be regarded as a beneficial resource to be used productively and not to be discarded as spoil materials.Recommendation and OutlookLand application of LDM from LP may not only provide substantial benefits that will enhance the environment, community, and society in south Florida, but also in other parts of the world especially those areas having tropical and subtropical climate with forage-based beef cattle pastures. The heavy and trace metal contents of LDM from LP were below the PEL and TEL. As such, the agricultural or livestock industry could utilize these LDM to produce forages (Part 2 of this study). LDM should be regarded as a beneficial resource, as a part of the ecological system. Further studies are still needed to determine whether the environmental and ecological implications of LDM application are satisfied over the longer term.

Assessing the efficacy of dredged materials from lake panasoffkee, Florida: Implication to environment and agriculture

Background, Aims and ScopeCurrent dredged material disposal alternatives have several limitations. Options for dealing with dredged materials include leaving them alone, capping them with clean sediments, placing them in confined facilities, disposing of them at upland sites, treating them chemically, or using them for wetlands creation or other beneficial uses The ability to reuse lake-dredge materials (LDM) for agricultural purposes is important because it reduces the need for offshore disposal and provides an alternative to disposal of the materials in landfills. Often these materials can be obtained at little or no cost to the farmers or landowners. Thus, forage production offers an alternative to waste management since nutrients in the LDM are recycled into crops that are not directly consumed by humans. The objective of this study (Part 2) were to: (1) assess dredge materials from Lake Panasoffkee, Florida as a soil amendment to establish bahiagrass (BG) in a subtropical beef cattle pasture in Sumter County, Florida; and (2) determine the effect of LDM application on the crude protein (CP) and nutrient uptake of BG. This series of two papers aims at providing assessment of the efficacy of lake-dredged materials especially its implication to environment (soil quality, Part 1) and agriculture (forage quality and pasture establishment. Part 2).MethodsThe experimental treatments that were evaluated consisted of different ratios of natural soil (NS) to LDM: LDMO (100% NS:0% LDM); LDM25 (75% NS:25% LDM); LDM50 (50% NS:50% LDM); LDM75 (25% NS:75% LDM); and LDM100 (0% NS:100% LDM). Bahiagrass plots at its early establishment were cut to a 5-cm stubble height on Julian days 112 and harvested to the same stubble height on Julian days 238 and on Julian days 546 following the double-ring method. Field layout was based on the principle of a completely randomized block design with four replications. Plant samples harvested at 546 Julian days were ground to pass through a 1-mm mesh screen in a Wiley mill. Ground forage was analyzed for crude protein. Ground forage samples were also analyzed for tissue P, K, Ca, Mg, Mn, Cu, Fe, Al, and Mo concentrations using an ICP spectroscopy. The effects of dredged materials addition on forage yield and on crude protein and nutrient uptake that were taken at 546 Julian days were analyzed statistically following the PROC ANOVA procedures.Results and DiscussionPart 1 of this study demonstrated that the heavy and trace metal contents of LDM were below the probable effect levels and threshold effect levels. As such, the agricultural or livestock industry could utilize these LDM to produce forages. Results showed consistently and significantly (p ≤ 0.001) higher BG biomass production and CP from plots amended with LDM than those of BG planted on plots with 0% LDM. Forage yield of BG during its establishment increased linearly (Forage Yield = 1724.3 + 25.64*LDM; R2 = 0.83; p ≤ 0.0001) with increasing rates of LDM application. The CP of BG also varied significantly with varying levels of LDM applications. The tissues of BG with 100% LDM had the greatest CP content while the lowest CP content was from the control plots (LDMO). The CP of BG increased linearly with increasing rates of LDM application. The crude protein response to BG application can be described by a linear equation: Crude Protein = 10.38 + 0.052*LDM; R2 = 0.85 p ≤ 0.0001. Addition of LDM had increased the levels of Ca by about 1811 % when compared with the level of soil Ca among plots with no LDM application. Liming the field could have some direct and indirect effects on the chemical status of the soils. The physiological functions performed by Ca in plants are not clearly defined, but it has been suggested that Ca favors the formation of and increases the protein content of mitochondria.ConclusionsBeneficial uses of dredged materials from LP, Florida are both economical and environmental. Often these materials can be obtained at little or no cost to the farmers or landowners. Results showed that dredged materials can be used as soil amendments (lime and fertilizer) for early establishment of BG in beef cattle pastures. Environmentally, dredging of sediments that are rich in CaCO3 should restore the 19.4-sq km LP by removing natural sediments from the lake bottom to improve the fishery, water quality, and navigation of the lake. The nutritional uptake of BG grown in unfertile sandy soils of Sumter County was enhanced significantly (p≤0.001) by LDM addition. Uptake of TKN, TP, K, Ca, and Mg were remarkably increased as a result of LDM.Recommendation and OutlookLand application of LDM from LP may not only provide substantial benefits that will enhance the environment, community, and society in south Florida, but also in other parts of the world especially those areas with forage-based beef cattle pastures and similar climatic conditions. The heavy and trace metal contents of these materials were below the PEL and TEL (see Part 1). As such, the agricultural or livestock industry could utilize these LDM to produce forages. LDM should be regarded as a beneficial resource, as a part of the ecological system. Although our results have demonstrated the favorable and beneficial effects of added LDM on the early establishment of BG in pasture fields., further studies are still needed not only in pastures of south Florida, but also in other areas with subtropical or tropical climatic conditions to determine whether the environmental and ecological implications of LDM application are satisfied over the longer term.

Biochars multifunctional role as a novel technology in the agricultural, environmental, and industrial sectors.

The utilization of biochar as an amendment to improve soil health and the environment has been a catalyst for the recent global enthusiasm for advancing biochar production technology and its management (Atkinson et al., 2010; Verheijen et al., 2010). This rapid rise in understanding biochar technologies is a pro-active response to the anticipated stresses of meeting future global nutrition demands while also sustaining environmental quality. Hearty research efforts using biochar are focusing on improving soil health characteristics to obtain higher crop yields. Moreover, there is increasing realization that sustainable food security will be difficult to maintain considering future climatic shifts and the impact on agronomic and environmental systems. Employment of biochar as a specialized soil amendment provides a practical approach to address these anticipated problems in the agronomic and environmental sectors (Mukherjee and Lal, 2013; Zhang and Ok, 2014). Biochar is produced by thermal pyrolysis of organic feedstocks under a very low oxygen atmosphere (Laird, 2008) or through hydrothermal carbonization of wet organic material by high pressure and mild temperatures (Libra et al., 2011). The thermal and hydrothermal processes, respectively, results in a product referred to as biochar and hydrochar. Both of these materials are highly porous, carbon [C] rich solids that contain a myriad of organic structures as well as inorganic elements. Biochars have been characterized using C nuclear magnetic resonance spectroscopy as having a high proportion of highly-condensed aromatic graphene-like structures (Baldock and Smernik, 2002; Novak et al., 2009; Cao et al., 2011), which are known to increase soil C sequestration because of their resistance to microbial oxidation (Glaser et al., 2002; Sigua et al., 2014). The inorganic chemical composition of the ash material is an important soil fertility characteristic since the ash is comprised of plant macro (e.g., N, Ca, K, P, etc.) as well as micro-nutrients (e.g., Cu Zn, B, etc.; Spokas et al., 2012; Ippolito et al., 2015). Besides boosting soil fertility conditions, biochar application to soils can increase their nutrient retention (Laird and Rogovska, 2015), improve water storage (Kinney et al., 2012; Novak et al., 2012), bind with pollutants (Uchimiya et al., 2010; Sun et al., 2011; Ahmad et al., 2014; Mohan et al., 2014), and mitigate greenhouse gas emissions (GHG; Cayuela et al., 2014). These reports demonstrate that biochar can have multi-functional roles in the agricultural and environmental sectors. Meanwhile, other sectors (e.g., engineering, electronic and medical) have also conducted research to capitalize on the mechanical and electronic characteristics of biochars and char-like materials. Biochars have been investigated as a solid fuel source (Cao et al., 2007), building insulating material (Lin and Chang, 2008), and industrial sorbent (Liu et al., 2010) and as a novel carbon material (Titirici et al., 2007). Biochars have been used as a sorbent for toxins ingested by humans (Bond, 2002) and as composite material for advancing human embryonic stem cell differentiation (Chen et al., 2012). The above narrative illustrates that biochars have a variety of applications in many sectors. To further identify and present salient examples highlighting biochars utility, two oral sessions and one poster session entitled ‘‘Biochar Soil Amendments for Environmental and Agronomic Benefits‘‘ were held at the 20th World Congress of Soil Science in Jeju, Korea on June 8 to 13, 2014 (www. 20wcss.org). In both oral sessions, 22 world experts were brought together to discuss their research results concerning biochar production and characterization, their reactions in soils, and involvement with various pollutants. Under the same scientificumbrella, 169 poster presentations reported on the involvement of biochars in improving soil quality, sequestering GHG emissions from soils, and ameliorating contaminated soils and water. During both oral sessions, the size of the audience ranged between 250– 300 participants and a very large number of visitors that engaged in vibrant discussions with poster presenters. Based on the exuberance shown between conference attendees and biochar presenters, it was decided that a platform was needed to capture the knowledge presented and discussed during these sessions. Therefore, a special issue in Chemosphere was organized. The scientific themes of the special issue were selected to have a broad appeal to biochar stakeholders, industry, and academia in agriculture and the environmental sectors. Ergo, the special issue was entitled ‘‘Biochars multifunctional role as a novel technology in the agricultural, environmental, and industrial sectors”.

Distribution and transport of atrazine as influenced by surface cultivation, earthworm population and rainfall pattern

Abstract Several laboratory studies were conducted to evaluate the effects of soil surface cultivation, earthworm ( Allolobophora caliginosa L) population, and rainfall pattern on 14C-atrazine (2-chloro-4-ethylamino-6-isopropylanunos-triazine) leaching through intact soil cores. Soil cores (16 cm dia x 20 cm deep) were collected from a seven year no-till (NT) corn field. Earthworms (0, 4, or 8 core−1) were introduced into the cores. Half of the cores were cultivated (2.5 cm depth) and the rest of the cores were left uncultivated prior to 14C-atrazine treatment (2.74 mg core−1). Cores were subjected to a rainfall pattern in which a low intensity rain (16 mm of rain in 2.5 h) was followed 48 h later by a high intensity rain (27 mm of rain in 1.5 h). The saturated hydraulic conductivities (Ksat) of cores with 0, 4, and 8 worms core−1 were 0.8, 3.4, and 5.3 cm h−1, respectively. Increasing the number of earthworms in each core from 0 to 8 worms, increases the amount of atrazine (% of applied) leached through untitled cores from 8.5 to 13.5% and for tilled cores from 1.0 to 5.0%. Much more atrazine was leached through untitled soil cores than tilled cores at both low and high rainfall intensities. The results of thus study suggest that herbicide transport is dependent on a combination of rainfall parameters, soil macroporosity, and disruptive surface cultivation.

Biochars impact on water infiltration and water quality through a compacted subsoil layer

Soils in the SE USA Coastal Plain region frequently have a compacted subsoil layer (E horizon), which is a barrier for water infiltration. Four different biochars were evaluated to increase water infiltration through a compacted horizon from a Norfolk soil (fine-loamy, kaolinitic, thermic, Typic Kandiudult). In addition, we also evaluated biochars effect on water quality. Biochars were produced by pyrolysis at 500 °C from pine chips (Pinus taeda), poultry litter (Gallus domesticus) feedstocks, and as blends (50:50 and 80:20) of pine chip:poultry litter. Prior to pyrolysis, the feedstocks were pelletized and sieved to >2-mm pellets. Each biochar was mixed with the subsoil at 20 g/kg (w/w) and the mixture was placed in columns. The columns were leached four times with Milli-Q water over 128 d of incubation. Except for the biochar produced from poultry litter, all other applied biochars resulted in significant water infiltration increases (0.157-0.219 mL min(-1); p<0.05) compared to the control (0.095 mL min(-1)). However, water infiltration in each treatment were influenced by additional water leaching. Leachates were enriched in PO4, SO4, Cl, Na, and K after addition of poultry litter biochar, however, their concentrations declined in pine chip blended biochar treatments and after multiple leaching. Adding biochars (except 100% poultry litter biochar) to a compacted subsoil layer can initially improve water infiltration, but, additional leaching revealed that the effect remained only for the 50:50 pine chip:poultry litter blended biochar while it declined in other biochar treatments.