Volcanic ash-derived soils are naturally deficient in the essential micronutrient B, but they also have maximum adsorption capacities (b(B)) that are as much as 40 times greater than in nonvolcanic soils, further exacerbating B availability. Because short-range-order (SRO) aluminosilicates (allophane and imogolite) and iron (Fe) oxyhydroxides are the main clay-sized minerals in these soils, we hypothesized that their relative abundances would explain variations in boron sorption capacity (b(B)). We characterized 23 volcanic ash-derived soils (Andisols and non-Andisols) from the Pacific coastal plain of Guatemala by X-ray diffraction, oxalate and pyrophosphate extractions, and thermal analysis, with four selected soils further examined by Mossbauer spectroscopy (MBS). Only soils with andic character (high SRO Si-Al content) contained considerable amounts of imogolite, with allophane in the clay fraction. Overall, soil SRO Al-Si phases were strongly correlated with clay B adsorption capacity (R = 0.65, p < 0.001) and clay specific surface area (R = 0.88, p < 0.001) suggesting that SRO Al-Si phases are the dominate influence on B behavior in these soils. Fe mineral composition was dominated (39%-71% of total Fe) by SRO Fe(III) oxyhydroxides (nanogoethite and ferrihydrite) of various crystallinities. In low allophane soils, SRO Fe phase abundance correlated with b(B) as did the abundance of low crystallinity kaolinite phases, suggesting these phases are important when SRO Si-Al content is low. Any efforts to predict B behavior or plan soil fertility treatments in volcanic-influenced soils needs to consider the impact of SRO phases.

Core Ideas Soil B availability in volcanic soils is governed by SRO minerals. Analyzing whole‐soil reactivity based on mineral surface abundance is proposed. Volcanic soils adsorb as much as 18‐fold higher than non‐volcanic soils. The reversibility of adsorption reactions decreases as andic character increases. pH in NaF can be used to reflect field B availability and application rates. Many crops in volcanic regions exhibit symptoms of B deficiency but do not respond to B fertilizer rates that solve deficiency problems in non–volcanic‐influenced soils. The US recommended rates are routinely adopted in these regions without accounting for differences in soil B dynamics. Because of the paucity of investigations and the resulting lack of understanding of B adsorption/desorption dynamics in volcanic ash–derived soils over the past 40 yr, it would be incorrect to extrapolate the few data available to all volcanic ash–derived soils because they have not been analyzed as a function of andic character. This paper aims to create an understanding of what soil properties govern B availability in volcanic‐influenced soils and to establish if there are low‐cost testing methods that can help estimate appropriate field B application rates in these soils. Boron adsorption/desorption isotherms were constructed for a group of volcanic ash–derived and non‐volcanic ash–derived soils, and the derived parameters were compared with various standard soil tests. Our results show that soil B availability in volcanic‐influenced soils is governed mainly by strong and stable B complexation with short‐range‐order (SRO) minerals. Boron adsorption maxima exhibit a wide variability not directly correlated with clay content but rather with reactivity quantified by SRO mineral and organic matter contents. Organic matter is not a significant variable explaining specific surface area for the overall group of soils, but it becomes significant for soils containing <200 g clay kg ‐1 , suggesting that a new approach to analyzing whole‐soil reactivity based on mineral surface abundance is needed. The maximum adsorption capacities of volcanic‐influenced soils can be as much as 18‐fold higher than for non‐volcanic soils, with the reversibility of adsorption reactions decreasing as andic character increases. These findings explain why standard B fertilizer rates fail to solve deficiency problems in volcanic‐influenced soils. Because pH in NaF is strongly related with acid‐oxalate Al (SRO minerals) and B desorption index, this low‐cost test can potentially be used as a measure of soil andic character to better reflect B availability and corresponding field application rates.

Soil Science Society of America JournalVolume 79, Issue 4 p. 1265-1265 Book Review Soils of South Africa: Their distribution, properties, classification, genesis, use and environmental significance Malcolm Sumner, Corresponding Author Malcolm Sumner Regents' Professor of Environmental Soil Science Emeritus malcolm296@gmail.com University of GeorgiaCorresponding author (malcolm296@gmail.com)Search for more papers by this author Malcolm Sumner, Corresponding Author Malcolm Sumner Regents' Professor of Environmental Soil Science Emeritus malcolm296@gmail.com University of GeorgiaCorresponding author (malcolm296@gmail.com)Search for more papers by this author First published: 24 July 2015 https://doi.org/10.2136/sssaj2015.0002br All rights reserved. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume79, Issue4July-August 2015Pages 1265-1265 RelatedInformation

In many parts of the world, crop root growth into subsoils is limited by physical (pans) and chemical barriers (toxic levels of Al and/or low levels of Ca). Plow and hard pans are usually either out of the reach of mechanical cultivation implements or require large amounts of energy for their disruption. Because lime does not readily move down the soil profile, its ameliorative effect is confined to the topsoil. On the other hand, gypsum (CaSO4.2H2O) readily moves down the profile where it supplies elevated levels of soluble Ca and precipitates Al. In addition, together with tap-rooted crops, it reduces the penetration resistance of subsoil pans allowing roots of other crops to proliferate in the subsoil. As a result, roots can access the subsoil where adequate quantities of water become available which were previously out of their reach. This additional water results in increased yields, particularly during drought periods. Many examples of the success of gypsum in overcoming subsoil physical and chemical limitations resulting in improved growth and yield of alfalfa (Medicago sativa), bermudagrass and fescue pastures (Cynodon dactylon, and Festuca arundinacea) and turf (Zoysia spp.), cotton (Gossypium hirsutum), maize (Zea mays), sorghum (Sorghum bicolor), and soybean (Glycine max) are presented.

Soil testing and plant analysis have been used as diagnostic tools for assessing fertilizer needs of crops for more than 50 years. During that time, considerable progress has been made in developing a plethora of improved extraction procedures and analytical techniques, forming a considerable legacy on which to build in the future. However, as laboratories grew and methods became entrenched, a reluctance to change methodologies has caused a certain degree of stagnation and in many cases has resulted in poor prognostic precision. Examples in the realm of soil testing are presented to show what might be gained by implementing improved technology that measures parameters that are the primary yield-determining factors. In addition, attention is focused on precision agriculture, where an urgent need exists to develop real-time assays of nutrient levels in the soil and plants so that the appropriate rates and types of fertilizer can be applied to increase yield uniformity within a field. With the increased disposal of organic residues on land, nutrient management plans for farms are now required. Because of the associated regulations, laboratories will have to introduce protocols for analyzing soil, tissue, and water appropriate to the purpose at hand accompanied by stringent quality assurance/quality control (QA/QC) systems to meet the legal requirements. No doubt, within a short time these constraints will be applied to normal crop land being fertilized with inorganic fertilizers as the green lobby grows and applies more pressure for a cleaner environment. The implications of these changes for the future is assessed.

Coal combustion in traditional powder-fed boilers produces two types of residues: (1) fly ash, which is a fine fraction dispersed in the flue gas and (2) bottom ash collected in the boiler. Fly ash is separated from flue gas by electrostatic precipitators or a variety of mechanical methods. Large emissions of sulfur dioxide (SO 2 ) from coal combustion are one of the major atmospheric pollutants. To minimize these emissions, fluidized bed combustion (FBC) and wet scrubbing technologies are used. The effect of fly ash application on soil water content depends on fly ash rate and soil texture. In contrast to agricultural land, potting mixtures and artificial soils create a market for fly ash that can be used to improve their texture and water-holding capacity. Because fly ash contains almost all elements and their concentrations depend on coal source, periodic monitoring of the chemical composition should be undertaken to ensure safe utilization. Gypsum is applied to soils to supply S and Ca for crops, ameliorate subsoil acidity, and improve soil physical condition and is recognized as a valuable soil amendment, being used on a commercial scale in many countries.

Major impediments to the land application of coal combustion byproducts (fly ash) for crop fertilization have been the presence of heavy metals and their relatively low and imbalanced essential nutrient concentration. Although nutrient deficiencies, in particular N, P, and K, may be readily augmented by adding organic wastes such as sewage sludge and animal manure, the indiscriminate application of mixtures to crops can cause excessive soil alkalinity, imbalanced nutrition (P, Mg), phytotoxicities (B, Mn, ammonia, nitrite), and unspecified contamination of the food chain by elements such as As. In this study, nutrient availability data and linear programming (LP) were used to solve these problems by formulating fly ash-biosolid triple mixtures which complied with both plant and soil fertilization requirements, and met existing U.S.A. environmental regulations for total As application in sewage sludge (EPA-503). Thirteen different fly ash samples were LP-formulated with sewage sludge, poultry manure, CaCO3, and KCl to yield 13 unique mixtures, which were then evaluated in greenhouse pot experiments. Results indicated that normal growth and balanced nutrition of sorghum (Sorghumbicolor L.) and soybean (Glycine max (L.) Merr.) crops were achieved in all mixtures, comparable to a balanced fertilizer reference treatment, and significantly better than the untreated control. Phytotoxic levels of B, NH3, NO2-, overliming problems, and excessive As levels which were previously encountered from indiscriminate use of these waste materials, were all well controlled by LP-formulated mixtures. Most fly ash quantities in mixtures were limited by either available B (< 4 kg ha-1) or total As (< 2 kg ha-1) restrictions during formulation, while the most alkaline fly ash was limited by its high calcium carbonate equivalence (CCE = 53.9%). These results confirmed that fly ash land application should not be at arbitrary fixed rates, but should be variable, depending on the soil, crop, and particularly the fly ash chemistry.

This study examined the effect of biosolids-borne nickel (Ni) and zinc (Zn) on nitrification process in two soils (Ultisols of the Cecil and Tifton series). Biosolids from Athens, GA, were spiked singly with increasing amounts of Ni or Zn chloride and then mixed with the soils at a weight ratio of 98.5:1.5 (soil: biosolid). The concentration of the spiked metals in the soil-biosolid mixtures ranged from 0 to 220 mg Ni and 0 to 1500 mg Zn kg(-1). The mixtures were repeatedly leached with water to observe changes in net nitrification and metal release into solution over time. Leached Zn concentrations that caused partial nitrification inhibition (reduction of net nitrification rates from 75% to 50% of control) were 5 to 19 mg kg(-1) and 6.6 to 10.5 mg kg(-1) in the Cecil and Tifton soil, respectively. Nitrification inhibition was manifested not only as net reduction in rates, but also as delay in the process. The prolonged recovery of inhibition caused lag phases of nitrification (10 and 20 days in the Cecil and the Tifton soil, respectively). In the Cecil soil the nitrification delays began when the leached Zn concentration reached 8.1 mg kg(-1) soil. The effect of Zn in the treatments with the least amount of Zn that caused full inhibition needed also time to be complete. It took 20 to 30 days (longer in the Cecil soil) until no NO3- appeared in leachate, after the small, but still detectable amounts of NO3-, which were present in the previous leachings. Inhibited nitrification was always associated with a reduced release of metals. This became evident after the easily soluble fraction of spiked metals was leached out. Therefore, it was a good bioindicator of Zn loading in biosolid treated soils. Excessive Zn was an inhibitor not only of nitrification, but also of its own release into the soil solution. Therefore, low concentrations of easily soluble Zn might well reflect impaired microbiological activity in the biosolid treated soils; they do not necessarily indicate lack of environmental hazard. Consequently, a low concentration of heavy metals in the solution of biosolid-amended soils is not always ecologically safe enough and, in that case, it would be effective to take soil microbial activity into consideration.

The thresholds for heavy metal loading of soils that do not impair microbially mediated processes need to be determined. This study assessed the limits for Zn in relation to the inhibition of nitrification. Different Zn concentrations in soil were achieved by spiking with ZnCl2 or from the long-term application of biosolids. Potentially available Zn was evaluated by fractionation using sequential extractions with water, 0.05 M CaCl2, and 0.11 M CH3COOH solutions at a soil:liquid ratio 1:40. pH (0.01 M CaCl2) and electrical conductivity were measured in all treatments. It was not possible to obtain very clear cutoffs of Zn concentrations based on nitrification inhibition, which could apply to different soils. However, water-extractable Zn fraction was best related to nitrification inhibition limits when soils were considered together. Three approximate ranges of nitrification inhibition were identified: 0 to 0.125 mg Zn L-1 (no inhibition); 0.125to 0.5 mg Zn L-1 (partial inhibition); and over 0.5 mg Zn L-1 (complete inhibition). For the same Zn loading, the water-soluble fraction was much lower in biosolid-amended soils than in the spiked ones. Consequently, biosolid-amended soils were more resilient toward Zn contamination. Weakly bounded Zn was a more reliable index than stronger bound fractions to determine common thresholds with respect to nitrification inhibition in the soils studied. Therefore, we suggest maximum Zn loadings based on the amounts in the soil solution rather than on total inputs or total content.

The relationship between soil solution ionic strength (IS) and the surface or counter-in charge density (CICD) is well described by the double layer theory. However, the magnitude of the counter-ion charge may be affected by phenomena that are likely to occur in variable charge subsoils, and research to investigate the extent of indifferent ion sorption as a function of IS is certainly needed. The objective was to study adsorption and desorption of ions in batch and column experiments, and to propose a mechanism that describes best the experimental observations in subsoils from the southeastern USA. Results showed that the cation and anion of an electrolyte were simultaneously adsorbed in approximately equivalent amounts with no net release of other ions into the soil solution. Ions were adsorbed in the Stern and diffuse layers of oppositely charged colloids since the subsoil was treated with dilute solutions …

Prediction of plant nutrient supply from fly ash and biosolids (sewage sludge and poultry manure) may enhance their agricultural use as crop fertilizer. Two mild extraction methods (42‐d equilibration with ion‐exchange resins; 2‐d equilibration with pH 4.8 buffered nutrient solution) and analysis of nutrient data by the Diagnosis and Recommendation Integrated System (DRIS) were tested with 29 fly ash samples, four biosolids samples, and their mixtures. The resin method was useful for major nutrient (N, P, K, Ca, Mg, S) extraction from fly ashes and organic materials, particularly where mineralizable fractions of N and P under aerobic conditions are required. However, resins were inefficient in extracting P from high‐Fe sewage sludges because organic waste samples caused premature failure of semipermeable membranes and fouling of resins. Extraction of fly ash with dilute buffered nutrient solution was more successful because micronutrient recovery was improved, major nutrients were correlated to the resin method, both addition and removal of nutrients were recorded, DRIS analysis was possible, and equilibration was rapid (2 d). The overall nutrient supply from these extremely variable fly ashes was: (high micronutrient, low major nutrient supply). For biosolids, the major nutrients ranked: P > N ≈ Ca > S > Mg > K (sewage sludges), and N > Ca ≈ K > P > Mg > S (poultry manures). In mixtures of fly ash with 26% sewage sludge the order was: Ca > S > N > Mg > P > K, while in mixtures of fly ash and 13% poultry manure, the nutrients ranked: Ca > K ≈ N ≈ S > Mg > P. Optimal plant nutrition (especially N–P–K balancing) should be possible by mixing these three waste materials.

Acid variable charge subsoils exhibit a positive charge, which retards the passage of anions through the soil profile. The objective was to study the NO adsorption isotherms and the effect of changing the subsoil positive charge on NO and Cl retention, estimate NO and Cl retardation in different subsoils, and quantify relationships between transport and adsorption parameters. Subsoils from different subtropical and tropical areas were used in column experiments. Four lime treatments and four leaching solutions were used to create different anion exchange capacities (AECs) in subsoils. In the Cecil subsoil (Fine, kaolinitic, thermic Typic Kanhapludult), NOT isotherms were linear between 5 and 30 mmol NOT LT". When forced through the origin, an L-curve N07 isotherm was observed at native and low soil pH. The NOT adsorption was largely affected by the changes in both pH and concentration of the leaching …

Anthropogenic wastes are accumulating at ever increasing rates. As an alternative to stockpiling and landfilling, land application of wastes is considered in terms of benefits to agriculture while protecting the environment. Beneficial reuse of wastes such as municipal wastewater, sewage sludge, animal manures, composts, byproduct gypsum, food processing and paper and pulp wastes are discussed both in terms of their benefits to agriculture and requirements from the standpoint of analyses required for monitoring. Clearly, many of these wastes are highly beneficial to crop production as fertilizer substitutes and soil ameliorants.

In the previous chapter, the process of production was presented as a universal property of vegetation, which provides the organic energy transformations that operate the living part of the biosphere. The discussion not only described the physiological actions that lead to the production that humans or other animals can use but also describes the regional patterns of production and then, in the final section, applies this information to forest systems. This is a logical place to begin because forest systems dominate the earth, considering the gradient of the boreal, temperate and tropical forest, with variants such as the Mediterranean, Pacific coast coniferous, and other forest types that make up the world biomes. Grasslands, tundra, and deserts represent other biomes that are unforested and have lower rates of production because of environmental limitations.

Arsenic (As) is the biggest environment contaminant in most of the soils where fly ash is applied. Usually, it is not mobile and strongly adsorbed on to soil particles. However, in gypsum and phosphorus amended soils As may be much more mobile. A study in repacked columns was conducted to determine whether or not As becomes mobile when Ca(H2PO4)2and CaSO4are used as leaching solutions, and to compare the competitive interactions between PO4-AsO4and SO4-AsO4. Arsenic concentration in leachate was found to be approximately ten times greater when Ca(H2PO4)2was used to leach the columns as compared to CaSO4. A maximum concentration of 800 μg As L-1was found in the leachate in this case, which is much higher than the groundwater limit of 50 μg L-1for drinking water established by the United States Environmental Protection Agency. In fly ash, the portion of arsenate non-specifically adsorbed is believed to be much lower than that of specifically adsorbed. Sulfate anions were able to displace only non-specifically adsorbed arsenate. In this case the concentration of As in leachate was found to be within acceptable limits. On the other hand, phosphate can compete with arsenate for all available adsorption sites, non-specific and specific. Phosphate displacement of both forms of arsenates increases As mobility in both control and fly ash treatments.

Nutrient imbalances, both deficiencies and excesses, are one reason for the poor acceptance of waste materials as fertilizer substitutes. Two greenhouse experiments were established using 24 different fly ashes with sewage sludge and poultry manure to estimate nutrient availability and imbalances to maize (Zea mays L.), The maximum maize growth attained with fly ash amendment of 80 Mg ha(-1) was significantly less (50%) than a fertilized control treatment. The additional growth improvements obtained from mixtures with sewage sludge or poultry manure ranged from 30 to 49% and 30 to 71%, respectively, Organic materials applied alone achieved only 54 and 62% of the maximum potential, while growth on poultry manure mixtures was up to 94% of the best performing fertilized treatment, Results of foliage and soil analyses suggest that P and K were the main nutrient deficiencies, while B phytotoxicity and an imbalance in the K/Ca/Mg ratio also were likely causes of plant growth reduction. Fly ashes did not contribute significant P or K to correct soil and plant deficiencies, but more often exacerbated the imbalances by precipitation or adsorption of soil P. Sewage sludge mixed at 26% and poultry manure at 13% (DM) with fly ash had negligible effect on availability of phytotoxic fly ash B, but were good sources of P (both) and K (poultry manure). Good agreement between plant nutrition in pot experiments and previous laboratory extraction studies implies that chemical analysis, efficient formulation and optimized application rates may overcome nutrient limitations for use of wastes as fertilizer substitutes.

Nitrate adsorption in subsoil affects nitrate leaching, which in tum can affect water quality. A model to describe the adsorption of nitrate in acidic variable charge subsoils in Georgia and other tropical and subtropical areas is proposed. In the first step, a portion of the effective charge that vanishes as a result of the overlapping of oppositely charged diffuse layers on different colloids, termed "the mutually neutralized charge", σM. is established. The "newly developed charge", σ N, is developed during the second step, in response to ionic strength increase in subsoil solution. The reestablishment of these two components of the effective charge causes "salt adsorption". The last step is "ionic exchange" with the corresponding effective charge component σ EX. The separation of ''temporarily effective" (σM + σ N) from "permanently effective" (σ [subscript EX) portions of the effective charge is very crucial when displacement and transport of ions like N₃- are considered, in order to understand that these ions are only temporarily adsorbed and can be immediately leached out by rain.