Levels In Soil Solution Research Articles

PHOSPHATE SORPTION CHARACTERISTICS OF GANGES MEANDER FLOODPLAIN SOILS OF BANGLADESH

Three representative soils belonging to Amjhupi, Ishurdi and Sara series from the Ganges meander floodplain soils in Jessore district were collected to observe phosphate sorption characteristics and to evaluate the best fitted adsorption equation for the soils. The highest phosphate sorption was observed in Amjhupi series and the lowest was in Sara soil series. Differences in P sorption were significantly (p<0.05) influenced by clay content, CEC and pH of the soils. Free CaCO3, EC, OM and available P were found insignificant in affecting P adsorption. The Langmuir equation was best fitted to the equilibrium P sorption data and maximum R-square. Amjhupi soil series would require more P to be supplied to maintain a desired P level in soil solution than others.

Response of phosphorus sensitive plants to arsenate

Arsenate (As (V)) is a highly toxic species of arsenic (As) which is also an excellent phosphate analogue. Plant species that are adapted to phosphorus (P) impoverished soil display a negative response to elevated phosphate due to an inability to downregulate P acquisition. Despite widespread As contamination and shared transport systems for As (V) and P uptake, little to no information is available on the response of P-sensitive plants to As (V). The aim of the study was to investigate the response of P-sensitive plants to As (V). One high (Hakea prostrata R.BR) and one moderate (Banksia seminuda B.Rye) P-sensitive species and one vegetable plant species (Cucumis sativus L.) were grown in nutrient solution containing different As (V) concentrations. Based on EC50 data from nutrient culture, Hakea prostrata was the most sensitive species to As (V) followed by B. seminuda and C. sativus. Critical exogenous concentrations of As that reduced plant growth by 50 % (EC50) in H. prostrata, B. seminuda and C. sativus were respectively 0.64, 0.76 and 1.08 μM for shoot and 0.66, 0.51, 1.07 μM for root. Hakea prostrata had the highest translocation factor (ratio of As concentration in shoot to root) of 0.11, followed by B. seminuda (0.03), and C. sativus (0.01). Plant species with high and moderate P sensitivity were associated with high sensitivity to As (V) exposure and accumulation in shoots. The increased sensitivity has important implications in ecological risk assessment and selection of plant species for rehabilitation. The impacts of As(V) at low P levels in soil solution is needed to inform contaminated site assessment and rehabilitation.

The effects of low-dose biochar amendments on arsenic accumulation in rice (Oryza sativa L.)

The accumulation of arsenic (As) in rice is one of the food security-related concerns in As-contaminated areas all over the world. Biochar, a potential green and cost-efficient amendment material, affects As mobility/phytoavailability in soil and As accumulation in rice plants to some extent, which remains unclear. Thus, three different biochars derived from rice straw, corn stalks, and bamboo were used to investigate the impacts of biochar amendments on As mobility/phytoavailability in As-contaminated soil using pot and microcosm experiments. The results showed a limited reduction (by 12-16%) in As accumulation in rice grains under a low-dose (0.5%, w/w) biochar amendment, although the three biochars displayed different physicochemical properties. In addition, the biochar amendments did not significantly decrease the As levels in the straw and roots, potentially because of the small changes in As mobility/phytoavailability in amended soil relative to the control. However, As levels in soil solution in the biochar treatment groups increased substantially, by 2.8-6.6 times, with increasing biochar doses (0.5-5%, w/w) in microcosm-based anaerobic incubation experiments, particularly at higher doses (3-5%, w/w). These results could be attributed to the biochar-enhancing activity of As(V)-/Fe(III)-reducing bacteria at a high biochar application rate. Our results suggested that applying high biochar doses may increase the release of As into the soil, resulting in As accumulation in rice plants. Therefore, to mitigate the health risk of As in As-contaminated paddy soils, the remediation technologies from biochar methods should be subjected to more evaluation.

Toxicity of Chromium to Root Growth of Barley as Affected by Chromium Speciation and Soil Properties

Tri-and hexavalent chromium have different chemical properties, and their levels of toxicity to plants are different. However, there is no limit set by the soil environmental quality risk control standard for Cr(Ⅲ) or Cr(Ⅵ). Therefore, studying the ecological toxicity of Cr has important implications for protecting the environment. Based on the dynamics of the Cr(Ⅲ) and Cr(Ⅵ) levels in soil solution collected from eight soils, the toxicity thresholds of the two Cr forms to barley roots were investigated through model calculation and correlation analysis under different soil properties. The results showed that both Cr forms and the soil properties had significant effects on the root length of barley. The effective concentrations of Cr(Ⅲ) added to the soils that led to 10% inhibition (EC10), 50% inhibition (EC50), and no-observed-effect concentrations (NOEC) were significantly higher than those of Cr(Ⅵ). The EC50 of Cr(Ⅲ) ranged from 298.8 to 2014.1 mg·kg-1 (6.7-fold variation); the EC50 of Cr(Ⅵ) ranged from 8.0 to 126.6 mg·kg-1 (15.8-fold variation). Under the same soil conditions, the EC50 of Cr(Ⅲ) was 2.8 to 101.7 times higher than that of Cr(Ⅵ), suggesting the higher phytotoxicity of Cr(Ⅵ) than Cr(Ⅲ). Correlation analysis showed that the pH and soil organic matter were the main factors that influenced the Cr toxicity thresholds, as indicated by the root length of barley. The concentration of chromium in the soil solution was below the detection limit of the TAS-990 when Cr(Ⅲ) was applied at 1280 mg·kg-1 (or less) to soils, whereas for Cr(Ⅵ), the level was 40 mg·kg-1 (or less). Cr(Ⅲ) adsorption to the soil was significantly stronger than that of Cr(Ⅵ). The toxicity of Cr(Ⅵ) was significantly higher than that of Cr(Ⅲ), which was also influenced by soil properties.

ЗАКОНОМІРНОСТІ РОЗПОДІЛУ ВАЖКИХ МЕТАЛІВ НА ТЕРИТОРІЇ ВІЙСЬКОВОГО ПОЛІГОНУ "ОЛЕШКІВСЬКІ ПІСКИ"

The results of ecological-geochemical researches of soil cover of "Oleshkivski pisky" military training site, using maximum allowable concentration and classification of chemical elements with respect to hazard classes are presented. Analytical works to identify gross content and heavy metals movable forms in soils were defined by methods of atomic absorption and mass-spectometry with inductively coupled plasma (ICPMS) as well as by using gamma-ray activation analysis and X-ray fluorescence analysis. Analysis and interpretation of the coefficients of heavy metal components concentration were conducted based on landscape and geochemical fundamentals. The regular network of the protoselection points was developed. This network is built taking into account landscape structure of the territory, and provides control over landscape and geochemical currents and barriers. The average index of soil cover pollution of the polygon was calculated taking into account different toxicity of the elements. This index reaches its maximum in the region of firing positions and military polygon. The average Zc index of the upper soil level is 32, which corresponds to the dangerous level of soil pollution. The research revealed the content of moveable forms of heavy metals in soil cover of the polygon in order to identify toxic and tolerant levels of heavy metals concentration and reserve sources of elements in soils, which can maintain optimal concentration level in soil solution. It was defined that content of heavy metals in three movable forms are represented in the following geochemical units, mg/kg: in acid soluble form – Mn > Zn > Pb > Cu > V > Ni > Co > Cd; in exchangeable form – Mn > Zn > Pb > V > Co = Ni > Cu > Cd; in water soluble form – Mn > Zn > Pb = V > Co > Ni > Cd > Cu. The article presents research results on accumulation intensity and the nature of distribution of gross and mobile heavy metals forms in soil and on their migration in the soil profile. The dominant technogenic geochemical unit was extracted: Cd > Hg > Pb > Cu > Zn > Ni > V > Co > Mn. Landscapes with maximum polyelement contamination have been identified.

Impacts of biochar and silicate fertilizer on arsenic accumulation in rice (Oryza sativa L.).

Human exposure to arsenic (As) through rice consumption is a global food safety issue, especially in Southeast Asia. To investigate the impacts of biochar amendment (rice husk and smooth cordgrass-derived biochar) and/or silicate fertilizer on As mobility/phytoavailability in soil and on As accumulation in rice, pot and microcosm experiments were conducted. The results showed that both single application of low doses of biochar (0.5%, w/w) and coapplication of biochar with silicate fertilizer decreased As levels in grain (brown rice) by 14-16%, but not in straw and roots. The biodilution of As in grain resulting from increased grain biomass (by 6-21%) could be mainly a response to the decline in grain As levels with biochar and/or silicate fertilizer amendment. However, both applications exerted limited effects to decrease the overall As uptake by rice grain and straw, potentially due to the small changes in As mobility/phytoavailability in amended soil relative to the control, although plant-available silicon (Si) from amendment could potentially inhibit As uptake. Furthermore, microcosm-based anaerobic incubation experiments demonstrated that As levels in soil solution increased (up to 11-14-fold) with increasing doses of biochar amendment (up to 5%, w/w), possibly due to biochar enhancing the reductive dissolution of iron (oxyhydr) oxides via an increase in the total number of iron-reducing bacteria (up to 1.6-3.2-fold). Our findings suggested that a low application rate of biochar may not be a very effective approach for mitigating As accumulation in rice, while a high application rate could enhance the health risk of As in As-contaminated flooded soil.

Fluoride in soil and plant

Fluorine is unique chemical element which occurs naturally, but is not an essential nutrient for plants. Fluoride toxicity can arise due to excessive fluoride intake from a variety of natural or manmade sources. Fluoride is phytotoxic to most plants. Plants which are sensitive for fluorine exposure even low concentrations of fluorine can cause leave damage and a decline in growth. All vegetation contains some fluoride absorbed from soil and water. The highest levels of F in field-grown vegetables are found up to 40 mg kg -1 fresh weight although fluoride is relatively immobile and is not easily leached in soil because most of the fluoride was not readily soluble or exchangeable. Also, high concentrations of fluoride primarily associated with the soil colloid or clay fraction can increase fluoride levels in soil solution, increasing uptake via the plant root. In soils more than 90 percent of the natural fluoride ranging from 20 to 1,000 μg g -1 is insoluble, or tightly bound to soil particles. The excess accumulation of fluorides in vegetation leads to visible leaf injury, damage to fruits, changes in the yield. The amount of fluoride taken up by plants depending on the type of plant, the nature of the soil, and the amount and form of fluoride in the soil should be controlled. Conclusively, fluoride is possible and long-term pollution effects on plant growth through accumulation of the fluoride retained in the soil.

Band-application of phosphorus with farm manure improves phosphorus use efficiency, productivity, and net returns of wheat on sandy clay loam soil

Phosphorus use efficiency (PUE) is very low in alkaline calcareous soils; however, it can be improved by using suitable application methods along with farm manure (FM). The present field study was conducted to optimize phosphorus (P) levels and application methods in order to maximize wheat yield, PUE, and net returns on calcareous soils with and without FM application. Five P soil solution levels, i.e. 0.00, 0.05, 0.10, 0.20, and 0.30 mg P L-1, were maintained according to the Freundlich model through the application of 0, 36, 61, 104, and 142 kg P2O5 ha-1, respectively. The calculated P (0, 36, 61, 104, and 142 kg P2O5 ha-1) was applied by broadcasting, band-placement, and top-dressing, with or without 300 kg ha-1 well-rotted FM. The results revealed that the band-placement technique at 104 kg P2O5 ha-1 improved PUE and wheat output with and without FM application. Furthermore, wheat grain and straw P uptake was high at 142 kg P2O5 ha-1. In addition, protein content and Olsen P were high at 142 kg P2O5 ha-1. The band-placement technique at 104 kg P2O5 ha-1 increased net returns and the cost/benefit ratio. FM application further augmented the productivity, PUE, and net returns under various P levels and application techniques. In conclusion, band-placement of P at 104 kg P2O5 ha-1 with FM improved yield, PUE, and net returns of wheat sown on sandy clay loam calcareous soils.

Beneficial use of a by-product from the phosphate fertilizer industry in tropical soils: effects on soil properties and maize and soybean growth

Phosphate fertilizers are critical for crop production in tropical soils, which are known for having high phosphate-fixing capacity and aluminum saturation, as well as low pH and calcium contents. Fluorine is a component of many phosphate rocks used to make phosphate fertilizers, via a process that generates hexafluorosilicic acid (H2SiF6). While many treatment technologies have been proposed for removal of fluorine in industrial facilities, little attention has been given to a process of neutralizing H2SiF6 with calcium oxide aiming to find out an alternative and sustainable use of a by-product with a great potential for beneficial use in tropical agriculture. This study evaluated the effect of a by-product of phosphoric acid production (fluorite with silicon oxide, hereafter called AgroSiCa) on soil properties as well as on growth of soybean and corn. Two experiments (2 crops) were conducted under greenhouse conditions in a completely randomized 3 × 5 × 2 × 3 factorial design as follows: three soils (Red Latosol, Red-Yellow Latosol, and Cambisol), five doses of AgroSiCa (0; 0.5; 1.0; 2.0; 4.0 t ha−1), two doses of phosphorus (2 × %clay and 4 × %clay), with three replicates, totaling 90 plots for each experiment. The application of AgroSiCa resulted in a slight increase of soil pH. Significant increases in calcium, phosphate, and silicon levels in soil solution and in shoots of maize and soybean were observed at all doses of AgroSiCa. We also found very low levels of fluoride in all soil leachates. Significant reduction of labile aluminum was found in all soils after the cultivation of maize and soybean. In sum, AgroSiCa improved soil properties and contributed to a better growth of both crops. Our results show that reacting H2SiF6 derived from the wet-process phosphoric acid production with calcium oxide leads to a by-product with potential for agricultural use, especially when applied in highly-weathered soils. Besides providing calcium and silicon to plants, the use of such by-product in soils with high phosphate-fixing capacity and high aluminum saturation delivers additional benefits, since fluoride and silicon can play an important role in improving soil conditions due to the formation of less plant-toxic forms of aluminum, as well as upon decreasing phosphate fixation, thus improving root development and making fertilizer-derived phosphate more available for plant growth.

EFFECT OF RICE STRAW AND NITRATE LEVELS IN SOIL SOLUTION ON NITROUS OXIDE EMISSION

Among the greenhouse gases, nitrous oxide (N2O) is considered important, in view of a global warming potential 296 times greater than that of carbon dioxide (CO2) and its dynamics strongly depend on the availability of C and mineral N in the soil. The understanding of the factors that define emissions is essential to develop mitigation strategies. This study evaluated the dynamics of N2O emissions after the application of different rice straw amounts and nitrate levels in soil solution. Pots containing soil treated with sodium nitrate rates (0, 50 and 100 g kg-1 of NO−3-N) and rice straw levels (0, 5 and 10 Mg ha-1), i.e., nine treatments, were subjected to anaerobic conditions. The results showed that N2O emissions were increased by the addition of greater NO−3 amounts and reduced by large straw quantities applied to the soil. On the 1st day after flooding (DAF), significantly different N2O emissions were observed between the treatments with and without NO−3 addition, when straw had no significant influence on N2O levels. Emissions peaked on the 4th DAF in the treatments with highest NO−3-N addition. At this moment, straw application negatively affected N2O emissions, probably due to NO−3 immobilization. There were also alterations in other soil electrochemical characteristics, e.g., higher straw levels raised the Fe, Mn and dissolved C contents. These results indicate that a lowering of NO−3 concentration in the soil and the increase of straw incorporation can decrease N2O emissions.

Effects of EDDS and plant-growth-promoting bacteria on plant uptake of trace metals and PCBs from e-waste–contaminated soil

The present study investigated the effects of the biodegradable chelant S,S-ethylenediaminedisuccinic acid (EDDS) and the plant-growth-promoting bacterium DGS6 on pollutant uptake by corn from e-waste–contaminated soils. The highest concentration and total uptake of Cu and Zn in corn shoots were observed in the presence of EDDS and DGS6+EDDS, respectively. The ΣPCB concentrations in shoots ranged from 0.53 to 0.72ngg−1, and the highest PCB concentration was observed in the presence of EDDS. This could be ascribed to the enhanced dissolved organic carbon, increased dissolution and efficient translocation of PCBs from roots to shoots, as well as potential root damage due to increased soluble metal levels in soil solution. In contrast, the highest total uptake of PCBs in shoots was observed in the presence of DGS6, likely due to enhanced shoot biomass and high levels of air deposition.

Sorption and Transport of Veterinary Pharmaceuticals in Soil—A Laboratory Study

Land application of manure can change soil chemical properties, thus affecting fate and mobility of agricultural antibiotics in soil. The main objective of this study was to examine the effects of dissolved organic C (DOC) and background electrolyte cation type on the sorption and transport of chlortetracycline (CTC), tylosin (TYL), and sulfamethazine (SMT) in two different soils. A series of batch isotherm and column miscible displacement experiments were conducted using surface and subsurface soils of Etowah clay loam (fine‐loamy, siliceous, semiactive, thermic Typic Paleudults) and Captina sandy loam (fine‐silty, siliceous, active, mesic Typic Fragiudults). Decreased retention of CTC and TYL to soils was observed in the presence of Ca2+ ion compared with Na+. For example, the Freundlich coefficient (KF) for TYL ranged from 67 to 341 under a Na+ system while it ranged from 17 to 173 under a Ca2+ system. Sorption of CTC and TYL decreased on the addition of DOC extracted from dairy manure, while SMT sorption increased by DOC addition. For example, in the Ca2+ system, CTC KF values without DOC ranged from 2.40 × 103 to 4.84 × 103 while they ranged from 1.52 × 103 to 2.86 × 103 with the addition of DOC. Column transport experiments generally agreed with the batch study results, showing increased CTC mass recovery in effluents (i.e., increased from 2.1–4.3% for both surface and subsurface soils) and decreased retardation factors (R) in the presence of dairy manure DOC (i.e., from 890–371). The reduced CTC adsorption may be explained by competition between the DOC and CTC for sorption sites or by the aqueous association of CTC with DOC. Elevated levels of DOC also resulted in increased mobility of TYL and SMT for surface soil column. In summary, changes in background electrolyte cation type and DOC level in soil solution caused by addition of animal manure can influence fate and transport of agricultural antibiotics in soils.

KURVA SORPSI FOSFAT MENURUT LANGMUIR DAN FREUNDLICH SEBAGAI PENDUGA KEBUTUHAN PUPUK FOSFAT PADA ANDISOLS SUMATERA BARAT

Andisols are among the most productive soils in the world, but these soils also strongly retained phosphate. The high capacity for phosphate sorption in Andisols is due to their high content of active Al and Fe compounds. The objectives of this study were to assess the effect of soil properties on P sorption, buffer capacities and requirements of some benchmark soil profiles in Mt. Marapi and Mt. Pasaman. The P sorption characteristics of Andisols from West Sumatra were described using Langmuir and Freundlich equations. The P sorption maximum in Mt. Pasaman soils was higher than in Mt. Marapi soils. The most important soil properties affecting P sorption and buffer capacities were oxalate Si and Fe, Al (Sio Feo and Alo), dithionite Al (Ald), pyrophosphate Al (Alp), which explained 89% of the variance in sorption maxima and 83% of P buffering indices. Allophane, Alo and Ald were positively correlated with P sorption maximum. Contrary to general assumption that organic matter had an inverse relation with P sorption maxima, in this study, however, there was no trend observed between P sorption maxima and organic carbon. Organic C has poor relationship with this parameter. Andisols from Mt. Marapi and Mt. Pasaman need P input between 320 to 7,800 mg P kg-1 to maintain the P level in soil solution at 0.2 mg kg-1.

Elevated CO2 concentration increase the mobility of Cd and Zn in the rhizosphere of hyperaccumulator Sedum alfredii

The effects of elevated CO2 on metal species and mobility in the rhizosphere of hyperaccumulator are not well understood. We report an experiment designed to compare the effects of elevated CO2 on Cd/Zn speciation and mobility in the rhizosphere of hyperaccumulating ecotype (HE) and a non-hyperaccumulating ecotype (NHE) of Sedum alfredii grown under ambient (350μll(-1)) or elevated (800μll(-1)) CO2 conditions. No difference in solution pH of NHE was observed between ambient and elevated CO2 treatments. For HE, however, elevated CO2 reduced soil solution pH by 0.22 unit, as compared to ambient CO2 conditions. Elevated CO2 increased dissolved organic carbon (DOC) and organic acid levels in soil solution of both ecotypes, but the increase in HE solution was much greater than in NHE solution. After the growth of HE, the concentrations of Cd and Zn in soil solution decreased significantly regardless of CO2 level. The visual MINTEQ speciation model predicted that Cd/Zn-DOM complexes were the dominant species in soil solutions, followed by free Cd(2+) and Zn(2+) species for both ecotypes. However, Cd/Zn-DOM complexes fraction in soil solution of HE was increased by the elevated CO2 treatment (by 8.01% for Cd and 8.47% for Zn, respectively). Resin equilibration experiment results indicated that DOM derived from the rhizosphere of HE under elevated CO2 (HE-DOM-E) (90% for Cd and 73% for Zn, respectively) showed greater ability to form complexes with Cd and Zn than those under ambient CO2 (HE-DOM-A) (82% for Cd and 61% for Zn, respectively) in the undiluted sample. HE-DOM-E showed greater ability to extract Cd and Zn from soil than HE-DOM-A. It was concluded that elevated CO2 could increase the mobility of Cd and Zn due to the enhanced formation of DOM-metal complexes in the rhizosphere of HE S. alfredii.

Effect of pH on boron adsorption in some soils of Paraná, Brazil

Temporary B deficiency can be triggered by liming of acid soils because of increased B adsorption at higher soil pH. Plants respond directly to the activity of B in soil solution and only indirectly to B adsorbed on soil constituents. Because the range between deficient and toxic B concentration is relatively narrow, this poses difficulty in maintaining appropriate B levels in soil solution. Thus, knowledge of the chemical behavior of B in the soil is particularly important. The present study investigated the effect of soil pH on B adsorption in four soils of Parana State, and to correlate these values with the physical and chemical properties of the soils. Surface samples were taken from a Rhodic Hapludox, Arenic Hapludalf, Arenic Hapludult, and one Typic Usthorthent. To evaluate the effect of pH on B adsorption, subsamples soil received the application of increasing rates of calcium carbonate. Boron adsorption was accomplished by shaking 2.0 g soil, for 24 h, with 20 mL of 0.01 mol L-1 NaCl solution containing different concentrations (0.0, 0.1, 0.2, 0.4, 0.8, 1.2, 1.6, 2.0, and 4.0 mg B L-1). Sorption was fitted to non-linear form of the Langmuir adsorption isotherm. Boron adsorption increased as concentration increased. Boron adsorption was dependent on soil pH, increasing as a function of pH in the range between 4.6 and 7.4, although the bonding energy has decreased. Maximum adsorption capacity (MAC) of B was observed in the Arenic Hapludalf (49.8 mg B kg-1 soil) followed by Arenic Hapludult (22.5 mg kg-1), Rhodic Hapludox (17.4 mg kg-1), and Typic Usthorthent (7.0 mg kg-1). The organic matter content, clay content, and aluminum oxide content (Al2O3) were the soils properties that affecting the B adsorption on Parana soils.

Irrigation with brackish water modifies the boron requirement of mungbean (Vigna radiata L.) on typic calciargid

The boron (B) sufficiency range for plant growth is narrow and its management is problematic under brackish irrigation water. This study was conducted to evaluate the B requirement of mungbean at different sodium adsorption ratios of irrigation waters (SARiw) [control, 8 and 16 (mmolc L−1)1/2]. The boron adsorption characteristics of a loamy soil were first determined in the laboratory by equilibrating 2.5 g soil with 0.01 M CaCl2 solution containing different B levels. Boron rates for a pot study were computed against different soil solution levels by fitting sorption data in a modified Freundlich model [x/m = K f (EBC)1/n ]. The maximum increase in shoot dry matter was 11.9% when B was applied at 1.29 mg kg−1 soil at control SARiw. Visual leaf B toxicity symptoms appeared at higher B rates and became severe at higher SARiw. By contrast to Ca, shoot concentrations of B and Na increased significantly with B application and SARiw. For optimum shoot growth, internal and external B requirements were 25 mg B kg−1 shoot dry matter and 0.39 mg B L−1 soil solution, respectively, at control SARiw. At higher SARiw, a lower concentration of B in plant shoots and soil solution had an inhibitory effect on plant growth.

Predicting Plant Phosphorus Requirements for Hawaii Soils using a Combination of Phosphorus Sorption Isotherms and Chemical Extraction Methods

Phosphorus (P) is an essential nutrient for plant growth and reproduction. One of the tasks of soil testing is to identify whether the soil P level is sufficient to meet crop requirements, and if not, to provide an estimate of the quantity of P that must be added for good growth of a given crop. Data for 12 soils (11 series) from Hawaii were used to develop correlations between critical P concentrations in soil solution derived from P sorption isotherms with P extracted with Mehlich 3, Olsen, or modified Truog solutions. Extractable P, in turn, was correlated with P fertilizer requirements. Critical P levels in soil solution reported in the literature for various crops ranged from 0.005 mg L−1 for cassava (Manihot esculenta) to 0.30 for lettuce (Lactuca sativa) and to 1.6 for nonmycorrhizal onions (Allium cepa). The P buffer coefficient, defined as the ratio of fertilizer P added to extractable P, averaged 2.2, 4.2, and 8.6 for the modified Truog, Olsen, and Mehlich 3, respectively. Phosphorus requirements for certain crops could be estimated by the following steps: (i) obtaining (possibly one time only) soil solution P levels via P sorption isotherm for a given soil (series or family), (ii) identifying the critical soil solution P for a given crop from the literature, (iii) regressing soil solution P against extractable P, and (iv) establishing relationships between extractable P and fertilizer P.

Potassium Buffering Capacity of Sandy Soils from Thua Thien Hue Province, Central Vietnam, as Related to Soil Properties

Most agricultural production in central Vietnam relies on sandy soils distributed along the sea coast. Because of their low exchangeable potassium (K) and low cation exchange capacity (CEC), careful adjustment of K fertilization on these soils is needed to minimize K leaching. Quantity/intensity curves were established on 24 sandy soils from Thua Thien Hue Province from which K buffering capacity (PBC) was calculated and compared with basic soil properties. Potassium buffering capacity was found to correlate best with soil texture and only a little with humus content, although these two characteristics are responsible for CEC. A simple equation based on sand content, which is easier to determine than clay content, is proposed to calculate optimum exchangeable K level as a function of target K level in soil solution.

DEPENDENCIA MICORRIZAL DE LAUREL (Ocotea sp.)

Se realizo un experimento en invernadero para determinar la dependencia micorrizal (dm) de laurel (Ocotea sp.). Para tal fin se utilizo un diseno experimental completamente al azar. Los tratamientos tuvieron un arreglo factorial 3x2 con cinco repeticiones, los cuales consistieron en la combinacion de tres niveles de fosforo (P) en la solucion del suelo (0.002, 0.02 y 0.2 mg L-1) y dos niveles de inoculacion micorrizal (inoculado y no inoculado) con Glomus aggregatum Schenck Smith. Se emplearon como variables respuesta el contenido de P foliar en funcion del tiempo. Al momento de la cosecha, se determinaron la masa seca aerea, el P total absorbido en la parte aerea, la colonizacion micorrizal y la dm. Los resultados indican que en algunos dias de muestreo el contenido de P foliar aumento significativamente con la inoculacion micorrizal en laurel al nivel de P en solucion de 0.2 mg L-1 pero no en los otros niveles de P. El contenido de P total absorbido no incremento significativamente. La dm fue del 28%, lo que permite clasificar esta especie como moderadamente dependiente.

Coarse Woody Debris in a Southern Appalachian Spruce-fir Forest of the Great Smoky Mountains National Park

Abstract Spruce-fir forests in the southern Appalachian Mountains receive high atmospheric nitrogen inputs and have high nitrate levels in soil solution and streamwater. High levels of excess nitrogen have been associated with reduced tree vigor. Additionally, the balsam woolly adelgid (Adelges piceae Ratz.) has killed the majority of endemic Fraser fir [Abies fraseri (Pursh) Poir.] trees, resulting in large amounts of coarse woody debris. As part of a biogeochemical study in the Great Smoky Mountains National Park, coarse woody debris was sampled to determine volume, mass, change in density, and change in concentration and content of carbon and nitrogen over the decomposition process. Dead wood volume was highly variable across the watershed, ranging from 4.5 m3 ha−1 to 306.8 m3 ha−1 for standing boles and from 21.2 m3 ha−1 to 402.7 m3 ha−1 for down boles. Wood density decreased significantly for all three major overstory species [red spruce (Picea rubens Sarg.), yellow birch (Betula alleghaniensis Britt...