Adsorption and Desorption of Copper in Pasture Soils

Abstract

Copper (Cu) is bound strongly to organic matter, oxides of iron (Fe) and manganese (Mn), and clay minerals in soils. To investigate the relative contribution of different soil components in the sorption of Cu, sorption was measured after the removal of various other soil components; organic matter and aluminum (Al) and Fe oxides are important in Cu adsorption. Both adsorption and desorption of Cu at various pH values were also measured by using diverse pasture soils. The differences in the sorption of Cu between the soils are attributed to the differences in the chemical characteristics of the soils. Copper sorption, as measured by the Freundlich equation sorption constants [potassium (K) and nitrogen (N)], was strongly correlated with soil properties, such as silt content, organic carbon, and soil pH. The relative importance of organic matter and oxides on Cu adsorption decreased and increased, respectively, with increasing solution Cu concentrations. In all soils, Cu sorption increased with increasing pH, but the solution Cu concentration decreased with increasing soil pH. The cumulative amounts of native and added soil Cu desorbed from two contrasting soils (Manawatu and Ngamoka) during desorption periods showed that the differences in the desorbability of Cu were a result of differences in the physico‐chemical properties of the soil matrix. This finding suggests that soil organic matter complexes of Cu added through fertilizer, resulted in decreased desorption. The proportions of added Cu desorbed during 10 desorption periods were low, ranging from 2.5% in the 24‐h to 6% in the 2‐h desorption periods. The desorption of Cu decreased with increasing soil pH. The irreversible retention of Cu might be the result of complex formation with Cu at high pH.     

Organic phosphate sorption by neutral and basic soils

Abstract

The sorption of several organic phosphates were measured on soil, peat and other organic and inorganic materials. The behavior of the phosphates on these materials differed from that reported for similar studies on acidic soil materials. In contrast to the sorption on acidic soils, where sorption maxima occur, the sorption on basic soils may reach a maximum but does not decline thereafter. Both clay and organic matter content govern the amount of sorption but calcium seems to account for the differences observed from those on acidic soil materials     

Sorption behavior of copper,zinc, and cadmium in response to simulated changes in soil properties

Abstract

Environmental changes and management practices which alter soil properties may affect the capacity of soils to sorb trace metals, such as copper (Cu), zinc (Zn), and cadmium (Cd), and thus influence the bioavailability and leach ability of the metals. Two agricultural soils were treated to partially oxidize organic matter and to decrease soil pH for evaluating the effects of acidification and organic matter oxidation on trace metal sorption onto soils. For the one soil with a pH value of 6.74 and organic carbon (C) content of 46.9 g‐kg^‐1, loss of 11% of its organic matter reduced by 97, 72, and 62% the original sorption capacity for Cu, Zn, and Cd, respectively, while the corresponding values caused by acidifying the soil one pH‐unit were 32, 16, and 29%. For the another soil with a pH of 4.69 and organic C content of 16.3 g‐kg^‐1, a decrease in pH by one unit resulted in a loss of 43, 21, and 52% of the sorption capacity for Cu, Zn, and Cd, respectively.     

Physicochemical properties of the soils associated with shifting cultivation in Northern Thailand with special reference to factors determining soil fertility

Abstract

Recently agricultural activity in the mountainous area of northern Thailand has increased and problems relating to soil fertility have arisen. In order to gain basic information about the soil properties associated with shifting cultivation, physicochemical properties of the surface soils (0–10 cm) and subsoils (30–40 cm) were investigated in selected villages in the area. The physicochemical properties of the soils studied are summarized as follows: 1) The soils were rich in organic matter, content of which ranged from 11.4 to 63.3 g C kg^?1 in the surface soil. 2) The pH(H₂O) of the soils mostly ranged from 5 to 7 and soil acidity was more pronounced in the deeper horizons. In the surface soils, exchangeable Ca and Mg were generally dominant, whereas exchangeable Al was often predominant in the subsoils. 3) Most of the soils showed a medium to fine texture with more than 30% clay. The clay mineral composition was characterized by various degrees of mixture of kaolin minerals and clay mica with, in some cases, a certain amount of 2:1-2:1:1 intergrades. 4) According to the ion adsorption curves, most of the B horizon soils were characterized by the predominance of permanent negative charges. On the other hand, organic matter contributed to the increase of variable negative charges in the surface soils. The content of organic matter and the percentage of the clay fraction were essential for determining the CEC of the soils of the surface 10 and 30–40 cm depths, respectively. Under the field conditions, the composition of exchangeable cations largely reflected the soil acidity. In addition, the content of organic matter also showed a significant correlation with that of available N in the surface soils. Thus, soil acidity both in the surface soils and subsoils, organic matter content in the surface soils, and clay content in the subsoils were considered to be the main factors that affected soil chemical fertility in the area.     

Influence of organic matter on selenite sorption by Andosols

Abstract

The influence of soil organic matter on selenite sorption was investigated in the selenite adsorption capacity and the surface particle charge change by ligand exchange reaction using the hydrogen peroxide (H₂O₂) treatment and the ignition treatment of two Andosols. The removal of organic carbon (C) in soils accelerated selenite sorption, implying that organic matter of soils had negative influence on the selenite adsorption on the soils. Positive charge decrease on soil particles, concomitant proton consumption, and release of silicon (Si), sulfate (SO₄ ^2‐), and organic C were observed in selenite sorption by the soils. The development of surface particle negative charge with selenite sorption was smaller in the H₂O₂‐treated soil than in the original soils and was scarcely observed in the ignition‐treated soil. It can be assumed that the increase of negative charge by selenite sorption was attributed to new negative sites borne by released insoluble organic matter and negative charge development directly by selenite sorption was small.     

Cadmium sorption by two acid soils as affected by clearing and cultivation

Abstract

The objective of this study was to determine the effect of clearing and cultivation on the sorption of cadmium (Cd) by two acid soils from Zimbabwe with differing cultivation stories. In their original state, not cleared‐not cultivated (virgin soils), the two soils exhibited noticeable and similar capacities to sorb Cd. The Mazowe soil contains the highest level of organic matter (40 g kg^‐1) and a effective cation exchange capacity (ECEC) of 144 mmol_c kg^‐1. Yet, Bulawayo soil (23.5 g kg^‐1 organic matter and ECEC of 146 mmol_c kg^‐1) has higher pH and Mn and Fe oxide content and these characteristics seemed to counteract the effect of lower organic matter. After 50 years of cultivation, The Mazowe soil has lost 60% of its organic matter and ECEC, and consequently the ability of its soil matrix to bind Cd has proportionally decreased. In Bulawayo (cleared in 1983 and first ploughed in 1984), on the contrary, the organic matter and ECEC of the cultivated soil remains over 95% of the values on its virgin counterpart. In this soil, the retaining ability for Cd has not still been affected. In the two soils Cd sorption was highly pH‐dependent. The extent of sorption was minimal under acidic conditions and increased sharply as the pH was raised. The immediate reversibility of the sorption process proved to be very low. When sorption and desorption data were compared it was clear that soil characteristics like high organic matter and oxide content which showed to enhanced Cd sorption, contributed at the same time to slow down the backward reaction.     

Role of Different Soil Fractions in Copper Sorption by Soils

Abstract

To evaluate contributions of organic matter, oxides, and clay fraction to copper (Cu) adsorption in six characterized soils, adsorption isotherms and distribution coefficients were obtained by a batch experimental method. Copper adsorption isotherms from untreated soil, organic matter removed from samples, and organic‐matter‐ and oxide‐removed samples were compared with curve patterns and correlated to Langmuir and Freundlich models. Copper sorption data on untreated soils described L or H‐curves, whereas in soils deprived of any component, their curves were S‐type. Distribution coefficients allowed knowing Cu adsorption capacity of untreated soil and of organic matter, oxides, and clay fraction. Soil organic matter is the main component that affects Cu adsorption as long as soil pH is near neutrality. At acid pH, oxides are the main component that affects Cu adsorption, although to a much smaller extent than organic matter near neutral conditions. Soil pH is the main soil factor that determines Cu adsorption.     

Capacity of selected Illinois soils to remove lead from aqueous solution

Abstract

Lead is being added to the environment in automotive exhausts and as an industrial pollutant. To understand its fate in the environment, it is necessary that factors affecting the capacity of soils to sorb Fb be determined.

The capacity of soils to sorb Fb from aqueous solutions vas measured for selected Illinois soils via column leaching experiments and adsorption isotherms. A regression equation was determined that predicted the capacity of a soil to sorb Fb based on its C.E.C., pH and soluble F level. Results of the regression analysis indicated that soil properties associated with increasing C.E.C., i.e. higher organic matter content, higher surface area, and higher clay content have a greater effect on Fb sorption than soil pH, and that soil pH has a greater effect than soluble P.     

Dissipation and sorption processes of polycyclic aromatic hydrocarbons (PAHs) to organic matter in soils amended by exogenous rich-carbon material

Purpose

The aim of the research was to assess the effect of biochar addition on aging, degradation, and sorption processes of polycyclic aromatic hydrocarbons (PAHs) to soil organic matter. The study was carried out as a sorption experiment in strictly controlled water and air conditions, which allowed for the accurate observation and prediction of PAH behavior in soils.

Materials and methods

Four soils were fortified with a PAH mixture (Fluorene-Flu, Anthracene-Ant, Phenanthrene-Phe, Pyrene-Pyr, Chrysene-Chry) at 20 mg kg^?1 of single-compound concentration level. The experiment was carried out in two trials: soils?+?5PAHs amended with biochar and soil?+?5PAHs without biochar addition with incubation times of 0, 1, 3, 6, and 9 months. After each interval time, the extractable (E-SOM) and stable organic matter (S-SOM) were measured as well as PAHs determined in two forms: total concentration (PAH-tot) and residual concentration (PAH-rest) after E-SOM extraction. The PAH loss and half-life times were estimated according to pseudo first-order kinetics equation.

Results and discussion

The amounts of PAH-tot in the soils without biochar decreased by an average of 92%, while in soil with biochar, this was 41% after 9 months of aging. The amount of PAHs-rest bounded with S-SOM after 9 months of incubation varied from 0.9 to 3.5% and 0.2 to 1.3% of the initial PAH concentration, respectively, for soils non-induced and induced by biochar. In soils without biochar, Flu, Ant, Phe, and Pyr exhibited similar T_1/2 (43–59 days), but Chry was characterized by a much higher and broader T_1/2 than other hydrocarbons (67–280 days). Biochar addition to the soils significantly influenced the half-life changes for all PAHs. The highest changes were noted for Phe (14-fold increase), and the lowest was for Flu (7-fold increase).

Conclusions

The addition of exogenous-rich carbon material such as biochar to the soil significantly changes the behavior and sorption potential of PAHs in the soil. Soils enriched with biochar are characterized by a higher persistence of PAHs, longer aging time, and lower affinity for sorption by native organic matter structures. Soils freshly polluted by PAH are mainly sorbed by E-SOM, which significantly increases their accessibility and reduces formation of bound-residues in the soil.

     

Sorption-desorption behaviors of heavy metals by biochar-compost amendment with different ratios in contaminated wetland soil

Purpose

Heavy metal pollution in soils has become a global environmental concern. The combination of biochar and compost has already been proved to be an attractive method in contaminated soil. The objective was to study the sorption-desorption characteristics of Cd, Cu, and Zn onto soil amended with combined biochar-compost.

Materials and methods

In this study, the soil was amended with combinations of biochar and compost with different ratios at 10% (w/w). To determine the sorption-desorption behaviors of heavy metals by biochar-compost amendment with different ratios, we determine the effects of different ratios on soil properties and use batch experiments to investigate sorption-desorption behaviors of Cd, Cu, and Zn.

Results and discussion

The results show that the Langmuir and Freundlich model can well describe the adsorption isotherm of Cd, Cu, and Zn in the soils with or without biochar-compost combinations. The incorporation of amendment combinations into soil significantly promotes the sorption affinity of soil on metals. The sorption capacity of Cd and Zn was improved as the compost percentage rose in biochar-compost more likely due to the increase of organic matter and available phosphorus, while that of Cu was stronger with 10 and 20% biochar addition in biochar-compost combinations likely as the result of the formation of new specific adsorption sites and the mobile Cu adsorption in compost after adding a certain amount of biochar in amendment mixtures. Additionally, a certain proportion of biochar applied into amendment mixtures could suppress desorption of Cd and Cu by pH change, and the Zn desorption rate gradually decreased as the compost ratio increased in amendment mixtures.

Conclusions

The results indicated that the various ratios between biochar and compost have a significant effect on sorption-desorption of metals in soil, which helps us consider the effective combination of biochar and compost in soil.

     

湘中紫色丘陵区不同植被类型根际与非根际土壤理化特征

[目的]探索湘中紫色丘陵区不同植被类型根际与非根际土壤的理化特征,为湘中地区生态修复提供理论依据。[方法]以典型抽样方法调查湘中丘陵区草丛(G)、草灌(GS)、灌木(S)和乔灌(AS)4种典型植被,研究其根际与非根际土壤理化性质的差异,通过典型相关分析揭示根际与非根际土壤理化指标间的耦合关系。[结果]研究区草丛和灌木根际土壤中细砂粒(0.25~0.05mm)含量分别显著(p0.05)低于乔灌63.84%和76.97%;粉粒(0.02~0.002mm)含量表现为草和灌木分别显著高于乔灌的38.48%和37.66%。根际土壤0.25~0.05mm微团聚体含量均表现为乔灌高于其他植被,0.02~0.002mm微团聚体含量均表现为灌木高于其他植被。草灌与灌木非根际土壤有机质含量显著(p0.05)低于根际土壤148.05%和121.92%,灌木和草灌根际土壤有机质含量显著(p0.05)高于乔灌土壤84.28%和92.08%;草灌根际土壤全氮含量显著(p0.05)高于非根际土壤83.33%,草灌根际土壤碱解氮含量显著(p0.05)高于乔灌土壤200.83%;不同植被类型根际/非根际土壤磷含量差异不明显,总体来看,同一植被根际土壤全磷含量低于非根际土壤,而有效磷表现为乔灌最低;乔灌根际土壤速效钾含量分别显著(p0.05)低于草丛和草灌土壤125.15%和137.71%,除草灌外,其余植被类型根际土壤全钾含量均低于非根际土壤。典范相关分析表明土壤有机质和全量养分含量,2~1,1~0.5,0.25~0.05mm土粒含量,2~1,1~0.5mm团聚体3组理化性状间相互关系密切。[结论]改善土壤理化性质,促进湘中丘陵地区生态恢复,应注重协调土壤养分、颗粒组成及团聚体之间的耦合关系。     

Urea Hydrolysis of Tea Soils as Influenced by Incubation Period,Soil pH,and Nitrification Inhibitor

Abstract

Laboratory incubation studies were conducted with south Indian tea soils to investigate the influence of soil pH, incubation period, and nitrification inhibitor on urea hydrolysis. The soils used in this experiment were sampled from six different regions of south India. The physicochemical properties, urea hydrolysis as influenced by soil pH, incubation period, and nitrification inhibitor were determined. There was a strong positive correlation between urease activity and organic‐matter content of tea soils, whereas physicochemical properties failed to show any relationship with urease activity. The urease activity was highest in Munnar soils. At 25°C, the activity reached maximum within 15 days after fertilizer application, and it was considerably high up to 36 days in the soils of Anamallais, 18 days in Munnar, and 27 days in other zones studied, which revealed the minimum interval between two successive urea fertilizer applications. Soils of different zones showed a different pattern of urease activity when the soil pH was changed artificially between 4 and 5.5. Addition of nitrification inhibitor [dicyandiamide, DCD] to urea prevented nitrate ion formation, resulting in the accumulation of desirable ammonium ions.     

Effects of biochar application in forest ecosystems on soil properties and greenhouse gas emissions: a review

Purpose

Forests play a critical role in terrestrial ecosystem carbon cycling and the mitigation of global climate change. Intensive forest management and global climate change have had negative impacts on the quality of forest soils via soil acidification, reduction of soil organic carbon content, deterioration of soil biological properties, and reduction of soil biodiversity. The role of biochar in improving soil properties and the mitigation of greenhouse gas (GHG) emissions has been extensively documented in agricultural soils, while the effect of biochar application on forest soils remains poorly understood. Here, we review and summarize the available literature on the effects of biochar on soil properties and GHG emissions in forest soils.

Materials and methods

This review focuses on (1) the effect of biochar application on soil physical, chemical, and microbial properties in forest ecosystems; (2) the effect of biochar application on soil GHG emissions in forest ecosystems; and (3) knowledge gaps concerning the effect of biochar application on biogeochemical and ecological processes in forest soils.

Results and discussion

Biochar application to forests generally increases soil porosity, soil moisture retention, and aggregate stability while reducing soil bulk density. In addition, it typically enhances soil chemical properties including pH, organic carbon stock, cation exchange capacity, and the concentration of available phosphorous and potassium. Further, biochar application alters microbial community structure in forest soils, while the increase of soil microbial biomass is only a short-term effect of biochar application. Biochar effects on GHG emissions have been shown to be variable as reflected in significantly decreasing soil N₂O emissions, increasing soil CH₄ uptake, and complex (negative, positive, or negligible) changes of soil CO₂ emissions. Moreover, all of the aforementioned effects are biochar-, soil-, and plant-specific.

Conclusions

The application of biochars to forest soils generally results in the improvement of soil physical, chemical, and microbial properties while also mitigating soil GHG emissions. Therefore, we propose that the application of biochar in forest soils has considerable advantages, and this is especially true for plantation soils with low fertility.

     

Sorption and desorption of selenium in different soils of the mediterranean area

Abstract

The adsorption of selenium (Se) in the selenate form and its desorption by phosphate in four soils with different physiochemical properties were studied in the laboratory. To determine adsorption isotherms for selenate 25 mL of solutions containing 1 to 100 ppm of Se were added to 2.5 g of soil. Desorption isotherms were determined by resuspending the samples in phosphate solution. The selenate sorption process was adequately described by the Freundlich equation. In pine forest and woodland soils, characterized by the highest organic matter content and cation exchange capacity (CEC) values, the isotherms were classified as L type, since the amount of Se sorbed appeared to move towards saturation. The organic matter content played the most important part in the adsorption of Se, while pH appeared to have a small effect on the ability of the soil to adsorb Se. The high CaCO₃ content of the pine forest soil may have contributed in increasing the Se adsorption notwithstanding the high pH value. The cultivated and arable soils showed a reduced sorption capacity. The sorption could be described by an S type curve. At low concentrations of Se the affinity of the solid phase was less than that of the liquid phase. By increasing the concentration of Se in solution, the affinity of the solid phase increased and the sorption was favored. Selenate desorption by water was negligible, whereas the amount of Se desorbed by phosphate varied among the different soils. The desorption experiments indicated that a significant portion of the sorbed Se was irreversibly retained. This suggests the existence of linkages which allow the release of Se in the soil solution only after physico‐chemical variation such as exchange with phosphate ions.     

Phosphate sorption characteristics of major soils in Okinawa,Japan

Abstract

Phosphate sorption isotherms were determined for 16 representative major soils developed from different parent materials on Okinawa. Phosphate sorption characteristics were satisfactorily described by the Langmuir equation, which was used to determine phosphorus (P) sorption maxima of the soils. Phosphate sorption maxima ranged from 630 to 2208 mg P kg^‐1 soil (mean 1,362 mg P kg^‐1). The standard P requirement (i.e., the amount of P required to attain 0.2 mg P L^‐1 equilibrium solution) followed the same trend as sorption maximum (r =0.94***), with values ranging from 132 to 1,020 mg P kg^‐1 soil (mean 615 mg P kg^‐1). This mean value corresponds to fertilizer addition of 923 kg P ha^‐1 indicating that the soils have high P fertilizer requirements. Results of simple linear regression analysis indicated that sorption maximum was significantly correlated with clay content, organic matter, oxalate iron (Fe), pyrophosphate Fe, DCB aluminum (Al), oxalate Al, and pyrophosphate Al, but not with DCB Fe, pH, or available P content. The best regression model for predicting sorption maximum was the combination of clay, organic matter, pyrophosphate Fe, and DCB Al which altogether explained 79% of the variance in sorption maximum. The equation obtained could offer a rapid estimation of P sorption in Okinawan soils.     

Effects of sediment components and TiO2 nanoparticles on perfluorooctane sulfonate adsorption properties

Purpose

Here, the roles of sediment components in perfluorooctane sulfonate (PFOS) adsorption onto aquatic sediments and relevant adsorption mechanisms were investigated in terms of adsorption isotherms and influences of TiO₂ nanoparticles (NPs) contamination.

Materials and methods

Due to the complexity of the sediments, instead of randomly selecting different component sediments, the selective dissolution method was used to better explore the effects of sediment compositions, such as sediment organic matter (SOM) and ferric oxides (dithionite–citrate–bicarbonate [DCB] Fe), and TiO₂ NPs pollution on PFOS adsorption. Mathematical equations (Freundlich, Langmuir, and Temkin) were used to describe the adsorption behavior of PFOS on different sediments and adsorption mechanisms of multiple pollutant interactions. Moreover, the characterization methods of zeta potential, nitrogen (N₂) adsorption–desorption, and scanning electron microscopy (SEM) analysis, as well as Fourier transform infrared (FT-IR) spectroscopy, explained effects of the sediment components and TiO₂ NPs on PFOS adsorption properties in view of physicochemical theories.

Results and discussion

The adsorption isotherms of PFOS on six tested sediments were all nonlinear (Freundlich model, R² = 0.992~1.000). The Freundlich sorption affinities (K_F) of PFOS on S (original sediments), S1 (sediment organic matter (SOM)-removed S), and S2 (ferric oxides (DCB Fe)-removed S1) were 0.232, 0.179, and 0.120, respectively. Both SOM and DCB Fe influenced the physicochemical properties of the sediments, e.g., zeta potential, specific surface area, and permanent negative charge. The addition of TiO₂ NPs increased the K_F of PFOS for S, S1, and S2 by approximately 9.9%, 14.5%, and 26.7%, respectively, by increasing the zeta potential and specific surface area (S_BET, S_ext, and S_micro) and by changing the water and oil properties of the three sediments. However, the addition of TiO₂ NPs decreased the linearity of the sorption isotherm (1/n). FT-IR spectroscopy showed that hydrophobicity, ion exchange, surface complexation, and hydrogen bonding interactions (non-fingerprint region) could all play a role in PFOS sorption onto tested sediments. However, the hypothesis of hydrogen bonding to promote PFOS adsorption on sediment layer silicates (fingerprint region) should be studied further.

Conclusions

The content of both SOM and DCB Fe affected the physicochemical properties of sediment. Both SOM and DCB Fe showed a positive relationship with sorption of PFOS on sediment. The addition of TiO₂ NPs increased PFOS sorption by altering the sediment surface properties. Hydrophobic interactions certainly impelled and ligand and ion exchange and hydrogen bonding (non-fingerprint region) could promote PFOS sorption on the sediments.

     

Biochar and biochar with N fertilizer as a potential tool for improving soil sorption of nutrients

Purpose

Biochar usually has a large specific surface area, and due to this, it increases the sorption capacity of the soil where it was applied. The objectives of this study were to (i) quantify the effects of biochar and biochar in combination with N fertilizer on the soil sorption parameters and (ii) quantify the effects of soil organic matter on the sorption parameters after application of biochar with and without N fertilizer.

Materials and methods

The experiment was established on Haplic Luvisol at the locality of Dolná Malanta (Slovakia) in 2014. The soil samples were collected once a month from the depth 0–0.2 m during 2014 to 2016. The field experiment included three rates of biochar application (B0?=?no biochar, B10?=?biochar at the rate of 10 t ha^?1, B20?=?biochar at the rate of 20 t ha^?1) and three levels of N fertilization (N0?=?no nitrogen, N40?=?nitrogen at the rate of 40 kg ha^?1, N80?=?nitrogen at the rate of 80 kg ha^?1).

Results and discussion

Overall, the decrease of the average values of hydrolytic acidity due to biochar and biochar combined with N fertilization resulted on average in an increase of sum of basic cation (SBC), cation exchange capacity (CEC), and sorption capacity of soil organic matter (CEC_SOM) in all treatments. However, this effect was the most intensive in B10N40. Despite the fact that the average values of sorption parameters improved, its dynamics during the investigated period were different. A significant decrease in CEC was observed from 2014 to 2016 in all treatments, except B0N0 and B10N0. A stable trend in CEC_SOM was observed only in B10N40. Humic substances and humic acids had a statistically significant positive effect on the SBC, CEC, and CEC_SOM only in B20N0 treatment. Negative correlations between the above mentioned parameters were observed in B10N80 treatment.

Conclusions

We conclude that the application of biochar and biochar combined with N fertilization had a positive influence on sorption parameters. However, its effects on SBC, CEC, and CEC_SOM decreased over time after its application.

     

Influence of Different Cultivation Practices on the Properties of Volcanic Soils on Santorini Island,Greece

Abstract

The influence of cultivation practice on the fertility of volcanic soils on Santorini, an important wine‐producing area of Greece, has been examined. In conventional agriculture, weed control, typically of N‐fixing species, is carried out using herbicides, whereas in organic practice it is achieved though plowing, leaving the soil vulnerable to erosion. Soil samples were taken from conventionally and organically cultivated vines and tomatoes and from abandoned vineyards at five locations. Biological indicators of soil quality were measured in addition to physicochemical properties. The loam sandy soils had an acid to slightly alkaline pH reaction, with low organic matter. Earthworms (Lumbricidae) were not found. Enchytreids were absent from conventional soils but were found in low abundance in organic and abandoned vineyard systems. Enzyme activity showed no dependence on cultivation systems but was low compared with other Greek soils. Organic practices adopted on Santorini have maintained soil fertility in the short term.     

Sorption isotherms for predicting potassium requirements of some Iowa soils

Abstract

The sorption isotherm technique was used in predicting potassium requirements of some Iowa soils for growing tomatoes, potatoes, celery and beans. Based on previous comparisons, all of these soils would require additional amounts of K for optimum yields of celery, potatoes, tomatoes and beans. According to Woodruff's energy of exchange concept of K availability, all the soils used in this study are potassium deficient. Amounts of K needed to maintain a specific level of K in sorption equilibrium solution appeared to be largely a function of physicochemical characteristics of the soil. Predicted K requirements of these soils for optimum yields of these crops are reported.