Nitrogen transformations in copper-contaminated soils and effects of lime and compost application on soil resiliency

 A neutral and an acidic soil were treated with different doses (0–3,000 mg Cu kg^–1 soil as CuSO₄) of copper. The percentages of inhibition of nitrification in both soils varied from 5 to 97%, but for the N mineralization these percentages varied from 8 to 65%. The toxic effect of Cu for basal nitrification and N mineralization was assessed as critical. Nitrification was more sensitive than ammonification to copper toxicity. It appears that an ecological dose of inhibition for nitrification and N mineralization higher than 10% is suitable as an indicator for Cu contamination. Soil resiliency assessed by N mineralization in the lime treatments varied from 11 to 154% in the sandy soil and from 70 to 168% in the sandy loam soil. A combined application of lime and compost significantly increased soil resiliency. The percentage increase varied from 904 to 1,390% in the sandy soil and from 767 to 2,230% in the sandy loam soil. It appears that compost was a powerful agent for recovering the soil fertility of Cu-contaminated soils as assessed by N transformation. The acidic sandy soil showed a lower capacity for recovery after Cu toxicity stress. Received: 27 February 1999     

Plant Response to Copper Toxicity as Affected by Plant Species and Soil Type

ABSTRACT

A greenhouse experiment was conducted to determine the bioavailability of copper (Cu) in clay loam and sandy clay loam soil. Lettuce (Lactuca sativa) and spinach (Spinacia oleracea) were grown in pots for 45 d. When mature, plants were treated for 15 additional days with 0, 100, 250, 500, or 1000 mg Cu kg^?1 as CuSO₄·5H₂O. After harvest, Cu in soils and plant tissues was determined. In soils, applied Cu raised total and EDTA-extractible Cu. Results also revealed that the amounts of Cu extracted from sandy clay loam soil (80%) were higher than those extracted from clay loam soil (70%). In plants, increasing soil Cu concentration increased plant concentration of the metal. Plant species vary in their capacity for Cu accumulation: Lettuce has a relatively higher potential for Cu uptake and translocation than does spinach. Cu accumulation also differs among plant organs. In lettuce, metal accumulation is higher in roots than in shoots, where 60% to 80% of the total Cu of the plant is located in the roots. However, in spinach, there is no significant difference in Cu content between roots and shoots. The transfer of the metal from soil to plant is higher for plants grown on sandy clay loam soil. For a given rate of applied Cu, metal content in plant tissues is higher on sandy clay loam soil due to its higher transfer coefficient (C_T) from soil to plant. Nevertheless, all crops studied showed a positive linear relationship between extractible soil Cu and plant Cu.     

Salinity and sodicity affect soil respiration and dissolved organic matter dynamics differentially in soils varying in texture

The individual effects of salinity and sodicity on organic matter dynamics are well known but less is known about their interactive effects. We conducted a laboratory incubation experiment to assess soil respiration and dissolved organic matter (DOM) dynamics in response to salinity and sodicity in two soils of different texture. Two non-saline non-sodic soils (a sand and a sandy clay loam) were leached 3–4 times with solutions containing different concentrations of NaCl and CaCl₂ to reach almost identical electrical conductivity (EC_1:5) in both soils (EC_1:5 0.5, 1.3, 2.5 and 4.0 dS m^?1 in the sand and EC_1:5 0.7, 1.4, 2.5 and 4.0 dS m^?1 in the sandy clay loam) combined with two sodium absorption ratios: SAR < 3 and 20. Finely ground wheat straw residue was added (20 g kg^?1) as substrate to stimulate microbial activity. Cumulative respiration was more strongly affected by EC than by SAR. It decreased by 8% at EC 1.3 and by 60% at EC 4.0 in the sand, whereas EC had no effect on respiration in the sandy clay loam. The apparent differential sensitivity to EC in the two soils can be explained by their different water content and therefore, different osmotic potential at the same EC. At almost similar osmotic potential: ?2.92 MPa in sand (at EC 1.3) and ?2.76 MPa in the sandy clay loam (at EC 4.0) the relative decrease in respiration was similar (8–9%). Sodicity had little effect on cumulative respiration in the soils, but DOC, DON and specific ultra-violet absorbance (SUVA) were significantly higher at SAR 20 than at SAR < 3 in combination with low EC in both soils (EC 0.5 in the sand and EC 0.7 and 1.4 in the sandy clay loam). Therefore, high SAR in combination with low EC is likely to increase the risk of DOC and DON leaching in the salt-affected soils, which may lead to further soil degradation.     

Short- and long-term effects of heavy metals on phosphatase activity in soils: An ecological dose-response model approach

Summary The aim of this study was to provide manageable data to help establish permissible limits for the pollution of soil by heavy metals. Therefore the short-and long-term effects of heavy metal pollution on phosphatase activity was studied in five different soil types. The results are presented graphically as logistic dose-response curves. It was possible to construct a curve for sand and silty loam soil but it was more difficult to establish a curve for sandy loam and clay soil and nearly impossible (except for Cu) for peat. The toxicity of the various metals can be compared on the basis of mmol values. In clay soils, for Cd, Cr, Cu, and Zn, the 50% effective ecological dose (ED₅₀) values were comparable (approximately 45 mmol kg^–1), but the ED₁₀ values were very different, at 7.4, 41.4, 15.1, and 0.55, respectively. At the ED₅₀ value, toxicity did not decrease with time and, in sandy soils, was approximately 2.6 mmol kg ^–1 dry soil for Cd, Cu, and Zn. In four out of five soils, the Cd toxicity was higher 1.5 years after the addition of heavy metal salts than after 6 weeks. Toxicity was least in the sandy loam, silty loam, and clay soil, and varied in general between 12 and 88 mmol kg^–1. In setting limits, the criteria selected (no-effect level, ED₁₀ or ED₅₀) determine the concentration and also the toxicity of the sequence. It is suggested that the data presented here could be very useful in helping to set permissible limits for heavy metal soil pollution.     

Carbon and net nitrogen mineralisation in two forest soils amended with different concentrations of biuret

Biuret is a known contaminant of urea fertilisers that might be useful as a slow release N fertiliser for forestry. We studied carbon (C), net nitrogen (N) mineralisation and soil microbial biomass C and N dynamics in two forest soils (a sandy loam and a silt loam) during a 16-week long incubation following application of biuret (C 23.3%, N 40.8%, O 30.0% and H 4.9%) at concentrations of 0, 2, 10, 100 and 1000 mg kg⁻¹ (oven-dried) soil to assess the potential of biuret as a slow-release N fertiliser. Lower concentrations of biuret specifically increased C mineralisation and soil microbial biomass C in the sandy loam soil, but not in the silt loam soil. A significant decrease of microbial biomass C was found in both soils at week 16 after biuret was applied at higher concentrations. C mineralisation declined with duration of incubation in both soils due to decreased C availability. Biuret at concentrations from 10 to 100 mg kg⁻¹ soil had a significantly positive priming effect on soil organic N mineralisation in both soils. The causes for the priming effects were related to the stimulation of microbial growth and activity at an early stage of the incubation and/or the death of microbes at a later stage, which was biuret-concentration-dependent. The patterns in NH₄⁺-N accumulation differed markedly between the two soils. Net N mineralisation and nitrification were much greater in the sandy loam soil than in the silt loam soil. However, the onset of net nitrification was earlier in the silt loam soil. Biuret might be a potential slow-release N source in the silt loam soil.     

Zeolite Effects on Immobile Water Content and Mass Exchange Coefficient at Different Soil Textures

The concern for groundwater pollution by agrichemicals through solute movement within the soil is widespread. Zeolite is a type of soil amendment that is utilized to improve physical properties of soil and ameliorate polluted soil. The high negative charge of the zeolite and its open space structure allows adsorption and access of heavy metals and other cations and anions. The objectives of this research were (i) to determine the effects of different application rates of zeolite (0, 2, 4, and 8 g kg^?1) on the immobile water content and mass exchange coefficient in a loam soil and then (ii) to determine the effects of optimum application rate of zeolite on the immobile water content and mass exchange coefficient of sandy loam and clay loam soils in saturated conditions by a mobile and immobile (MIM) model. In a disturbed soil column, a method was proposed for determination of MIM model parameters, that is, immobile water content (θ_im), mass exchange coefficient (α), and hydrodynamic dispersion coefficient (D_h). Breakthrough curves were obtained for different soil textures with different zeolite applications in three replicates, by miscible displacement of chloride (Cl^?1) in disturbed soil column. Cl^?1 breakthrough curves were evaluated in terms of the MIM model. The results showed that the pore water velocity calculated based on the total soil volumetric water content (θ_im+ θ_m) and real pore water velocity calculated based on the mobile water content (θ_m) increased in the loam soil with an increase in zeolite application rate, so that, between these different rates of zeolite application, the maximum value of pore water velocity and real pore water velocity occurred at zeolite application rates of 8.6 and 11.5 g kg^?1, which are indicated as the optimum application rates. However, the comparison between different soils showed that the zeolite application rate of 8 g kg^?1 could increase pore water velocity of sandy loam and loam soils by 31% more than that of clay loam soil. The immobile water content and mass exchange coefficient of loam soil were correlated with the zeolite application rate and reduced with an increase in the rate of applied zeolite. In a comparison between different soils at zeolite application rate of 8 g kg^?1, the immobile water contents of the zeolite-treated soil decreased by 57%, 60%, and 39% on sandy loam, loam, and clay loam soils, respectively, compared with the untreated soil. Furthermore, zeolite application could reduce mass exchange coefficient by 9%, 43%, and 21% on sandy loam, loam, and clay loam soils, respectively. A positive linear relationship was found between θ_im and α. Zeolite application increased real pore water velocity of sandy loam soil by 39% and 46% compared with loam and clay loam soils, respectively. In other studies there was a decrease in ammonium and nitrate leaching due to the zeolite application, and therefore, an increase in real pore water velocity due to zeolite application in sandy loam soil, as compared with the loam and clay loam soils, may not show more rapid movement of solute and agrichemicals to the groundwater.     

Influence of texture on habitable pore space and bacterial-protozoan populations in soil

Summary Soil texture affects pore space, and bacterial and protozoan populations in soil. In the present study we tested the hypothesis that bacteria are more protected from protozoan predation in fine-textured soils than in coarse-textured soils because they have a larger volume of protected pore space available to them. The experiment consisted of three sterilized Orthic Black Chernozemic soils (silty clay, clay loam, and sandy loam) inoculated with bacteria, two treatments (with and without protozoa), and five sampling dates. The soils were amended with glucose and mineral N on day 0. On day 4 bacterial numbers in all three soils were approximately 3×10⁹ g^–1 soil. The greatest reduction in bacteria due to protozoan grazing occurred between day 4 and day 7. Compared to the treatment without protozoa, bacteria in the treatment with protozoa were reduced by 68, 50, and 75% in the silty clay, clay loam, and sandy loam, respectively. On day 4, 2 days after the protozoan inoculation, all protozoa were active. The numbers were 10330, 4760, and 15 380 g^–1 soil for the silty clay, clay loam, and sandy loam, respectively. Between day 4 and day 7, the period of greatest bacterial decline, total protozoa increased greatly to 150480, 96160, and 192100 g^–1 soil for the three soils, respectively. Most protozoa encysted by day 7. In all soils the addition of protozoa significantly increased CO₂–C evolution per g soil relative to the treatment without protozoa. Our results support the hypothesis that bacteria are more protected from protozoan predation in fine-textured soils than in coarse-textured soils.     

Glutamic acid decomposition as a sensitive measure of heavy metal pollution in soil

The effect of added heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) on the rate of decomposition of glutamic acid was studied in four Dutch soil types in order to determine if such measurements would serve as sensitive indicators of heavy metal pollution in soil. The time required to reach the maximum respiration rate (referred to as the decomposition time) with glutamic acid was linearly related to increasing concentrations of Ni in a sandy loam soil.Changes in decomposition time were measured 18 months after addition of 55, 400 or 1000 mg kg^? of Cd, Cr, Cu, Ni, Pb or Zn respectively to sand, silty loam, clay and sandy peat soils. A significant increase in the decomposition time occurred with a concentration of 55 mg kg^?1 of Cd, Cu or Zn in the sand soil. At 400mgkg^?1 adverse effects in the various soils are distinct. The sensitivity of the decomposition time of glutamic acid as a method to measure soil pollution is discussed.     

Desorption behaviour of lead in two calcareous soils as affected by Pb level without and with compost supply

A laboratory study was performed to investigate the influence of soil texture (sandy loam vs. clay loam), Pb supply (as Pb(NO₃)₂ without or with compost) and Pb levels on the extraction of available Pb by diethylene triamine pentaacetic acid (DTPA) and its desorption patterns at ten shaking periods. The soils were polluted with five Pb levels without or with compost and incubated for 1 month. Kinetic models commonly used to study the release of the nutrients were used in this study. Results showed that Power function model described the pattern of Pb desorption better than other models. The amount of extracted Pb increased as the Pb levels increased and was found to be higher in sandy loam soil treated with Pb without compost than that of clay loam soil treated with Pb with compost. The a value (Pb desorption constant) was the highest in sandy loam soil amended with Pb without compost. The lowest value of a, however, was observed in clay loam soil amended with Pb with compost. The ab coefficient (initial desorption rate of Pb) was higher in sandy loam than clay loam soil, demonstrating higher initial release rates of Pb in the coarser-textured soil. Addition of Pb without compost resulted in a higher increase in ab value in comparison with Pb with compost, in both the soils.     

Influence of phosphorus application on growth and cadmium uptake of spinach in two cadmium‐contaminated soils

A pot experiment was conducted to investigate the influence of phosphate (P) application on diethylene triamine pentaacetic acid (DTPA)–extractable cadmium (Cd) in soil and on growth and uptake of Cd by spinach (Spinacia oleracea L.). Two soils varying in texture were contaminated by application of five levels of Cd (NO₃)₂ (0, 20, 30, 40, and 60 mg Cd kg^–1). Three levels of KH₂PO₄ (0, 12, and 24 mg P kg^–1) were applied to determine immobilization of Cd by P. Spinach was grown for 60 d after seeding. Progressive contamination of soils through application of Cd affected dry‐matter yield (DMY) of spinach shoot differently in the two soils, with 67% reduction of DMY in the sandy soil and 34% in the silty‐loam soil. The application of P increased DMY of spinach from 4.53 to 6.06 g pot^–1 (34%) in silty‐loam soil and from 3.54 to 5.12 g pot^–1 (45%) in sandy soil. The contamination of soils increased Cd concentration in spinach shoots by 34 times in the sandy soil and 18 times in the silty‐loam soil. The application of P decreased Cd concentration in shoot. The decrease of Cd concentration was higher in the sandy soil in comparison to the silty‐loam soil. Phosphorus application enhanced DMY of spinach by decreasing Cd concentration in soil as well as in plants. The results indicate that Cd toxicity in soil can be alleviated by P application.     

Influence of compost amendments on the hydraulic functioning of brownfield soils

This study assessed the impact of compost on the hydraulic properties of three soils (sandy loam, clay loam and diesel‐contaminated sandy loam) with relatively poor physical quality typical of brownfield sites. Soils were amended with two composts at 750 t/ha. Samples were also collected from a clay‐capped brownfield site, previously amended with 250, 500 or 750 t/ha of compost. Water‐release characteristics and saturated hydraulic conductivity were determined for all soils and physical quality indicators derived. Unsaturated flow in field profiles after compost application with two depths of incorporation and two indigenous subsoils was simulated using Hydrus‐1D. Compost generally increased water retention. Hydraulic conductivity tended to decrease following compost application in sandy loam but increased in clay and clay loam, where compost addition resulted in a larger dominant pore size. Although compost improved physical quality indicators, they remained suboptimum in clay and clay loam soil, which exhibited poor aeration, and in the contaminated sandy loam, where available water capacity was limited, possibly due to changes in wettability. Increasing application rates in the field enhanced water retention at low potentials and hydraulic conductivity near saturation but did not alter physical quality indicators. Numerical simulation indicated that the 500 t/ha application resulted in the best soil moisture regime. Increasing the depth of incorporation in the clay cap improved drainage and reduced waterlogging, but incorporation in more permeable subsoil resulted in prolonged dry conditions to greater depths.     

Effect of High‐Molybdenum Compost on Soils and the Growth of Lettuce and Barley

A pot experiment evaluated the growth of lettuce (Lactuca sativa L.) and barley (Hordeum vulgar) and accumulation of molybdenum (Mo) in plants and soils following amendments of Mo compost (1.0 g kg^?1) to a Truro sandy loam. The treatments consisted of 0 (control), 12.5, 25, and 50% Mo compost by volume. The Mo compost did not affect dry‐matter yield (DMY) up to 25% compost, but DMY decreased at the 50% compost treatment. The 50% compost treatments increased the soil pH an average of 0.5 units and increased the nitric acid (HNO₃)–extractable Mo to 150 mg kg^?1 and diethylenetriaminepentaacetic acid (DTPA)–extractable Mo to 100 mg kg^?1 in the growth medium; the same treatment increased tissue Mo concentration to 569 and 478 mg kg^?1 in the lettuce and barley, respectively. Plants grown in the 25% compost produced about 55 mg kg^?1 of total Mo in the growth medium; this resulted in tissue Mo concentration of 348 mg kg^?1 in lettuce and 274 mg kg^?1 in barley without any phytotoxicity. Our results suggested that 55 mg Mo kg^?1 soil would be an appropriate limit for Mo loading of soil developed from compost additions, a value which is presently greater than the Canadian Council for Ministers of the Environment (CCME) Guidelines for the use of type B compost in Canada.     

Ryegrass yield and nutrient status after biochar application in two Mediterranean soils

This study was conducted to evaluate whether biochar, produced by pyrolysis at 300°C from rice husk and grape pomace (GP), affects plant growth, P uptake and nutrient status. A 3-month period of ryegrass (Lolium perenne L.) cultivation was studied on two Mediterranean agricultural soils. Treatments comprised control soils amended only with compost or biochar, and combinations of biochar plus compost, with the addition of all nutrients but P (FNoP) or without any fertilization at all (NoF). Application of both types of biochar or/with compost, in the presence of inorganic fertilization except P, significantly increased (P < 0.05) dry matter yield of ryegrass (58.9–77.6%), compared with control, in sandy loam soil, although no statistically significant increase was observed in loam soil. GP biochar and GP biochar plus compost amended loam soil harvests gave higher P uptake than control, in the presence of inorganic fertilization except P, whereas in sandy loam soil, a statistical increase was recorded only in the last harvest. In addition, Mn and Fe uptake increased with the addition of the amendments in both soils, while Ca increased only in the alkaline loam soil. Biochar addition could enhance ryegrass yield and P uptake, although inorganic fertilization along with soil condition should receive special attention.     

在盐水浇灌条件下堆肥对土壤性质、小麦生长以及作物营养的影响

A greenhouse experiment was conducted to test and compare the suitability of saline compost and saline irrigation water for nutrient status amendment of a slightly productive sandy clay loam soil,to study the macronutrient utilization and dry matter production of wheat(Triticum aestivum c.v.Gemmiza 7) grown in a modified soil environment and to determine the effects of compost and saline irrigation water on soil productivity.The sandy clay loam soil was treated with compost of five rates(0,24,36,48,and 60 m 3 ha-1,equivalent to 0,3,4.5,and 6 g kg-1 soil,respectively) and irrigation water of four salinity levels(0.50(tap water),4.9,6.3,and 8.7 dS m-1).The results indicated that at harvest,the electrical conductivity(EC) of the soil was significantly(P < 0.05) changed by the compost application as compared to the control.In general,the soil salinity significantly increased with increasing application rates of compost.Soluble salts,K,Cl,HCO 3,Na,Ca,and Mg,were significantly increased by the compost treatment.Soil sodium adsorption ratio(SAR) was significantly affected by the salinity levels of the irrigation water,and showed a slight response to the compost application.The soil organic carbon content was also significantly(P < 0.05) affected by application of compost,with a maximum value of 31.03 g kg-1 recorded at the compost rate of 60 m 3 ha-1 and the irrigation water salinity level of 8.7 dS m-1 and a minimum value of 12.05 g kg 1 observed in the control.The compost application produced remarkable increases in wheat shoot dry matter production.The maximum dry matter production(75.11 g pot-1) occurred with 60 m 3 ha-1 compost and normal irrigation water,with a minimum of 19.83 g pot-1 with no addition of compost and irrigation water at a salinity level of 8.70 dS m-1.Significant increases in wheat shoot contents of K,N,P,Na,and Cl were observed with addition of compost.The relatively high shoot N values may be attributed to increases in N availability in the tested soil caused by the compost application.Similarly,significant increases in the shoot contents of Na and Cl may be ascribed to the increase in soil soluble K and Cl.The increases in shoot P,N,and K contributed to the growth stimulation since P supplied by the compost was probably responsible in saline and alkaline soils where P solubility was very low.     

Soil microbial activity and community composition: Impact of changes in matric and osmotic potential

As saline soils dry, the salt in the remaining solution phase is concentrated and the microbes are subjected to both water and osmotic stress. However, little is known about the interactive effect of matric potential (MP) and osmotic potential (OP) on microbial activity and community structure. We conducted an experiment in which two non-saline soils, a sand and a sandy loam, were pre-incubated at optimal water content (for microbial activity) but different osmotic potentials achieved by adding NaCl. The EC of the saturated paste (ECe) ranged between 1.6 and 11.6 dS m⁻¹ in the sand and between 0.6 and 17.7 dS m⁻¹ in the sandy loam. After the 14-day pre-incubation, the soils were dried to different water contents: 25-35 g kg⁻¹ in the sand and 95-200 g kg⁻¹ in the sandy loam. Water potential (WP, the sum of osmotic + matric potential) ranged from −0.7 to −6.8 MPa in the sand and from −0.1 to −4.4 MPa in the sandy loam. After addition of ground pea straw to increase the concentration of readily available substrate, respiration was measured over 14 days and microbial community composition was assessed by phospholipid fatty acid analysis (PLFA) at the end of the experiment. In both soils, cumulative respiration at a given soil water content (WC) decreased with decreasing osmotic potential, but the effect of decreasing water content differed between the two soils. In the sand, cumulative respiration at the two lowest water contents (WC25 and WC28) was always significantly lower than that at the highest water content (WC35). In the sandy loam, cumulative respiration was significantly lower at the lowest water content (WC95) compared to the highest water content (WC200) only in treatments with added salt. The reduction of cumulative respiration at a given WP was similar in the two soils with a 50% reduction compared to the control (optimal water content, no salt added) at WP −3 MPa. In the sand at WP <−2 MPa, the reduction in fungal fatty acids was greater than that of bacterial fatty acids whereas in the sandy loam, the response of bacteria and fungi to decreasing WP was similar. In both soils, microbial biomass decreased by 35-50% as WP decreased to about −2 MPa but then remained stable with further decreases of WP. Microbial community composition changed with WP in both soils. Our results suggest that there are two strategies by which microbes respond to water potential. A decrease in WP up to −2 MPa kills a proportion of the microbial community, but the remaining microbes adapt and maintain their activity per unit biomass. At lower WP however, the adaptation mechanisms are not sufficient and although the microbes survive, their activity per unit biomass is reduced.     

Comparison of Chemical Methods for Assessing Nitrogen Mineralization in Two Calcareous Soils Treated with Organic Materials

Reliable and quick methods for measuring nitrogen (N)–supplying capacities of soils (NSC) are a prerequisite for using N fertilizers. This study was conducted to develop a routine method for estimation of mineralizable N in two calcareous soils (sandy loam and clay soils) treated with municipal waste compost or sheep manure. The methods used were anaerobic biological N mineralization, mineral N released by 2 M potassium chloride (KCl), ammonium (NH₄ ⁺) N extracted by 1 N sulfuric acid (H₂SO₄), NH₄ ⁺-N extracted by acid potassium permanganate (KMnO₄), and NH₄ ⁺-N released by oxidation of soil organic matter using acidified potassium permanganate. The results showed that oxidizable N extracted by acid permanganate, a simple and rapid measure of soil N availability, was correlated with results of the anaerobic method. Oxidative 0.05 N KMnO₄ was the best method, accounting for 78.4% of variation in NSC. Also, the amount of mineralized N increased with increasing level of organic materials and was greater in clay soil than sandy loam soil.     

Nitrogen and potassium mineralization from winery solid waste composts in sandy and sandy loam soils

This study aimed at quantifying nitrogen (N) and potassium (K) released from winery solid waste (WSW) composts during laboratory incubation to address deficiency in two texturally distinct soils. Composts had 4, 10, 20, 30, 40% (w/w) of filter materials (FMs) mixed with grape marc and pruning canes. The composts were mixed with the soils at equivalent rate of 200 kg N ha^?1 and incubated for 42 days. Quantitatively higher (p < 0.05) ammonium N content was recorded in sandy than sandy loam soil during the incubation duration while exchangeable K was increased in K-deficient sandy soil. Cumulative total mineralized N (TMN) measured during the incubation duration ranged from 59 mg kg^?1 to 672 mg kg^?1 depending on compost type and soil texture while a 10-fold increase in compost FMs content resulted in 144% and 139% increases in cumulative mineralized K in sandy and sandy loam textured soil, respectively. Percent N mineralized from the composts relative to the amount applied during the incubation duration was less than 54% reflecting the composts and soils inherent characteristics. The high ammonium N and K mineralized suggests that farmers must be cautious in utilizing these composts for field crops production due to the potential environmental risks.     

施用碱稳定固体减轻酸性土壤的酸度和铝毒

A pot experiment was catried out to study alleviation of soil acidity and Al toxicity by applying analkaline-stabilised sewage sludge product (biosolids) to an acid clay sandy loam (pH 5.7) and a strongly acidsandy loam (pH 4.5). Barley (Hondeum vulgare L. cv. Forrester) was used as a test crop and was grownin the sewage sludge-amended (33.5 t sludge DM ha^-1) and unamended soils. The results showed that thealka1ine biosloids increased soil pH from 5.7 to 6.9 for the clay sandy loam and from 4.5 to 6.0 for the sandyloam. The sludge product decreased KCl-extractable Al from 0.1 to 0.0 cmol kg^-1 for the former soil and from 4.0 to 0.1 cmol kg^-1 for the latter soil. As a result, barley plants grew much better and grain yield increased greatly in the amended treatments compared with the unamended controls. These observations indicate that alkaline-stabilised biosolids can be used as a liming material for remedying Al phytotoxicity instrongly acid soils by increasing soil pH and lowering Al bioavailability.     

Suppression of methane oxidation in aerobic soil by nitrogen fertilizers,nitrification inhibitors,and urease inhibitors

Concentrations of CH₄, a potent greenhouse gas, have been increasing in the atmosphere at the rate of 1% per year. The objective of these laboratory studies was to measure the effect of different forms of inorganic N and various N-transformation inhibitors on CH₄ oxidation in soil. NH ₄ ⁺ oxidation was also measured in the presence of the inhibitors to determine whether they had differential activity with respect to CH₄ and NH ₄ ⁺ oxidation. The addition of NH₄Cl at 25 g N g^-1 soil strongly inhibited (78–89%) CH₄ oxidation in the surface layer (0–15 cm) of a fine sandy loam and a sandy clay loam (native shortgrass prairie soils). The nitrification inhibitor nitrapyrin (5 g g^-1 soil) inhibited CH₄ oxidation as effectively as did NH₄Cl in the fine sandy loam (82–89%), but less effectively in the sandy clay loam (52–66%). Acetylene (5 mol mol^-1 in soil headspace) had a strong (76–100%) inhibitory effect on CH₄ consumption in both soils. The phosphoroamide (urease inhibitor) N-(n-butyl) thiophosphoric triamide (NBPT) showed strong inhibition of CH₄ consumption at 25 g g^-1 soil in the fine sandy loam (83%) in the sandy clay loam (60%), but NH ₄ ⁺ oxidation inhibition was weak in both soils (13–17%). The discovery that the urease inhibitor NBPT inhibits CH₄ oxidation was unexpected, and the mechanism involved is unknown.     

Soil carbon responses to past and future CO2 in three Texas prairie soils

Changes in soil carbon storage could affect and be affected by rising atmospheric CO₂. However, it is unlikely that soils will respond uniformly, as some soils are more sensitive to changes in the amount and chemistry of plant tissue inputs whereas others are less sensitive because of mineralogical, textural, or microbial processes. We studied soil carbon and microbial responses to a preindustrial-to-future CO₂ gradient (250–500 ppm) in a grassland ecosystem in the field. The ecosystem contains three soil types with clay fractions of 15%–55%: a sandy loam Alfisol, a silty clay Mollisol, and a black clay Vertisol. Soil and microbial responses to atmospheric CO₂ are plant-mediated; and aboveground plant productivity in this ecosystem increased linearly with CO₂ in the sandy loam and silty clay. Although total soil organic carbon (SOC) did not change with CO₂ treatment after four growing seasons, fast-cycling SOC pools increased with CO₂ in the two clay soils. Microbial biomass increased 18% and microbial activity increased 30% across the CO₂ gradient in the black clay (55% clay), but neither factor changed with CO₂ in the sandy loam (15% clay). Similarly, size fractionation of SOC showed that coarse POM-C, the youngest and most labile fraction, increased four-fold across the CO₂ gradient in the black clay, but increased by only 50% across the gradient in the sandy loam. Interestingly, mineral-associated C, the oldest and most recalcitrant fraction, declined 23% across the gradient in the third soil type, a silty clay (45% clay). Our results provide evidence for priming in this soil type, as labile C availability and decomposition rate (measured as soil respiration and soil C mineralization) also increased across the CO₂ gradient in the silty clay soil. In summary, CO₂ enrichment in this grassland increased the fast-cycling SOC pool as in other CO₂ studies, but only in the two high-clay soils. Priming in the silty clay could limit SOC accumulation after prolonged CO₂ exposure. Because soil texture varies geographically, including data on soil types could enhance predictions of soil carbon and microbial responses to future CO₂ levels.