Bioavailability of DOC in leachates, soil matrix solutions and soil water extracts from beech forest floors

The biodegradability of dissolved organic carbon (DOC) in different fractions from the forest floor was studied. Soil leachate (SL, the soil solution in macropores which is freely drained from forest floor after rainfall), the soil matrix solution (SMS, the soil solution in meso-/micropores of the soil matrix), and soil water extracts (SWE) from two different beech forest floors were compared. Zero-tension and tension lysimeters were used to collect SL and SMS, respectively. Loss of DOC (during 21 days) and respiration of CO₂-C (during 7 days) were used as conventional measures of the availability of DOC. Bacterial production, measured using the leucine incorporation technique, and bacterial growth efficiency were also estimated. All methods were used to study differences in biodegradability between plots with and without ground flora (Deschampsia flexuosa or Anemone nemorosa) and different type of forest floor (with an organic (O) horizon or a mull (A) horizon). There were no differences in bioavailability of DOC from soil solutions extracted from plots with and without ground flora. The bioavailability of DOC in the different collected soil solutions varied, however. DOC in SWE was the most available, with a mean of 39% of DOC-loss in 21 days, and 18% of DOC being respired in 7 days. DOC in soil matrix solution was the least available of the soil solutions (7% respired), significantly less than DOC in soil leachate (11% respired). The methods measuring biodegradation of DOC, DOC-loss and CO₂-C respiration gave similar results and were comparable to bacterial production and bacterial growth efficiency, with the exception of SWE from the O-horizon at the D. flexuosa site, which had low bacterial production and bacterial growth efficiency, indicating a limitation of the bacterial growth. This study is one of the first to use bacterial production and bacterial growth efficiency for measuring bioavailability in terrestrial environments, giving an extra dimension for the process of biodegradation of DOC.     

Survey of the plant-available silicon status of agricultural soils in Louisiana

Adequate silicon nutrition in plants has shown positive effects on the growth and yield of the crop and physico-chemical properties of the soil. Hence, this study was initiated to survey the plant-available silicon in the agricultural soils of different parishes of Louisiana. Soil samples were collected from 212 representative agricultural fields of 27 agrarian parishes of Louisiana. Poor correlations between deionized water, calcium chloride, and other extractants suggest that the unbuffered calcium chloride extraction may reflect only a transient status of soil soluble silicon similar to deionized water extraction procedure. Also, acetic acid-2 extraction procedure may reflect the net effects of the sorption/desorption reactions by extracting the readily as well as the slowly releasable silicon that control solubility, thus giving a true measure of current availability. Compared to the previously established critical soil silicon levels, several agricultural fields of Louisiana were deemed to be low in plant-available silicon.     

Release of silicon from rice straw under flooded conditions

It is estimated that nearly 20 kg of SiO₂ is removed from the soil by rice plants for producing 100 kg brown rice (Takahashi 1987). Although there is a large amount of silicon in soil, little is available to the rice plant. To supply a sufficient amount of silicon to the rice plant for healthy growth, therefore, it is nccessary to supply various silicon materials to the soil. Rice straw application to the soil is one of the means.     

Simultaneous fluometuron and norflurazon analysis in soil extracts and leachates

Abstract

Rapid, methanol‐extraction techniques for fluometuron (N, N‐dimethyl‐N'‐[3‐(trifluoromethyl) phenyl] urea) and norflurazon (4‐chloro‐5‐(methylamino)‐2‐(3‐(trifluoromethyl)phenyl)‐3(2(H)‐pyridazinone) from fortified soils have been reported to attain >90% recoveries. Analytical methods involving chromatographic separation coupled with fluorescence detection have also been described. The objectives of this study were to describe an analytical method for the simultaneous detection of fluometuron and norflurazon using ultraviolet spectro‐scopy in soil leachates and extracts and to examine the influence of residence time on herbicide recovery from fortified soil. The analytical method requires a gradient HPLC system, a reverse‐phase C‐18 column, and ultraviolet spectroscopy at a wavelength of 240 nm. The method is characterized by high reproducibility (spike recovery and diluted sample results are generally within 10% of the expected herbicide concentrations), low limits of detection (less than 1 (μg/L in soil leachates and 20 μg/L in soil extracts, depending on organic carbon content), and an applicable concentration range of more than two orders of magnitude. The recovery of fluometuron and norflurazon from fortified soils was significantly influenced by equilibration time, loading rate, and soil type (assuming zero chemical degradation). Most significantly, as herbicide contact time with the soil increased, recovery decreased. Thus, herbicide recoveries determined in the laboratory may not provide a true measure of herbicide recoveries from field soils.     

Hydrogen and aluminum inhibition of soybean root extension from limed soil into acid subsurface solutions

Soybean [Glycine max (L.) Merr. cv. ‘Ransom'] root elongation under varying concentrations of solution hydrogen (H) and aluminum (Al) was investigated in a vertical split‐root system. Roots extending from a limed and fertilized soil compartment grew for 12 days into a subsurface compartment with solutions adjusted to either different pH values from 3.7 to 5.5 or a factorial combination of pH (4.0,4.6, and 5.2) and Al (0,7.5, 15, and 30 μM) levels. Ionic forms of Al were estimated with GEOCHEM and solution Al was determined with ferron. Boron (B) (18.5 μM) and zinc (Zn) (0.5 μM) were supplied to all solution treatments, in addition to 2000 μM Ca, after preliminary studies at pH 5.2 without Al indicated that their omission inhibited length of tap roots and their laterals in the subsurface compartment. Both H⁺ and Al inhibited the length of lateral roots more than tap roots. Lateral roots failed to develop on tap roots at pH<4.3 or in treatments with 30 μM Al. Relative tap root length (RRL) among treatments receiving Al correlated with Al as measured by reaction with ferron for 30s. Ferron‐reactive Al was correlated to GEOCHEM‐predicted Al³⁺ activity (r=0.99). A 50% reduction in RRL occurred with either 2.1 μM Al³⁺ activity or 4.9 uM ferron‐reactive Al. The absence of shoot and soil‐root biomass differences among solution treatments in the split‐root system indicated that differences in root growth in the subsurface compartment were not directly confounded with differences in top growth.     

Immobilization of soil copper using organic and inorganic amendments

This experiment aimed to immobilize Cu in polluted agricultural soils via the application of agrochemicals to reduce its bioavailability to plants. A greenhouse pot experiment was established using a Cu contaminated vineyard topsoil collected from a farm in Greece. The soil was mixed with inorganic [i.e., zeolite (Z), Al‐oxide (AX), Mn‐oxide (MX), and phosphate rock (PR)] as well as organic amendments [i.e., activated charcoal (AC), commercial peat soil material (CP), and compost from olive oil processing wastes (COW)] with an application rate of 2.5% and cultivated by corn (Zea maize). After plant harvesting, Cu was measured separately in the aboveground biomass and roots, respectively, whereas the soil samples were analyzed for DTPA‐extractable and geochemical fractions of Cu (soluble + exchangeable fraction, sorbed and carbonate fraction, Fe‐/Mn‐oxides fraction, and organic fraction). The immobilizing agents, except MX, reduced the soluble plus exchangeable Cu in the treated soil. The lowest concentrations of the soluble plus exchangeable Cu occurred in the soil amended with AC followed by CP, AX, COW, PR, and Z, respectively. The amendments decreased the uptake of Cu by corn. Concentrations of Cu were between 11 and 38% lower in the above ground biomass and 19 and 48% lower in the roots than the control. The organic amendments were more effective than the inorganic additives. The AC was the most effective organic additive and AX was the most effective inorganic amendment.     

The dynamic nature of plant-available manganese during storage of a calcareous soil

Summary The effect of length of dry storage period and subsequent moist incubation on the availability of Mn was examined in a calcareous soil. Increasing the time of dry storage (for up to 4 years) generally increased the availability of Mn as determined by plant growth and Mn concentration in wheat and barley. Moist incubation of stored soil had variable effects on Mn availability depending on how long the soil had been stored before use and on the method used to assess Mn availability. When assessed by Mn concentration in plant tissues, increasing the moist incubation time (from 0 to 30 days) of soil stored dry for 4 years increased Mn availability in soil initially and thereafter decreased it. However, incubation time had little effect on Mn availability in soil stored for only 1 year or soil used fresh from the field. When Mn availability was assessed using a chemical extractant (DTPA; diethylenetriaminepentaacetic acid), both soils showed an initial increase in Mn availability immediately on wetting. However, Mn availability in the soil stored for only 1 year decreased rapidly and remained consistently below that of soil stored for 4 years. In the latter soil, Mn availability also decreased but only after a few days. Microbial studies indicated that there was a decrease in the ratio of Mn oxidising to Mn reducing microorganisms with increasing storage time. Inoculation of one soil with another suggested that the factor responsible for the low Mn availability in soils stored for a short period could be transferred to soils stored for a longer period. These results suggest that the change in Mn availability in a calcareous soil with dry storage is a result of changes in microbial populations that cannot be fully restored by moist incubation.     

高聚物土壤改良剂的研究进展

本文综述了高聚物土壤改良剂的分类及其改良土壤的作用机理 ,以及在提高土壤肥力 ,减少水土流失 ,改良干旱土壤 ,盐碱地和污染土壤的再生等方面的应用     

Use of paper mill residuals as soil amendments

Abstract

Different admixtures of soil, paper mill sludge and fly ash were evaluated in greenhouse and field experiments as a final cover for landfills. The admixtures and three grass legume mixtures were evaluated for germination, plant height, biomass production, and root penetration. Admixtures with equal parts soil, sludge and fly ash and with three parts sludge, one part fly ash and one pan soil performed the best in the greenhouse experiment. Heavy metal translocation was not a problem in the admixtures because of the high pH and low metal concentrations.     

Calcium alleviation of hydrogen and aluminum inhibition of soybean root extension from limed soil into acid subsurface solutions

Alleviation by calcium (Ca) of inhibition of soybean [Glycine max (L.) Merr. cv. ‘Ransom'] root elongation by hydrogen (H) and aluminum (Al) was evaluated in a vertical split‐root system. Roots extending from a limed and fertilized soil compartment grew for 12 days into a subsurface compartment containing nutrient solution with treatments consisting of factorial combinations of either pH (4.0, 4.6, and 5.5) and Ca (0.2, 2.0, 10, and 20 mM), Al (7.5, 15, and 30 μM) and Ca (2.0,10, and 20 mM) at pH 4.6, or Ca (2, 7, and 12 mM) levels and counter ions (SO₄ and Cl) at pH 4.6 and 15 μM Al. Length of tap roots and their laterals increased with solution Ca concentration and pH value, but decreased with increasing Al level. Length of both tap and lateral roots were greater when Ca was supplied as CaSO₄ than as CaCl₂, but increasing Ca concentration from 2 to 12 mM had a greater effect on alleviating Al toxicity than Ca source. In the absence of Al, relative root length (RRL) of tap and lateral roots among pH and Ca treatments was related to the Ca:H molar activity ratio of solutions (R²≥0.82). Tap and lateral RRL among solutions with variable concentrations of Al and Ca at pH 4.6 were related to both the sum of the predicted activities of monomeric Al (R²≥0.92) and a log‐transformed and valence‐weighted balance between activities of Ca and selected monomeric Al species (R²≥0.95). In solutions with 15 μM Al at pH 4.6, response of tap and lateral RRL to variable concentrations of CaSO₄ and CaCl₂ were related to predicted molar activity ratios of both Ca:Al³⁺ (R²≥0.89) and Ca:3 monomeric Al (R²≥0.90), provided that AISO₄ and AI(SO₄)₂ species were excluded from the latter index. In all experiments H and Al inhibited length of lateral roots more than tap roots, and a greater Ca:H or Ca:Al concentration ratio was required in solutions to achieve similar RRL values as tap roots.     

四种土壤调理剂对镉、铅的吸附效果研究

采用等温吸附试验研究了主要原料为麦饭石(M)、蒙脱石(T)、牡蛎壳(O)和硅钙矿(S)4种土壤调理剂对溶液中镉和铅的吸附效果。结果表明,4种土壤调理剂对镉和铅的吸附均可用Langmuir方程进行描述;相比而言,4种土壤调理剂对镉吸附量的大小顺序为O调理剂>S调理剂>M调理剂>T调理剂,对铅吸附量的大小顺序为M调理剂>S调理剂>O调理剂>T调理剂;随溶液pH值的增大各调理剂的吸附量逐渐减小,尤其当Cd溶液pH值>8,Pb溶液pH值>6,各调理剂的吸附量迅速降低。     

Response of Desmodium heterocarpon and Gaiactia elliottii to rhizobia and soil amendments

Responses of the tropical legumes, Desmodium heterocarpon and Galactia elliottii, to inoculation with rhizobia and fertilization with N and P were evaluated in greenhouse experiments. Although inoculation with rhizobia was effective in some instances, improvements in plant growth were not obtained in the presence of naturally occurring microbial populations on the Florida Spodosol soil. Phosphorus at 50 kg P/ha increased herbage and root growth of G. elliottii, but not of D. heterocarpon. Seedling growth responses to N indicate that high rates of N fertilization (in combination with heavy grazing) might be effectively used to enhance seedling vigor of D. heterocarpon oversown on bahiagrass (Paspalum notatum) pastures.     

Influence of organic and mineral amendments on microbial soil properties and processes

Microbial diversity in soils is considered important for maintaining sustainability of agricultural production systems. However, the links between microbial diversity and ecosystem processes are not well understood. This study was designed to gain better understanding of the effects of short-term management practices on the microbial community and how changes in the microbial community affect key soil processes. The effects of different forms of nitrogen (N) on soil biology and N dynamics was determined in two soils with organic and conventional management histories that varied in soil microbial properties but had the same fertility. The soils were amended with equal amounts of N (100 kg ha⁻¹) in organic (lupin, Lupinus angustifolius L.) and mineral form (urea), respectively. Over a 91-day period, microbial biomass C and N, dehydrogenase enzyme activity, community structure of pseudomondas (sensu stricto), actinomycetes and α proteobacteria (by denaturing gradient gel electrophoresis (DGGE) following PCR amplification of 16S rDNA fragments) and N mineralisation were measured. Lupin amendment resulted in a two- to five-fold increase in microbial biomass and enzyme activity, while these parameters did not differ significantly between the urea and control treatments. The PCR–DGGE analysis showed that the addition of mineral and organic compounds had an influence on the microbial community composition in the short term (up to 10 days) but the effects were not sustained over the 91-day incubation period. Microbial community structure was strongly influenced by the presence or lack of substrate, while the type of amendment (organic or mineral) had an effect on microbial biomass size and activity. These findings show that the addition of green manures improved soil biology by increasing microbial biomass and activity irrespective of management history, that no direct relationship existed among microbial structure, enzyme activity and N mineralisation, and that microbial community structure (by PCR–DGGE) was more strongly influenced by inherent soil and environmental factors than by short-term management practices.     

Designing relevant biochars as soil amendments using lignocellulosic-based and manure-based feedstocks

Purpose

Biochars are a by-product of the biofuel processing of lignocellulosic and manure feedstocks. Because biochars contain an assemblage of organic and inorganic compounds, they can be used as an amendment for C sequestration and soil quality improvement. However, not all biochars are viable soil amendments; this is because their physical and chemical properties vary due to feedstock elemental composition, biofuel processing, and particle size differences. Biochar could deliver a more effective service as a soil amendment if its chemistry was designed ex ante with characteristics that target specific soil quality issues. In this study, we demonstrate how biochars can be designed with relevant properties as successful soil amendments through feedstock selection, pyrolysis conditions, and particle size choices.

Materials and methods

Biochars were produced by pyrolysis of parent lignocellulosic feedstock sources—peanut hull (PH; Archis hypogaea), pecan shell (PS; Carya illinoensis), switchgrass (SG; Panicum virgatum), pine chips (PC; Pinus taeda), hardwood wastes (wood), and poultry litter manure (PL; Gallus domesticus), as well as blends of these feedstocks at temperatures ranging from 250 to 700 °C. Additionally, blended feedstocks were made into pellets (>2 mm) prior to pyrolysis at 350 °C. Dust-sized (<0.42 mm) biochar was obtained through grinding of pelletized biochars. After chemical characterization, the biochars were evaluated as fertility amendments in a Norfolk soil (fine-loamy, kaolinitic, thermic, Typic Kandiudult) during two different pot incubation experiments.

Results and discussion

PL biochars were alkaline and enriched in N and P, whereas biochar from lignocellulosic feedstocks exhibited mixed pH and nutrient contents. Blending PL with PC resulted in lower biochar pH values and nutrient contents. In pot experiment 1, most biochars significantly (P?<?0.05) raised soil pH, soil organic carbon, cation exchange capacity, and Mehlich 1 extractable P and K. PL biochar added at 20 g?kg^?1 resulted in excessive soil P concentrations (393 to 714 mg?kg^?1) and leachate enriched with dissolved phosphorus (DP, 22 to 70 mg?L^?1). In pot experiment 2, blended and pelletized PL with PC feedstock reduced soil pH and extractable soil P and K concentrations compared to pot experiment 1. Water leachate DP concentrations were significantly (P?<?0.05) reduced by pelletized biochar blends.

Conclusions

Short-term laboratory pot experiments revealed that biochars can have different impacts at modifying soil quality characteristics. Keying on these results allowed for creating designer biochars to address specific soil quality limitations. In the process of manufacturing designer biochars, first, it is important to know what soil quality characteristics are in need of change. Second, choices between feedstocks, blends of these feedstocks, and their accompanying particle sizes can be made prior to pyrolysis to create biochars tailored for addressing specific soil quality improvements. Utilization of these principles should allow for effective service of the designed biochar as a soil amendment while minimizing unwanted ex facto soil quality changes and environmental effects.     

Response of two sorghum genotypes to soil lime and sodium chloride amendments

Abstract

Salinity affects plants by interaction between sodium (Na) and calcium (Ca). Two sorghum (Sorghum bicolor) genotypes ('Hegari’ and ‘NB‐9040') were studied for the Na x Ca interaction in a soil amended with 2% calcium carbonate (CaCO₃) and with 0, 12.3, 24.6, and 36.9 mmol sodium chloride (NaCl)/kg soil. The two genotypes were similar in their response to soil NaCl in their shoot and root growth but differed in response to lime. The salinity‐tolerant Hegari was suppressed by high Ca concentration in the soil, mainly in the low‐NaCl treatments, and responded by a lower concentration of potassium (K) and magnesium (Mg) in the leaves, which was associated with leaf‐chlorosis. Since Na uptake was reduced by Ca, the main effect of salinity on plant growth was by the accumulation of chloride (Cl) in the leaves.     

Spectrophotometric determination of silicon in soil solutions by flow injection analysis: Reduction of phosphate interference

Abstract

A flow injection analysis (FIA) procedure for the determination of dissolved silica (0.04–20 mg/L Si) in aqueous solution has been optimized to reduce phosphate interference. Determinations are based on measurement of absorbance at 790 nm of heteropoly molybdenum blue formed by reduction with ascorbic acid at room temperature. Phosphate did not interfere in a 15‐fold excess. The optimized procedure was tested on soil solutions isolated by centrifugation of various horizons from a Typic Haplohumod. Si concentrations of 1.3–4.8 mg/L Si were found with a variation coefficient of about 2. Results obtained compared well with those obtained by a manual reference method and a proprietary FIA method except in solutions high in dissolved humic material where slightly higher values were obtained by the optimized method. In a standard addition mode the optimized method yielded 5–15% lower values than in the ordinary mode. This difference was reduced by persulfate oxidation of organic matter. Soil solutions investigated were very low in phosphate but phosphate spiking experiments demonstrated that phosphate interference was less than in model solutions matched in metal ion concentrations and insignificant in solutions low in humic material and with less than 10 mg/L P. Dissolved silica was unstable in a solution isolated from an organic horizon of high biological activity.     

Chemical evaluation of vegetables grown with conventional or organic soil amendments

Abstract

Garden vegetables were grown with “organic”; or “commercial”; fertilizer amendments to the soil. Plot preparation and other general cultural practices were identical. Tomatoes, potatoes, peppers, lettuce, onions and peas were planted, and leaf tissue and edible produce were harvested. N, P, K, Ca and Mg and content of ascorbic acid were determined in some of the produce. Certain vegetables were evaluated by a trained taste panel for palata‐bility differences. Generally, the conventional plots produced more yield of vegetables, although seasonal variation was greater than variation due to soil amendments. Mineral content was essentially the same from both regimes. The taste panel preferences were not consistent. From these data, it was concluded that the two methods of vegetable production were equal for quality and nearly equal for yield over the two years.     

Influence of inorganic fertilizers and organic amendments on soil organic matter and soil microbial properties under tropical conditions

 Soil organic matter level, mineralizable C and N, microbial biomass C and dehydrogenase, urease and alkaline phosphatase activities were studied in soils from a field experiment under a pearl millet-wheat cropping sequence receiving inorganic fertilizers and a combination of inorganic fertilizers and organic amendments for the last 11 years. The amounts of soil organic matter and mineralizable C and N increased with the application of inorganic fertilizers. However, there were greater increases of these parameters when farmyard manure, wheat straw or Sesbania bispinosa green manure was applied along with inorganic fertilizers. Microbial biomass C increased from 147 mg kg^–1 soil in unfertilized soil to 423 mg kg^–1 soil in soil amended with wheat straw and inorganic fertilizers. The urease and alkaline phosphatase activities of soils increased significantly with a combination of inorganic fertilizers and organic amendments. The results indicate that soil organic matter level and soil microbial activities, vital for the nutrient turnover and long-term productivity of the soil, are enhanced by use of organic amendments along with inorganic fertilizers. Received: 6 May 1998     

Evaluation of nitrogen availability in a soil treated with organic amendments

Abstract

In the search for an approach which could be used to predict available nitrogen (N) in organic amendments, biological and chemical methods were investigated in laboratory and growth chamber studies. Two biological methods [maize plants (Zea mays L.) grown in pots, and soil‐amendment mixtures incubated aerobically at 2, 4, 6, 8, 12, and 16 weeks], and four chemical methods [autoclave, 0.5M potassium permanganate (KMnO₄), pepsin, and 6M hydrochloric acid (HCl)] were compared to determine N availability in 36 organic amendments applied to soil. Total N mineralized in a soil amended with different organic amendments ranged from‐12 to 428 mg N/kg soil. The highest value was obtained from sludge number 11 and the lowest from cow manure 2, urban refuse, and grape‐marc. In general, the aerobically‐treated sewage sludges gave higher N‐mineralization rates than other amendments. The 6M HCl and autoclave methods were more suitable for predicting N availability in these organic amendments than either the pepsin or KMnO₄ methods. Prediction of N availability in the growth chamber experiments improved if several chemical and biological methods were combined in a multiple regression analysis.     

Long-term effects of organic and synthetic soil fertility amendments on soil microbial communities and the development of southern blight

The effects of tillage and soil fertility amendments on the relationship between the suppressiveness of soils to southern blight and soil physical, chemical and biological factors were examined in experimental station plots in North Carolina. Main plots were either tilled frequently or surface-mulched after one initial tillage. Organic soil amendments including composted cotton gin trash, composted poultry manure, an incorporated rye-vetch green manure, or synthetic fertilizer were applied to subplots in a split-plot design experiment. Incidence of southern blight was lower in surfaced-mulched than tilled soils. Incidence of southern blight was also lower in soils amended with cotton gin trash than those amended with poultry manure, rye-vetch green manure or synthetic fertilizer. Soil water content was negatively correlated with the incidence of disease in both years. Disease incidence was negatively correlated with the level of potassium, calcium, cation exchange capacity (CEC), base saturation (BS) and humic matter in 2002, and net mineralizable nitrogen in 2001. Although, populations of thermophilic organisms were significantly higher in soils amended with cotton gin trash than the other three fertility amendments in each year, there was no significant correlation between the populations of thermophiles and incidence of the disease. Bacterial community diversity indices based on community-level physiological profiling (CLPP) and denaturing gradient gel electrophoresis (DGGE) were significantly higher in soils amended with cotton gin trash than those amended with poultry manure, green manure or synthetic fertilizer. There was a significant negative correlation between the incidence of southern blight, and CLPP and DGGE diversity indices. Greater differences in the richness of bacterial functional groups than genotypes were observed. These results demonstrate that organic soil fertility amendments and cotton gin trash in particular, reduced the development of the disease and affected soil physical, chemical and biological parameters.