Tillage Effects on Soil Quality Indicators and Nematode Abundance in Loessial Soil under Long‐Term No‐Till Production

Abstract: Soil quality indicators and nematode abundance were characterized in a loessial soil under long‐term conservation tillage to evaluate the effects of no‐till, double‐disk, chisel, and moldboard plow treatments. Indicators included soil electrical conductivity (EC), soil texture, soil organic matter (SOM), and total particulate organic matter (tPOM). Nematode abundance was positively correlated with EC, silt content, and total POM and negatively correlated with clay content. Clay content was the main source of variation among soil quality indicators and was negatively correlated with nematode abundance and most indicators. The gain in SOM in the no‐till system amounted to 10887 kg over the 24 years or 454 kg ha^?1 year^?1, about half of this difference (45%) resulting from soil erosion in plowed soils. The balance of gain in SOM with no till (249 kg ha^?1 year^?1) was due to SOM sequestration with no till. No‐till management reduced soil erosion, increased SOM, and enhanced soil physical characteristics.     

Dissolved and Soil Organic Carbon after Long‐Term Conventional and No‐Tillage Sorghum Cropping

Abstract

Distribution of dissolved (DOC) and soil organic carbon (SOC) with depth may indicate soil and crop‐management effects on subsurface soil C sequestration. The objectives of this study were to investigate impacts of conventional tillage (CT), no tillage (NT), and cropping sequence on the depth distribution of DOC, SOC, and total nitrogen (N) for a silty clay loam soil after 20 years of continuous sorghum cropping. Conventional tillage consisted of disking, chiseling, ridging, and residue incorporation into soil, while residues remained on the soil surface for NT. Soil was sampled from six depth intervals ranging from 0 to 105 cm. Tillage effects on DOC and total N were primarily observed at 0–5 cm, whereas cropping sequence effects were observed to 55 cm. Soil organic carbon (C) was higher under NT than CT at 0–5 cm but higher under CT for subsurface soils. Dissolved organic C, SOC, and total N were 37, 36, and 66%, respectively, greater under NT than CT at 0–5 cm, and 171, 659, and 837% greater at 0–5 than 80–105 cm. The DOC decreased with each depth increment and averaged 18% higher under a sorghum–wheat–soybean rotation than a continuous sorghum monoculture. Both SOC and total N were higher for sorghum–wheat–soybean than continuous sorghum from 0–55 cm. Conventional tillage increased SOC and DOC in subsurface soils for intensive crop rotations, indicating that assessment of C in subsurface soils may be important for determining effects of tillage practices and crop rotations on soil C sequestration.     

Optimum Soil Acidity Indices for Dry Bean Production on an Oxisol in No‐Tillage System

Abstract

Soil acidity is one of the major yield constraints to crop production in various parts of the world. Quantifying optimum soil acidity indices is an important strategy for achieving maximum economic crop yields on acid soils. Five field experiments were conducted for three consecutive years using dry bean as a test crop on an Oxisol. The lime rates used were 0, 12, and 24 Mg ha^?1 for creating a wide range of soil acidity indices in a no‐tillage cropping system. Grain yield of dry bean was significantly increased by improving soil pH, base saturation, calcium (Ca), magnesium (Mg), and potassium (K) saturation and reducing aluminum (Al) saturation. These soil acidity indices were higher in the 0‐ to 10‐cm soil layer than the 10‐ to 20‐cm soil layer for maximum grain yield. Across two soil depths, optimum values for maximum bean yield were pH 6.5, base saturation 67%, Ca saturation 48%, and Mg saturation 19%. Bean yield linearly increased with increasing K saturation in the range of 1.5 to 3% across two soil depths. There was a significant linear decrease in grain yield with increasing Al saturation in the range of 0 to 8% across two soil depths. Optimal values of soil indices for maximum bean yield can be used as a reference for liming and improving yield of bean crop on Oxisols in a no‐tillage cropping system. Yield components, such as pod number, grain per pod, and 100‐grain weight were significantly improved with liming, and bean yield was significantly associated with these yield components.     

Yield,Nutrient Uptake,and Soil Chemical Properties as Influenced by Liming and Boron Application in Common Bean in a No‐Tillage System

Abstract

In Oxisols, acidity is the principal limiting factor for crop production. In recent years, because of intensive cropping on these soils, deficiency of micronutrients is increasing. A field experiment was conducted on an Oxisol during three consecutive years to assess the response of common bean (Phaseolus vulgaris L.) under a no‐tillage system to varying rates of lime (0, 12, and 24 Mg ha^?1) and boron (0, 2, 4, 8, 12, 16, and 24 kg ha^?1) application. Both time and boron (B) were applied as broadcast and incorporated into the soil at the beginning of the study. Changes in selected soil chemical properties in the soil profile (0- to 10‐ and 10- to 20‐cm depths) with liming were also determined. During all three years, gain yields increased significantly with the application of lime. However, B application significantly increased common bean yield in only the first crop. Only lime application significantly affected the soil chemical properties [pH; calcium (Ca²⁺); magnesium (Mg²⁺); hydrogen (H⁺)+ aluminum (Al³⁺); base saturation; acidity saturation; cation exchange capacity (CEC); percent saturation of Ca²⁺, Mg²⁺, and potassium (K⁺); and ratios of exchangeable Ca/Mg, Ca/K, and Mg/K] at both soil depths (0–10 cm and 10–20 cm). A positive significant association was observed between grain yield and soil chemical properties. Averaged across two depths and three crops, common bean produced maximum grain yield at soil pH_w of 6.7, exchangeable (cmol_c kg^?1) of Ca²⁺ 4.9, Mg²⁺ 2.2, H⁺+Al³⁺ 2.6, acidity saturation of 27.6%, CEC of 4.1 cmol_c kg^?1, base saturation of 72%, Ca saturation of 53.2%, Mg saturation of 17.6%, K saturation of 2.7%, Ca/Mg ratio of 2.8, Ca/K ratio of 25.7, and Mg/K ratio of 8.6. Soil organic matter did not change significantly with addition of lime.     

Influence of Tillage and Nutrient Sources on Yield Sustainability and Soil Quality under Sorghum–Mung Bean System in Rainfed Semi‐arid Tropics

The crop production in rainfed semi‐arid tropical (SAT) Alfisols is constrained by low soil organic matter, poor soil fertility, soil structural infirmities, and scarce moisture availability. To offset some of these constraints, a long‐term study of tillage [conventional (CT) and reduced (RT)] and conjunctive nutrient‐use treatments was conducted in SAT Alfisol at Hyderabad, India, under sorghum–mung bean system. The order of performance of the treatments in increasing the sorghum yield was 2 Mg gliricidia loppings + 20 kg nitrogen (N) through urea (T4) (93.2%) > 4 Mg compost + 20 kg N through urea (T3) (88.7%) > 40 kg N through urea (T2) (88.5%) > 4 Mg compost + 2 Mg gliricidia loppings (T5) (82.2%). In the case of mung bean, where half as much N was applied as was to the sorghum, the order of performance of the treatments in increasing the grain yields was T3 (63.6%) >T5 (60.3%) >T4 (58.0%) >T2 (49.6%). Tillage significantly influenced the hydraulic conductivity only, whereas the conjunctive nutrient‐use treatments significantly influenced the predominant physical, chemical, and biological soil‐quality parameters. Among the conjunctive nutrient‐use treatments, T5 was found to be superior in influencing the majority of the soil‐quality parameters and increased the organic carbon by 21.6%, available N by 24.5%, dehydrogenase activity by 56.1%, microbial biomass carbon by 38.8%, labile carbon by 20.3%, and microbial biomass nitrogen by 38.8% over the unamended control and proved superior most in improving soil quality.     

Influence of pH on Productivity,Nutrient Use Efficiency by Dry Bean,and Soil Phosphorus Availability in a No‐Tillage System

Abstract

Low pH is one of the most yield‐limiting factors for crop production in Cerrado soils. The objective of this study was to determine influence of soil pH on grain yield and its components, and use of nutrients by dry bean in a no‐tillage system in an Oxisol (Typic Haplorthox) of the Cerrado region of Brazil. Five field experiments were conducted for three consecutive years. The pH levels were low (5.3), medium (6.4), and high (6.8), created by applying lime at the rates of 0, 12, and 24 Mg ha^?1. Grain yield and its components were significantly influenced by soil pH. Adequate pH for grain yield and its components was 6.4. Maximum variation in grain yield was measured by shoot dry weight, and minimum variation was due to 100‐grain weight. Nutrient utilization efficiency was in the order of magnesium (Mg) > phosphorus (P) > calcium (Ca) > potassium (K) > nitrogen (N) > copper (Cu) > manganese (Mn) > zinc (Zn) > iron (Fe). Soil extractable P increased linearly with increasing pH in the range of 5.3 to 7.3. These results show that adequate soil pH is an important soil acidity index in improving bean yield in Brazilian Oxisols.     

Residue Decomposition and Fate of Nitrogen‐15 in a Wheat Crop under Different Previous Crops and Tillage Systems

Abstract

Nitrogen (N) management may be improved by a thorough understanding of the nutrient dynamics during previous‐crop residue decomposition and its impact on fertilizer N fate in the soil–plant system. An experiment was conducted in the Argentine Pampas to evaluate the effect of maize and soybean as previouscrops and plow‐till and no‐till methods on N dynamics and ¹⁵N‐labeled fertilizer uptake during a wheat growing season. Maize and soybean residues released N under both tillage treatments, but N release was faster from soybean residues and when residues were buried by tillage. Net immobilization of N on decomposing residues was not detected. A regression model that accounted for 92% of remaining N variability included time, previous crop, and tillage treatment as independent variables. The rapid residue decomposition with N release was attributed to the high temperatures of the agroecosystem. The recovery of ¹⁵N‐labeled fertilizer in the wheat crop, soil organic matter, and decomposing residues was not statistically different between previous crop treatments or tillage systems. Crop uptake of fertilizer N averaged 52% across treatments. Forty percent of fertilizer N was removed in grains. Immobilization of labeled N on soil organic matter was substantial, averaging 34% of the ¹⁵N‐labeled fertilizer retained, but was very small on decomposing residues, averaging 0.2–3.0%. Fertilizer N not accounted for at harvest in the soil–plant system was 12% and was ascribed to losses. Previous crop or tillage system had no impact on wheat yield, but when soybean was the previous crop, N content of grain and straw+roots increased. Discussion is presented on the potential availability of N retained in wheat straw, roots, and soil organic matter for future crops.     

Soil fertility in a long‐term fertilizer trial with different tillage systems

The presented results originate from a field experiment established in 1972 on an Eutric cambisol with two main factors: soil tillage (conventional‐, reduced‐, and no‐tillage) and NPK fertilization. The test plants were maize and winter wheat in two years rotation.

The long‐term soil fertility without and with optimum fertilization, the influence of fertilization, tillage and crop sequence on grain yields, the organic carbon content (C_org) and the nitrate infiltration are discussed.

In the course of years without any NPK fertilization grain yields of maize and winter wheat decreased significantly and reached a minimum level which was modified however by the actual climatic conditions. The analogous yield level of optimum NPK fertilization at maize showed a growing tendence while at wheat it remained mostly constant.

The method of soil tillage influenced grain yield of winter wheat to a lesser extent than the yield of maize. Grain yields of maize and winter wheat were consistently lower with no‐till as compared to reduced or conventional tillage, however the differences with w. wheat were much smaller. The effect of tillage was especially high at N₀ P₀ K₀. Crop rotation had a positive effect on the yields of maize. For winter wheat at N₀ P₀ K₀ oneself was the better forecrop, while at optimum N and PK maize performed a little better. C_orgcontent of soil slightly increased in the course of 25 years not only on the fertilized plots but on the nil plots too. Increasing N‐doses showed only a little effect on the C_org. There was a little positive effect of no‐till on C_org content of soil as well as compared fall ploughing. Soil tillage did not much influence the total amount of nitrate in the soil profile. The distribution of nitrate‐N in the soil profile was more affected by the actual climatical circumstances than by the system of tillage. However big nitrate accumulations were found in the subsoil according to different soil tillage systems at some other times, as well as lack of it, which suppose the possibility of a relative quick nitrate infiltration.     

Integration of Soil pH with Soil‐Test Values of Zinc for Prediction of Yield Response in Rice Grown in Mollisols

Seventeen Mollisols having pH_(1:2) in the range of 6.00 to 8.42 were analyzed with five extractants, and the extractable zinc (Zn) ranges were 0.84 to 2.75 mg Zn kg^?1 soil for diethylenetriaminepentaacetic acid (DTPA) (pH 7.3), 0.91 to 2.72 mg Zn kg^?1 soil for DTPA + ammonium bicarbonate (pH 7.6), 1.82 to 7.18 mg Zn kg^?1 soil for Mehlich 3, 1.22 to 3.83 mg Zn kg^?1 soil for ethylenediaminetetraacetic acid (EDTA) + ammonium carbonate, and 0.88 to 1.18 mg Zn kg^?1 soil for 1 mol L^?1 magnesium chloride (MgCl₂) (pH 6.0). Zinc extracted by DTPA (pH 7.3) and Mehlich 3 showed significant positive correlation with sand content, whereas only Mehlich 3 showed negative correlation with soil pH. All extractants showed significant positive correlation with each other except for 1 mol L^?1 MgCl₂‐extractable Zn, which had significant positive correlation with only Mehlich 3– and EDTA + ammonium carbonate–extractable Zn. A greenhouse experiment showed that Bray's percentage yield of rice was poorly correlated to extractable soil Zn but had a significant and negative linear correlation with soil pH (r = ?0.662, significant at p = 0.01). Total Zn uptake by rice had a significant positive correlation with 1 mol L^?1 MgCl₂– and Mehlich 3–extractable Zn. A proposed parameter (p extractable Zn + p OH^?) involving both soil extractable Zn and pH terms together showed significant and positive correlation with Bray's percentage yield and total Zn uptake of rice. The calculated values of critical limits of soil Zn in terms of the proposed parameter were 14.1699 for DTPA (pH 7.3), 13.9587 for DTPA + ammonium bicarbonate, 13.7016 for Mehlich 3, 13.9402 for EDTA + ammonium carbonate, and 14.1810 for 1 mol L^?1 MgCl₂ (pH 6.0). The critical limits of Zn in rice grain and straw were 17.32 and 22.95 mg Zn kg^?1 plant tissue, respectively.     

Application of Near Infrared Reflectance Spectroscopy for the Assessment of Soil Quality in a Long‐Term Pasture

Abstract

The objective of the present study was to assess the ability of near infrared reflectance spectroscopy (NIRS) to analyze chemical soil properties and to evaluate the effects of different phosphorus (P) and potassium (K) fertilization rates on soil quality in different layers of a long‐term pasture. The NIRS calibrations were developed for humus, total Kjeldahl nitrogen (N_Kjeldahl), and several humic substances (HA1, “mobile” humic acids fraction; ΣHA, sum of humic acids; FA1, “mobile” fulvic acids; ΣFA, sum of fulvic acids, etc.) using soil samples of rather heterogeneous origin, collected during 1999–2003. Different spectral preprocessing and the modified partial least squares (MPLS) regression method were explored to enhance the relation between the spectra and measured soil properties. The equations were employed for the quality prediction of a sod gleyic light loam (Cambisol) in five PK fertilization treatments. The soil was sampled in 2000 and 2003 in three field replicates at depths of 0–10, 10–20, 20–30, and 30–50 cm, n=60 samples yr^?1. The best coefficients of correlation, R², between the reference and NIRS‐predicted data were as follows: for N_Kjeldahl, 0.965; humus, 0.938; HA1, 0.903; HA2, 0.905; HA3, 0.924; ΣHA, 0.904; and FA1, 0.911; and ΣFA, 0.885. Our findings suggest that it is feasible to use NIRS for the assessment of the effects of the inorganic PK fertilizer on the soil quality in different depths of a long‐term pasture.     

Bioavailability of Heavy Metals in Biosolids‐Amended Soil

Abstract

A single biosolids application was made to 1.5×2.3 m confined plots of a Davidson clay loam (Rhodic Kandiudult) in 1984 at 0, 42, 84, 126, 168, and 210 Mg ha^?1. The highest biosolids application supplied 750 and 600 kg ha^?1 of Cu and Zn, respectively. Corn (Zea mays L.), from 1984 to 2000, and radish (Raphanus sativus L.) and romaine lettuce (Lactuca sativa var. longifolia), from 2001 to 2004, were grown at the site to assess heavy‐metal bioavailability. Extractable (0.005 diethylenetriamine (DTPA) and Mehlich 1) Cu and Zn were determined on 0 to 15‐cm depth samples from each plot. Corn yield increased with biosolids rate each year until 1993 to 1997, when yield decreased with biosolids rate because of phytotoxicity induced by low (<5.0) soil pH. The corn yield reduction was reversed between 1998 and 2000 upon raising the soil pH to approximately 6.0 by limestone addition following the 1997 season. Between 2001 and 2004, radish and lettuce yields were either not affected or slightly increased with biosolids rate, even as soil pH declined to below 5.5. Plant‐tissue metal concentrations increased with biosolids rate and as pH declined but were always within the normal range of these crops. Mehlich 1 and DTPA extractable metals increased linearly with biosolids rate. Extractability of Cu and Zn decreased approximately 50% over the past 20 years despite a decrease in soil organic matter concentration and greater than 95% conservation of the metals.     

Relationship between the Agricultural Management of a Semi‐arid Soil and Microbiological Quality

Abstract

The establishment of the incidence of different agricultural management practices on soil microbiological quality has become an issue of wide concern. This study was aimed to (i) determine the effect of different agricultural management practices (ecological, integrated, conventional, and conventional with the addition of pig slurry) on the microbial activity of a semi‐arid soil at two different stages (cropped and fallow) and (ii) adapt an existing quantitative method to assess the microbiological soil quality in the different management systems. Several microbial and biochemical parameters, as well as two water‐soluble carbon (C) fractions, were measured in the soil samples. Significant differences (P<0.05) were found between the different agricultural management systems for most of the microbiological parameters during the cropped period. Factorial analysis indicated that adenosine triphosphate (ATP), microbial biomass C, diphenol oxidase activity, urease activity, and water‐soluble carbohydrates had a high weight in factor 1. These parameters were selected to form part of the equation for calculating a microbiological quality index. During the cropped period, the ecological management yielded the highest score of the microbial quality index, whereas, during the fallow period, no differences were found among the index scores of the different agricultural management systems.     

Stretching Soil Sampling to Watershed: Evaluation of Soil‐Test Parameters in a Semi‐arid Tropical Watershed

Soil sampling is an integral component of fertility evaluation and nutrient recommendation for efficient use of nutrients in crop production. Little attention has been devoted to evaluating methodology for sampling watersheds under dryland agriculture. A stratified random sampling methodology for sampling the Appayapally watershed in Mahabubnagar district of Andhra Pradesh state in the semi‐arid tropical region of India was adopted and evaluated. The watershed has an area of about 500 ha, with gentle sloping lands (<1% slope), and 217 farmers own land in the watershed. The soils are Alfisols. A total of 114 soil samples were collected from the top 15‐cm layer to represent the entire watershed. Each sample was a composite of 7–8 cores, randomly collected from the area represented by a crop and group of farmers. The soil samples were air dried, ground, and analyzed for pH, electrical conductivity (EC), organic carbon (C), total nitrogen (N), and extractable phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), sulfur (S), zinc (Zn), manganese (Mn), iron (Fe), copper (Cu), and boron (B). Statistical analysis of the results on soil fertility parameters showed that the mean‐ or median‐based results of soil tests performed in the study did not differ significantly when the sample set size varied from 5 to 114 (100% of the population). Our results indicate that farmers' fields in the Appayapally watershed are uniform in the chemical fertility parameters studied, and even a small sample set size can represent the whole population. However, such a sampling strategy may be applicable only to watersheds that are very gently sloping and where fertilizer use is very low, resulting in an overall low fertility in the whole watershed.     

Heavy‐Metal Contamination of Soil and Vegetables in Wastewater‐Irrigated Agricultural Soil in a Suburban Area of Hanoi,Vietnam

The To Lich and Kim Nguu Rivers, laden with untreated waste from industrial sources, serve as sources of water for irrigating vegetable farms. The purposes of this study were to identify the impact of wastewater irrigation on the level of heavy metals in the soils and vegetables and to predict their potential mobility and bioavailability. Soil samples were collected from different distances from the canal. The average concentrations of the heavy metals in the soil were in the order zinc (Zn; 204 mg kg^?1) > copper (Cu; 196 mg kg^?1) > chromium (Cr; 175 mg kg^?1) > lead (Pb; 131 mg kg^?1) > nickel (Ni; 60 mg kg^?1) > cadmium (Cd; 4 mg kg^?1). The concentrations of all heavy metals in the study site were much greater than the background level in that area and exceeded the permissible levels of the Vietnamese standards for Cd, Cu, and Pb. The concentrations of Zn, Ni, and Pb in the surface soil decreased with distance from the canal. The results of selective sequential extraction indicated that dominant fractions were oxide, organic, and residual for Ni, Pb, and Zn; organic and oxide for Cr; oxide for Cd; and organic for Cu. Leaching tests for water and acid indicated that the ratio of leached metal concentration to total metal concentration in the soil decreased in the order of Cd > Ni > Cr > Pb > Cu > Zn and in the order of Cd > Ni > Cr > Zn > Cu > Pb for the ethylenediaminetetraaceitc acid (EDTA) treatment. The EDTA treatment gave greater leachability than other treatments for most metal types. By leaching with water and acid, all heavy metals were fully released from the exchangeable fraction, and some heavy metals were fully released from carbonate and oxide fractions. The concentrations of Cd, Cr, Cu, Ni, Pb, and Zn in the vegetables exceeded the Vietnamese standards. The transfer coefficients for the metals were in the order of Zn > Ni > Cu > Cd = Cr > Pb.     

Re‐analysis of the Relationship between Organic Carbon and Loss‐on‐Ignition in Soil

The suitability of loss‐on‐ignition (LOI) as an alternative to direct measurement of organic carbon (OC) has been debated for decades without resolution. The literature contains an abundance of different linear regression models to describe the LOI–OC relationship, most based on untransformed values of LOI and OC. Such regression is suspect because the variables are unable to occupy Euclidean space. Logratio transformation—based on relative rather than absolute differences—eliminates this constraint. Re‐analysis of the relationship on new and 10 previously published datasets using logratio techniques reveals that the relationship is nonlinear and that the profusion of regression models is in part a function of the range of LOI. Although LOI may offer a crude estimate of OC at high LOI levels, OC/LOI ratios when LOI is less than about 25% are too variable for reliable OC estimation, and interstudy comparisons remain dubious. Direct measurement of OC is recommended.     

Automated Collector of Terrestrial Systems Used for the Gathering of Soil Atmospheric‐Gas Emissions

Soil greenhouse gas (GHG) emissions are complex, and their study requires considerable sampling of field spatial and temporal differences. Manual and simple automated gas‐collection techniques used at multiple sites during specific time intervals are labor intensive. The objective of this work was to construct a device that can independently collect GHG samples with the accuracy and precision of manually drawn samples. An automated collector of terrestrial systems (ACTS) is a 24‐h, 7‐d/week programmable sampler used in the field for real‐time gathering and containment of soil GHG emissions. The sampler opens and closes an exterior soil gas chamber, mixes gases in the chamber by turning fans on/off, and utilizes programmable circuits to purge the system and draw a sample from the chamber with a pneumatic‐driven syringe. Each sample was stored in an evacuated vial held in a 30‐vial capacity carousel. Vial content was analyzed for carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) at the U.S. Department of Agriculture (USDA)–Agricultural Research Services (ARS) Agroecosystem Management Research Unit (AMRU). A Tracor MT‐220 gas chromatograph (GC) configured with a thermal conductivity detector (TCD) was used for CO₂ analysis, and an automated gas‐sampling system (AGSS) attached to a Varian 3700 GC configured with flame ionization detection (FID) and electron capture detection (ECD) was used for CH₄ and N₂O analysis. Field and laboratory mean values and coefficients of variation (standards and field concentrations of CO₂, CH₄, and N₂O ranging from ambient to 71 kg ha^?1 d^?1 had coefficients of variation ranging from 1.2 to 4.2%) were similar between ACTS and manually drawn samples. Results showed strong correlation (R² = 0.81 to 1.00) between sampling methods. The sampler design provides a realistic and inexpensive approach for collecting emission samples while reducing human error associated with adverse sampling conditions and fatigue. The ACTS has potential for use in monitoring and comparing management practices in terrestrial systems to determine their contribution to GHG emissions.     

Use of Chromameter‐Measured Color Parameters in Estimating Color‐Related Soil Variables

Abstract

Soil color is a soil property that may be used as an interpreting index in estimating processes and properties. Quantifying color allows one to obtain information for rapidly estimating the related processes in soils. CIELAB color parameters L*, a*, and b* of ground (air‐dried and sieved) soil samples and aggregate surfaces of four soil profiles formed in calcareous colluviums in northern Turkey were analyzed. Values of color parameters measured in ground and intact soils were compared and related to soil properties by the regression technique. Results revealed that the L* value obtained with a ground soil sample was a significant predictor of organic matter in A horizons (p < 0.001). Although calcic horizons yielded the highest L* values, no significant relationship was obtained between calcium carbonate contents and lightness of soils in any of horizons studied. The parameters of b* could adequately be used to quantify dithionite‐extractable iron oxide contents in soils studied. The results further showed that the CIELAB color parameters obtained with ground samples were more informative than that of aggrevated samples in relating color parameters to soil properties.     

Distribution of Forms of Zinc and Their Association with Soil Properties and Uptake in Different Soil Orders in Semi‐arid Soils of Punjab,India

Abstract

Profiles of semi‐arid–zone soils in Punjab, northwest India, were investigated for different forms of zinc (Zn), including total, diethylenetriamine penta‐acetic acid (DTPA)-extractable, soil solution plus exchangeable (Zn), Zn adsorbed onto inorganic sites, Zn bound by organic sites, and Zn adsorbed onto oxide surfaces. Irrespective of the different fractions of Zn present, its content was higher in fine‐textured Alfisols and Inceptisols than in coarse‐textured Entisols. In general, the higher content of Zn was observed in the surface horizon and then decreased in the subsurface horizons. However, none of the forms of Zn exhibited any consistent pattern of distribution. Organic matter and size fractions (clay and silt) had a strong influence on the distribution of different forms of Zn. Based upon the linear coefficient of correlation, the soil solution plus exchangeable Zn, adsorbed onto inorganic sites, and DTPA‐Zn increased with increase in organic carbon but decreased with increase in pH and calcium carbonate content. Total Zn increased with increase in clay and silt content. Among the different forms, Zn bound by organic sites, water soluble plus exchangeable Zn and Zn adsorb onto oxide (amorphous surfaces) were all correlated with DTPA extractable Zn. The uptake of Zn was more in recent floodplain Entisols than very fine textured Alfisols and Inceptisols. Among the different forms soil solution +exchangeable and DTPA‐extractable Zn was positively correlated with total uptake of Zn.     

Upper Profile Changes Over Time in an Appalachian Hayfield Soil Amended with Coal Combustion By‐products

Abstract

Large amounts of flue gas desulfurization (FGD) and fluidized bed combustion (FBC) by‐products from burning coal, consisting primarily of gypsum, are available for potential use as a soil amendment. However, information is limited on longer‐term changes in chemical and physical properties induced over time and over small depth increments of the upper soil profile after applying these amendments. This study examined longer‐term effects in an abandoned Appalachian pasture soil amended with various liming materials and coal combustion by‐products (CCBPs). Soil chemical and physical properties were investigated over time and depths. The results indicated limited dissolution and movement of the calcium (Ca) and magnesium (Mg) applied with the chemical amendments, except for Ca and Mg associated with sulfate. However, sufficient dissolution occurred to cause significant increases in exchangeable Ca and Mg and decreases in exchangeable Al that were reflected in corresponding increases in soil pH. These beneficial effects persisted over time and were confined to the upper 0‐ to 15‐cm depth of the profile. The greatest benefits appeared to be in the upper 0‐ to 5‐cm surface layer. Both Ca and Mg applied as calcitic dolomitic limestone tended to be immobilized in the upper 0‐ to 5‐cm layer of the soil profile; Ca more so than Mg. The presence of S applied in the FGD and FBC amendments appeared to enhance the mobility of Ca and Mg. The ratio of Ca/Mg in HCI extracts from the calcitic dolomitic treatment was close to that of applied calcitic dolomite, implying that the inactive component in soil might be the original calcitic dolomite particles. Soil physical properties measured over small depth increments showed that application of the amendments improved the saturated hydraulic conductivity only in the upper 0‐ to 5‐cm depth and had little or no significant effect on the dry bulk density and plant‐available water.