Organic‐Matter Lability and Carbon‐Management Indexes in Agrosylvopasture System on Brazilian Savannah

Abstract

The effect of the introduction of an agrosylvopasture (SASP) system on the changes in the carbon (C) of the soil and its lability were studied. Since 1993, this system has been annually implanted in Paracatu, MG. It was planted under eucalyptus forest abandoned after three cuts, when the brachiaria grass was established. The eucalyptususes were planted at 10×4 m spacing, and the following crops have been grown between the lines: rice in the first year, soybean in the second, and brachiaria in the third. After the third year, pasture of the meat cattle begins on brachiaria and remains until the end of the system cycle that was foreseen for the 11th year. A savannah area and another one with eucalyptusus under a conventional system were used as references to natural condition and the way the area is used before plantation of the SASP, respectively. Some samples aged 1, 2, 3, 6, and 10 years were collected in SASP. According to the obtained results, the following conclusions were drawn: (i) the C contents and stocks were affected before and during the plantation of the SASP by the use and management of SASP, as they were reduced in the first years of the system establishment but improved at the 10th year; (ii) the C from the particulate free light fraction (C_FLLP) that was extracted by potassium permangate (KMnO₄) was sensitive to the use and management, and so reflected the changes in total organic C (TOC); (iii) the more labile fractions of C that were extracted at different concentrations of sulfuric acid (H₂SO₄) satisfactorily reflected the changes in both use and management, whereas the less labile fractions were just slightly affected; and (iv) the C management index (IMC) calculated from C_FLLP was the most sensitive to the changes in use and management. However, when calculated from the C fraction 1 extracted by 3M H₂SO₄ (C_F1), it showed better reliability.     

Mechanical Grinding for Particulate Organic‐Matter Analysis

Abstract

Particulate organic matter (POM) is recognized as a valuable measure of labile soil organic matter. The method usually requires hand‐sieving through a 2‐mm sieve. Hand‐sieving has not been widely adopted by soil testing laboratories, where samples are generally mechanically ground. Composites of 20–25 cores (2×15 cm) were collected from a long‐term crop rotation×fertility treatment study in central Pennsylvania and from 11 central and eastern Pennsylvania farms. Subsamples of each sample were hand‐sieved through a 2‐mm sieve or mechanically ground and analyzed for POM carbon (C). The POM‐C of hand‐sieved and ground samples were similar except for one site with large POM concentrations; at this site, grinding generated lower POM‐C yields than hand‐sieving. Grinding soil samples may be an effective means to increase the availability of POM analysis, but additional work is necessary to determine if this method decreases POM yield, particularly in high POM samples.     

Influence of Dissolved Organic Matter on the Solubility of Heavy Metals in Sewage‐Sludge‐Amended Soils

Abstract

Sewage‐sludge‐amended soils generally contain elevated levels of organic matter and heavy metals compared to control soils. Because organic matter is known to complex with heavy metals, the solubility behavior of the organic matter in such soils may exert a significant influence on the solubility of the metals. Little is known about such a process. Using batch experiments in which the solubility of organic matter in a heavily sludge‐amended soil was artificially manipulated, we show that the solubilities of the heavy metals copper (Cu), nickel (Ni), and lead (Pb) show a strong positive relationship to the solubility of organic matter, particularly at high pH. The results suggest that under field conditions, spatiotemporal variations in the solid–solution partitioning of organic matter may have a bearing on the environmental significance (mobility and bioavailability) of these heavy metals.     

Humic Substance Fractions and Attributes of Histosols and Related High‐Organic‐Matter Soils from Brazil

Abstract

Knowledge of the distribution of soil organic matter (SOM) fractions is important in managing soils toward a sustainable agricultural system in a tropical environment. However, data on Histosols is limited. This study developed 19 profiles of Histosols and soils with high organic-matter content from different regions of Brazil. Soil organic matter was fractionated into fulvic acids (FAF), humic acids (HAF), and humin (HUM). The ratios HAF/FAF and AE (alkaline extract)/HUM were calculated. The objectives were to evaluate the method for SOM fractionating in Histosols and related soils and to correlate the distribution of organic fractions with other soil attributes. The humic fractions presented significant correlations with other soil attributes, the best being the correlation between FAF and nutrient level. The HAF and HUM presented high correlation with cationic exchange capacity, active acidity (H⁺) and pH. Humin and the alkaline extract absorbance measured at 380 nm and 465 nm and presented good correlation with total organic carbon.     

Effects of Linear Alkylbenzene Sulphonates (LASs) on Exogenous Organic Matter Content and Evolution in Sewage Sludge–Amended Soils

Abstract

Linear alkylbenzene sulphonates (LASs) are anionic surfactants commonly used in commercial detergents. A potential risk associated with the recycling of sewage waste materials is the presence of LASs and their primary degradation products, which could accumulate in sludge, especially during anaerobic processing. The long‐term accumulation of these contaminants in soils and especially the potential disturbance of soil functions need to be studied in more detail. In our study, the influence of the amendment added to an agricultural soil with different organic wastes containing LASs on organic matter content and nitrogen (N) content evolution and mineralization was studied in field conditions. A completely randomized 3×3 factorial arrangement, representing two sewage sludge types (composted and uncomposted) and three levels of LAS presence (0, 15, and 30 g/m²) in treated soils, was established using field plots (7×2 m); the results are compared with untreated plots. Statistical models based on covariance analysis were used to understand the dynamics of and the main factors influencing carbon (C) and N mineralization in sewage sludge amended–soils in the presence of LAS. LAS seemed to alter nitrogen mineralization, especially the nitrate dynamics.     

Influence of Organic Manure on Organic Phosphorus Fraction in Soils

The transformation of organic P(Po) from organic manures in two types of soils (ultisol and entisol) and the influences of external addition of organic substance or inorganic P(Pi) on Po under the condition of the 60% maximum water capacity were investigated.The results obtained from Po fractionation experiments indicated that all the Po fractions except for the highly resistant Po fraction decreased during incubation.Application of pig feces and cow feces could largely increase each fraction of Po in the soils.Immediately after application of organic manure into the soils a large part of labile and moderately labile Po from organic manure was transferred into moderately resistant Po,which might be due to the fact that Ca-or Mg-inositol P was precipitated into Fe-inositol P.However,the availability of Po from organic manure in the soils would increase again after incubation because of the transformation of moderately labile and resistant Po fractions into labile Po fractions.Addition of cellulose or Pi into the soils showed a good effect on increasing all the Po fractions except for the highly resistant Po,and this effect was much more pronounced when cellulose was applied in combination with Pi.Therefore,in view of the effect of organic manure on improving P nutrition to plant,attention should be paid to both the Po and the organic substances from organic manure,It is suggested that application of Pi fertilizer combined with organic manure may be referred to as an effective means of protecting Pi from chemical fixation in soil.     

Tillage and Forage System Effects on Forage Yields and Nutrient Uptake under Broiler Litter–Amended Soils

Abstract

Planting and harvesting high‐yielding forage grasses may remove phosphorus (P), copper (Cu), and zinc (Zn) from surface soils with a long history of broiler litter application. A study was conducted in Alabama's Sand Mountain region from 1998 to 2000 to determine tillage and forage systems best suited for removing nutrients from such overloaded soils. Tillage treatments included no‐till, moldboard plowing, chisel plowing, and each combined with paraplowing. Forage treatments included bermudagrass (Cynodon dactylon (L.) Pers.) cv. Russell, tall fescue (Festuca arundinacea Schreb.) cv. Kentucky‐31, and an annual rotation of ryegrass (Lolium multiflorum Lam.) and sorghum sudangrass (Sorghum bicolor L. Moench×Sorghum vulgare sudanense). The annual rotation produced highest yields and P uptake. Moldboard plowing the annual rotation further increased yields. It appears the annual rotation best removes P, Cu, and Zn via plant uptake. Tillage reduced P concentrations in the soil surface in the following order: moldboard>chisel>no‐till.     

Molybdenum Determination in Mehlich‐1 and Mehlich‐3 Soil Test Extracts and Molybdenum Adsorption in Brazilian Soils

Abstract

The extractant Mehlich‐1 is routinely used in Brazil for determination of soil nutrients, whereas Mehlich‐3 has been suggested as a promising extractor for soil fertility evaluation. Both were used for extraction of molybdenum (Mo) in Brazilian soils with Mo dosage by the KI+H₂O₂ method. The Langmuir and Freundlich isotherms were used to study soil Mo adsorption. Mehlich‐1 extracted more Mo than Mehlich‐3 in soils with high contents of organic matter, clay, and iron (Fe) oxides. Mehlich‐3 and Mehlich‐1 extractions correlated positively and significantly with amorphous Fe oxides, crystalline Fe oxides, and organic matter. Molybdenum recovering rates correlated to crystalline Fe oxides and clay contents but not to organic matter, pH, and Mo adsorption capacity. Amorphous and crystalline Fe oxides, clay, and organic matter were responsible for most of the Mo adsorption. The Langmuir isotherm described better the Mo adsorption to soil amorphous Fe oxides and organic matter than the Freundlich isotherm.     

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.     

Loss‐on‐Ignition in the Determination of Pools of Organic Carbon in Soils of Forests and Afforested Arable Fields

Abstract

Loss‐on‐ignition (LOI) and concentration of organic carbon (Cc) were determined on pristine forest soils and soils from afforested arable fields. The objectives were to investigate the relation between the Cc of soil estimated indirectly from LOI and true Cc from dry combustion (C_LECO) and further to evaluate how the applied analytical method affects the carbon pool estimates. According to results, LOI was a good indicator of Cc in the organic layer. As regards mineral soil, however, C_LECO/LOI ratio significantly decreased with increasing depth, and the ratio changed differently in soils underlying forest sites as opposed to the soils from former fields. The results indicate that estimation of carbon pools from conversion factors would lead to considerable bias and that direct measurement of Cc is preferable to the use of any Cc/LOI ratio. The results also emphasize the need for elimination of carbonate carbon when measuring Cc from the soil of arable fields.     

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.     

Effect of Organic Matter and Salinity on Ethylenediaminetetraacetic Acid–Extractable and Solution Species of Cadmium and Lead in Three Agricultural Soils

Abstract

A study was conducted to investigate the chemical speciation of added cadmium (Cd) and lead (Pb) and their availability as influenced by fresh organic matter (OM) and sodium chloride (NaCl) in three agricultural soils. The soils were treated with 20 mg Cd/kg as cadmium nitrate [Cd(NO₃)₂ · 4H₂O], 150 mg Pb/kg as lead nitrate [Pb(NO₃)₂], 20 g/kg alfalfa powder, and 50 mmol/kg of NaCl and then incubated for 3 months at 60% water‐holding capacity (WHC) and constant temperature (25 °C). Subsamples were taken after 1, 3, 6, and 12 weeks of incubation, and electrical conductivity (EC), pH, dissolved organic carbon (DOC), and concentrations of cations and anions were determined in the 1:2.5 soil/water extract. Available Cd and Pb were determined in 0.05 M ethylenediaminetetraacetic acid (EDTA) extract. Concentrations of organic and inorganic species of Cd and Pb in soil solution were also predicted using Visual Minteq speciation program. The most prevalent species of dissolved Pb and Cd in the soils were Pb‐DOC and Cd²⁺ species, respectively. Salinity application increased the available and soluble Cd significantly in the acid and calcareous soils. It, however, had little effect on soluble Pb and no effect on available Pb. Organic‐matter application decreased availability of added Pb significantly in all soils. In contrast, it raised soluble Pb in all soils except for the acid one and approximated gradually to the added Pb with time. Impact of OM on available Cd was somewhat similar to that of Pb. Soluble Cd increased by OM application in the calcareous soil, whereas it decreased initially and then increased with time in the other soils.     

Effects of Soil Texture and CaCO3 on Turnover of Organic Material in Chao Soils

Decomposition experiments of ^14C-labelled sickle alfalfa in chao soils of different texture and these soils after removal of CaCO3 were carried out under field and laboratory conditions respectively.The amount of residual ^14C in,or ^14CO2 evolved from,the soils at intervals after the beginning of devomposition were measured and the distribution of native and labelled C between particle size fractions isolated from these soils was edtermined.Results showed that contents of both labelled (^14C) and non-labelled (^12C) carbon decreased with increasing particle size.The enrichment factor for ^14C was higher than that for ^12C in the clay fraction,the reverse being true for the silt enrichment factors.The effect of soil texture on the decomposition of plant material could not be observed in chao soils when the clay content was lower than 270g kg^-1,while it became obvious once CaCO3 was removed was correlated from these soils.The decomposition rate of plant material in the soil from which the native CaCO3 Was removed was correlated significantly to both the clay content of the soil and the application rate of CaCO3.A preliminary correction equation describing the effect of clay and CaCO3 on the decomposition of organic material in chao soil was derived from the results obtained.     

Effect of Ionic Strength and pH on Cadmium Adsorption by Brazilian Variable‐Charge Soils

Batch adsorption experiments were conducted to assess the effects of pH and ionic strength (I) on cadmium (Cd) adsorption by two Brazilian Oxisols. Adsorption envelopes were constructed through soil sample reactions with 0.01, 0.1, and 1 mol L^?1 calcium nitrate [Ca(NO₃)₂] solutions containing 5 mg L^?1 of Cd, with an increasing pH value from 3 to 8. The adsorption increased drastically with increasing pH, varying from 20 to 90% in a narrow pH range (4–6 in topsoil and 5–6 in subsoil). Gibbs energy (ΔG) for Cd adsorption was negative, and the phenomenon became more thermodynamically spontaneous with an increase in pH. Under the standard 0.01 mol L^?1 I and at pH close to natural, the ΔG values ranged from ?796 to ?3427 J mol^?1. No effect of I was observed on the ΔG values for Cd adsorption at pH values less than 6. At values greater than pH 6, sharp changes in the Cd adsorption pattern were observed on subsoil samples. The only soil attribute significantly correlated with the spontaneity of Cd adsorption was the effective cation exchange capacity, ECEC (r = 0.97; p < 0.1).     

Capability of Loss‐on‐Ignition as a Predictor of Total Organic Carbon in Non‐Calcareous Forest Soils

Abstract

Accurate analyses of large numbers of soil samples are needed in order to reduce the uncertainty of carbon inventories. Loss‐on‐ignition (LOI) is still considered the most convenient assessment method, but its accuracy and precision for predicting total organic carbon (TOC) is questioned. However, our estimation of measurement precision for different samples showed comparable relative standard deviations (RSDs) for LOI and TOC determinations. Highest precision was found in forest floor samples (RSD<1.2%) and lowest (RSD 5–10%) in sandy soil samples low in organic matter. Forest floor samples (n=66) and non‐calcareous mineral soil samples (n=654) were used to calibrate and validate predictive equations. Excellent linear relationships were found. For a wide range of soils the bivariate predictive equation TOC=?0.1046 Clay+0.5936 LOI (r²=0.98) was developed and validated. After correction for clay content, slopes averaged remarkably close to the traditional 0.58 conversion factor.     

Clay,Organic Carbon,Available P and Calcium Carbonate Effects on Phosphorus Release and Sorption–Desorption Kinetics in Alluvial Soils

Information on phosphorus (P) release kinetics and sorption–desorption in soils is important for understanding how quickly reaction approaches equilibrium and replenishes the depleted soil solution. Laboratory experiments were conducted to study the P release and sorption–desorption kinetics in soils differing in clay, soil organic carbon (SOC), available P, and calcium carbonate (CaCO₃) contents. Phosphorus release from soils proceeded in two phases: initially faster phase followed by a slower phase as equilibration progressed. Elovich equation (R² ≥ 0.97**) described well the P release versus time data. P release coefficients for power function were significantly correlated with available P and SOC. Freundlich sorption constants increased with increase in clay and CaCO₃ content. With increase in SOC and available P concentration in soils, substantial reduction in sorption constants was observed. It was concluded that for efficient P management, it is important to take into account soil texture, the existing soil P level, SOC content, and soil calcareousness.     

Enhanced Phosphorus Fertilizer (Carbond P®) Supplied to Maize in Moderate and High Organic Matter Soils

Carbond P (CBP) fertilizer often increases P uptake and crop yields in low P and organic matter soils. A glasshouse study was conducted with maize (Zea mays L.) grown in moderate or high organic matter soil with 0, 5, 15, 45, or 135 kg phosphorus pentoxide (P₂O₅) ha^?1 applied as either ammonium polyphosphate (APP) or CBP. In the high organic matter soil, both CBP and APP fertilization resulted in similar increases in biomass yield and P concentration and uptake. This was also observed in the moderate organic matter soil for maize P concentration, but biomass yield and total P uptake were significantly greater for CBP than APP at the two lowest P rates of fertilization and significantly higher for APP than CBP at the highest P application rate. The presence of high organic matter in the soil seemed to negate the effects of the organic acid bonded P found in CBP.     

2,4‐D Movement in Allophanic Soils from Two Contrasting Climatic Regions

Abstract

Allophanic top‐ and subsoils from the Mexican and Newzealand Central Volcanic Plateau, as well as a nonallophanic sandy loam soil, were sampled to study the impact of organic matter and allophane content on 2,4‐D fate. High sorption rates were found, especially in the two topsoils from Mexico and New Zealand, with distribution coefficient (K _d ) obtained from displacement experiments in packed columns equal to 7.61 and 8.43 L kg^?1 respectively. 2,4‐Dichlorophenoxyacetic acid transfer through the soil columns was found to be in chemical nonequilibrium and was well predicted using a two‐site sorption model. For the two allophanic top soils, K _d obtained from batch was very different to the K _d obtained from column experiments. Either the equilibrium could not be reached in batch or the two‐site model was not able to describe the wide range of sorption sites present in the highly reactive organic matter and allophane components.     

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.     

Metal‐Associated Forms and Speciation in Biosolid‐Amended Oxisols

Abstract

The objective of this study was to determine the effects of pH and ionic strength on the distribution and speciation of zinc (Zn), copper (Cu), and cadmium (Cd) in surface soil samples from two Brazilian Oxisols amended with biosolids. Soils and biosolids were equilibrated in an experimental dual‐chamber diffusion apparatus that permits the soils and biosolids to react through a solution phase via diffusion across a membrane. After equilibrium was reached, soil and biosolids samples were sequentially fractionated to identify various solid forms of Zn, Cu, and Cd. Metal concentrations in the solution phase were determined and mass balance calculated. Equilibrating pH had no major effect on Cu solubility from biosolids and, at pH range from 4 to 7, most Cu remained in the biosolids. Soluble Zn and Cd concentration increased with decreasing pH because of the increased solubility of the biosolids. Copper and Zn were primarily associated with the residual fraction and Fe oxides in one soil, but were primarily associated with chemically unstable fractions, or adsorbed to the surface of oxides, in the other soil. In both soils, Cd was primarily associated with readily bioavailable fractions. The effect of pH on the metal distribution was more evident than the ionic strength effect. Free ions were the predominant metal species in solution, especially at lower pH values.