The effect of sewage‐sludge on the heavy metal content of soils and plant tissue

Abstract

Domestic sewage sludge applied to farm fields at a rate of 44.9 kg/ha in a mixture with lime and sawdust was found to increase the soil levels of cadmium, chromium, copper, lead, mercury, nickel and zinc. The average levels in sludge treated soil were: 0.11, 0.56, 3.59, 2.72, 0.068, 1.49 and 2.57 ppm, respectively. The increases were small and the overall loading factors were well below recommended maximums. The uptake of these heavy metals by grass and legume plants was variable with cadmium, copper and zinc levels being higher in those plants growing in the sludge treated soils but only copper was significantly higher. The heavy metal contents found were all within the levels normally found in grass and legume plants. The higher mean concentration in plants growing on the sludge treated soils were cadmium 0.495; chromium 1.22; copper 12.3; lead 1.54; mercury 0.022; nickel 4.08 and zinc 28.4 ppm.     

A new soil test method for the determination of plant‐available cadmium in soils

Abstract

A new soil test procedure using 1M NH₄Cl was developed for the extraction of plant‐available cadmium (Cd) from soils. Five grams of soil is weighed into a 50‐mL polyethylene vial to which 30 mL of 1M NH₄Cl solution is added. The soil suspension is then shaken on a horizontal shaker for 16 h at 25°C at 180 cycles per min. The suspension is then centrifuged at 2,500g for 5 min and the supernatant filtered through a 0.45 μm nitrocellulose filter under vacuum. Cadmium in the extract is then determined at 228.8 nm on a graphite furnace equipped atomic absorption spectrophotometer. A highly significant correlation was observed between the natural logarithm (In) of 1M NH₄Cl‐extractable Cd in soils and the Cd content in the grain of durum wheat (Triticum turgidum var. durutn L.) grown on the same soils (r = 0.974, p = 3.8 x 10^‐7). In comparison with several commonly used extradants, such as ABDTPA, CaCl₂, NH₄OAc, and NH₄NO₃, the 1M NH₄Cl‐extracted Cd from soils was found to be a better index of Cd availability.     

Copper availability in two soils amended with eleven annual applications of copper‐enriched hog manure

Abstract

Relatively high amounts of Cu are found in manure of hogs (Sus scrofa domesticus) maintained on diets containing growth‐stimulating levels of Cu. While disposal of Cu‐enriched hog manure through repeated long‐term application to agricultural land is commonly practiced, concern exists regarding Cu availability in these soils. Field studies were conducted on a Bertie fine sandy loam (Aquic Hapludults) and a Starr‐Dyke clay loam (Fluventic Dystochrepts‐Typic Rhodudults), located in the Coastal Plain and Piedmont regions of Virginia. The objective was to examine the effects of long‐term Cu application on corn (Zea mays L.) growth and to ascertain the Cu sorption capacity of these soils. Field plots were treated with Cu‐enriched hog manure or CUSO₄ (on an equivalent Cu basis) annually. Manure amendments totaled about 240 t ha^‐1 (dry weight) over an 11 yr period (1978 through 1989). The manure averaged 1300 mg Cu kg^‐1 (dry weight) over this time period totaling 340 kg Cu ha^‐1. Sorption isotherms were determined for sorption of Cu by the Bertie and Starr‐Dyke soils. In comparison with unamended control plots, studies conducted in 1989 showed an early season stunting effect for corn grown on the CUSO₄ treated Bertie soil. No differences in plant heights were observed for corn grown in CuSO₄ treated Starr‐Dyke soil or control plots. Plant growth rates were increased on plots amended with Cu‐enriched hog manure. Copper sorption capacity of Bertie and Starr‐Dyke soils increased following several annual applications of manure.     

Assessment of soil and plant analysis laboratories in the West Asia‐North Africa Region

Abstract

Although limited amount of water is the primary constraint to agricultural productivity in the rainfed area of West Asia and North Africa (WANA), yields are also low because of the poor mineral nutrient status of soils. Yields can, therefore, be considerably increased by judicious fertilizer use. Laboratories for soil and plant analysis are essential for identifying nutrient constraints and providing a basis for efficient fertilizer use, through correlation studies to establish suitable soil testing extractants and calibration studies with crop responses. The Soils Laboratory at the International Center for Agricultural Research in the Dry Areas (ICARDA) has initiated a quality control program among the national agricultural research systems (NARS) in the countries of the WANA region. The efforts include linkages with the Wageningen International Soil Analytical Exchange Program, in‐country training courses, and a laboratory analysis manual. Continued improvement in laboratory performance is dependent upon knowledge of the capabilities of such laboratories and identification of their constraints. This presentation reports a fact‐finding survey of laboratories from 16 countries of the WANA region—mainly public, from universities and ministries of agriculture, and some private or commercial ones—based on a questionnaire about analyses, facilities, methodologies, quality assurance, personnel training, and management. Future efforts to improve the quantity and quality output from of these laboratories will address such deficiencies.     

Evaluation of soil extractants to estimate available micronutrients under wheat‐field conditions

Abstract

Three extracting reagents were evaluated by correlation analyses to provide the best index of Zn, Cu, Mn and Fe availability to wheat (Triticum aestivum L.) plants growing under open field conditions. Twenty one soils were selected to obtain the widest range in properties of soils of the land wheat cultivated. The magnitude of the extractive power varied in the following order: 6NHCl ? EDTA + NH₄OA_C, pH4.65 > DTPA‐TEA, pH 7.3. The mild extractants, EDTA and DTPA, gave the same order of removal of micronutrients being Zn < Cu < Fe < Mn. The acid extractant was on the contrast more effective on Cu and Fe with respect to Zn and Mn, respectively. Wheat concentrations of Zn, Mn and Fe were significantly correlated to soil micronutrients. Highly significant relationships were found for Zn extracted by DTPA solution (r = 0.737***) and for Mn and Fe extracted by EDTA solution (r = 0.710*** and r = 0.564**). Plant Zn and Mn were also well predicted by the acid extraction. The absence of correlation for plant Cu vs. soil Cu occurred probably because of wheat concentrations almost constant, ranging from 5.0 to 8.0 mg/kg.     

Effects of copper on the decomposition of plant residues,microbial biomass,and β-glucosidase activity in soils

Abstract

Two types of soils (Brown Lowland soil and Ando soil), which were artificially enriched with different amounts of Cu, were incubated with or without pulverized orchard grass for 12 weeks at 25°C. For both soils with and without orchard grass amendment, the amount of CO₂ evolved over the 12-week period of incubation decreased by the enrichment with Cu at a concentration exceeding 1,000 mg kg^?1 soil. The decrease of the mineralization of added orchard grass in the Cu-enriched soil was conspicuous especially during the initial period of incubation. The amount of microbial biomass C at the end of the incubation was significantly reduced by the Cu enrichment regardless of the amendment with orchard grass. The relative decrease of the soil microbial biomass was much greater than that of the soil respiration. The amount of biomass C was negatively correlated with the amount of 0.1 M CaCl₂-extractable Cu as a logarithmic function. On the other hand, the β-glucosidase activity at the end of the incubation was not significantly affected by the presence of Cu in the soils without orchard grass amendment and increased with the increase in the amount of enriched Cu in the orchard grass-amended soils.     

Polymorphisms in two homeologous γ-gliadin genes and the evolution of cultivated wheat

The polymorphisms in two -gliadin genes GAG56D and GAG56B on the D- and B-genomes of polyploid wheat, respectively, were investigated by sequencing PCR products and by PCR-RFLP. Of GAG56D, two alleles fo and ok were previously known to occur in hexaploid wheat. Here, we found that 16 sequenced fragments of GAG56D from six recognized subspecies of Triticum aestivum, including 13 contributed by this study, were identical to either the fo or the ok allele. Considering published evidence, it was concluded that the investigated alleles of GAG56D stemmed from two different Aegilops tauschii plants and thus two independent origins of hexaploid wheat. Compared to GAG56D-sequences obtained from 10 accessions of Ae. tauschii, the fo and ok alleles clustered with fragments from three accessions collected in the Caspian region. By sequencing fragments of GAG56B, four distinct allelic groups were found among cultivated wheats, typical of bread wheat (p-aes), durum wheat of gliadin 45-type (a), durum wheat of gliadin 42-type (p-dur) and Timopheev's wheat (p-tim), respectively. Interestingly, the a allele found in gliadin 45-type durum wheat was shared by European spelt cultivars, which strongly supported the hypothesis that European spelt originated from a hybridization event between a tetra- and hexaploid wheat. The data also suggested that emmer might have been domesticated more than once. Phylogenetic analysis of GAG56-fragments obtained from putative B/G-genome donors excluded all candidate species as immediate donors of the B/G-genome, but instead indicated a monophyletic origin of all GAG56B alleles found in polyploid wheat, i.e. including T. timopheevii.     

Nitrogen accumulation efficiency: Relationship between excess fertilizer and soil‐plant biological activity in winter wheat

The point at which nitrogen (N) applied approaches 100% recovery in the soil once plant and microbial sinks have been saturated has not been determined in winter wheat (Triticum aestivum L.) production systems. In dryland winter wheat, subsoil accumulation has not been found to occur until N rates exceed that required for maximum yield. Many conventional N rate experiments have not properly evaluated subsoil N accumulation due to the lack of equally spaced N rates at the high end of the spectrum over which accumulation is expected to occur. Therefore, the objectives of this study were to (i) determine when soil profile accumulation efficiencies reach 100% in continuous winter wheat production and (ii) to evaluate the potential for nitrate‐nitrogen (NO₃ ^‐N) leaching in continuous winter wheat when extremely high rates of fertilizer N are used. Two field experiments (T505 and T222) were conducted for two years using ten N rates (preplant‐incorporated) ranging from 0 to 5376 kg N ha¹. No additional preplant fertilizer was applied in the second year. Following the first and second year wheat harvest, soil cores were taken to 2.4 m and bulk density, ammonium‐nitrogen (NH₄‐N) and NO₃‐N were determined. Crop N‐use efficiency (NUE) (N uptake treated ‐ N uptake check/rate applied) and soil profile inorganic N accumulation efficiencies (NAE) [net inorganic N accumulation in the soil profile/(fertilizer applied ‐ net N removed in the crop)] changed with fertilizer rate and were inversely related. Priming (increased net mineralization of organic N pools when low rates of fertilizer N are applied) may have occurred since increased NUE was observed at low N rates. The highest N‐accumulation efficiencies were at N rates of 168 and 448 kg ha^‐1 in experiments T505 and T222, respectively. At both T222 and T505, no subsoil accumulation of NH₄‐N or NO₃‐N beyond 100 cm was observed for any of the N treatments when compared to the 0‐N check, even when N rates exceeded 448 kg ha^‐1.     

Reactions of copper sulfate with wetland‐taro soils in Hawaii

Abstract

The environmental impact of copper sulfate (CuSO₄#lb5H₂O) must be evaluated before the chemical can be registered as a pesticide to control the apple snail (Pomacea canaliculata) in Hawaii's wetlands. To help achieve this goal, we investigated the sorption‐desorption reactions of CuSO₄#lb5H₂O with six wetland‐taro soils (Tropaquepts) of Hawaii. Our results indicated that: (i) copper (Cu) was sorbed rapidly: 98.0–99.9% of the added Cu was removed from solution within one hour when the loading rate was less than or equal to 300 mg Cu kg^‐1 [initial Cu concentration = 30.0 mg Cu L^‐1 or 12 kg (ha‐cm)^‐1 as CuSO₄#lb5H₂O which is 10 times the maximum recommended rate of pesticide applications, (ii) Cu sorption increased as soil pH increased from 5.0 to 8.0, and (iii) sorption capacity varied from 210 mg Cu kg^‐1 in a Tropaquept from Kauai Island to 500 mg Cu kg^‐1 in another Tropaquept from Maui Island, after seven days of incubation at soil‐solution pH 6.0 and total solution Cu concentration of 0.10 mg Cu L^‐1, a Cu level deemed toxic to some living organisms. It appears that more Cu was sorbed (less Cu remained in solution) if the soil contained high organic carbon (C) and low indigenous Cu. Also, there was an inverse relationship between Cu sorption and desorption by the soils tested: the more Cu a soil can sorb, the tighter it holds Cu, and the less Cu it releases. Since soil pH increases by 1 to 1.5 units upon flooding and Cu sorption increases with increasing pH, the recommended practice of flooding the soil for at least 48 hours between CuSO₄#lb5H₂O application and crop planting should be followed.     

Mehlich‐1‐ and DTPA‐extractable lead in soils in relation to soil properties

Abstract

Mehlich‐1 and DTPA extractants are frequently used to predict metal availability in soils. Metal extractability by the acid or chelate extractant reflects the metal characteristics and metal‐soil interactions. In this study, samples of eight topsoils from the southeastern United States were incubated with added lead (Pb) at the rate of 40 mg#lbkg^‐1. After five months in the greenhouse, Mehlich‐1 and DTPA extractants were employed to extract Pb in both metal‐amended and natural soils. For the natural soils, Pb concentration in the DTPA extractant was always higher than that in the Mehlich‐1 extractant. This indicates that the DTPA chelate extractant is able to dissolve some Pb in soils which is not solubilized by protons. The negative correlation found between Mehlich‐1‐extractable Pb and soil clay content might result from two mechanisms: i) strong association between Pb and soil surfaces, or ii) readsorption of Pb during extraction. None of the correlations between DTPA‐extractable Pb and soil properties was significant, suggesting that the DTPA‐extractable Pb is not heavily dependent on soil properties. The DTPA extractant showed a high ability to solubilize Pb in the natural soils possibly due to a high affinity of Pb for soil organic matter.     

Variation of plant‐test phosphorus for individual lupin and wheat tops

Abstract

Two field experiments measured variation of phosphorus (P) concentration in dried tops (plant‐test P) of individual lupin (Lupinus angustifolius cv. Merrit) and wheat (Triticum aestivum cv. Cadoux) plants collected from random locations in experimental plots treated with different levels of superphosphate. Plant‐test P for the individual tops varied by between 4 to 65% of mean values. Coefficient of variation for the 10 individual plants per plot varied from 10 to 24%. For each plot, mean plant‐test P for the 10 individual tops were similar to values for bulk samples of 30 plants collected at random within the plot. It is concluded that a bulk sample of 30 lupin or wheat plant tops need to be collected from uniform areas in farmer paddocks to provide a representative estimated of the current P status of the crop.     

Association of cadmium,zinc, copper,and nickel with components in naturally heavy metal‐rich soils studied by parallel and sequential extractions

Abstract

In this study, a new parallel and sequential extraction procedure was proposed to investigate the solubility of metals [cadmium (Cd), zinc (Zn), copper (Cu), and nickel (Ni)] and their association with soil components in naturally metal‐rich soils of Norway. Two different soils, alum shale (clay loam) and moraine (loam), developed on alum shale minerals were used. Each soil had two pH levels. For parallel and successive extractions, H₂O, 0.1M NH₄OAc (soil pH), 0.3M NH₄OAc (soil pH), 1M NH₄OAc (soil pH), and 1M NH₄OAc (pH 5.0) were used. A significant amount of Cd was extracted by NH₄O Ac related to concentration of NH₄OAc in the extracting solution. The amounts of Zn, Cu, and Ni extracted by these reagents were almost negligible except with 1M NH₄OAc (pH 5.0). Thus these metals were strongly bound to soil components. A seven step sequential extraction procedure was applied to evaluate the association of metals with soil constituents. The extractions were performed sequentially by extracting the soil with reagents having an increasing dissolution strength: 1M NH₄OAc (soil pH), 1M NH₄OAc (pH 5.0), 1M NH₂OH.HCl (in 25% HOAc), 1M NH₂OH.HCl (in 0.1M HNO₃), 30% H₂O₂ (in 0.1M HNO₃), 30% H₂O₂ (1M HNO₃), and aqua regia. In both soils at both pH levels investigated, appreciable percentages of total Cd (20–50%) were found associated with the NH₄OAc extractable fraction (mobile fraction). For Zn, Cu, and Ni, the percentage of total metal extracted with NH₄OAc was low (<4%), but it increased significantly by introducing a reducing agent (NH₂OH.HCl). The NH₂OH.HCl‐extractable fraction was the greatest fraction (>60%) for all four metals examined. These results suggest that among the metals studied, only Cd was easily desorbed from soil and should be considered mobile and potentially bioavailable. Other metals (Zn, Cu, and Ni) were strongly associated with the soil components and should be considered less available to plants. Using the sequential fractionation technique as a measure of availability, mobility and potential bioavailability of these four metals in the alum shale soils were: Cd>Zn>Ni>Cu.     

Nitrogen balance in a soil‐wheat system under plow‐ and no‐tillage in the argentine humid pampa

Abstract

Changing conventional tillage to conservation tillage systems affects nitrogen (N) cycling in agroecosystems. Our objective was to evaluate the role of soil organic pools, specially plant residues, as sources‐sinks of nitrogen in an humid and warm temperate environment cropped to wheat, under plow‐ and no‐tillage. The experimental site was in the Argentine Pampa on a Typic Hapludoll. A balance‐sheet method was used: Nupt+Nres=Nsow+Nmin, where Nupt=N uptake by the crop at harvest; Nsow=soil mineral N as NH₄ and NO₃ at 0–90 cm depth, one month before sowing, plus N added as fertilizer; Nres=residual soil mineral N as NH₄ and NO₃ at 0–90 cm depth, at harvest; Nmin=N mineralized from humus and plant residues during wheat growing period. Nupt did not differ between tillage systems. Nitrogen supply by the mineral N pool, estimated by the difference Nsow‐Nres, was ca. 150 kg N ha^‐1 in both tillage systems. Plant residues decomposed and released N under both treatments. This organic N pool decreased 77% along the crop cycle. Nmin, calculated using the balance equation was 83 kg N ha^‐1, and did not differ between tillage managements, representing 35% of Nupt. This results highlight the importance of the organic pools as sources of N for wheat in the Humid Pampa. They also brink our attention on the importance for evaluate residue decomposition and humus mineralization in warm‐temperate regions when fertilizer requirements are determined, in order to minimize environmental hazard and economic losses by overfertilization.     

A quick‐test procedure for soil and plant tissue nitrates using test strips and a hand‐held reflectometer

Abstract

Development of a nitrate quick‐test for use by fanners or field consultants would likely encourage the use of plant tissue and soil nitrate tests as a means to improve nitrogen management. To evaluate a quick‐test method, nitrate concentrations in plant tissue and soils were measured using commercially available nitrate test strips and a hand‐held reflectometer. The results were compared with those obtained with standard laboratory methods. Test strip accuracy and precision and reflectometer precision were determined over a 10 day period using standard KNO₃solutions and colored paper strips. Coefficients of variation ranged from 22.4 to 9.5 percent for the test strips and from 3.5 to 1.6 percent for the reflectometer. Quick‐test results were highly correlated with laboratory results for both plant tissue nitrate (r=0.87) and soil nitrate (r=0.98) concentrations. Results indicated that test strips provide a rapid, reasonably accurate and precise method to determine nitrate concentrations in both soil and plant material     

Use of loss‐on‐ignition to assess soil organic carbon in forest soils

Abstract

Forest floor and mineral soils were collected from 169 conifer and hardwood forested plots across Minnesota, Wisconsin, and Michigan. Regression equations were developed between LOI and organic C for 20% of the samples (n=337), and LOI was then used to predict organic C on all of the samples. Results indicated that LOI is a good estimator of organic C in these soils, but that separate equations were needed for different soil strata. Percent organic C in forest floors was greater in conifer stands compared to hardwood (means of 35.1 and 30.1%, respectively)     

Relationship of soil properties to p‐fixing capacity of soils in northern Idaho

Abstract

Phosphorus sorption studies were conducted on volcanic ash influenced surface horizons of 29 northern Idaho soils. Results show that the amount of P sorbed was significantly correlated with citrate‐dithionite extractable aluminum (r = .64**), but not with Fe. Other significantly correlated soil properties were: percent base saturation (r = ‐.73**), percent clay (r = .42**), and exchangeable acidity (r = .39*).     

Orthophosphate and organic phosphate in the soil solution of four sandy soils in relation to pH‐evidence for humic‐FE‐(AL‐) phosphate complexes

Abstract

Soil from the Ap‐horizon of four acid sandy soils differing mainly in Corg content was adjusted to pH values between 3 and 7.5 with NaOH and HCl respectively and incubated for two weeks. Afterwards, displaced soil solution was obtained and analyzed.

The concentrations of Fe, Al, and P showed a broad minimum in the pH range from 4 to 6. The concentration of these elements strongly increased with the increase of pH to 7.5. Acidification below pH values of 4 led to a slight increase.

Separation of dissolved organic carbon by ultrafiltration before the photometric orthophosphate determination decreased measured concentrations in comparison to direct determination in two of the four soils. This decrease was more pronounced for soil solutions with higher concentrations of organic carbon. The effect of acid hydrolysis of organic phosphorus during orthophosphate determination can be explained by existence of humic‐Fe‐(Al phosphate complexes in the soil solution. These complexes can account for more than 50% of the total organic P in solution.     

Influence of air drying and soil gas‐phase carbon dioxide on DTPA‐extractable iron in calcareous soils

Abstract

The extraction of a field‐moist soil with DTPA will result in a level of extractable iron (Fe) lower than that of the air‐dried soil. Soil gas‐phase carbon dioxide (CO₂) levels may be considerably higher than ambient atmospheric levels, especially in wet soils in the field. This study was undertaken to determine whether gas‐phase CO₂ level influences the quantity of Fe extracted by DTPA. Three moist calcareous soils were incubated for 21 days, each at three different partial pressures of CO₂, after which the moist soils were extracted with DTPA. A sample of each soil was also air dried, and was subsequently extracted with DTPA. In each case, DTPA‐extractable Fe from the moist sample was lower than that from the air‐dried sample; however, DTPA‐extractable Fe increased with increasing CO₂ partial pressure of in the moist soils. DTPA‐extractable Fe concentration for a given soil following air drying was not significantly influenced by the CO₂ partial pressure during incubation of the originally field‐moist soil. DTPA‐extract pH of the moist soils followed the same trend as soil‐solution pH (i.e., as CO₂ concentration of the soil gas‐phase increased, soil solution pH and DTPA extract pH both decreased); however, the slope of the pH versus log P_CO2 curve was less pronounced in the DTPA extract due to the buffering capacity of the triethanolamine. From this study, it is concluded that elevated soil gas‐phase CO₂ partial pressure does not contribute to the lower level of DTPA‐extractable Fe observed when the extraction is performed on a field‐moist versus an air‐dried soil; increased CO₂ partial pressure actually resulted in a slight increase in concentration of DTPA‐extractable Fe obtained from a field‐moist soil.     

Interrelationships of minerals in soil‐plant‐animal system at Kuti Ranch,Malawi

Abstract

An experiment was conducted in the central region of Malawi to study the relationship of minerals in soil‐plant‐animal systems to enable prediction of mineral status of beef cattle. Soil, forage and tissues (blood, bone and liver biopsy samples) were collected from cows at the same time in February, April, May, October and December for three consecutive years. Brahman x Malawi Zebu cows were supplemented with mono‐ and di‐calcium phosphate, salt and copper (plus cobalt and selenium) boluses.

Bone, liver and serum minerals (calcium, phosphorus, copper and zinc) correlated poorly to specific minerals in either forage or soil. A few minerals could explain more than 16% of their variation in animal tissues. Consequently, it was concluded that correlation coefficients among soil, plant and animal tissues are low or nonexistent. Therefore, until high, significant, reliable and reproducible correlation coefficients are established among soil, plant animal tissues, prediction of mineral status of animals by regression analysis from mineral content of soil or plants is likely to remain imperfect.     

Residual effects of sewage‐sludge application on plant and soil‐profile chemical composition

Abstract

Long‐term effects on plant and soil‐profile chemical composition imposed by a residential sewage sludge were studied on an Oxisol from Hawaii. Sludge was applied at 0, 45, 90, and 180 Mg/ha in 1983. An NPK‐fertilized treatment was included for comparison. Sudangrass (Sorghum bicolorL. Moench) was grown as a test crop in the 1983–84 and 1986–87 seasons. Soil samples for chemical analysis were taken in 1987 at three depths: 0–23 cm, 23–46 cm, and 46–69 cm.

Beneficial effects of sludge, measured 3 years after application (beginning of the 1986's planting), were evident by large yield increases on sludge‐amended soils relative to the unamended and the NPK‐fertilized soils. The first cutting produced approximately 5 Mg/ha of dry matter from the sludge treatments, regardless of rate, as compared with 3 and 1.5 Mg/ha from the NPK and the 0 treatments. Regrowths showed similar effect, though less dramatic; average yields were 2.6 Mg/ha with sludge and 1.6 Mg/ha without.

Heavy‐metal concentrations in plants were generally unaffected by sludge applications; probably because (i) heavy‐metal contents of the sludge were low, and (ii) soil pH was increased by sludge.

Remarkable increases in pH, exchangeable Ca and extractable P, and resultant decreases in exchangeable Al, in all three soil layers of sludge‐amended soils suggest that surface application of a low heavy‐metal sludge could serve to correct subsoil acidity and enhance subsoil P availability.