Management of mine spoil for crop productivity with lignite fly ash and biological amendments

Long-term field trials using lignite fly ash (LFA) were carried out in rice crops during the period 1996-2000 at Mine I, Neyveli Lignite Corporation, Tamil Nadu. LFA, being alkaline and endowed with an excellent pozzolanic nature, silt loam texture, and plant nutrients, has the potential to improve the texture, fertility, and crop productivity of mine spoil. The rice crops were the first, third, fifth, and sixth crops in rotation. The other crops, such as green gram (second) and sun hemp (fourth), were grown as green manure. For experimental trials, LFA was applied at various dosages (0, 5, 10, 20, 50, 100, and 200 t/ha), with and without press mud (10 t/ha), before cultivation of the first crop. Repeat applications of LFA were made at the same dosages in treatments of up to 50 t/ha (with and without press mud) before cultivation of the third and fifth crops. Press mud, a lightweight organic waste product from the sugar industry, was used as an organic amendment and source of plant nutrients. Also, a recommended dosage of chemical fertilizer, along with gypsum, humic acid, and biofertilizer as supplementing agents, was applied in all the treatments, including control. With one-time and repeat applications of LFA, from 5 to 20 t/ha (with and without press mud), the crop yield (grain and straw) increased significantly (p < 0.05), in the range from 3.0 to 42.0% over the corresponding control. The maximum yield was obtained with repeat applications of 20 t/ha of LFA with press mud in the third crop. The press mud enhanced the yield in the range of 1.5-10.2% with various dosages of LFA. The optimum dosage of LFA was 20 t/ha for both one-time and repeat applications. Repeat applications of LFA at lower dosages of up to 20 t/ha were more effective in increasing the yield than the corresponding one-time applications of up to 20 t/ha and repeat applications at 50 t/ha. One-time and repeat applications of LFA of up to 20 t/ha (with and without press mud), apart from increasing the yield, evinced improvement in the texture and fertility of mine spoil and the nutrient content of crop produce. Furthermore, some increase in the content of trace and heavy metals and the level of gamma-emitters in the mine spoil and crop produce was observed, but well within the permissible limits. The residual effect of LFA on succeeding crops was also encouraging in terms of eco-friendliness. Beyond 20 t/ha of LFA, the crop yield decreased significantly (p < 0.05), as a result of the formation of hardpan in the mine spoil and possibly the higher concentration of soluble salts in the LFA. However, the adverse effects of soluble salts were annulled progressively during the cultivation of succeeding crops. A plausible mechanism for the improved fertility of mine spoil and the carryover or uptake of toxic trace and heavy metals and gamma-emitters in mine spoil and crop produce is also discussed.     

Fly ash as a liming material for cotton

A field experiment was conducted to determine the effect of fly ash from a coal combustion electric power facility on soil acidity in a cotton (Gossypium hirsutum L.) field. Fresh fly ash was applied to a Bosket fine sandy loam (fine-loamy, mixed, thermic Mollic Hapludalf) soil with an initial soil pH(salt) of 4.8. The fly ash was equivalent to 42 g kg(-1) calcium carbonate with 97% passing through a 60 mesh (U.S. standard) sieve. Fly ash was applied one day before cotton planting in 1999 at 0, 3.4, 6.7, and 10.1 Mg ha(-1). No fly ash was applied in 2000. Within 60 d of fly ash application in 1999, all rates of fly ash significantly increased soil pH above 6.0. Manganese levels in cotton petioles were reduced significantly by 6.7 and 10.1 Mg ha(-1) of fly ash. Soil boron (B) and sodium (Na) concentrations were significantly increased with fly ash. In 1999, B in cotton leaves ranged from 72 to 84 mg kg(-1) in plots with fly ash applications. However, no visual symptoms of B toxicity in plants were observed. In 1999, cotton lint yield decreased on average 12 kg ha(-1) for each Mg of fly ash applied. In 2000, cotton yields were significantly greater for the residual 3.4 and 6.7 Mg fly ash ha(-1) plots than the untreated check. Due to the adverse yield effects measured in the first year following application, fly ash would not be a suitable soil amendment for cotton on this soil at this time.     

Growth and elemental accumulation by canola on soil amended with coal fly ash

To explore the agronomic potential of an Australian coal fly ash, we conducted two glasshouse experiments in which we measured chlorophyll fluorescence, CO2 assimilation (A), transpiration, stomatal conductance, biomass accumulation, seed yield, and elemental uptake for canola (Brassica napus) grown on soil amended with an alkaline fly ash. In Experiment 1, application of up to 25 Mg/ha of fly ash increased A and plant weight early in the season before flowering and seed yield by up to 21%. However, at larger rates of ash application A, plant growth, chlorophyll concentration, and yield were all reduced. Increases in early vigor and seed yield were associated with enhanced uptake of phosphorus (P) by the plants treated with fly ash. Fly ash application did not influence accumulation of B, Cu, Mo, or Zn in the stems at any stage of plant growth or in the seed at harvest, except Mo concentration, which was elevated in the seed. Accumulation of these elements was mostly in the leaves, where concentrations of Cu and Mo increased with any amount of ash applied while that of B occurred only with ash applied at 625 Mg/ha. In Experiment 2, fly ash applied at 500 Mg/ha and mixed into the whole 30 cm soil core was detrimental to growth and yield of canola, compared with restricting mixing to 5 or 15 cm depth. In contrast, application of ash at 250 Mg/ha with increasing depth of mixing increased A and seed yield. We concluded that fly ash applied at not more than 25 Mg/ha and mixed into the top 10 to 15 cm of soil is sufficient to obtain yield benefits.     

Increasing bioavailability of phosphorus from fly ash through vermicomposting

Due to the environmental problems created by large-scale fly ash generation throughout the world, efforts are being made to recycle these materials. An important component of the recycling effort is using fly ash to improve low-fertility soils. Because availability of many nutrients is very low in fly ash, available ranges of such nutrients must be improved to increase the effectiveness of fly ash as a soil amendment. In the present study, we assessed the possibility of increasing P bioavailability in fly ash through vermicomposting in a yard experiment. Fly ash was mixed with organic matter in the form of cow (Bos taurus) dung at 1:3, 1:1, and 3:1 ratios and incubated with and without epigeic earthworm (Eisenia fetida) for 50 d. The concentration of phosphate-solubilizing bacteria (PSB) was found to increase many fold in the earthworm-treated series of fly ash and organic matter combinations compared with the series without earthworm. This helped to transform considerable amounts of insoluble P from fly ash into more soluble forms and thus resulted in increased bioavailability of the nutrients in the vermicomposted series. Among different combinations of fly ash and organic matter, P availability in fly ash due to vermicomposting was significantly higher in the 1:1 fly ash to cow dung treatment compared with the other treatments.     

Valorization of solid waste in sugar factories with possible applications in India : A review

Sugar production is a major agro-based industry in India that generates various solid wastes viz. sugarcane trash, bagasse, press mud and bagasse fly ash. This work examines the state-of-the-art in innovative value added products that can be obtained from the transformation of these wastes. Challenges in implementing these waste valorization solutions are also highlighted. It is observed that the extent of research and adoption of these solutions vary considerably. Both industry involvement as well as government encouragement is required in translating the research findings into commercial products.     

Influence of fly ash on soil physical properties and turfgrass establishment

A field study (1993-96) assessed the benefits of applying unusually high rates of coal fly ash as a soil amendment to enhance water retention of soils without adversely affecting growth and marketability of the turf species, centipedegrass [Eremochloa ophiuroides (Munro) Hack.]. A Latin Square plot design was employed that included 0 (control, no ash applied), 280, 560, and 1120 Mg ha-1 application rates of unweathered precipitator fly ash. The fly ash was spread evenly over each plot area, rototilled, and allowed to weather under natural conditions for 8 mo before seeding. High levels of soluble salts, indicated by the electrical conductivity (EC) of soil extracts, in tandem with an apparent phytotoxic effect from boron (B), apparently inhibited initial plant establishment as shown by substantially lower germination counts in treated soil. However, plant height and rooting depth were not adversely affected, as were the dry matter (DM) yields throughout the study period. Ash treatment did not significantly influence water infiltration rate, bulk density, or temperature of the soil, but substantially improved water-holding capacity (WHC) and plant-available water (PAW). Enhanced water retention capacity improved the cohesion and handling property of harvested sod.     

Management of Fly Ash Through Vermicomposting: A Rational Approach

Fly ash is a by‐product of coal combustion in thermal power plants. Its generation poses several environmental problems, the most important ones being its capacity for causing pollution and the need for large storage areas to keep it out of the environment. Fly ash management remains a major concern in the 21st century; however, despite these challenges, the material has great potential for beneficial use in agriculture due to its efficacy in modifying and improving soil health and improving crop performance. Vermicomposting is an excellent technique for reducing the toxic heavy metals in fly ash through the introduction of earthworms. The activities of several earthworm species minimize the solubility of heavy metals and increase the bioavailability of major nutrient elements such as phosphorous (P) and nitrogen (N). This article provides a comprehensive review of the scope and benefits of vermiremediating fly ash, demonstrating the abilities of different species of earthworms to accumulate heavy metals and increase the availability of plant nutrients. On the basis of a literature survey, the authors have concluded that adopting vermicomposting technology promises increased, effective fly ash utilization for agricultural benefits.     

Soft subgrades’ stabilization by using various fly ashes

This publication presents the results of research involving different types of self-cementing fly ashes (without any other activators) for the stabilization of four different types of soft subgrades from various road sites in Wisconsin, USA. The strength approaches were applied to estimate the optimum mixture design and to determine the thickness of the stabilized layer. The stabilized soil samples were prepared by mixing fly ash at different contents at varying water contents. The performance of fly ash stabilized subbase depends both on the specific source of fly ash and the engineering properties of soils. It is suggested that the performance analysis of fly ash should be based upon the laboratory tests such as index properties, compaction, unconfined compressive strength and CBR tests of a specific site. This is suggested rather than using the study of the physical properties and chemical composition of fly ash and soil. As disclosed in the literature, the strength gain due to stabilization depends mainly upon three factors; ash content, molding water content and compaction delay. The samples were subjected to unconfined compression strength and California bearing ratio (CBR) tests after 7 days curing time to develop water content–strength relationship. To evaluate the impact of compaction delay that commonly occurs in the field during construction, the sets of samples were compacted 2 h later after mixing with water. The unconfined compression strength and CBR tests were performed and used to determine the thickness of the stabilized layer in pavement design. All of these factors were taken into account throughout this research.     

Hybrid poplar and forest soil response to municipal and industrial by-products: a greenhouse study

Little research has been conducted in the Lake States (Minnesota, Wisconsin, and Michigan) to evaluate the effects of municipal and industrial by-product applications on the early growth of short rotation woody crops such as hybrid poplar. Anticipated shortages of harvestable-age aspen in the next decade can be alleviated and rural development can be enhanced through the application of by-products to forest soils. This study was conducted to evaluate the effects of inorganic fertilizer, boiler ash, biosolids, and the co-application of ash and biosolids application on tree growth and soil properties by measuring hybrid poplar clone NM-6 (Populus nigra L. x P. maximowiczii A. Henry) yield, nutrient uptake, and select post-harvest soil properties after 15 wk of greenhouse growth. Treatments included a control of no amendment; agricultural lime; inorganic N, P, and K; three types of boiler ash; biosolids application rates equivalent to 70, 140, 210, and 280 kg available N ha(-1); and boiler ash co-applied with biosolids. All of the by-products treatments showed biomass production that was equal to or greater than inorganic fertilizer and lime treatments. A trend of increased biomass with increasing rates of biosolids was observed. Soil P concentration increased with increasing rates of biosolids application. None of the by-products treatments resulted in plant tissue metal concentrations greater than metal concentrations of plant tissue amended with inorganic amendments. Biosolids, boiler ash, and the co-application of biosolids and boiler ash together on forest soils were as beneficial to plant growth as inorganic fertilizers.     

油田钻井废泥浆固化处理研究

文章结合油田的现场实际情况,针对该区钻井废泥浆污染物的特性,研究了固化的最佳工艺条件,并对固化效果进行评价。通过多组固化处理定性对比实验,从多种处理剂中筛选出处理效果较好的水泥、粉煤灰、石灰和黄土作为固化处理废泥浆的固化剂原材料。利用筛选出的固化剂组成,设计正交实验,确定固化剂最佳配方为每100mL泥浆添加10g水泥、20g粉煤灰、8g石灰、15g黄土。影响因素对固化处理效果的影响实验结果表明:当废泥浆固相含量在30%～70%,固化温度在20～40℃之间,固化时间能够满足7d的条件下,固化效果最佳。     

Changes in Soil Aggregate,Carbon, and Nitrogen Storages Following the Conversion of Cropland to Alfalfa Forage Land in the Marginal Oasis of Northwest China

Maintenance of soil organic carbon (SOC) is important for sustainable use of soil resources due to the multiple effects of SOC on soil nutrient status and soil structural stability. The objective of this study was to identify the changes in soil aggregate distribution and stability, SOC, and nitrogen (N) concentrations after cropland was converted to perennial alfalfa (Medicago sativa L. Algonguin) grassland for 6 years in the marginal oasis of the middle of Hexi Corridor region, northwest China. Significant changes in the size distribution of dry-sieving aggregates and water-stable aggregates, SOC, and N concentrations occurred after the conversion from crop to alfalfa. SOC and N stocks increased by 20.2% and 18.5%, respectively, and the estimated C and N sequestration rates were 0.4 Mg C ha⁻¹ year⁻¹ and 0.04 Mg N ha⁻¹ year⁻¹ following the conversion. The large aggregate (>5 mm) was the most abundant dry aggregate size fraction in both crop and alfalfa soils, and significant difference in the distribution of dry aggregates between the two land use types occurred only in the >5 mm aggregate fraction. The percentage of water-stable macroaggregates (>2, 2–0.25 mm) and aggregate stability (mean weight diameter of water-stable aggregates, WMWD) were significantly higher in alfalfa soils than in crop soils. There was a significant linear relationship between total SOC concentration and aggregate parameters (mean weight diameter) for alfalfa soils, indicating that aggregate stability was closely associated with increased SOC concentration following the conversion of crops to alfalfa. The SOC and N concentrations and the C/N ratio were greatest in the >2 mm water-stable aggregates and the smallest in the 0.25–0.05 mm aggregates in crop and alfalfa soils. For the same aggregate, SOC and N concentrations in aggregate fractions increased with increasing total SOC and N concentrations. The result showed that the conversion of annual crops to alfalfa in the marginal land with coarse-texture soils can significantly increase SOC and N stocks, and improve soil structure.     

Enhancing the Ability of a Soil Moisture‐based Index for Agricultural Drought Monitoring by Incorporating Root Distribution

Agricultural drought differs from meteorological, hydrological, and socioeconomic drought, being closely related to soil water availability in the root zone, specifically for crop and crop growth stage. In previous studies, several soil moisture indices (e.g., the soil moisture index, soil water deficit index) based on soil water availability have been developed for agricultural drought monitoring. However, when developing these indices, it was generally assumed that soil water availability to crops was equal throughout the root zone, and the effects of root distribution and crop growth stage on soil water uptake were ignored. This article aims to incorporate root distribution into a soil moisture‐based index and to evaluate the performance of the improved soil moisture index for agricultural drought monitoring. The Huang‐Huai‐Hai Plain of China was used as the study area. Overall, soil moisture indices were significantly correlated with the crop moisture index (CMI), and the improved root‐weighted soil moisture index (RSMI) was more closely related to the CMI than averaged soil moisture indices. The RSMI correctly identified most of the observed drought events and performed well in the detection of drought levels. Furthermore, the RSMI had a better performance than averaged soil moisture indices when compared to crop yield. In conclusion, soil moisture indices could improve agricultural drought monitoring by incorporating root distribution.     

Properties of several fly ash materials in relation to use as soil amendments

Fly ash samples from five power stations in Western Australia and Queensland, and two soils used for horticulture in Western Australia, were evaluated for a series of physical and chemical properties. Soils were comprised primarily of coarse sand-sized particles, whereas most of the fly ashes were primarily fine sand- and silt-sized particles. Hydraulic conductivities in the fly ashes were 105- to 248-fold slower than in the soils. The water-holding capacities of fly ashes at "field capacity" were three times higher than those of the soils. Extractable P in the fly ashes (except Tarong and Callide) were 20- to 88-fold higher than in the soils. The pH showed considerable variation among the different sources of fly ash, with samples from Muja being the most acidic (pH = 3.8; 1:5 in CaCl2 extract) and from Gladstone the most alkaline (pH = 9.9). The toxicity characteristic leaching procedure (TCLP) values indicate that the potential for release of trace elements from the fly ashes was well below regulatory levels. When applied at sufficient rates (e.g., to achieve 10% w/w in surface layers) to sandy soils, fly ash altered texture and increased water-holding capacity. Depending on the source of fly ash used, such amendments could also provide P and aid nutrient retention by increasing the phosphorus retention index (PRI) and/or cation exchange capacity (CEC). The considerable variability in physical and chemical properties among the fly ash samples evaluated in the present study supports the notion that field trials are essential to the future development of soil amendment strategies making use of any particular source of fly ash.     

RESPONSE FUNCTIONS OF CROPS YIELD TO SOIL MOISTURE STRESS1

: A methodology for determining an optimal irrigation policy to obtain maximum economic yield of crops is presented. The method is based on an empirical response function, relating crop yield to soil moisture stress in different stages of plant growth. The function was developed from data obtained in field experiments on several crops and may be useful in determining when and how much to irrigate. Additionally, a mathematical expression is derived from that function which estimates the economic loss if irrigation is not applied in the opportune moment.     

Utilization of washed MSWI fly ash as partial cement substitute with the addition of dithiocarbamic chelate

The management of the big amount of fly ash as hazardous waste from the municipal solid waste incinerator (MSWI) has encountered many problems in China. In this study, a feasibility research on MSWI fly ash utilization as partial cement substitute in cement mortars was therefore carried out. MSWI fly ash was subjected to washing process to reduce its chlorine content (from 10.16% to 1.28%). Consequently, it was used in cement mortars. Ten percent and 20% replacement of cement by washed ash showed acceptable strength properties. In TCLP and 180-day monolithic tests, the mortars with washed ash presented a little stronger heavy metal leachability, but this fell to the blank level (mortar without washed ash) with the addition of 0.25% chelate. Therefore, this method is proposed as an environment-friendly technology to achieve a satisfactory solution for MSWI fly ash management.     

Acidification-neutralization processes in a lignite mine spoil amended with fly ash or limestone

A laboratory experiment was conducted to investigate the longterm effects of amending sulfide-rich lignite mine spoil with fly ash (originating from a coal-fired power station and largely comprised of aluminosilicates) and/or agricultural limestone. The experiment was carried out with soil moisture maintained at field capacity or alternate cycles of wetting and drying. Results obtained suggest that the principal acidification processes were oxidation of sulfide and formation of hydroxysulfate (FeOHSO4), whereas the main neutralization processes were weathering of aluminosilicates in fly ash-treated samples and dissolution of calcium carbonate in limestone-treated samples. The highest dose of limestone rapidly raised the pH of the spoil, but this increase was not maintained throughout the one-year experiment. In contrast, fly ash-treated samples showed a more sustained increase in pH, attributable to the gradual weathering of aluminosilicates. The best results (i.e., good short- and long-term neutralization) were obtained in samples treated with both fly ash and limestone. The low liming capacity of the fly ash (47.85 cmol kg(-1)) means that it must be used in large quantities, an advantage in achieving the further aim of disposing of the fly ash.     

The reuse of municipal solid waste incinerator fly ash slag as a cement substitute

The results of the treatment of fly ash from a municipal solid waste incinerator (MSWI) by melting are described, and the safety and the effectiveness of using the slag produced by this melting treatment are studied. The properties of the MSWI fly ash slag were analyzed, to evaluate the feasibility of its reuse as a substitute for part of the cement required in mortar preparation. This MSWI fly ash slag was found to be comprised mainly of SiO₂ and CaO, which can be substituted for up to 20% of the cement content in mortar, without sacrificing the quality of the resultant concrete. In fact, the concrete thus produced has greater compressive strength, 10% higher than that without the substitution. The setting time of the fresh mortar becomes lengthens as increasing amounts of cement are replaced; while the spread flow value increases with the increasing percentage of cement substitution. X-ray diffraction analysis reveals that when the W/C=0.38 and the curing AGE=28 days, the crystal patterns in the mortar samples, prepared with different amounts of cement having been replaced by MSWI fly ash slag are similar. According to the results of the toxic characteristic leaching procedure analysis, MSWI fly ash slag should be classified as general non-hazardous industrial waste, that meets the effluent standard. Therefore, the reuse of MSWI fly ash slag is feasible, and will not result in pollution due to the leaching of heavy metals.     

A study of the extraction of vanadium and nickel in oil-fired fly ash

Annual production of oil-fired fly ash in Taiwan is approximately 43 000 tons, of this approximately 13 000 tons is electrostatically precipitated, the rest is cyclonically collected. Structurewise, both consist of porous unburned carbon, vanadium and nickel oxide, and water-soluble sulfate. Electrostatically precipitated fly ash contains large amounts of ammonium sulfate. If these ashes are not properly disposed of, they become environmental problems, such as dusting, leakage of acid liquids, and pollution with heavy metals. This paper discusses the experimental extraction of vanadium and nickel from oil-fired fly ash. The results indicated that leaching of oil-fired fly ash in 0.5 N of sulfuric acid led to an extraction of 65% vanadium, 60% nickel, and 42% iron, along with an increase in the concentration of sulfuric acid. When leached in 2 N sodium hydroxide solution, the extraction of vanadium was 80%, and the extraction of nickel was negligible. If leached in an ammonia water, the extraction of nickel increased, along with an increase in the concentration of ammonia in water. When leached with 4 N ammonia water, the extraction of nickel was 60%, the extraction of vanadium was less than that obtainable from leaching in sulfuric acid solution or in sodium hydroxide solution. If electrostatically precipitated fly ash was leached in a solution of 0.25 N ammonia water and 2 N ammonium sulfate, it would yield an extraction of 60% nickel and 8% vanadium—leading to a selective extraction of nickel. This study has established an extraction flowsheet in which fly ash was first leached in an ammoniacal solution containing ammonium sulfate to recover nickel. The leached residues were then leached in an alkaline solution to recover vanadium.     

Resource conservation strategies for rice‐wheat cropping systems on partially reclaimed sodic soils of the Indo‐Gangetic region,and their effects on soil carbon

The Indo‐Gangetic plain is characterized by intensive agriculture, largely by resource‐poor small and marginal farmers. Vast swathes of salt‐affected areas in the region provide both challenges and opportunities to bolster food security and sequester carbon after reclamation. Sustainable management of reclaimed soils via resource conservation strategies, such as residue retention, is key to the prosperity of the farmer, as well as increases the efficiency of expensive initiatives to further reclaim sodic land areas, which currently lay barren. After five years of experimentation on resource conservation strategies for rice‐wheat systems on partially reclaimed sodic soils of the Indo‐Gangetic region, we evaluated changes in different soil carbon pools and crop yield. Out of all resource conservation techniques which were tested, rice‐wheat crop residue addition (30% of total production) was most effective in increasing soil organic carbon (SOC). In rice, without crop residue addition (WCR), soils under zero‐tillage with transplanting, summer ploughing with transplanting and direct seeding with brown manuring showed a significant increase in SOC over the control (puddling in rice, conventional tillage in wheat). In these treatments relatively higher levels of carbon were attained in all aggregate fractions compared to the control. Soil aggregate sizes in meso (0.25‐2.0 mm) and macro (2‐8 mm) ranges increased, whereas micro (< 0.25 mm) fractions decreased in soils under zero‐till practices, both with and without crop residue addition. Direct seeding with brown manuring and zero tillage with transplanting also showed an increase of 135% and 95%, respectively, over the control in microbial biomass carbon, without crop residue incorporation. In zero tillage with transplanting treatment, both with and without crop residue showed significant increase in soil carbon sequestration potential. Though the changes in accrued soil carbon did not bring about significant differences in terms of grain yield, overall synthesis in terms of balance between yield and carbon sequestration indicated that summer ploughing with transplanting and zero tillage with transplanting sequestered significantly higher rates of carbon, yet yielded on par with conventional practices. These could be appropriate alternatives to immediately replace conventional tillage and planting practices for rice‐wheat cropping systems in the sodic soils of the Indo‐Gangetic region.     

Pesticide applications of copper on perennial crops in California, 1993 to 1998

Inorganic copper is used as a broad-spectrum fungicide and bacteriocide on a variety of agricultural crops. After application, the copper residue typically accumulates in the upper 15 cm of soil. Data from the California Pesticide Use Reports were used to estimate the augmentation of copper in the soil that resulted from pesticide applications for the six years from 1993 to 1998 on 12 crops that are grown without rotation. The estimated mean mg Cu kg(-1) soil added to the upper 15 cm during the six years was the following: walnut (Juglans regia L.), 28; peach [Prunus persica (L.) Batsch var. persica], 22; nectarine [Prunuspersica (L.) Batsch var. nucipersica (Suckow) C.K. Schneid], 19; cherry (Pseudolmedia oxyphyllaria Donn. Sm.), 18; rice (Orvza sativa L.), 16; apricot (Prunus armeniaca L.), 11; orange [Citrus sinensis (L.) Osbeck) and plum (Prunus domestica L. subsp. domestica ), 9; lemon [Citrus limon (L.) Burm.f.] and almond [Prunus dulcis (Mill.) D.A. Webb], 6; pear (Pyrus communis L.), 4; and grape (Vitis vinifera L.), 3. In addition, for the first five of these crops, we estimated the area that was treated with each level of kg Cu ha(-1). For example, for walnut orchards, we estimated that 12 500 ha, or 17% of the planted area, was treated with a quantity of Cu that would increase the total concentration of Cu in the upper 15 cm of soil by at least 50 mg Cu kg(-1) soil. A comparison of the amount of Cu per unit planted area that was applied in the first and second half of the study indicated that the intensity of copper use is either relatively constant or increasing, depending on the crop. The findings are discussed in relation to the potential effect of continued long-term use of Cu pesticides on soil sustainability.