Characterization of composted olive mill wastes to predict potential plant disease suppressiveness

Despite its proven agronomic value, the plant disease suppressive effect of composts from olive waste has not been adequately investigated. In the present study, the disease suppressive potential of two olive waste (OW) composts against soil-borne plant pathogens was investigated. Both OW composts showed sizeable, active microbial populations, which were able to grow actively on chitin and cellulose. In plate inhibition trials, OW compost water extracts (CWEs) exerted a significant inhibitory effect on the growth of the pathogens Fusarium oxysporum f.sp. lycopersici (Fol), Pythium ultimum, Phytophtora infestans, Sclerotina sclerotiorum and Verticillium dahliae; and in pot experiments, the OW composts significantly reduced P. ultimum damping-off and Fol wilt diseases on tomato seedlings. The disease suppressive effect of OW composts seems to be due to the combined effects of suppression phenomena caused by the presence of microorganisms competing for both nutrients and space as well as by the activity of specific antagonistic microorganisms.     

Compost-Induced Suppression of Pythium Damping-Off Is Mediated by Fatty-Acid-Metabolizing Seed-Colonizing Microbial Communities

Leaf composts were studied for their suppressive effects on Pythium ultimum sporangium germination, cottonseed colonization, and the severity of Pythium damping-off of cotton. A focus of the work was to assess the role of fatty-acid-metabolizing microbial communities in disease suppression. Suppressiveness was expressed within the first few hours of seed germination as revealed by reduced P. ultimum sporangium germination, reduced seed colonization, and reduced damping-off in transplant experiments. These reductions were not observed when cottonseeds were sown in a conducive leaf compost. Microbial consortia recovered from the surface of cottonseeds during the first few hours of germination in suppressive compost (suppressive consortia) induced significant levels of damping-off suppression, whereas no suppression was induced by microbial consortia recovered from cottonseeds germinated in conducive compost (conducive consortia). Suppressive consortia rapidly metabolized linoleic acid, whereas conducive consortia did not. Furthermore, populations of fatty-acid-metabolizing bacteria and actinobacteria were higher in suppressive consortia than in conducive consortia. Individual bacterial isolates varied in their ability to metabolize linoleic acid and protect seedlings from damping-off. Results indicate that communities of compost-inhabiting microorganisms colonizing cottonseeds within the first few hours after sowing in a Pythium-suppressive compost play a major role in the suppression of P. ultimum sporangium germination, seed colonization, and damping-off. Results further indicate that fatty acid metabolism by these seed-colonizing bacterial consortia can explain the Pythium suppression observed.     

Compost amendments enhance peat suppressiveness to Pythium ultimum,Rhizoctonia solani and Sclerotinia minor

Peat is the most common organic material used for the preparation of potting mix because of its homogeneous and favorable agronomic characteristics. However, this organic material is poorly suppressive against soilborne pathogens and fungicides are routinely used to manage damping-off diseases. In the present study, we investigated the suppressive capability of five compost – peat mixtures towards the plant pathogens Pythium ultimum, Rhizoctonia solani and Sclerotinia minor – Lepidium sativum pathosystems. For all organic media, 18 parameters were measured including enzymatic activities (glucanase, N-acetyl-glucosaminidase, chitobiosidase and hydrolysis of fluorescein diacetate), microbiological (BIOLOG® EcoPlates?, culturable bacteria and fungi), and chemical features (pH, EC, total, extractable and humic carbon, total and organic N, NH₄–N, total protein and water content). In addition, ¹³C-CPMAS-NMR spectroscopy was used to characterize the organic materials. Peat amended with composts reduced disease damping-off caused by P. ultimum, R. solani and S. minor in 60% of the mixtures and compost derived from animal manure showed the largest and most consistent disease suppression. Sterilization decreased or eliminated suppressiveness of 42.8% of the mixtures. The most useful parameters to predict disease suppression were different for each pathogen: extractable carbon, O-aryl C and C/N ratio for P. ultimum, alkyl/O-alkyl ratio, N-acetyl-glucosaminidase and chitobiosidase enzymatic activities for R. solani and EC for S. minor. Our results demonstrate that the addition of composts to peat could be useful for the control of soilborne pathogens.     

Suppression of Root Rot on Peas, Beans and Beetroots Caused by Pythium ultimum and Rhizoctonia solani through the Amendment of Growing Media with Composted Organic Household Waste

In pot experiments under controlled environmental conditions, composted organic household waste showed a suppression of soilborne plant pathogens. The addition of 8 %, 10 % and 30 % compost to the potting material which was artificially infested with Pythium ultimum or Rhizoctonia solani considerably reduced the incidence of disease in different varieties of host plants. It became evident that the degree of protection provided by compost depends upon the amount of compost added and upon the vulnerability of the host plant to infection. In an experiment using increasing levels of inoculum, the compost proved suppressive to the pathogen even under extreme disease conditions. This suppressive effect was still evident in compost which had been stored for prolonged periods.     

Microbial Properties of Composts That Suppress Damping-Off and Root Rot of Creeping Bentgrass Caused by Pythium graminicola

Composts prepared from a variety of feedstocks were tested for their ability to suppress seedling and root diseases of creeping bentgrass caused by Pythium graminicola. Among the most suppressive materials in laboratory experiments were different batches of a brewery sludge compost and a biosolids compost from Endicott, N.Y. Batches of these composts that were initially not suppressive to Pythium damping-off became more suppressive with increasing compost age. Leaf, yard waste, food, and spent mushroom composts as well as certain biosolids, cow manure, chicken-cow manure, and leaf-chicken manure composts were not suppressive to Pythium damping-off. In some cases, turkey litter, chicken manure, chicken-leaf, and food waste composts were inhibitory to creeping bentgrass seed germination in laboratory experiments. Microbial populations varied among all of the composts tested. Bacterial populations were high in all composts except the turkey litter compost, in which populations were 1,000- to 10,000-fold lower than in the other composts tested. Among the highest populations of heterotrophic fungi and antibiotic-producing actinomycetes were those found in all batches of the brewery sludge compost, whereas the lowest populations were found in turkey litter, chicken manure, and food waste composts. Heat treatment of suppressive composts reduced populations of bacteria, fungi, and actinomycetes in all composts tested. Disease suppressiveness was also reduced or eliminated in heated composts. Amending heated composts with small amounts of nonheated compost restored suppressive properties and partially restored microbial populations to wild-type levels. A strong negative relationship between compost microbial activity (as measured by the hydrolysis of fluorescein diacetate) and Pythium damping-off severity was observed. When composts were applied to creeping bentgrass in field experiments, a significant level of suppressiveness was evident with some composts when disease pressure was high (i.e., disease ratings high in uninoculated plots). A 1991 batch of turkey litter compost and the 1990 batch of Endicott biosolids were consistently suppressive to foliar symptoms of Pythium root rot on creeping bentgrass. This study indicates that suppression of Pythium diseases of creeping bentgrass in batches of brewery sludge and Endicott biosolids composts, and possibly in other suppressive composts examined in less detail in this study, is related directly to the microbial activities in the composts. On the other hand, the mechanisms of Pythium suppression in turkey litter and perhaps other poultry-based composts is not related directly to the compost microbial activity. Although turkey litter showed a lack of suppressiveness in laboratory bioassays and low microbial populations and activity, it resulted in a significant and consistent level of suppressiveness in field experiments. Therefore, the microbiological properties of Pythium-suppressive composts may differ substantially, and measurements of microbial populations and activity may not be predictive of the level of disease suppression in all composts.     

Effect of chitin waste-based composts produced by two-phase composting on two oomycete plant pathogens

Biphasic composts were prepared by first mixing peat moss and sawdust with a nitrogen-rich biomass such as chitinous waste or cow manure and composting them until termination of the thermophilic phase. These partially stabilized composts were then amended with shrimp waste inducing a second thermophilic phase. Filter-sterilized water extracts obtained from two mature biphasic composts (SP₂W₂+S and MPW+S) reduced the growth of two oomycete plant pathogens, Phytophthora fragariae var. rubi and Pythium ultimum. Both SP₂W₂+S and MPW+S composts significantly reduce the incidence of cucumber damping-off caused by Pythium ultimum as compared to a commercial brand of compost made from shrimp waste and peat moss. Hydrolysis products of chitin were unlikely to be responsible for growth inhibition since no oligomeric forms of chitin were detected in SP₂W₂+S. The shrimp waste amendment carried out after the first thermophilic phase modified the microbial populations of biphasic composts. Following the amendment, the proportion of branched-chain microbial fatty acids typical of Gram-positive bacteria increased considerably suggesting that this group of bacteria became more prevalent within the total microbial population. These data suggests that the two-phase composting process promotes the proliferation of Gram-positive bacteria antagonistic to oomycete plant pathogens.     

Assessment of survival of Listeria monocytogenes,Salmonella Infantis and Enterococcus faecalis artificially inoculated into experimental waste or compost

Aims: To evaluate survival of pathogenic strains, Listeria monocytogenes and Salmonella Infantis and a sanitation indicator Enterococcus faecalis in composts at different stages of the composting process and during storage. Methods and Results: The studied pathogenic and indicator strains, originally isolated from compost, were inoculated into compost samples from the various stages of the composting process. During incubation, indigenous microflora diversity was monitored with DGGE analysis. After 90 days of incubation, strain survival was observed in compost sampled before the beginning of the cooling phase, and DGGE analysis demonstrated an increase of microbial diversity up to the cooling phase. However, inoculated strains were not detected in composts after 30, 60 or 90 days of incubation in compost sampled after the start of the cooling phase. Microbial diversity also became stable, and DGGE profiles reached a maximum number of bands at this stage. Conclusions: Strain survival was not observed in stabilized composts. The cooling phase seems to be the turning point for pathogen survival and at this stage the indigenous microflora appeared to play a significant role in suppression. Significance and Impact of the Study: The importance of indigenous microflora in the survival of pathogens in four different composts was demonstrated. Stabilized composts were recommended for spreading on land.     

Impact of compost application on Fusarium wilt disease incidence and microelements contents of basil plants

Fusarium oxysporum was isolated from stem of basil plants showing symptoms of wilt, stem blight and collar root rot. Pathogenicity tests indicated that F. oxysporum f. sp. basilici is the causal agent of this disease. This is the first report of this pathogen in Egypt. The suppressive effects of six types of composts on Fusarium wilt disease incidence in basil were evaluated under greenhouse conditions. The effectiveness of these composts and their relation to the microelements content in treated plants was also assessed. Soil treatments with Khaya and Eucalyptus composts significantly reduced the infection percentage and disease severity of basil wilt. Otherwise, the applications of Araucaria, Datura, Ficus and Azadirachta composts showed no effect on both infection percentage and disease severity. Moreover, the Khaya and Eucalyptus compost treatments increased the levels of Iron (Fe), Zinc (Zn) and Manganese (Mn) in treated basil plants than application of Araucaria, Datura, Ficus and Azadirachta composts. In the case of Copper (Cu) content, it was significantly higher only in Eucalyptus-compost-treated plants than in other compost applications. These composts not only reduced the disease incidence but also increased both fresh and dry weight (FW and DW) and microelements contented in basil treated plants. In general, although soil amendment with either Khaya or Eucalyptus compost can reduce the disease incidence of Fusarium wilt on basil plants, microelements contented; FW and DW of these effects can be variable depending on their levels added in soil. According to the results of this study, it can be concluded that the use of compost in the soil as an organic fertiliser increased exchangeable form of microelements in the soil and also the availability of these elements by basil plants.     

The effects of spent mushroom compost and municipal solid waste compost on Phytophthora drechsleri in vivo and in vitro

Leached spent mushroom compost (SMC), municipal solid waste compost (MSWC) and their extracts, were tested to suppress Phytophthora drechsleri in cucumber plants. The composts were mixed with sand-loam soil in sterile and non-sterile types and were used to assess suppressiveness against P. drechselri in greenhouse experiments. The extracts of composts, in both sterile and non-sterile types, were applied to evaluate their effect in suppression of pathogen in vitro. The results of the experiments showed that all applications rate of non-sterile SMC were significantly effective in the control of the pathogen. However the sterile SMC amendments did not have a positive effect on the pathogen suppression in vitro or in vivo, as it was expected. In greenhouse experiments, both composts were effective in controlling pathogen at the rate of 15%, but the treatments amended with higher rate of MSWC did not show a positive effect. The treatments amended with MSWC (15%) and SMC (25%) showed the most suppressive effect in controlling the pathogen. The extract of leached-SMC could inhibit P. drechselri in petri dish.     

Compost-induced suppression of Pythium damping-off is mediated by fatty-acid-metabolizing seed-colonizing microbial communities

Leaf composts were studied for their suppressive effects on Pythium ultimum sporangium germination, cottonseed colonization, and the severity of Pythium damping-off of cotton. A focus of the work was to assess the role of fatty-acid-metabolizing microbial communities in disease suppression. Suppressiveness was expressed within the first few hours of seed germination as revealed by reduced P. ultimum sporangium germination, reduced seed colonization, and reduced damping-off in transplant experiments. These reductions were not observed when cottonseeds were sown in a conducive leaf compost. Microbial consortia recovered from the surface of cottonseeds during the first few hours of germination in suppressive compost (suppressive consortia) induced significant levels of damping-off suppression, whereas no suppression was induced by microbial consortia recovered from cottonseeds germinated in conducive compost (conducive consortia). Suppressive consortia rapidly metabolized linoleic acid, whereas conducive consortia did not. Furthermore, populations of fatty-acid-metabolizing bacteria and actinobacteria were higher in suppressive consortia than in conducive consortia. Individual bacterial isolates varied in their ability to metabolize linoleic acid and protect seedlings from damping-off. Results indicate that communities of compost-inhabiting microorganisms colonizing cottonseeds within the first few hours after sowing in a Pythium-suppressive compost play a major role in the suppression of P. ultimum sporangium germination, seed colonization, and damping-off. Results further indicate that fatty acid metabolism by these seed-colonizing bacterial consortia can explain the Pythium suppression observed.     

Biological Control of Stem Canker and Black Scurf on Potato by Date Palm Compost and its Associated Fungi

The suppressive effects of two different types of date palm composts and some of their indigenous microorganisms were evaluated in vitro and on potato plants inoculated with Rhizoctonia solani. Fungi isolated from composts screened against R. solani by dual cultural assays on PDA showed a significant inhibition of pathogen mycelium growth as compared with untreated control. The type of hyphal interactions between R. solani and each tested antagonist was observed by light microscopy. Microscopic observations carried out at the confrontation zone of both agents showed different mechanisms of actions: mycelia lyses, mycoparasitism and/or formation of mycelia cords via anatomosis between mycelia filaments. Unsterilized and sterilized compost extracts were tested for efficacy against R. solani using agar‐well diffusion method or by pouring the extracts on PDA. Two sterilization methods were used: a filtration through a microfilter of 0.22 microns or autoclaving. Results showed that compost extract lost its activity after heating or filtration, confirming that chemical factors in compost had no direct inhibiting effect on the pathogen. The suppressiveness of composts was mainly due to their biotic component. Series of greenhouse trials showed that black scurf and stem canker incidence and severity were significantly reduced in peat–sand amended with compost compared with the untreated control. However, the potential suppressive effect of cattle manure and date palm compost (CMC) was higher than sheep manure and date palm compost (SMC). On potato seed tubers pre‐inoculated with the selected fungal isolates from compost, there was variability in the reduction of disease severity among treatments. Plant growth was unaffected by the application of fungal antagonists or by CMC amendment; however, an increase in the total yield was observed by the SMC potting mix compared with untreated control.     

Microbially mediated growth suppression and death of salmonella in composted sewage sludge

The role of compost microflora in the suppression of salmonella regrowth in composted sewage sludge was investigated. Microbial inhibition studies of salmonella growth were conducted on nutrient agar, in composts that had been subjected to different temperatures in compost piles, and in radiation sterilized composts inoculated with selected fractions of the compost microflora. Agar assays of inhibition indicated that bacteria and actinomycetes were not suppressive to salmonellae, but a few fungi were. However, compost inoculation assays showed consistently that fungi were not suppressive, but bacteria and actinomycetes were. In compost inoculation assays, microbial antagonists, when present, either killed salmonellae or reduced their growth rate. No suppression of salmonellae occurred in compost taken from 70°C compost-pile zones despite the presence and growth of many types of microbes. With greater numbers and kinds of microbes in 55°C compost, salmonella growth was suppressed 100–10,000-fold. Salmonellae died when inoculated into compost from unheated zones (25–40°C) of piles. Prior colonization of compost with only noncoliform gram-negative bacteria suppressed salmonellae growth 3,000-fold. Coliforms when inoculated prior to salmonellae accounted for 75% of salmonella die-off. Mesophilic curing to allow colonization of curing piles in their entirety by gram-negative bacteria, especially coliforms, should be an effective way to prevent repopulation by salmonellae.     

Comparative evaluation of composts and dried powdered biomass of botanicals for organic management of downy mildew of sorghum

The biomass of 10 selected botanicals was evaluated as soil amendments, in the form of composts and dry powder biomass, to compare their potential to suppress downy mildew disease caused by oosporic inoculum of Perenosclerospora sorghi. Eight botanicals (Allium cepa, Lantana camara, Polyalthia longifolia, Hyptis suaveolens, Azadirachta indica, Nerium oleander Eucalyptus globulus and Tamarindus indica) proved effectively in the form of dry biomass powder at 4% (w/w) rate to control infection by oospores, while two (Croton sparsiflorus and Tagetes erecta) promoted it. In the form of composts (2% rate), the efficacy of botanicals was generally found reduced with the appearance of more disease than negative control in case of all botanicals except one (A. cepa). At the 4% compost rate, only four botanicals namely, A. cepa, P. longifolia, H. suaveolens and L. camara were found to suppress the disease. At higher amendment rates of 6, 8 and 10%, six botanicals suppressed the disease. Dry powders are not only superior in disease suppression but confer additional benefits like reduced bulk, increased shelf life, consistent composition and results.     

Evaluation of Compost Amendments for Control of Vascular Wilt Diseases

Vascular wilt fungal pathogens cause heavy economic losses to a wide range of crops; amongst them are Fusarium oxysporum f. sp. melonis (FOM) and Verticillium dahliae Kleb. Several strategies for controlling these pathogens have been introduced, such as soil solarization, resistant rootstocks and biological control. In this study, the suppressive ability of seven different compost amendments and the plant growth-promoting rhizobacterium Paenibacillus alvei K165 (with proven activity against V. dahliae ) were tested against FOM in melon and V. dahliae in eggplant. It was shown that K165 had a suppressive effect against the pathogens in all experiments. On the contrary, the composts exhibited a narrow spectrum of effectiveness against the pathogens. Two composts were effective against V. dahliae and one against FOM. Moreover, we investigated the potential of the various compost samples and K165 to induce resistance in an Arabidopsis thaliana – V. dahliae or FOM model system. It was demonstrated that three composts and K165 were effective against V. dahliae ; whereas, one compost and K165 were effective against FOM. In a naturally V.dahliae infested field, the ability of K165 to enhance the suppressive effect of one of the compost amendments, was evaluated. It was demonstrated that fortification of the compost with strain K165 significantly reduced disease severity, whereas the single application of the compost was not sufficient to significantly protect the plants.     

Use of Trichoderma harzianum and Gliocladium vitens for the Biological Control of Post-emergence Damping-off and Root Rot of Cucumbers Caused by Pythium ultimum

The antagonist strains Gliocladium virens G2 and Trichoderma harzianum T3 originally isolated from Pythium suppressive peat, and two benomyl-resistant strains of T. harzianum, T12B and T95, were evaluated as biological control agents of damping-off and root rot of cucumbers in sphagnum peat caused by Pythium ultimum. All strains were equally effective when applied as 1 % peat-bran preparations, whereas the effectiveness of disease control was reduced at higher concentrations of the antagonists. The two wild-type strains were also found to be effective when applied as conidial suspensions, and in this case no reduction in disease control was seen at higher concentrations. G. virens G2 and T. harzianum T12B showed antibiotic activity against P. ultimum in in vitro tests; however there were no signs of mycoparasitism of P. ultimum by any of the antagonist strains.     

Use of composts to manage corky root disease in organic tomato production

Corky root disease of tomato caused by Pyrenochaeta lycopersici is an economically important disease in organic tomato production. This study aimed to evaluate the effects of various composts consisting of green manure, garden waste and horse manure against corky root disease through bioassay under greenhouse conditions, where soil naturally infested with P. lycopersici was used as a root substrate. The various composts were mixed at a rate of 20% (v/v) with the infested soil. Disease severity (measured as infected roots) in the unamended soil was compared with that in the soil–compost mixtures. One of the composts made from garden waste significantly reduced the disease, whereas horse manure compost significantly stimulated it. Lower concentrations of NH₄‐N and total carbon and a higher concentration of Ca in the substrate were correlated with lower level of corky root disease. Addition of green manure or garden waste compost to the infested soil increased total microbial activity or population density of copiotrophic bacteria and actinomycetes, respectively. However, increased microbial activity or microbial population in soil–compost mixtures was not associated with a reduction in corky root disease severity in the present study.     

Bark morphological and chemical features are differentially correlated with disease resistance and yield in hybrid poplar taxa

In the southeastern United States, the establishment of short-rotation intensively cultured plantations of hybrid poplar has been hindered by its susceptibility to stem cankers. We evaluated the tradeoffs between biomass yield and disease tolerance in hybrid poplar genotypes belonging to P. deltoides × P. maximowiczii (DM), P. deltoides × P. nigra (DN), P. trichocarpa × P. maximowiczii (TM), and P. deltoides × P. deltoides (DD) taxa. We hypothesized that canker resistant genotypes will have thicker bark but bark thickness and biomass yield will be negatively correlated. After two growing seasons, the DD genotypes developed thicker bark compared to the genotypes of other taxa and bark thickness was not correlated with biomass yield in the DD genotypes (R² = 0.002). However, in the TM, DM, and DN genotypes, bark thickness was negatively correlated with biomass yield (R² = 0.33–0.77). Disease incidence studies revealed that the DM genotypes were most susceptible to canker whereas no disease was detected in DD genotypes. Furthermore, bark analysis conducted by Fourier transform infrared spectroscopy coupled with multivariate analysis showed that that DD genotypes to be chemically separate from the three hybrid genotypes and that bark chemistry was correlated with canker disease incidence. Taken together, these results reveal that it is possible to generate hybrid poplar genotypes with thicker bark, disease resistance, and higher biomass yields. This insight should guide further efforts to develop genetically improved hybrid poplar genotypes, both in terms of biomass yield and disease tolerance, for cultivation in the southeastern United States. Hybrid poplar cultivation in southeastern United States is hindered by its susceptibility to stem cankers. We evaluated tradeoffs between yield and canker disease resistance in various hybrid poplar genotypes. After two growing seasons, the DD genotypes showed disease resistance and developed thicker bark that was chemically distinct from the other genotypes. Bark thickness was not correlated with yield in the DD genotypes but was negatively correlated with yield in the other genotypes. These results will guide the development of hybrid poplar genotypes that are both disease resistant and high yielding for cultivation in the southeastern United States.     

Carbon mineralization characteristics of compost made from pruning material

To investigate carbon (C) mineralization characteristics of compost made from pruning material (PM), C mineralization parameters were evaluated, including mineralizable C (C₀), apparent activation energy (E_a), and the rate constant of mineralization (k). These properties were also examined in conventional composts made from dung (D), fallen leaves (L), and bark (B). No significant differences among the plant composts (L, B and PM) were observed for E_a. Notably, the values of the respective indicators were significantly greater in PM, L and B than in D. The C₀ of PM was significantly greater than that of the other composts. Conversely, the k-value for PM was significantly smaller than that for the other composts. These results indicate that PM supplies a substantial amount of mineralizable C that persists for a long time after the PM has been mixed with soil.

     

Utilization of seaweed Ulva sp. in Paracas Bay (Peru): experimenting with compost

In Paracas Bay (Peru), large quantities of Ulva sp. interfere with various important activities of the zone. In this context, the present study was undertaken to evaluate the effect of adding Ulva sp. in compost piles and the quality of the resulting composts. Six compost piles were prepared using, straw, green material mixture, cow manure and Ulva in different quantities (9, 17 and 28% of volume) and forms. Several variables were monitored during the process and the chemical characteristics of the final composts were determined. Aerial biomass achieved by maize plants was also evaluated for each compost at different compost/sand proportions. Results show that the compost pile made with Ulva powder registered the highest temperature and the longest thermophilic phase. Piles prepared with 28% washed Ulvapresented anoxic conditions at the beginning and had higher electrical conductivity values. Carbon/Nitrogen ratio diminished appropriately in all piles and there was no negative effect observed on the pH of the piles. Compost prepared with Ulva had lower contents of Total Kjeldahl Nitrogen, and produced maize plants aerial biomass.     

Modification of Fertility of Soil Materials for Restoration of Acid Grassland Habitat

Use of composts for habitat restoration offers advantages in terms of efficient use of resources. Chemical amendment of compost to reduce its pH and P availability was investigated in order to improve suitability for use in reclamation of blocky quarry waste to acidic grassy heathland. The effect of these amendments was observed on competition between two grass species: Agrostis capillaris and Festuca ovina. A factorial, pot‐scale greenhouse experiment was set up using two composts (one a mixture of green waste and catering waste, and the other a mixture of green waste and sewage sludge). In addition, two soils were collected from upland acidic grassland to provide a natural comparison. S⁰ was applied to reduce soil pH, and Fe(OH)₃ from a coal waste treatment plant was applied to counteract the expected increase in P availability due to acidification of the composts by S⁰. Addition of S⁰ significantly reduced soil solution pH and addition of Fe(OH)₃ significantly reduced soil solution P concentration. In one compost S⁰ reduced the biomass of F. ovina while increasing that of A. capillaris, whereas Fe(OH)₃ had no significant effect on the biomass of either species. Although S⁰ and Fe(OH)₃ did adjust the chemical properties of the soil solution, Fe(OH)₃ did not bind P strongly enough to make it unavailable to plants. Further work is required, however, the use of chemically amended composts provides a sustainable sink for organic wastes and we conclude from this study that they have great potential for large‐scale restoration of blocky waste tips.