Use Of Organic Wastes Research Articles

Nitrate and phosphate leaching in a Phaeozem soil treated with biosolids, composted biosolids and inorganic fertilizers

The use of organic wastes in agriculture may increase the production of crops by incorporating organic matter and nutrients into the soil, and by improving its physical characteristics; however, this use may cause environmental problems such as the leaching of certain ions. The objective of this study was to establish possible nitrogen and phosphorus leaching under real field conditions in Phaeozem soils. The experimental work was performed in a corn (Zea mays L.) field where three plots were conditioned with inorganic fertilizer, three plots with 4.5 Mgha(-1) of biosolids on dry basis, and three plots with the same amount of composted biosolids. The quality of biosolids and composted biosolids complied with the Mexican Official Standards. Soil water samples were collected with suction cups during two agricultural cycles and were analysed. Soil samples were also taken and analysed. The N-NO(3) concentrations in soil water fluctuated between 0.9 and 98mgL(-1) in the composted biosolid treatment, between 0.7 and 64 mgL(-1) in the biosolid treatment, and between 1 and 61 mgL(-1) in the inorganic fertilizer treatment. The maximum concentration of N-NO(2) and N-NH(3) in soil water was 1.02 and 2.65 mgL(-1), respectively. The greatest percentage of nitrogen leached is produced when inorganic fertilizer is used (37.4% and 24.0% N leached in the first and second years, respectively), followed by composted biosolids (17.1% and 13.5% N leached in the first and second years, respectively) and last by biosolids (11% for both years). This difference could be related to the form in which nitrogen is present in the fertilizers, while commercial fertilizer is as inorganic nitrogen, organic wastes are basically presented as organic nitrogen. The maximum PO(4)(3-) concentration in soil water was 1.9 mgL(-1) in the composted biosolid treatment, 1.7mgL(-1) in the biosolid treatment and 0.9 mgL(-1) in the inorganic fertilizer treatment. The estimated percentage of leached phosphorus was less than 1% for all treatments. The minimum leaching that occurred seemed to be due to a sorption-precipitation process.

Use of waste for heat, electricity and transport—Challenges when performing energy system analysis

This paper presents a comparative energy system analysis of different technologies utilising organic waste for heat and power production as well as fuel for transport. Technologies included in the analysis are second-generation biofuel production, gasification, fermentation (biogas production) and improved incineration. It is argued that energy technologies should be assessed together with the energy systems of which they form part and influence. The energy system analysis is performed by use of the EnergyPLAN model, which simulates the Danish energy system hour by hour. The analysis shows that most fossil fuel is saved by gasifying the organic waste and using the syngas for combined heat and power production. On the other hand, least greenhouse gases are emitted if biogas is produced from organic waste and used for combined heat and power production; assuming that the use of organic waste for biogas production facilitates the use of manure for biogas production. The technology which provides the cheapest CO2 reduction is gasification of waste with the subsequent conversion of gas into transport fuel.

Phytotoxicity and fertilising potential of olive mill wastewaters for maize cultivation

The use of organic wastes as agricultural amendment is an effective strategy to regenerate degraded soils and represents an economical alternative that provides a local source of fertiliser. Olive mill wastewaters are widely known for their fertilising value. However, they can still not be recommended as a safe practice because of their potential ecological risks. Here, the effect of olive mill wastewaters on maize is investigated. Olive mill wastewater samples were collected in semi-modern and traditional mills of the Marrakech area, Morocco. Samples were analysed for pH, electrical conductivity and total phenolic content. Major phenolic compounds were identified and quantified. Phytotoxicity was assayed in the laboratory using maize seedlings, and under field conditions. Field fertilisation was conducted through land application accompanied or not by foliar spray according to a fractionated application mode. Our results show a high variability in physicochemical characteristics of wastewaters, notably for phenolic profiles. Variable toxicity levels were also attributed to each sample according to its salinity and phenolic load. Under field conditions, a 9% reduction of seedling emergence was observed in olive mill wastewater-pre-treated soil as compared with the control. However, olive mill wastewater-fertilised plots showed a net improvement in plant height of 10–11% compared with the control. A yield improvement reached 28% over that of the control when the plants were amended both by land application and foliar spray. These results show that the large variability in olive mill wastewaters composition constitutes a major limiting factor for their re-use in agricultural systems. Olive mill wastewaters can be used as a safe agronomic amendment provided the application is moderate and progressive and critical development stages are avoided, notably the preliminary development stages. Foliar fertilisation using olive mill wastewaters is also revealed to be a promising way to manage these effluents.

Effect of compost enriched with N and L-tryptophan on soil and maize

Composting provides an excellent way to manage the huge volume of organic waste and convert it into a useful soil amendment. The effectiveness of composted organic waste can be further improved by enriching and blending it with nutrients and biologically active substances. The resulting value-added composts can be used at substantially low rates such as a few hundred kg per ha compared with conventional use of organic wastes in tons per ha. This approach could have practical significance in reducing the use of chemical fertilizer for sustainable agriculture and the environment. L-tryptophan is a precursor of the growth hormone indole acetic acid and is known to stimulate plant growth at extremely low concentrations. Here, we studied the effect of composted fruit and vegetable wastes, enriched with N at 133 g kg−1 compost, with or without L-tryptophan at 10 mg kg−1 compost, on soil and maize crops. The enriched compost was applied at 300 kg ha−1 to a sandy clay loam soil either by mixing with the top 15-cm soil layer in pots or as a band placement along the maize plants grown in the field. The compost was applied alone and in combination with 40 or 80 kg ha−1 urea N and compared with a treatment containing 160 kg N ha−1, a full dose of N fertilizer alone, while P and K fertilizers were applied in all the treatments. Our results show that application of the enriched compost to soil increased aggregate stability by up to 24.8% and water retention by up to 43.1% compared with untreated control. A gradual increase in the concentration of indole acetic acid in compost, ranging from 1.02 to 3.34 mg kg−1, was observed when compost was treated with its precursor L-tryptophan. The results of pot and field experiments revealed that compost enriched with N and L-tryptophan in the presence of 80 kg N fertilizer significantly increased cob and grain yields, by up to 19.8 and 21.4%, respectively, compared with a full dose of N fertilizer. These findings suggest that enrichment of composted organic wastes with N and L-tryptophan can change them into a value-added organic product that could be used as a soil amendment at rates as low as 300 kg ha−1 to increase crop production on a sustainable basis.

Bio-conversion of organic wastes for their recycling in agriculture: an overview of perspectives and prospects

Largely accessible organic wastes can be turned into valuable compost product for raising crops organically on one hand, and get them disposed off safely at the other end. Straight use of organic wastes has tribulations like transportation and handling, wider C:N ratio, high application rates, nutrient overloading, weed seeds, pathogens, and metal toxicities. Composting bestows a tactic for coping high volumes of organic wastes in environmentally sound and desirable manners. Composted materials are remarkably regarded for their ability to improve soil health and plant growth, and suppress pathogens and plant diseases. Currently several composting systems have become available; ranging from a crude and slow windrows method, to the most speedy and computer monitored in-vessel system. Scientific investigations of this biological cum chemical process have reached to molecular level. Value addition of compost through beneficial microorganisms, mineral materials and fertilisers is also being considered. The nature and composition of materials put into composting is imperative for its quality rationale. On the whole, principles and processes governing composting are not so straightforward that ordinary enterprises could develop efficient composting facilities for the treatment of organic wastes. In this scenario, accessibility of comprehensive information to the scientific community as well as environmental protection agencies is imperative. This review article brings together the current information necessary for effective composting of organic wastes from different origins with diversified characteristics under various situations. It also covers the schematic description of well known composting systems, and various factors controlling the process.

Total And Immobilized Enzymatic Activity Of Organic Materials Before And After Composting

The evaluation of residual organic materials as a source of enzymatic activities immobilized in the humus matrix is a little explored research area, particularly in the case of organic materials derived from municipal wastes. Enzymes catalyze most soil reactions essential for soil functionality. The advantage of humus enzyme-complexes (immobilized enzymes) with regards to free enzymes is that the former are protected in the humic colloid, being more resistant to denaturing agents and other adverse soil conditions. This explains the interest in use of organic wastes (which are produced in an increasingly amount and consequently are economical) as a source of immobilized enzymes, which could be concentrated and used to improve the quality of degraded or contaminated soils. The goal of this study was (i) to assess the potential of sewage sludge (SS) and the organic fraction of municipal solid waste (MSW), as well as their respective composts (CSS and CMSW) as sources of enzymes, (ii) to determine the proportion of such enzymes which are immobilized in the humic matrix of these organic materials, and (iii) to determine the effect of the composting process on the total and the immobilized enzymatic activities of the organic materials. Dehydrogenase (DHA), urease, protease-BAA, alkaline phosphatase (ALP), β-glucosidase (GLA) and o-diphenol oxidase (DPO) activities were determined both in the organic materials and in their humic extracts (except DHA). Sewage sludge had the highest total values of urease, protease-BAA, ALP and DHA activity (12.7 μol NH4+-N g−1 h−1, 40.6 μmol NH4+-N g−1 h−1, 75.7 μmol PNP g−1 h−1 and 0.3 μmol INTF g−1 h−1, respectively), which decreased with composting, but MSW had the highest total value of DPO activity. For both organic materials, a low percentage of total enzymatic activities were linked to humus (0.6-22%), except in the case of DPO activity. The SS and MSW composting process had a positive effect on the urease, protease-BAA, DPO and ALP immobilization in the humic matrix, as reflected by the higher immobilized activity/total activity ratios in the compost than in the fresh materials.

Role of Humification Processes in Recycling Organic Wastes of Various Nature and Sources as Soil Amendments

AbstractRecycling the large amounts of organic wastes produced by agriculture, forestry, urban and industrial activities as soil, organic amendments are the most popular and efficient option for avoiding their dispersion in the environment and restoring, maintaining, and/or improving the content of soil organic matter. Chemical stability and biological maturity are two important factors for the successful use of organic wastes in agriculture with limited risk for the surrounding environment. Stabilization and maturation of raw organic wastes inherently imply the achievement of an extensive humification, that is, a wide conversion of easily degradable organic matter to refractory organic compounds that resemble native soil humic substances (HS). Soil HS are the most important components of soil organic matter responsible of several soil functions and processes. As a consequence, the amount and quality of HS‐like fractions in any organic amendment are believed to be of primary importance for its agronomic efficacy, environmental safety and economic value. The first part of this review focuses on the chemical and physico‐chemical changes occurring in the humic substances (HS) ‐like fractions of organic wastes of various nature and sources subjected to common treatment processes aimed at producing environmentally‐safe soil amendments with beneficial agronomic properties. The second part discusses the composition, structure, and chemical reactivity of the HS‐like components in organic amendments of various origins and nature, and their effects on native soil HS. The review concludes by highlighting the need for innovative research targeted mainly to achieve a better fundamental understanding of the molecular structure and reactivity of soil HS and HS‐like fractions in organic amendments, the mechanisms of HS formation and transformations in the natural environment and during the treatment processes of raw organic wastes, the interactions with metals and organic xenobiotics, and the direct physiological effects that HS may exert on plants.

Evaluation of chemical and ecotoxicological characteristics of biodegradable organic residues for application to agricultural land

The use of organic waste and compost as a source of organic matter and nutrients is a common practice to improve soil physico-chemical properties, meanwhile reducing the need for inorganic fertilisers. Official guidelines to assess sewage sludge and compost quality are mostly based on total metal content of these residues. Measurement of the total concentration of metals may be useful as a general index of contamination, but provides inadequate or little information about their bioavailability, mobility or toxicity when the organic residue is applied to the soil. However, ecotoxicity tests provide an integrated measure of bioavailability and detrimental effects of contaminants in the ecosystem. In the present study, three different types of biodegradable organic residues (BORs) have been considered: sewage sludge from municipal wastewater treatment (SS), compost from the organic fraction of unsorted municipal solid waste (MSWC), and garden waste compost (GWC). The BORs were subjected to chemical characterisation and total metal quantification (Cd, Cr, Cu, Ni, Pb and Zn), in order to verify their suitability for land application. Water leachability was determined through the DIN 38414-S4 method, while the modified BCR sequential extraction procedure was used for metal speciation. Ecotoxicity of the BORs was studied by direct and indirect bioassays. Direct toxicity bioassays were: plant growth tests with cress ( Lepidium sativum L.) and barley ( Hordeum vulgare L.), and earthworm ( Eisenia fetida) mortality. On the other hand, indirect exposure bioassays, with leachate from the residues, took into account: luminescent bacteria ( Vibrio fischeri), seed germination ( L. sativum and H. vulgare) and Daphnia magna immobilization. As far as total metal concentration is concerned, with particular reference to Zn, SS resulted neither suitable for the use in agriculture nor compatible to be disposed of as an inert material into landfill, according to the Directive 1999/31/EC. Zinc in SS was mainly present in exchangeable form (28.5%), appearing as highly bioavailable. As a consequence, SS exhibited either high ecotoxicity effects with the indirect exposure bioassays or significant mortality with the earthworm bioassay. Total content of metals in MSWC allowed its classification as “stabilised biowaste”, according to 2nd draft [DG Env.A.2. Working document of Biological treatment of biowaste — 2nd draft. Directorate-General Environment, Brussels, 12th February; 2001. accessed in: http://europa.eu.int/comm/environment/waste/facts_en.htm, at 10/09/2002] while leachate, on the basis of the concentration of these contaminants, could be classified as “inert waste”. This residue showed significant ecotoxicity effects with direct exposure bioassays as well as with the luminescent bacteria bioassay. However, it resulted less toxic than SS. Finally, GWC could be classified as a Class 2 compost, with no detectable toxic effects on the organisms used in the bioassays, except for the luminescent bacteria. In this case, an EC 50 of 73.0% was observed. Considering the results, the use of a battery of toxicity test in conjunction with chemical analysis should be suggested, in order to correctly assess possible environmental risks deriving from disposal or land application of biodegradable organic residues.

Microbial biomass and activity of an agricultural soil amended with the solid phase of pig slurries

Information about the mineralisation rates and effects on soil microorganisms must be obtained prior to the rational use of organic wastes in agriculture or forestry. The objective of this work was to study the mineralisation of two manures derived from the solid phase of pig slurries and the effects on the soil microbial biomass of an agricultural soil. Samples of this soil were mixed at two different rates with two manures derived from the solid phase of pig slurry (composted, CSP, and non-composted, NSP), and then were incubated during 163 days. Carbon mineralised from manures was fitted to first-order kinetic model, and small differences were found between manures despite the composting of one of them. Approximately 45% of the C added was mineralised in the experimental period. The soil microbial biomass C (C mic) was increased by the amendments according to the application rate. The sudden increases of the qCO 2 in the treated samples were ephemeral. The most appreciable differences between these manures were those related with net N mineralisation, being greater in the NSP-treated samples. The application of the solid phase of pig slurries, composted or not, could be a feasible practice to enhance in a short-term the microbial biomass of agricultural soils. In order to avoid an excessive release of inorganic N, the use of composted materials is preferred.

Effect of vermicomposting process on pesticide sorption capability using agro-industrial wastes

The aim of this work was to study the use of organic wastes from olive oil (alperujo), winery, and alcohol industries (vine shoots, spent grape marc, lees cake, and biosolids vinasse) as sorbents for pesticide control. The pesticide sorption capability of these organic wastes and the effect of vermicomposting process was also studied. The insecticide imidacloprid and different herbicides (diuron, metsulfuron-methyl, sulfuron-methyl, and flazasulfuron) were applied. The vermicomposting process was more effective for the agro-industrial wastes with a low lignin content. The sorption capacity of these wastes, natural or previously vermicomposted, was low for the anionic herbicides with respect to hydrophobic pesticides. Adsorption isotherms by the different wastes of confidor (imidacloprid 20% w/v) and diurokey (diuron 80% w/w) fit the Freundlich model (R 2 > 0.933). The larger K f values (231–138 µg1/n−1mL−1g−1) correspond to the spent grape marc, untreated or vermicomposted, due to the high lignin content of this waste.

Effects of Two Organic Wastes in Combination with Phosphorus on Growth and Chemical Composition of Spinach and Soil Properties

Most agricultural soils in Iran are usually low in organic matter (OM). Therefore, increasing OM in these soils is of great concern. Environmental pollution caused by chemical fertilizers has created an interest in the integrated use of organic wastes with inorganic fertilizers. The main purpose of this greenhouse study was to evaluate the impact of two organic wastes and phosphorus (P) on the growth, and elemental composition of spinach (Spinacia oleracea L.) and soil chemical properties. Treatments consisted of four levels of municipal waste compost, MWC (0, 1, 2, and 4%), five rates of poultry manure, PM (0, 1, 2, 3, and 4%), and three P levels (0, 25, and 50 mg kg−1 as KH2PO4). Application of P and MWC alone or in combination significantly increased the top dry weight of spinach. However, spinach growth was markedly increased up to 3% PM and suppressed with the higher rate, probably due to an excess of soluble salts in the soil. Moreover, the enhancing influence of P on spinach seedling growth was more pronounced at lower levels of MWC and PM. Plant P concentration tended to increase with increasing P, MWC, and PM application rates, whereas nitrogen (N) concentration was only affected by the two organic wastes treatment. Manganese (Mn) concentrations decreased, and copper (Cu), lead (Pb), and cadmium (Cd) increased by soil P application. However, P addition significantly decreased zinc (Zn) concentration only in MWC-treated spinach. Spinach plants enriched with either of the two biosolids accumulated more Mn, Zn, Pb, Cd, chloride (Cl), and sodium (Na) than control plants. Furthermore, spinach grown on MWC-amended soil contained higher Mn, Zn, Cu, and Pb and lower N, Cl, and Na than those raised on PM-treated soil. Postharvest soil sampling indicated that application of the two biosolids significantly increased concentration of soluble salts, (ECe), OM, TN, NaHCO3-extractable P, and DTPA-extractable iron (Fe), Mn, Zn, Cu, Pb, and Cd.

Behaviour of simazine in soil amended with the final residue of the olive-oil extraction process

Addition of organic wastes to agricultural soils is becoming a common practice as a disposal strategy and to improve the physical and chemical soil properties. However, in order to optimise the use of organic wastes as soil amendments, their effect on the behaviour of other compounds that are also used in agriculture, such as pesticides, needs to be assessed. In this work, we have investigated the effects of the addition of the final solid residue of the new technology of olive-oil extraction ( extracted alperujo or solid olive-mill waste, SOMW2) on the sorption, degradation and leaching of the herbicide simazine in a sandy loam soil. The results are compared with those of a previous study, where the intermediary by-product of the olive-oil processing technology ( unextracted alperujo or SOMW1) was applied to the same soil. The soil was amended in the laboratory with SOMW2 at two different rates (5% and 10% w/w). Simazine sorption isotherms showed a great increase in herbicide sorption after SOMW2 addition to soil. SOMW2 addition also increased sorption irreversibility. Incubation studies revealed reduced biodegradation of simazine in the soil amended with SOMW2 compared to the unamended soil. Breakthrough curves of simazine in handpacked soil columns showed that SOMW2 addition retarded the vertical movement of the herbicide through the soil and greatly reduced the amount of herbicide available for leaching. Interestingly, the results were quantitatively different from those obtained for the intermediary by-product SOMW1, illustrating the importance of the specific characteristics of the organic amendment in determining its effect on pesticide behaviour.

Recycling of sewage sludge and household compost to arable land: fate and effects of organic contaminants, and impact on soil fertility

Effective use of organic wastes for agricultural production requires that risks and benefits be documented. Two types of sewage sludge, household compost and solid pig manure were studied under field and greenhouse conditions to describe their fertilizer value and effects on soil properties and soil biota, the fate of selected organic contaminants, and their potential for plant uptake. A 3-year field trial on two soil types showed no adverse effects of waste amendment on crop growth, and a significant fertilizer value of one sludge type. Accumulation of N and Pi was indicated, as well as some stimulation of biological activity and micro-arthropod populations, but these effects differed between soil types. There was no detectable accumulation of polycyclic aromatic hydrocarbons (PAH), di(2-ethylhexyl)phthalate (DEHP), nonylphenol and ethoxylates (NP+NPE) or linear alkylbenzene sulfonates (LAS) after three repeated waste applications, and no plant uptake was suggested by analysis of the third crop. A plot experiment with banded sludge was conducted to examine sludge turnover and toxicity in detail. Less than 5% of NP or LAS applied in organic wastes was recovered after 6 months, and less than 6% of DEHP applied was recovered after 12 months. Potential ammonium oxidation (PAO) at 0–1 cm distance from the banded sludge was stimulated despite toxic concentrations in the sludge, which suggested that contaminants were degraded inside sludge particles. Phospholipid fatty acid (PLFA) profiles suggested a gradual shift in the composition of the microbial community within sludge, partly due to a depletion of degradable substrates. A pot experiment with sludge-amended soil and soil spiked with contaminants showed no plant uptake of NP, DEHP or LAS. Degradation of LAS and NP added in sludge was delayed and the degradation of DEHP was faster than when the contaminants were added directly to the soil. In conclusion, adverse effects of organic waste application on soil or crop were not found in this study, and for some waste products positive effects were observed.

Bioconversion of organic waste by the year 2010: to recycle elements and save energy

Abstract The needs and problems existing in the field of cultivation systems and waste management concerning elements and energy, as well as pollution, health, environment, and economy are described. The lack of reproducible biofertilisers of high quality calls for an efficient use of organic waste as a renewable raw material. Each 100 000 inhabitants in Sweden generate organic waste with considerable economic values in terms of nitrogen, phosphorus, and potassium; US$ 600 000 from the organic fraction of municipal solid waste and US$ 900 000 from human excreta as liquid organic waste, meanwhile only US$ 160 000 is recovered from the sewage sludge after the wastewater has passed the wastewater treatment plants. Most of the existing systems for handling solid and liquid waste are of old-fashioned design and cause large losses of nutrient elements. Therefore, pollution of air, water, soil, and vegetation, mainly by emissions from organic uaste, continues. Bioconversion is microbial transformation and upgrading of various organic wastes to products of high value. The elements can be efficiently recycled in completely closed local bioconversion systems with subsystems for collection, pre-processing, processing, and application of end-products. Solid and liquid organic waste from the municipality can provide renewable raw material for manufacturing of reproducible biofertilisers and of biogas. Suggestions are made on how to improve the present situation by the re-orientation of technology. A scenario for bioconversion by the year 2010 is presented.

Phosphorus Loss in Agricultural Drainage: Historical Perspective and Current Research

AbstractThe importance of P originating from agricultural sources to the nonpoint source pollution of surface waters has been an environmental issue for decades because of the well‐known role of P in eutrophication. Most previous research and nonpoint source control efforts have emphasized P losses by surface erosion and runoff because of the relative immobility of P in soils. Consequently, P leaching and losses of P via subsurface runoff have rarely been considered important pathways for the movement of agricultural P to surface waters. However, there are situations where environmentally significant export of P in agricultural drainage has occurred (e.g., deep sandy soils, high organic matter soils, or soils with high soil P concentrations from long‐term overfertilization and/or excessive use of organic wastes). In this paper we review research on P leaching and export in subsurface runoff and present overviews of ongoing research in the Atlantic Coastal Plain of the USA (Delaware), the midwestem USA (Indiana), and eastern Canada (Quebec). Our objectives are to illustrate the importance of agricultural drainage to nonpoint source pollution of surface waters and to emphasize the need for soil and water conservation practices that can minimize P losses in subsurface runoff.

Goats and garbage in Khartoum, Sudan: A study of the urban ecology of animal keeping

Waste management in developing world urban areas is an acute problem which is linked to high growth rates and abatement methods less advanced than in the developed world. Existing neighborhood waste management practices often include the use of organic waste as a feed supplement for urban livestock (mainly goats, but also sheep and cattle). These urban animals bring economic benefits to less affluent residents, who would suffer an economic loss if their supply of urban waste was reduced or eliminated by an organized waste collection and disposal strategy. This paper employs a survey of 319 Greater Khartoum households to derive an estimate of waste intake per urban animal, and illustrate demographic factors (e.g., rural or urban roots, income, education, number of children) which influence animal keeping. A loglinear/logit model is developed to predict animal-keeping households. This model can be applied by waste management planners to estimate the frequency of urban animals in developing world urban areas.

Phosphorus solubility changes with time in organically amended soil in a mediterranean environment

Abstract As in other areas of the world, in the Middle East, phosphorus (P) is also a vital element in agricultural production. Laboratory studies have shown how inorganic P changes with time after application. With increased interest in the use of organic wastes, the extent to which seasonal change, characteristic of the Mediterranean climate, affects transformation of organic P alone and in combination with fertilizer P has been given attention. This preliminary pot experiment, conducted under outdoor conditions, examined changes in sodium bicarbonate (NaHCO3)‐extractable P over a 19‐month period in soil amended with organic matter as farmyard manure (5%) and superphosphate (100 mg/kg P). During the initial cool winter season's incubation, there was no change in available P. With the onset of the warmer dry season, NaHCO3‐extractable P declined rapidly. The rate of decrease was greater, and the onset earlier with inorganic P alone. Organic matter reduced the P Sorption maxima and increased desorption. T...

Potential use of plant residue wastes in forests of northwestern Germany

Increasing amounts of waste and limited space for its deposition require alternative waste management practices, such as the use of organic wastes for amelioration of forest soils. The effects of plant residue waste application to forest soils were assessed by laboratory incubation, and by field experimentation at two sites with contrasting soil properties. The wastes used were a fresh and shredded material and a mature compost, both from plant residues, and were nutrient rich with high contents of bases and low concentrations of heavy metals. Long-term laboratory incubation showed no difference in total N mineralization between fresh organic waste, mature organic compost and beech litter. The nitrification rates in the organic wastes were higher, however. Carbon dioxide evolution was higher from fresh organic waste, and lower from mature organic compost than for beech litter. Neither liming nor addition of different soils, which served as inocula, significantly influenced N or C mineralization in wastes. Of total potassium in fresh organic waste 80% was released during a 67 day incubation period. Seepage water samples from an acid brown earth and a Terra fusca-Rendzina site showed negligible differences between concentrations of most elements for waste application and control plots. However, in both soils potassium and chloride concentrations were highest under mature compost. After 21 months, the pH of humus and mineral soil below waste layers had not increased. The basicity of waste will deacidify acid forest soils in the long term. The flora which established after waste addition included many non-forest plants and indicated very good nitrogen supply in the soil. As a result of potential leaching of nitrate, waste applications to nutrient-rich or N saturated forest ecosystems may be an environmental risk.