Decomposition of peat,biogenic municipal waste compost,and shrub/grass compost added in different rates to a silt loam

An incubation experiment was carried out to test the effects of biogenic municipal waste (compost I) and shrub/grass (compost II) composts in comparison to peat on respiration and microbial biomass in soil. The amounts of these three substrates added were linearly increased in the range of field application rates (0.5%, 1.0%, 1.5%, 2.0%). The sum of CO₂ evolved during the incubation was markedly raised by the three substrates and increased with the rate of substrate concentration. However, the percentage of substrate mineralized to CO₂ decreased with the addition rate from 103 to 56% for compost I, from 81 to 56% for compost II, and from 21 to 8% for peat. During the first 25 days of incubation, compost I enlarged the biomass C content, which remained constant until the end. In contrast, compost II did not raise biomass C initially. But at the end of the incubation, the biomass C content of all 4 compost II treatments almost reached the level of the respective compost I treatment. The increase was significantly larger the more of the two composts was added. In contrast to the two composts, the addition of peat did not have any significant effect on microbial biomass C. The average qCO₂ values at day 25 declined in the order compost I > compost II > peat, at day 92 the order was changed to compost II > peat > compost 1. This change in the order was caused by a significant decrease in qCO₂ values of the compost I treatments, a significant increase in qCO₂ values of the peat treatments and constant qCO₂ values in the compost II treatments.     

Long-term effects of compost amendment of soil on functional and structural diversity and microbial activity

We studied the effects of applying different composts (urban organic waste, green waste, manure and sewage sludge), mineral fertilizer and compost plus mineral fertilizer on chemical, biological and soil microbiological parameters over a 12‐year period. The organic C and total N levels in soils were increased by all compost and compost + N treatments. Microbial biomass C was significantly (P ≤ 0.05) increased for some compost treatments. In addition, basal respiration and the metabolic quotient (qCO₂) were significantly higher in all soils that had received sewage sludge compost. The Shannon diversity index (H), based on community level physiological profiling, showed a higher consumption of carbon sources in soils treated with compost and compost + N compared with the control. The utilization of different guilds of carbon sources varied amongst the treatments (compost, compost + N or mineral fertilizer). Cluster analysis of polymerase chain reaction‐denaturing gradient gel electrophoresis patterns showed two major clusters, the first containing the mineral fertilization and compost treatments, and the second, the composts + N treatments. No differences in bacterial community structure could be determined between the different types of compost. However, the results suggest that long‐term compost treatments do have effects on the soil biota. The results indicate that the effects on the qCO₂ may be due to shifts in community composition. In this study, it was not possible to distinguish with certainty between the effects of different composts except for compost derived from sewage sludge.     

Nitrogen Uptake by Radish,Spinach and “Chingensai” from Composted Tea Leaves,Coffee Waste and Kitchen Garbage

A pot experiment was conducted to determine the effects of the application of composted tea leaves (TC), coffee waste (CC), and kitchen garbage (KC) on the nitrogen and nitrate accumulated in radish (Raphanus sativus L. cv. ‘radicula pers’), Chingensai (Brassica campestris L. cv. ‘Choyo No. 2’), and spinach (Spinacia oleracea L. cv. ‘Ban chu paruku’) as compared with the effect of inorganic ¹⁵N labeled fertilizer (IN) application. The compost was applied at the rate of 24 g kg^?1 soil, corresponding to about 250 to 300 kg N ha^?1; the A value method was used to estimate nitrogen uptake. Dry matter production was significantly higher in the IN and TC treatments than in the KC and CC treatments for all the species and tissue. Of the composts used, TC was most effective in increasing N uptake and N content in the vegetables. The composts derived N recovery as a percentage of total N uptake varied with plant species, 50.8%-62.9% in radish root, 35.3%-60.4% in radish leaf, 29.9%-48.2% in spinach leaf, and 31.3%-54.8% in Chingensai leaf. The N-use efficiencies of IN, TC, CC, and KC were 6.3%, 6.3%, 5.3%, and 6.6% in radish root; 13.6%, 9.7%, 8.4%, and 6.7% in radish leaf; 22.4%, 14.4%, 3.6%, and 5.8% in spinach leaf; and 61.2%, 39.5%, 25.5%, and 21.5% in Chingensai leaf, respectively. Nitrate accumulation in edible portions was highest in plants provided with IN as compared with those grown with composts, and nitrate content in radish root was markedly higher than that in the leaf. It is observed that the fate of compost derived N differed noticeably with vegetable species, plant part, and compost source.     

Maize and pea germination and seedling growth responses to compost generated from biowaste of selected invasive alien plant species

Plant biowaste of alien species represents a potential resource for compost production. This study investigated the seed and seedling responses of maize and pea to composts generated from the biowaste of four invasive species in eThekwini, South Africa: Acacia podalyriifolia, Hedychium gardnerianum, Litsea glutinosa, and Tithonia diversifolia. Except for a 40% concentration of T. diversifolia, leachates of the biowaste from the four species had no marked effects on germination. In seedling growth studies, Berea Red soil (control) was supplemented with composts produced using combinations of the four species (A. podalyriifolia + T. diversifolia [T1], A. podalyriifolia + H. gardnerianum [T2], L. glutinosa + T. diversifolia [T3], and L. glutinosa + H. gardnerianum [T4]), and a commercial compost (T5). Carbon and nitrogen levels of the biowaste composts were higher than the control, while their associated C/N ratios were low enough to encourage microbial growth, facilitate rapid decomposition, and support plant growth. A comparison of percentage seedling production, growth rate, and biomass production between the commercial compost and alien biowaste treatments revealed all parameters to be statistically comparable among T5, T1, and T3 for maize, and between T5 and T1 for pea. These superior biowaste composts did not enhance growth relative to the commercial compost, but supported growth to the same extent. However, N and P levels in T1 and T3 were lower than the commercial compost and appear to have altered biomass allocation patterns in both species relative to the commercial compost. The results suggest that there is potential to use invasive alien plant biowaste to improve soil for agricultural purposes.     

Soil Physical Properties and Organic Matter Fractions Under Forages Receiving Composts,Manure or Fertilizer

A field study was conducted to assess the benefits, with respect to soil physical properties and soil organic matter fractions of utilizing composts from a diversity of sources in perennial forage production. A mixed forage (timothy-red clover (Trifolium pratense L.) and monocrop timothy (Phleum pratense L.) sward were fertilized annually with ammonium nitrate (AN) at up to 150kg and 300 N ha^?1 yr^?1, respectively, from 1998-2001. Organic amendments, applied at up to 600 kg N ha^?1 yr^?1 in the first two years only, included composts derived from crop residue (CSC), dairy manure (DMC) or sewage sludge (SSLC), plus liquid dairy manure (DM), and supplied C to soil at 4.6 and 9.2 (CSC), 10.9 (SSLC), 10.0 (DMC) 2.9 (DM) Mg C ha^?1. Soil samples (0-5cm; 5-10cm;10-15cm) were recovered in 2000 and 2001. Improvements in soil physical properties (soil bulk density and water content) were obtained for compost treatments alone. Composts alone influenced soil C:N ratio and substantially increased soil organic carbon (SOC) concentration and mass (+ 5.2 to + 9.7 Mg C ha^?1). Gains in SOC with AN of 2.7 Mg C ha^?1 were detectable by the third crop production year (2001). The lower C inputs, and more labile C, supplied by manure (DM) was reflected in reduced SOC gains (+ 2.5 Mg C ha^?1) compared to composts. The distribution of C in densiometric (light fraction, LF; >1.7 g cm^?3) and particulate organic matter (POM; litter (>2000μm); coarse-sand (250-2000μm); fine-sand (53-250μm) fractions varied with compost and combining fractionation by size and density improved interpretation of compost dynamics in soil. Combined POM accounted for 82.6% of SOC gains with composts. Estimated compost turnover rates (k) ranged from 0.06 (CSC) to 0.09 yr^?1 (DMC). Composts alone increased soil microbial biomass carbon (SMB-C) concentration (μg C g^?1 soil). Soil available C (C_ext) decreased significantly as compost maturity increased. For some composts (CSC), timothy yields matched those obtained with AN, and SOC gains were derived from both applied-C and increased crop residue-C returns to soil. A trend towards improved C returns across all treatments was apparent for the mixed crop. Matching composts of varying quality with the appropriate (legume/nonlegume) target crop will be critical to promoting soil C gains from compost use.     

Hydrolase activities, microbial biomass and bacterial community in a soil after long-term amendment with different composts

The use of composts in agricultural soils is a widespread practice and the positive effects on soil and plants are known from numerous studies. However, there have been few attempts to compare the effects of different kinds of composts in one single study. The aim of this paper is to investigate to what extent and to which soil depth four major types of composts would affect the soil and its microbiota.In a crop-rotation field experiment, composts produced from (i) urban organic wastes, (ii) green wastes, (iii) manure and (iv) sewage sludge were applied at a rate equivalent to 175 kg N ha⁻¹ yr⁻¹ for 12 years. General (total organic C (C_org), total N (N_t), microbial biomass C (C_mic), and basal respiration), specific (enzyme activities related to C, N and P cycles), biochemical properties and bacterial genetic diversity (based on DGGE analysis of 16S rDNA) were analyzed at different depths (0-10, 10-20 and 20-30 cm).Compost treatment increased C_org at all depths from 11 g kg⁻¹ for control soil to 16.7 g kg⁻¹ for the case of sewage sludge compost. Total N increased with compost treatment at 0-10 cm and 10-20 cm depths, but not at 20-30 cm. Basal respiration and C_mic declined with depth, and the composts resulted in an increase of C_mic and basal respiration. Enzyme activities were different depend on the enzyme and among compost treatments, but in general, the enzyme activities were higher in the upper layers (0-10 and 10-20 cm) than in the 20-30 cm layer. Diversity of ammonia oxidizers and bacteria was lower in the control than in the compost soils. The type of compost had less influence on the composition of the microbial communities than did soil depth.Some of the properties were sensitive enough to distinguish between different compost, while others were not. This stresses the need of multi-parameter approaches when investigating treatment effects on the soil microbial community. In general, with respect to measures of activity, biomass and community diversity, differences down the soil profile were more pronounced than those due to the compost treatments.     

Effects of Compost Sources and Seeding Treatments on Germination and Emergence of Four Turfgrass Species

Greenhouse pot trials were conducted to compare the effects of compost sources and planting treatments on turfgrass germination and emergence. Eight seeding treatments and 4 turfgrass types were factorially combined and replicated four times in a completely randomized block design. The seeding treatments were: 1) seed planted on surface of 2.6 cm compost overlying soil, 2) seed planted on soil surface below 0.65 cm compost, 3) seed planted on soil surface below 1.3 cm compost, 4) seed planted on soil surface below 2.6 cm compost, 5) seed planted on soil surface covered with a 2.6 cm straw mat, 6) seed planted below 1.3 cm soil, 7) seed planted below 1.3 cm of 1:1 compost:soil mix, and 8) seed planted on soil surface. Tall fescue (Festuca arundinacea Schreb.), Kentucky bluegrass (Poa pratensis L.), bermudagrass (Cynodon dactylon L.), and zoysiagrass (Zoysia japonica Steud.) were used as the bioassay crops. The experimental design was repeated over time using composts produced with the following feedstocks: yard waste, food waste, dairy manure, biosolids, and paper mill sludge. Emerged seedlings were counted at 11 days for tall fescue, at 3 weeks for Kentucky bluegrass and at 7 weeks for bermudagrass and zoysiagrass. There were significant (P<0.05) effects of seeding treatment x turfgrass type on germination and emergence for each compost type. All of the composts appeared to be well stabilized using routine compost laboratory testing except the biosolids compost, whose use resulted in the lowest overall germination and emergence rate. The highest rates of germination and emergence occurred in the treatments in which the seeds were planted on the surface, regardless of whether the surface was compost or soil. The lowest rate of germination and emergence occurred where the seed was placed under 2.6 cm compost, regardless of compost maturity.     

Nitrogen and Phosphorus Availability in Groundfish Waste and Chitin-Sludge Cocomposts

Seafood processing generates a substantial volume of wastes. This study examined the feasibility of converting the fish waste into useful fertilizer by composting. Groundfish waste and chitin sludge generated from the production of chitin were composted with red alder or a mixture of western hemlock and Douglas-fir sawdust to produce four composts: alder with groundfish waste (AGF); hemlock/fir with groundfish waste (HGF); alder with chitin sludge (ACS); and hemlock/fir with chitin sludge (HCS). The resulting AGF had a higher total N and a lower C:N ratio than the other three composts. A large portion of the total N in the AGF, HGF, and HCS composts was in inorganic forms (NH₄⁺-N and NO₃^?-N), as opposed to only two percent in the ACS compost. Alder sawdust is more quickly decomposed, which favored N retention and limited nitrification during the composting period. It was less favorable than the hemlock/Douglas fir sawdust for composting with chitin sludge. Corn growth on soil amended with compost was dependent upon both compost type and rate. Nitrogen and P availabilities in all composts except the ACS were high and compost addition enhanced corn yields, tissue N and P concentrations, and N and P up-take. Neither the total N concentration nor the C:N ratio of the composts was an effective measure of compost N availability in the soil. Because soil inorganic N test levels correlated well with the corn biomass, tissue N and N uptake, they should be an effective measure of the overall compost effects on soil N availability and corn growth response. Phosphorus concentration, which increased linearly with increasing compost rates, was related to soil P availability from compost additions and correlated well with corn biomass, tissue P concentration and P uptake under uniform treatments of N and K fertilizers. Composting groundfish waste with alder or hemlock/Douglas-fir sawdust can produce composts with sufficient amounts of available N and P to promote plant growth and is considered to be a viable approach for recycling and utilizing groundfish waste.     

Evaluation of Seed Germination and Growth Tests for Assessing Compost Maturity

Experiments involved the comparison of three procedures used to determine compost maturity/phytotoxicity. The three tests evaluated were the CCME germination test (1996), a modified Zucconi et al. (1981) extract and a direct seed procedure. Three different plant species and seven types of ‘composts’ were used. The species were cress (Lepidium sativum), radish (Raphanus sativus), and Chinese cabbage (Brassica chinensis). Germination and growth experiments were performed on three types of mature composts: 1) racetrack manure-food waste; 2) two different samples of municipal solid waste; and 3) racetrack manure-sewage sludge), two types of immature composts (farmyard manure-food waste and farmyard manure-yard waste-food waste], and a control (soil or water). Four replicates for each species, ‘compost’ and test procedure were evaluated. The study concluded that the commonly used compost extract test and the compost-soil germination and growth tests were not sensitive enough to detect differences between mature and immature ‘composts’, that other test(s) must be used to evaluate compost maturity.     

Effects of aeration and moisture during windrow composting on the nitrogen fertilizer values of dairy waste composts

The objective of this work was to evaluate the effects of turning and moisture addition during windrow composting on the N fertilizer values of dairy waste composts. Composted-dairy wastes were sampled from windrow piles, which received four treatments in a 2×2 factorial of turning (turning vs. no turning) and moisture addition (watering vs. no watering) at two stages of maturity (mature vs. immature). Composts were characterized for their chemical properties. An 84-day laboratory incubation of soils with addition of the composts at two levels was conducted to evaluate the inorganic N accumulation patterns from the variously treated composts. Chemical analyses of variously treated composts did not differ between compost treatments or maturity. In contrast, the inorganic N accumulation patterns differed between soils that received immature versus mature turned composted-dairy wastes. The results suggested that turning was a more important factor than moisture addition affecting the composting process. There was no significant difference in inorganic N accumulation patterns among soils that received different immature composts, while the N accumulation patterns observed for soils that received different mature composts depended on compost treatments. Soils amended with mature composts treated by frequent turning had higher N mineralization potentials (N₀), mineralization rate constants (K), and initial potential rates (N₀K) in comparison to soils with composts that had not been turned. Soils with mature composts treated by watering had a higher N₀, lower K, and therefore similar N₀K when compared to soils with composts that had not been watered. Soils that received mature composts treated by watering and frequent turning had higher N mineralization potentials and N₀ to total organic N ratios than soil alone, which suggested that intensive management of composting would ensure positive N fertilizer values of dairy waste composts, if the appropriate composting duration is completed.     

Soil‐microbial response to sugarcane filter cake and biogenic waste compost

An incubation experiment was carried out to examine the N‐immobilizing effect of sugarcane filter cake (C : N = 12.4) and to prove whether mixing it with compost (C : N = 10.5) has any synergistic effects on C and N mineralization after incorporation into the soil. Approximately 19% of the compost‐C added and 37% of the filter cake–C were evolved as CO₂, assuming that the amendments had no effects on the decomposition of soil organic C. However, only 28% of the added filter cake was lost according to the total‐C and δ¹³C values. Filter cake and compost contained initially significant concentrations of inorganic N, which was nearly completely immobilized between day 7 and 14 of the incubation in most cases. After day 14, N remineralization occurred at an average rate of 0.73 µg N (g soil)^–1 d^–1 in most amendment treatments, paralleling the N mineralization rate of the nonamended control without significant difference. No significant net N mineralization from the amendment N occurred in any of the amendment treatments in comparison to the control. The addition of compost and filter cake resulted in a linear increase in microbial biomass C with increasing amounts of C added. This increase was not affected by differences in substrate quality, especially the three times larger content of K₂SO₄‐extractable organic C in the sugarcane filter cake. In most amendment treatments, microbial biomass C and biomass N increased until the end of the incubation. No synergistic effects could be observed in the mixture treatments of compost and sugarcane filter cake.     

Compost Practices for Improving Soil Properties and Turfgrass Establishment and Quality on a Disturbed Urban Soil

Urban land disturbance degrades physical, chemical, and biological soil properties by removing topsoil and compacting the remaining subsoil. Such practices create a soil environment that is unfavorable for vegetation establishment. A 3-year field study was conducted to compare the effects of various one-time compost application treatments on soil properties and re-vegetation of a disturbed soil. A disturbed urban soil received the following treatments: (1) inorganic fertilizer; (2) 2.5-cm-depth surface-applied compost; (3) 2.5-cm-depth incorporated compost; (4) 5.0-cm-depth incorporated compost; (5) inorganic fertilizer plus 0.6-cm compost blanket; and (6) inorganic fertilizer plus straw mat cover. The plots were seeded with a mixture of tall fescue Festuca arundinacea Shreb.: ‘Magellan,’ ‘Coronado Gold,’ ‘Regiment,’ and ‘Tomcat,’ perennial ryegrass Lolium perenne L. ‘Linn’, and Kentucky bluegrass Poa pratenis L. ‘Baron.’ Soil chemical and physical attributes and plant growth and quality parameters were measured during 840 days following study establishment. Soil C, N, P, K, Ca, and Mg, and turfgrass growth and quality were increased and soil bulk density was reduced by amending with composts. Incorporation of compost into soil improved soil and plant attributes more than unincorporated surface application, but the differences diminished with time. Compost benefits increased with time. One-time applications of compost can provide immediate and long-term benefits to soil and plant attributes, but there may be no need to incorporate the compost into soil, particularly if the soil has recently been loosened by tillage.     

Compost and P amendments for stimulating microorganisms and maize growth in a saline soil from Pakistan in comparison with a nonsaline soil from Germany

A 92 d greenhouse pot experiment with maize (Zea mays L.) was carried out with a strongly saline soil from Pakistan (P‐s) in comparison with a nonsaline soil from Germany (G‐s) similar in pH and texture. The aim was to evaluate salinity effects on the decomposition of compost and effects of compost and P amendments on (1) plant growth and (2) microbial‐biomass formation. The yield of maize shoot‐C and root‐C increased in both soils in the order nonamended control < +triple superphosphate (TSP) (A1) < +compost (A2) < +(compost + TSP) (A3) < +TSP‐enriched compost (A4). In comparison with the control, the highest yield in treatment A4 was nearly doubled on the G‐s, but was increased more than 8‐fold on the saline P‐s. Averaging the three compost treatments, 32% of the compost added was decomposed in the German soil and 36% in the Pakistani soil on the basis of the compost recovered as particulate organic matter. These data were roughly in agreement with the CO₂‐evolution data. This indicates that the decomposition of compost was not affected by salinity. Compost‐derived CO₂ was mainly evolved until day 32, the root‐derived CO₂ from day 74 until the end of the experiment. The addition of compost resulted in higher contents of microbial biomass C and biomass P, but also in that of NaHCO₃‐extractable P. These three properties were significantly interrelated (r = 0.64–0.85), but on a lower level of significance than the relationships between shoot‐C, root‐C, and NaHCO₃‐extractable P (r = 0.90–0.93). Applying compost enriched with TSP (incubation of compost and TSP for 24 h) provided considerably more P to plants and microorganisms than the separate addition of these two components. The results suggest that the role of the microbial biomass as a sink and source for available P deserves further attention.     

Effects of Different Types of Composts on Soil Characteristics and Morphological Traits of Two Dry Rangeland Species

Today, environmental protection and safe crop production are very important. The management of soil elements by compost is considered as important for sustainable agriculture. The mode of action of the composts is very different between various plant species. To evaluate the effects of different composts on soil structural and chemical properties and on morphological traits of two dry rangeland species (atriplex; Atriplex lentiformis and mesquite; Prosopos juliflora), a study was conducted in Fars Province of Iran during the year 2010. The study was a factorial experiment based on a randomized complete block design with three replications. Treatments included compost types: solid (SC) and liquid compost or compost tea (LC), solid-liquid mixture (XSL) and control (Con; non used compost) as the first factor, and two pasture plant species as the second factor. The results showed that the compost application had significant and positive effects on morphological traits such as plant height, stem diameter, plant volume, crown length, width, and area, and caused 15, 51.18, 70.67, 34.18, 18.35, and 64.94% increase on these morphological traits, respectively. Although soil acidity was not significantly affected by compost and species, the effects of compost were significant on organic matter percentage, soil phosphorous, and potassium contents. Soil nitrogen percentage was affected by both species and compost. Compost application caused a decrease in the amount of sodium compared with the control. Overall, the results of this study suggested that within the compost types, liquid compost was an advisable biofertilizer in a similar climate. Furthermore, the LC and the XSL are recommended for improving the morphological traits and the soil characteristics, respectively.     

Evaluating the Impact of Combined Application of Biochar and Compost on Hydro-physical Properties of Loamy Sand Soil

ABSTRACT

Biochar, compost and their combination are important organic amendment materials for improving the hydro-physical properties of sandy soils. Series of soil columns experiments were conducted for investigating the application effects of date palm biochar and compost on evaporation, moisture distribution, infiltration, sorptivity (Sp), saturated hydraulic conductivity (K_sat) and water holding capacity (WHC) at application rates of 1%, 2%, 3% and 4% (10, 20, 30 and 40 g kg^?1). The columns were filled manually with air-dried soil with 35 cm depth and the thickness of surface amended layer was 10 cm (T10) and 20 cm (T20) from soil surface at bulk density of 1400 kg m^?3. The results showed that the behavior of soil moisture distribution was influenced by application of biochar, compost and biochar-compost mixture. Moreover, in the amended layer T10, applying biochar at rate of 1%, 2%, 3% and 4% reduced significantly cumulative evaporation by 5.8%, 10.8%, 12.8% and 16.1%, respectively. Meanwhile, the reduction for the biochar-compost mixture at application rates of 1%, 2%, 3% and 4% was 10%, 12.2%, 14.5% and 20%, respectively. In layer T20, applying biochar at rate of 1%, 2%, 3% and 4% reduced cumulative evaporation by 10.24%, 13.0%, 18.3% and 21.5% but this reduction amounted to 18.2%, 21%, 23% and 24% for the biochar-compost mixture, respectively. It was generally observed that the highest application rate (4%) for applied amendments was the most effective impact on Sp, K_sat and WHC compared with other rates.     

Immature Compost Suppresses Weed Growth Under Greenhouse Conditions

The influence of immature municipal solid waste-biosolids composts on emergence and mean days to emergence (MDE) of several weed species was evaluated in a pot trial under greenhouse conditions. The experiment consisted of placing a 7.5 cm deep layer of three-day-old immature compost, a mature and stable compost, an artificial medium or control sand as a mulch on ivyleaf morning glory seeds. Immature three-day-old compost decreased percentage emergence, shoot and root dry weight, and increased MDE of ivyleaf morning glory. In an experiment with eight-week-old immature compost utilizing mulching depths of 2.5, 5, 7.5, 10 cm and the untreated control on seeds of three weed species, common purslane did not emerge under any of the immature compost treatments. The MDE of ivyleaf morning glory and barnyard grass increased linearly as immature compost depths increased. Next, eight economically important weed species were sown in pots with either mature or immature (eight-week-old) compost utilizing mulching depths of 2.5 and 10 cm, in addition to an untreated control. Control pots yielded higher percentages of emergence than compost treatments for all species evaluated. Common purslane, large crabgrass, pig-weed, Florida beggarweed, and dichondra did not emerge through a 10-cm deep layer of mature compost mulch, or 2.5 or 10 cm deep layer of immature mulch. Significant compost maturity/depth interactions were observed for percent emergence on common purslane, ground cherry, large crabgrass, Florida beggarweed, and ivyleaf morning glory. A thinner layer was required to suppress germination using immature eight-week-old compost as compared to mature and stable compost. Immature (three-day or eight-week-old) compost containing acetic acid concentrations of 2474 and 1776 mg.kg^?1 respectively reduced percentage emergence of several economically important weed species. These studies suggest that immature composts can be used to control weeds under conditions where spatial separation is maintained between the crop and the compost and phytotoxic fermentation products do not affect the health of the mulched plants and where odors associated with such partially stabilized products do not pose problems.     

Nitrogen mineralization,N<Subscript>2</Subscript>O production and soil microbiological properties as affected by long-term applications of sewage sludge composts

A field study was conducted to investigate the long-term effect of surface application of sewage sludge composts vs chemical N fertilizer on total N, total C, soluble organic C, pH, EC, microbial biomass C and N, protease activity, deaminase activity, urease activity, gross and net rates of N mineralization and nitrification, CO₂ evolution, and N₂O production. Soil samples were taken from five depths (0–15, 15–20, 20–30, 30–40, and 40–50 cm) of a long-term experiment at the University of Tokyo, Japan. Three fields have been receiving sewage sludge composted with rice husk (RH), sawdust (SD), or mixed chemical fertilizer NPK (CF), applied at the rate of 240 kg N ha^–1 each in split applications in summer and autumn since 1978. Significantly higher amounts of total N and C and soluble organic C were found in the compost than in the CF treatments up to the 40-cm soil depth, indicating improved soil quality in the former. In the CF treatment, soil pH values were significantly lower and electrical conductivity values were significantly higher than those of compost-treated soils of up to 50 cm depth. Soil microbial biomass C and N, CO₂ evolution, protease, deaminase, and urease activities were significantly higher in the compost than in the CF treatments due to greater availability of organic substrates that stimulated microbial activity. Gross N mineralization rates determined by ¹⁵N dilution technique were eight and five times higher in the SD and RH treatments than in the CF treatment, respectively, probably due to high levels of microbial and enzyme activities. Net N mineralization rates were also significantly higher in the compost treatments and were negative in the CF treatment indicating immobilization. Net nitrification rates were higher in compost treatments and negative in the CF treatment. Nitrous oxide productions from compost treatments were higher than the CF treatment due to the greater availability of mineral N as a result of higher mineralization and nitrification rates and soluble organic C in the former. Most of the measured parameters were highest in the surface soil (0–15 cm) and were significantly higher in the SD treatment than in the RH treatment.     

Microbial biomass and activity in composts of different composition and age

The aim of this study was to perform a comparison of microbial activity and biomass in biowaste (BWC), yard waste (YWC), and cattle‐manure composts (CMC) of different age. Two different methods for either biomass (microbial C following fumigation‐extraction and microbial lipid phosphate) or activity measurements (CO₂‐production rate and fluorescein diacetate hydrolysis) provided comparable information, as judged from their strong correlation. Microbial biomass and activity declined with time in all composts. Microbial biomass C was strongly correlated with microbial activity but was even stronger correlated with pH. CMC proved to be very distinct from the two other compost types by having the highest biomass and the lowest specific activity (i.e., activity per unit biomass). The microbiological properties analyzed allow us to discriminate among different compost types, helping to assign their potential applications.     

Relating Compost Measures of Stability And Maturity to Plant Growth

Assessment of compost maturity is important for successful use of composts in agricultural and horticultural production. We assessed the “maturity” of four different sawdust-based composts. We composted sawdust with either cannery waste (CW), duck manure (DM), dairy (heifer) manure (HM) or potato culls (PC) for approximately one year. Windrows were turned weekly for the first 60 days of composting, covered for four winter months and then turned monthly for six more months. We measured compost microbial respiration (CO₂ loss), total C and N, C:N ratio, water soluble NO₃-N and NH₄-N, dissolved organic carbon (DOC), pH and electrical conductivity at selected dates over 370 days. Compost effects on ryegrass biomass and N uptake were evaluated in a greenhouse study. We related compost variables to ryegrass growth and N uptake using regression analysis. All composts maintained high respiration rates during the first 60 days of composting. Ammonium-N concentrations declined within the first 60 days of composting, while NO₃-N concentrations did not increase until 200+ days. After 250+ days, DM and PC composts produced significantly more ryegrass biomass than either CW or HM composts. Total C, microbial respiration and water-extractable NO₃-N were good predictors of compost stability/maturity, or compost resistance to change, while dissolved organic carbon, C:N ratio and EC were not. The compost NO₃-N/CO₂-C ratio was calculated as a parameter reflecting the increase in net N mineralization and the decrease in respiration rate. At ratio values >8 mg NO₃-N/mg CO₂-C/day, ryegrass growth and N uptake were at their maximum for three of the four composts, suggesting the ratio has potential as a useful index of compost maturity.     

Nitrogen Availability from Compost in High Tunnel Tomato Production

High yield agricultural systems, such as high tunnel (HT) vegetable production, require a large supply of soil nutrients, especially nitrogen (N). Compost is a common amendment used by HT growers both to supply nutrients and to improve physical and biological soil properties. We examined commercially-available composts and their effects on soil N, plant N uptake, and tomato yield in HT cultivation. In addition, a laboratory study examined N and carbon (C) mineralization from the composts, and the usefulness of compost properties as predictors of compost N mineralization was assessed under field and laboratory conditions. The field study used a randomized complete block design with four replications to compare four compost treatments (all added at the rate of 300 kg total N ha^?1) with unamended soil and an inorganic N treatment (110 kg N ha^?1). Tomatoes were grown in Monmouth, Maine during the summers of 2013 and 2014. Compost NO₃^?-N and NH₄⁺-N application rates were significantly correlated with soil NO₃^?-N and NH₄⁺-N concentrations throughout the growing season. Marketable yield was positively correlated with compost total inorganic N and NO₃^?-N in both years, and with NH₄⁺-N in 2014. There were no significant differences among composts in percentage of organic N mineralized and no correlations were observed with any measured compost property. In the laboratory study, all compost-amended soils had relatively high rates of CO₂ release for the initial few days and then the rates declined. The compost-amended soils mineralized 4%–6% of the compost organic N. This study suggested compost inorganic N content controls N availability to plants in the first year after compost application.