O. Kostov

Microbial indicators for sawdust and bark compost stability and humification processes

Abstract To what extent some microbial index ratios are suitable for use as early criteria for the level of compost stability during aerobic composting of coniferous sawdust and bark at mesophilic conditions was studied. Evolution of the specific respiration activity (CO 2 -C/biomass C) and the ratios between some groups of microorganisms were followed as a function of composting time. The specific respiration activity was found to be an early and most reliable indicator of compost stability. The peroxidase and polyphenoloxidase enzyme activity during composting, as well as the composition of newly-formed humus substances were studied. The duration of composting increased the quality of newly-formed humus substances (C h.a. :C f.a ratio; Ca-complexed humic acid and resistance of organo-mineral complexes). The quality of humus substances could be used to assess compost stability. However, the results can be applied only under defined conditions.

Aerobic composting of plant wastes and their effect on the yield of ryegrass and tomatoes

Vine branches, rice husks and flax residues were composted. The dynamics of biomass carbon, C/N ratios and nitrification were studied. The highest quality level and the most stabilized composts with the highest values of total N (1.3–1.6%) and the smallest C/N ratios (8.0–9.0) were found with the vine branch composts. Compost application significantly increased the yield of tomatoes (24.0–61.1%) and the quality of fruits compared to soil treated with mineral fertilizers and manure. Inoculation of the vine branch compost with a Cephalosporium sp. had a positive effect on the yield and the quality of both ryegrass and tomatoes. The stabilization of the microbial biomass C level in the composts coincided with the beginning of intensive nitrification. Inoculation lowered the conductivity values and nitrate contents in all composts. It appeared that when nitrate N concentrations in the composts were more than 5% of the total N, NO3 accumulation in the fruits could result. However, the results can be applied to similar substrates and conditions of composting.

Cucumber cultivation on some wastes during their aerobic composting

Abstract Composting waste from vine branches, flax residues and grape prunings, husks and seeds was assessed as a technique to produce a medium for cucumber production under glasshouse conditions. The composts were treated with N, P, K, Cu, Mg, Fe and marble at the very beginning of the composting. During the growing period, the composts maintained a higher temperature in the root zone, a higher CO 2 production and a higher microbial biomass C level than the manured soil. They also released nutrients in accordance with the plant demands. The nitrate concentration in fresh fruits was significantly lower in the compost treatments than in the manured soil. Fruit production on the composts started 10–12 days earlier and the compost treatments showed a significantly higher yield (six times higher for the first month and 48–79% for the whole period). This simple technology had better economics than the use of manured soil.

Microbial activity of Cu contaminated soils and effect of lime and compost on soil resiliency.

In vineyards, the long-term use of copper fungicides has increased soil Cu concentrations that can adversely affect the number and activities of soil microorganisms. To better understand this phenomenon and to ameliorate such harmful effects, an incubation experiment was carried out with a sandy loam and a sandy soil to which increasing rates of CuSO4 were added. By this treatment, the basal soil respiration (7-55%) and decomposition of added vine branches (46-86%) was inhibited. At the application rate of 500 mg Cu kg−1, soil microbial biomass-C was inhibited (7-66%) in the sandy soil and stimulated (2-10%) in the sandy loam soil. The specific respiration rate was a reliable indicator for Cu stress, and it increased with time and higher Cu concentrations before lime and compost applications. Total number of bacteria and streptomycetes were also strongly inhibited. Fungal population was significantly more tolerant to copper toxicity than the bacteria. A stimulation of fungal population at a dose of 500 mg Cu kg−1 in both soils was observed. A criterion such as “stimulation” lasting for more than 60 days can also be used as indication of Cu contamination of soils. The order of inhibition (on day 125) at a dose of 500 mg Cu kg−1 soil was as follows: A. sandy loam soil (pH> 7.0) — fungi < biomass-C < basal soil respiration < bacteria < streptomycetes; B. sandy soil (pH< 6.0) — fungi < basal soil respiration < biomass-C < bacteria < streptomycetes. The application of lime increased soil recovering ability at a moderate rate (for CO2 production – 22-70% and for biomass-C- 39-156%), but the combination of lime and compost significantly increased soil resiliency (for CO2 production- 16-518% and for biomass-C- 103-693%). The soil resiliency assessed by number of bacteria in compost treatments was 30-120% in sandy loam soil and 92-700% in the sandy soil. Compost and lime application increased the number of streptomycetes from 52 to 500% in sandy loam soil and from 100 to 700% in sandy loam soil. Fungal population was less increased in sandy soil as compared to sandy loam soil. The ecological dose higher than 5% inhibition of microbial processes and microorganisms appears to be suitable to assess Cu contamination of soils. CO2 production, biomass-C and specific respiration rate were less sensitive indicators as compared to streptomycetes and bacteria. It appears that compost application effectively promoted the recovery of soil microbial activity and soil fertility of Cu contaminated soils.

Nitrogen transformations in copper-contaminated soils and effects of lime and compost application on soil resiliency

Abstract A neutral and an acidic soil were treated with different doses (0–3,000 mg Cu kg–1 soil as CuSO4) of copper. The percentages of inhibition of nitrification in both soils varied from 5 to 97%, but for the N mineralization these percentages varied from 8 to 65%. The toxic effect of Cu for basal nitrification and N mineralization was assessed as critical. Nitrification was more sensitive than ammonification to copper toxicity. It appears that an ecological dose of inhibition for nitrification and N mineralization higher than 10% is suitable as an indicator for Cu contamination. Soil resiliency assessed by N mineralization in the lime treatments varied from 11 to 154% in the sandy soil and from 70 to 168% in the sandy loam soil. A combined application of lime and compost significantly increased soil resiliency. The percentage increase varied from 904 to 1,390% in the sandy soil and from 767 to 2,230% in the sandy loam soil. It appears that compost was a powerful agent for recovering the soil fertility of Cu-contaminated soils as assessed by N transformation. The acidic sandy soil showed a lower capacity for recovery after Cu toxicity stress.

Production of Tomato Seedlings on Composts of Vine Branches and Grape Prunings, Husks and Seeds

Compost mixtures and composts from vine branches and grape prunings, husks and seeds were studied to evaluate their possibility of substituting the conventional peat mixture for tomato seedling production. Specific respiration rate (CO2/biomass C ratio) and intensity of nitrification appear to be reliable criteria for compost stability. Compost mixtures and composts showed better agrochemical properties than the peat mixture, resulting in increased plant growth. It was found that tomato seedlings on compost mixtures and composts had a higher dry matter content, total mass, length and diameter of stems and number of leaves. They were ready to be transplanted four to five days earlier than plants grown on peat mixture. The results clearly indicate that peat mixture can be substituted by compost mixtures and composts. Furthermore, they have a better economic value.

Cation Exchange and Reducing Capacities as Criteria for Compost Quality

ABSTRACT Cation exchange capacity (CEC) and reducing capacity (RC) in relation to compost stability and quality were studied. The results show that grape prunings, husks and seeds compost and vine branches compost were nearly stabilized after 120 days of composting. The CEC of the vine branches compost (23.1–66.5 cmol kg−1) and the grape prunings, husks and seeds compost (98.3–138.7 cmol kg−1) was high during that period. Their reduction power was low and the quality of these composts was very good. The CEC of sawdust composts was noticeably lower (2.9–14.4 cmol kg−1) after 180 days. After 360 days of composting they were nearly stabilized and the CEC drastically increased (80.9–83.8 cmol kg−1). The reduction power of the sawdust composts was high during one full year and they could be applied to the soil with precautions within this period. Next to the cation exchange capacity the reducing capacity appeared to be a reliable and important criterion for compost quality, especially with respect to the prote...

Amelioration of composting process by fertilizers

Six different composts, four of them produced from oil palm residues and two commercial composts, were studied for their stability and quality. The composts were analyzed for their total C, total N, C/N ratio, mineral N, nitrogen mineralization index, CO2 production, biomass C, specific respiration rate, germination rate, pH values and plant growth index. Composts of oil palm (Elaeis guineesis) trunk and oil palm empty fruit bunch treated with N and P showed good stability and higher quality as compared to other composts. Their C/N ratios were the lowest (14-18) but their pH values were comparatively low (4.6-6.4). They had a good amount of total N (0.95-1.84%) with higher nitrate than ammonium nitrogen. The specific respiration rates were very low (0.25-0.63) which is an indication that these two composts are stable. Plant growth test supported conclusions based on the microbiological tests. Their properties were considered as suitable for planting media application. Compost quality can be further improved by adding bunch ash, which has high values of pH and is also a by-product from the oil palm industry. The applied nitrogen mineralization index could not be used with all kinds of composts as stability index. Both of the commercial composts showed high C/N ratios (34-68) and very low values of total and mineral nitrogen compared to oil palm residues composts. They were considered having low nutritional value and not recommended for planting media application.