The effect of organic and inorganic fertiliser amendments is often studied shortly after addition of a single dose to the soil but less is known about the long-term effects of amendments. We conducted a study to determine the effects of long-term addition of organic and inorganic fertiliser amendments at low rates on soil chemical and biological properties. Surface soil samples were taken from an experimental field site near Cologne, Germany in summer 2000. At this site, five different treatments were established in 1969: mineral fertiliser (NPK), crop residues removed (mineral only); mineral fertiliser with crop residues; manure 5.2 t ha −1  yr −1 ; sewage sludge 7.6 t ha −1  yr −1 or straw 4.0 t ha −1  yr −1 with 10 kg N as CaCN 2  t straw −1 . The organic amendments increased the C org content of the soil but had no significant effect on the dissolved organic C (DOC) content. The C/N ratio was highest in the straw treatment and lowest in the mineral only treatment. Of the enzymes studied, only protease activity was affected by the different amendments. It was highest after sewage amendment and lowest in the mineral only treatment. The ratios of Gram+ to Gram− bacteria and of bacteria to fungi, as determined by signature phospholipid fatty acids, were higher in the organic treatments than in the inorganic treatments. The community structure of bacteria and eukaryotic microorganisms was assessed by denaturing gradient gel electrophoresis (DGGE) and redundancy discriminate analyses of the DGGE banding patterns. While the bacterial community structure was affected by the treatments this was not the case for the eukaryotes. Bacterial and eukaryotic community structures were significantly affected by C org content and C/N ratio.

Structure and function of the soil microbial community in a long-term fertilizer experiment

Total soil organic matter content is a key attribute of soil quality since it has far-reaching effects on soil physical, chemical, and biological properties. However, changes in contents of organic carbon (C) and total nitrogen (N) occur only slowly and do not provide an adequate indication of important short-term changes in soil organic matter quality that may be occurring. Labile organic matter pools can be considered as fine indicators of soil quality that influence soil function in specific ways and that are much more sensitive to changes in soil management practice. Particulate organic matter consists of partially decomposed plant litter, and it acts as a substrate and center for soil microbial activity, a short-term reservoir of nutrients, a food source for soil fauna and loci for formation of water stable macroaggregates. Dissolved (soluble) organic matter consists of organic compounds present in soil solution. This pool acts as a substrate for microbial activity, a primary source of mineralizable N, sulfur (S), and phosphorus (P), and its leaching greatly influences the nutrient and organic matter content and pH of groundwater. Various extractable organic matter fractions have also been suggested to be important, including hot water-extractable and dilute acid-extractable carbohydrates, which are involved in stabilization of soil aggregates, and permanganate-oxidizable C. Measurement of potentially mineralizable C and N represents a bioassay of labile organic matter using the indigenous microbial community to release labile organic fractions of C and N. Mineralizable N is also an important indicator of the capacity of the soil to supply N for crops. It is concluded that individual labile organic matter fractions are sensitive to changes in soil management and have specific effects on soil function. Together they reflect the diverse but central effects that organic matter has on soil properties and processes. (c) 2005 Elsevier Inc.

Labile Organic Matter Fractions as Central Components of the Quality of Agricultural Soils: An Overview

A fluorimetric microplate enzyme assay has been developed to study enzyme diversity in soil as an approach to understanding functional diversity. The microplate assay allows a large number of soil samples and/or enzymes to be analysed in a short time. The substrates used are conjugates of the highly fluorescent compounds 4-methylumbelliferone (MUB) and 7-amino-4-methyl coumarin (AMC). The main advantage of using fluorimetrically-labelled substrates is that product formation can be measured directly in the microplate without previous extraction and purification of the product. A detailed protocol for this new technology is presented and some potential applications are outlined. A comparative study was carried out between the new microplate fluorimetric assay and a standard colorimetric enzyme assay based on p-nitrophenyl substrates. The kinetics of β-glucosidase and phosphatase activities were investigated in soils with different fertilizer backgrounds. Both methods generated similar values for Vmax (maximum rate of activity) whereas the affinity of β-glucosidase and phosphatase for their respective substrates (as indicated by Km values, Michaelis–Menten constant) was up to two orders of magnitude greater for the 4-methylumbelliferyl substrates compared to the p-nitrophenyl substrates.

A microplate fluorimetric assay for the study of enzyme diversity in soils

Our understanding of the relationship between the decomposition of soil organic matter (SOM) and soil temperature affects our predictions of the impact of climate change on soil-stored carbon. One current opinion is that the decomposition of soil labile carbon is sensitive to temperature variation whereas resistant components are insensitive. The resistant carbon or organic matter in mineral soil is then assumed to be unresponsive to global warming. But the global pattern and magnitude of the predicted future soil carbon stock will mainly rely on the temperature sensitivity of these resistant carbon pools. To investigate this sensitivity, we have incubated soils under changing temperature. Here we report that SOM decomposition or soil basal respiration rate was significantly affected by changes in SOM components associated with soil depth, sampling method and incubation time. We find, however, that the temperature sensitivity for SOM decomposition was not affected, suggesting that the temperature sensitivity for resistant organic matter pools does not differ significantly from that of labile pools, and that both types of SOM will therefore respond similarly to global warming.

Similar response of labile and resistant soil organic matter pools to changes in temperature

http://dzumenvis.nic.in/microbes and metals interaction/pdf/indicators for evaluating soil quality.pdf

Indicators for evaluating soil quality

Methods in soil biology , Methods in soil biology , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Methods in soil biology.

Methods in Soil Biology.

Nitrification is the conversion of inorganic or organic nitrogen from a reduced to a more oxidized state. Chemoautotrophic bacteria are largely or solely responsible for nitrification in soil with a pH above 5.5 (Focht and Verstraete 1977), at a lower pH there is evidence for the presence of acid-tolerant heterotrophic nitrifiers (Schimel et al. 1984). The heterotrophic nitrifiers (e.g. few bacteria, such as strains of Arthrobacter, and fungi, such as Aspergillus) do not derive energy from the oxidation of NH4 +. In arable soils the production of nitrate by heterotrophs appears to be insignificant in relation to that brought about by the chemoautotrophs (Paul and Clark 1989). In contrast, 90% of the potential nitrification in acid forest soils is produced by heterotrophs (Kilham 1987).

Nitrification and Denitrification

Proteins are important constituents of both seed and root exudates, they are a primary structural and functional component of plant cell walls, and represent a third of the total nitrogen in soil (O’Sullivian et al. 1991). Proteins are supplied to soil from all dead organisms, plants and animals. Proteins in soil are decomposed readily by many bacteria and fungi. During degradation, extracellular proteases produce oligopeptides from proteins, resulting in the subsequent release of low molecular weight compounds which are assimilated by microorganisms. Upon the release of proteases from microbial cells these soil enzymes become physically adsorbed onto soil colloids or covalently bound to soil organic matter. These immobilized enzymes show a high degree of resistance to proteolysis. In contrast, proteases are inhibited by desiccation.

Enzymes Involved in Nitrogen Metabolism

Wassergesattigte Boden werden unter aeroben Bedingungen bei 25°C inkubiert. Der aus organischen N-Verbindungen freigesetzte NH4+-N und NO3--N werden kolorimetrisch bestimmt.

Richard Öhlinger

Papers

Methods in soil biology.

Methods in Soil Biology.

Nitrification and Denitrification

Enzymes Involved in Nitrogen Metabolism

Bestimmung der N-Mineralisation im anaeroben Brutversuch