D. S. Jenkinson

Bio: D. S. Jenkinson is an academic researcher from The Hertz Corporation. The author has contributed to research in topics: Soil water & Soil organic matter. The author has an hindex of 70, co-authored 138 publications receiving 39442 citations. Previous affiliations of D. S. Jenkinson include University of Hertfordshire & University of Reading.

An extraction method for measuring soil microbial biomass c

Abstract: The effects of fumigation on organic C extractable by 0.5 M K2SO4 were examined in a contrasting range of soils. EC (the difference between organic C extracted by 0.5 M K2SO4 from fumigated and non-fumigated soil) was about 70% of FC (the flush of CO2-C caused by fumigation during a 10 day incubation), meaned for ten soils. There was a close relationship between microbial biomass C, measured by fumigation-incubation (from the relationship Biomass C = FC/0.45) and EC given by the equation: Biomass C = (2.64 ± 0.060) EC that accounted for 99.2% of the variance in the data. This relationship held over a wide range of soil pH (3.9–8.0). ATP and microbial biomass N concentrations were measured in four of the soils. The (ATP)(EC) ratios were very similar in the four soils, suggesting that both ATP and the organic C rendered decomposable by CHCl3 came from the soil microbial biomass. The C:N ratio of the biomass in a strongly acid (pH 4.2) soil was greater (9.4) than in the three less-acid soils (mean C:N ratio 5.1). We propose that the organic C rendered extractable to 0.5 m K2SO4 after a 24 h CHCl3-fumigation (EC) comes from the cells of the microbial biomass and can be used to estimate soil microbial biomass C in both neutral and acid soils.

Chloroform fumigation and the release of soil nitrogen: A rapid direct extraction method to measure microbial biomass nitrogen in soil

Abstract: A new “direct extraction” method for measuring soil microbial biomass nitrogen (biomass N) is described. The new method (fumigation-extraction) is based on CHC13 fumigation, followed by immediate extraction with 0.5 M K2SO4 and measurement of total N released by CHC13 in the soil extracts. The amounts of NH4-N and total N extracted by K2SO4 immediately after fumigation increased with fumigation time up to 5 days. Total N released by CHC13 after 1 day fumigation (1 day CHC13-N) and after 5 days fumigation (5 day CHC13-N) were positively correlated with the flush of mineral N (FN) in 37 soils that had been fumigated, the fumigant removed and the soils incubated for 10 days (fumigation-incubation). The regression equations were 1 day CHC13-N = (0.79 ± 0.022) FN and 5 day CHC13-N = (1.01 ± 0.027) FN, both regressions accounting for 92% of the variance in the data. In field soils previously treated with 15N-labelled fertilizer, the amounts of labelled N, measured after fumigation-extraction, were very similar to the amounts of labelled N mineralized during fumigation-incubation; both were about 4 times as heavily labelled as the soil N as a whole. These results suggest that fumigation-extraction and fumigation-incubation both measure the same fraction of the soil organic N (probably the cytoplasmic component of the soil microbial biomass) and that measurement of the total N released by CHC13 fumigation for 24 h provides a rapid method for measuring biomass N.

The effects of biocidal treatments on metabolism in soil—V: A method for measuring soil biomass

Abstract: A new method for the determination of biomass in soil is described. Soil is fumigated with CHCl3 vapour, the CHCl3 removed and the soil then incubated. The biomass is calculated from the difference between the amounts of CO2 evolved during incubation by fumigated and unfumigated soil. The method was tested on a set of nine soils from long-term field experiments. The amounts of biomass C ha−1 in the top 23 cm of soil from plots on the Broadbalk continuous wheat experiment were 530 kg (unmanured plot), 590 (plot receiving inorganic fertilizers) and 1160 (plot receiving farmyard manure). Soils that had been fallowed for 1 year contained less biomass than soils carrying a crop. A calcareous woodland soil contained 1960 kg biomass C ha−1, and an unmanured soil under permanent grass 2020. The arable soils contained about 2% of their organic C in the biomass; uncultivated soils a little more—about 3%.

Measurement of microbial biomass phosphorus in soil

Abstract: A method for measuring the amount of P held in soil micro-organisms (biomass P) is described and the assumptions on which it is based are discussed. Biomass P is calculated from the difference between the amount of inorganic P (Pi) extracted by 0.5 (Spm) NaHCO3 (pH 8.5) from fresh soil fumigated with CHCl3 and the amount extracted from unfumigated soil. Some CHCl3-released Pi is sorbed by soil during fumigation and extraction: an approximate allowance for this is made by incorporating a known quantity of Pi during extraction and correcting for recovery. Most of the P released is in inorganic form and the proportion increases with duration of fumigation. Non-microbial P is little, if at all, affected by fumigation. Microbial biomass P is calculated from CHCl3-released Pi by dividing by 0.4, i.e. by assuming that 40% of the P in the biomass is rendered extractable as Pi by CHCl3. Measurements of biomass P must be done in fresh soil, CHCl3 releases much less P in air-dry soil.

An extraction method for measuring soil microbial biomass c

Abstract: The effects of fumigation on organic C extractable by 0.5 M K2SO4 were examined in a contrasting range of soils. EC (the difference between organic C extracted by 0.5 M K2SO4 from fumigated and non-fumigated soil) was about 70% of FC (the flush of CO2-C caused by fumigation during a 10 day incubation), meaned for ten soils. There was a close relationship between microbial biomass C, measured by fumigation-incubation (from the relationship Biomass C = FC/0.45) and EC given by the equation: Biomass C = (2.64 ± 0.060) EC that accounted for 99.2% of the variance in the data. This relationship held over a wide range of soil pH (3.9–8.0). ATP and microbial biomass N concentrations were measured in four of the soils. The (ATP)(EC) ratios were very similar in the four soils, suggesting that both ATP and the organic C rendered decomposable by CHCl3 came from the soil microbial biomass. The C:N ratio of the biomass in a strongly acid (pH 4.2) soil was greater (9.4) than in the three less-acid soils (mean C:N ratio 5.1). We propose that the organic C rendered extractable to 0.5 m K2SO4 after a 24 h CHCl3-fumigation (EC) comes from the cells of the microbial biomass and can be used to estimate soil microbial biomass C in both neutral and acid soils.

Organic matter and water-stable aggregates in soils

Abstract: Summary The water-stability of aggregates in many soils is shown to depend on organic materials. The organic binding agents have been classified into (a) transient, mainly polysaccharides, (b), temporary, roots and fungal hyphae, and (c) persistent, resistant aromatic components associated with polyvalent metal cations, and strongly sorbed polymers. The effectiveness of various binding agents at different stages in the structural organization of aggregates is described and forms the basis of a model which illustrates the architecture of an aggregate. Roots and hyphae stabilize macro-aggregates, defined as > 250 μm diameter; consequently, macroaggregation is controlled by soil management (i.e. crop rotations), as management influences the growth of plant roots, and the oxidation of organic carbon. The water-stability of micro-aggregates depends on the persistent organic binding agents and appears to be a characteristic of the soil, independent of management.