Environmental Engineering Reference
In-Depth Information
et al.
2001
). The assay quantifies cellulose decomposition on the basis of the
reduction in tensile strength of cellulose fibers, referred to as cotton tensile strength
loss (CTSL), of a standardized cotton fabric. Since the assay uses a standardized
cotton fabric (97 % holocellulose; Shirley Institute Test Fabric, Didsbury, England)
(Latter and Harrison
1988
), it provides a method for normalizing substrate quality
between sites (Harrison et al.
1988
).
Cotton strips can be inserted vertically into the soil with a flat spade or sharp-
shooter shovel that is at least as wide as the strip. One end of the strip is trapped
between the blade edge and the soil surface. The spade is then inserted into the soil,
pulling the strip with it. Two sets of strips are used. One set is inserted and removed
immediately. These serve as control or reference strips. The remaining strips are
left in the soil for one to several weeks, depending on the expected rate of
decomposition. Upon removal from the soil, strips are immediately washed in
freshwater to remove debris and soil and then washed again in deionized water.
The sample strips are dried at room temperature and then stored in plastic bags.
The strips are cut into 3 cm wide horizontal segments and reduced to 2 cm segments
by fraying. Segments are used to accommodate soil variability with depth that may
impact decomposition rates. Tensile strength is measured from each segment with a
tensometer (e.g., Monsanto Type-W) equipped with 7.5 cm wide jaws adjusted to
3 cm spacing. Temperature and humidity affect the results so all measurements
should be are carried out at 18-22
C and 100 % relative humidity (facilitated by
soaking the strips in deionized water). Individual losses in tensile strength are
calculated relative to the reference strips for each site.
Walton and Allsopp (
1977
) presented the benefits of this assay: (i) cellulose is a
major component of plant remains; (ii) the decomposition of dead plant remains is a
major biological process; (iii) cellulose provides a major food source for a wide
variety of soil organisms; (iv) cotton is a natural substrate; and (v) degradation of
any organic material begins with bond breaking, leading to changes in tensile
strength. However, different litter constituents do not decompose at the same
different rate (Minderman
1968
) and Howard (
1988
) concluded that the rate of
breakdown of pure cellulose added to soil cannot reflect litter decomposition rate.
Walton and Allsopp (
1977
) concluded that this technique is best employed for
comparative assessments of biological activity in different soils.
7.4.5 Soil Respiration
7.4.5.1 Overview
Soil respiration, or more accurately soil surface CO
2
efflux, is the release of CO
2
from the soil surface to the atmosphere. It results primarily from respiration by plant
roots and soil microorganisms and may comprise 50-80 % of ecosystem respiration
(Davidson et al.
2002
; Giardina and Ryan
2002
). Conceptually, respiration reflects
substrate decomposition in soils and in many texts soil respiration is included in
