Soil Organic Matter Management: The Roles of Residue Quality in C Sequestration and N Supply - Sustainable Management of Soil Organic Matter - page 152

Fig. 3.7.1. Changes in soil organic matter content over time on ex-pasture sites, including fitted

regressions.

Fig. 3.7.2. Changes in soil organic matter content over time on arable sites (fitted regressions
only for clarity).

to range from 2.6 to 3.9% (measured organic matter levels ranged between
2.7 and 4% in 1996).
Regression analysis was used to establish whether there was a relation-
ship between the 'stabilized' and total soil organic matter contents
measured in 1996 and soil structural stability. There was a weak positive
relationship between total soil organic matter contents and structural
stability ( P = 0.05, adjusted r 2 ( adj ) = 20%; y = 0.39 + 7.3/(1 + EXP(4.4
( x − 4.1)))). Surprisingly, there appeared to be a much stronger relation-
ship between 'stabilized' soil organic matter levels and soil structural
stability ( P = 0.002, adjusted r 2 ( adj ) = 74%; y = −3.1 + 11.4/(1 + EXP
(2.9( x − 4.0)))). However, this relationship was very dependent on the 'sta-
bilized' organic matter estimates for sites A, B and L.
There was no relationship ( P > 0.05) between soil structural stability
and the clay, silt (fine and coarse) and sand (fine and medium) content
of the soils. Also, the strength of the relationships between soil structural
stability and total/'stabilized' organic matter levels was not improved by the
inclusion of sand, silt and clay content data.