『Abstract
The ability of the soil to supply some of the crop nitrogen (N)
requirements via the mineralization of organic matter is of economic
and environmental importance to producers and society. Water,
or its absence, controls microbial activity in soil and thus rates
of net N mineralization. Development of a general relationship
between soil water content and net N mineralization rate can therefore
improve prediction of soil N mineralization and hence soil N supply.
The objectives of this study were to use previously published
data sets to: 1) evaluate a new biophysical water function to
predict the effect of soil water content on net soil N mineralization
rate and 2) examine the effect of the origin of the soil and soil
properties on the response of soil N mineralization to water content.
A biophysical water function was developed which included the
contribution of two physical processes: the wetting of surfaces
presented by soil particulate matter (i.e. clays, organic matter),
and the filling of free volume between the particles (i.e. pores).
Scaled water-filled pore space (WFPS) between a minimal and optimal
value for mineralization was used as the unit for water content.
Four different water functions were compared in this study (biophysical,
sigmoidal（後のiの頭は¨）, logistic and Gaussian)
and although they explained a similar percentage of the variability
in scaled mineralization rate, the functions had distinctly different
shapes. The biophysical water function was found to be valid across
a range of soil properties and origins. The biophysical water
function includes a surface activity parameter (λ) which was found
to be consistently about 0.80, indicating that 80% of the mineralization
reaction takes place at a surface. The shape of the biophysical
water function was found to be controlled to a large extent by
parameter b which reflects the increase in net N mineralization
rate associated with surface wetting. Parameter b was found to
vary with climatic zone of soil origin and soil properties. The
b parameter was higher for soils from warmer (≧6℃) than colder
(＜6℃) climatic zones; higher for soils from wetter (≧760 mm) than
dryer (＜760 mm) climatic zones; higher for sandy and loamy compared
with clayey and silty soils; and higher for soils low in soil
organic C (SOC)(＜20 g kg-1) content. The biophysical
function presented in this study was found to show a behavior
representative for the underlying biological processes and has
the advantages that the three fitted parameters all have a biophysical
interpretation that allows new and original biological interpretations
based on the fitted parameters related to surface and pore domains.
Keywords: Climatic zones; Moisture response; Soil properties;
WFPS』
1. Introduction
2. Theory
2.1. A biophysical model for the water content dependence
of net N mineralization rate
2.2. The surface term
2.3.The volume term
3. materials and methods
3.1. Data sets
3.2. Parameterization of water units
3.3. Fitting the water content response function and comparison
of land use, climate zone and soil properties
3.4. Fixing parameter values
3.5. Applicability of the water content function for field prediction
3.6. Statistics
4. Results
4.1. Fitting of the moisture response function
4.2. Influence of the land use, climate zone and soil properties
on the biophysical water function
4.3. Effects of fixing parameter values
4.4. Applicability of the moisture function for field prediction
5. Discussion
5.1. Fitting of the moisture response function
5.2. Influence of the land use, climate and soil properties on
the moisture response function
5.3. Applicability of the moisture function for field prediction
6. Conclusions
Acknowledgments
References