Agriculture Reference
In-Depth Information
frequency of fallows) are markedly different from those where the APSIM-
Residue module was developed and most widely used. So it is appropriate
that the performance of that module is examined in more detail in this
environment.
This study contained three elements: the APSIM-Residue module was
parameterized using experimental data (Robertson and Thorburn, Chapter
3.1) from two sites. The applicability of the parameter values to other
sugarcane systems was then assessed against independent measurements
of decomposition at another site. Finally, the impact of different residue
decomposition rates, resulting from the different parameterizations, on
simulated yield was assessed from longer term systems simulations for two
of the sugarcane residue management experiments.
Methods
Field experiments
Sugarcane residue decomposition was measured over 1 year within three
longer-term residue management field experiments, referred to as Mackay
Early (harvested in July each year), Mackay Late (harvested in November)
and Harwood Early (harvested in July) by Robertson and Thorburn
(Chapter 3.1), who fully describe the methods employed. Harwood is
located approximately 1500 km south of Mackay, and has a temperate
climate compared with the tropical climate at Mackay (Robertson and
Thorburn, Chapter 3.1). After harvest of a sugarcane crop, crop residues
were left on the soil surface (as is common practice in the Australian sugar
industry) and 8-10 quadrats, 1.5 m
0.75 m in area, were established in
each replicate plot of each experiment. A known mass of residue was
enclosed within each quadrat. Residue in the quadrats was in direct contact
with the soil, but enclosed over the top with fine nylon mesh ~20 mm in
diameter. The mass of residue in individual quadrats was measured
destructively over 12 months. Daily weather was measured at each site.
In addition to these measurements, soil moisture was logged hourly
with Campbell CR10X dataloggers and CS615 water content reflecto-
meters in one replicate plot of the experiments. Measurements were made
over the 0-50 mm soil depth interval, and at 75 and 175 mm depth. Daily
average values were calculated from the data.
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The APSIM Model
The APSIM model configuration used in this study consisted of modules
for soil N and C (APSIM-SoilN), soil water (APSIM-SoilWat) and surface
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