Agriculture Reference
In-Depth Information
Fig. 4.34.
Relational diagram for the onion growth and development simulation
model ALCEPAS, based on the general crop growth simulation model SUCROS87.
AMX, gross assimilation rate at light (PAR) saturation of an individual leaf (kg/ha/h);
DVS, development stage of bulb onion crop (50% emergence = 0; 50% bulbing =
1; leaf fall (maturity) = 2); EFF, maximum PAR use efficiency of a leaf (kg/J (i.e. at
low PAR)); KDF, extinction coefficient for PAR in leaf canopy; LAI, leaf area index;
SLA, specific leaf area (cm
2
/g) (from de Visser, 1994a. Courtesy of
Journal of
Horticultural Science and Biotechnology
).
equations for the longevity of leaves and its variation with temperature; (iii)
KDF, the PAR extinction coefficient of the leaf canopy (Eqn 4.2); and (iv) an
equation describing how the partition of new growth between leaves and bulbs
changes with developmental stage (the graph of this function was of the same
form as in Fig. 4.27).
A function to describe how partition of new growth to roots changed with
developmental stage was derived from published work. The photosynthesis
parameters: (i) AMX, the PAR saturated assimilation rate of a leaf; (ii) EFF, the
PAR use efficiency of a leaf at low PAR; and (iii) the scattering coefficient of
leaves for PAR were not measured or known, but were found by running the
model with growth data from field experiments and optimizing for the values of
these parameters. The optimized values were close to those previously used in
SUCROS87 for spring wheat (Spitters
et al.
, 1989).
ALCEPAS combines the determinants of crop growth and yield outlined at
the beginning of this chapter, encapsulated in SUCROS87, with a model
incorporating much of the information described above that is particular to the
