2. Materials and methods
We started with a combination of literature data and data from
pot and field experiments to calibrate and evaluate ORYZA2000
for Jasmine rice variety KDML105. Special attention was paid to
the calibration of ORYZA2000’s parameters that describe photoperiod
sensitivity. Next, we used ORYZA2000 to simulate attainable
yields for real farmers’ fields along different toposequence positions.
We analysed the yield gap by comparing these attainable
yields with experimental yields obtained in the same fields. We
then used ORYZA2000 and the experimental data to estimate the
yield increase that could be obtained by specifically alleviating
nitrogen (N) and water constraints through fertilization and irrigation,
respectively. Finally, we used statistical analysis to compare
the main effects and the interactions of spatial variation caused by
geographical location of the fields (village, toposequence position),
temporal variation caused by climate variability (year), and crop
management (fertilizer-N and water) of simulated yield and yield
gaps; and to determine the exceedance probability (p) of seasonal
rainfall.