The CERES-wheat model (1) was used to estimate the optimum time of sowing of wheat after rice at Nashipur in northern Bangladesh, and the SWAGMAN® Destiny model (2) was used to examine the trade-off between yield and net recharge of the watertable for wheat after rice at Griffith, NSW, Australia. The models were calibrated and validated against independent data sets prior to running the simulations. At Nashipur, the effect of sowing date, ranging from 1 Sept to 1 Jan, on the yield of cv. Kanchan was investigated, on a sandy loam soil, with low initial soil mineral N and a full profile of extractable water. The crops were supplied with 50 kg N/ha at panicle initiation and a total of 200 mm in 2 irrigations during grain filling. At Griffith, wheat cv. Janz was sown early (24 Apr) and late (29 June) on a Mundiwa clay loam soil with deep drainage of 0.1 mm/d. The model was run for initial watertable depths (WTD) of 0.5, 1 and 1.5 m, watertable salinities of 1 and 20 dS/m, and with wet or intermediate starting soil water contents (SWCs) (wet = drained upper limit (DUL) throughout profile; intermediate = average of DUL and lower limit to 1.5 m depth, then DUL below 1.5 m). Early and late sowings were compared for crops grown with or without irrigation. Irrigation was applied when cumulative ET reached 60 mm, using 100% irrigation efficiency, with irrigation water salinity of 0.2 dS/m. Ten years of local daily weather data were used for all simulations.
