In no-till management, the crop residue is left on the soil surface. The effect of residue on water relations of soil, and
subsequently that of plant are highly dependent on weather conditions. This study was aimed to evaluate the effect of
maize residue (3.85 mg ha-1) on water relations of rainfed chickpea, using model CYRUS. Firstly, this model was
recoded in Qbasic programming; then a simple sub-routine was added to include the effect of crop residue; finally, it
was run for long-term daily weather data (1961-2004) of Maragheh (winter-dominant rainfall), Iran. It was revealed
that, as compared to control, the residue treatment results in that the value of fraction transpiration soil water in
rooting depth [FTSW: ranges from 0 (wilting point) to 1 (field capacity)] to be 2.72% higher during emergence (E)
to flowering (R1), 10.02% higher across R1 to pod initiation (R3), 7.59% higher for R3 to pod filling (R5), 1.82%
higher during R5 to pod yellowing (R7) and 1.32% more over R7 to maturity (R8). Across the S-E, E-R1, and R1-
R3 periods, the value of evapotranspiration (ET) was higher for non-mulching conditions, as compared to mulching
conditions. On the other hand, across the R5-R7 and R7-R8 period, that of ET appeared to be higher for mulching
than non-mulching conditions. The difference between named conditions for transpiration appeared to be negligible
across R3-R5 period; while it was considerable over other periods. Across the E-R1 period, the transpired water from
covered-soil was 56.89 mm, which is about 3.34 mm higher than that from bared-soil. This increasing effect of
residue was 6.8% across R3-R5 period, 23.0% across R5-R7, and 35.1% across R7-R8. Considering the ratio of
transpiration to evaporation, the mentioned beneficial impact of residue was more considerable across reproductive
stages (R1-R8), than across vegetative stage (E-R1). The difference between bared- and covered-soil for named ratio
was 0.14 over E-R1 period, 2.00 over R1-R3 period, 3.49 over R3-R5 period, 4.87 over R5-R7 period, and 2.98 over
R7-R8 period
