| Abstract: | In most cases, rice production is associated with flooding irrigation and the efficiency of irrigated water use (WUEi) is
generally lower for production of rice than for other crops. We have examined the effects of various irrigation regimes on
water consumption in a well-puddled paddy field, as well as on dry matter production, grain yield and physiological responses
of the plants. Four sets of conditions were studied, with two replications, in the well-puddled paddy field: Continuous flooding
irrigation treatment (CSF); three intermittent irrigation treatments, designated II-0, II-1 and II-2, in which plants were
re-irrigated when the water potential of the soil fell below 0, –10, and –20 kPa at a depth of 5 cm, respectively. Water consumption
was lower during II-0 than during CSF because the percolation rate was reduced by the reduction in the hydraulic head of the
ponded water. Intermittent irrigation led to the repeated shrinking and swelling of soil during II-1 and II-2 and, therefore,
soil cracks developed rapidly. Since they became the major routes of water percolation, these soil cracks increased water
consumption during II-1 and II-2 above that during CSF and II-0. There were no significant differences in dry matter production
and grain yield between CSF and II-0, but both were significantly greater than in the case of II-1 and II-2. Therefore, WUEi
increased in the following order: II-0, CSF, II-2, II-1, although the difference was very small between II-1 and II-2. A lower
crop growth rate (CGR) resulted from a decrease in the net assimilation rate (NAR) during II-1 and II-2, and there was also
a reduction in the leaf area index (LAI) during II-2. Early senescence with ripening and water stress around midday decreased
the rate of photosynthesis in leaves, causing the lower NAR. These physiological responses of the plants were responsible
for the reduction on the dry matter production and grain yield in the intermittent irrigation.
This revised version was published online in June 2006 with corrections to the Cover Date. |
