Contents & Foreword, Characterizing And ... - IRRI books

Water table depth (cm)500Shallow water tableMedium water tableDeep water table–50–100–150O N D J F M A M J J A S OMonthFig. 3. Shallow, medium, and deep water table scenarios used inORYZA simulations to explore rainfed rice yields in Jakenan. Themethod of deriving the scenarios from 1995-98 measured data isdescribed in the text. Solid triangles indicate the means of the measureddata (or the actual data when there was only one water tablevalue measured). Vertical bars indicate standard errors of the means(when there was more than one water table value).Yield explorationPotential yield. The simulated, long-term average potential rice yield is shown inFigure 4 as a function of date of sowing. The potential yields ranged from 6 to8 t ha –1 , and were within the yield range of well-managed irrigated rice as observed inBogor, West Java, and in Genteng, East Java, by Makarim and Las (1993). The standarderrors of the average values were low, indicating little variation in potential yieldacross years. Rice sown in the typical gogorancah period (November-December) hada lower potential yield (on average 6 t ha –1 ) than rice planted in the typical walikjerami period (February-March, average yield = 7 t ha –1 ). This lower potential yieldin the gogorancah period was caused mainly by the low radiation during the crop’sreproductive stage (Fig. 1B). The variation in potential yield for crops sown in November-December,however, was relatively larger than for crops sown in February-March.Rainfed yield. The simulated, long-term average rainfed rice yield is shown inFigure 4 as a function of date of sowing for situations with a shallow, medium, anddeep groundwater table. The yield of rainfed rice sown from mid-November to theend of March differed significantly among the three water table depth scenarios. Duringthis period, rainfed yields reached the potential yield level with the shallow watertable, but decreased with deeper water table depths. For crops sown at the end of therainy season and in the dry season (roughly April-November), the yield was very lowand yield differences among the water table scenarios disappeared. The low yields inthis season are attributed to inadequate water supply from rainfall and from the ground-Effect of climate, agrohydrology, and management . . . 65