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<br />, <br /> <br />1. The largest 3-year average yield for corn recew1ng a single <br />inseason irrigation was obtained by irrigating corn during early <br />silk emergence, at both Tribune and Manahattan. <br /> <br />2. Irrigating during early silk emergence increased yields over <br />no in season irrigation by 45 bushels per acre at Manhattan and <br />by 47 bushel s per acre at Tribune. <br /> <br />3. Corn irrigated at blister stage had the smallest 3-year average <br />yield of corn receiving a single inseason irrigation, at both Tribune <br />and Manhattan. ' <br /> <br />4. Corn yield was extremely sensitive to timing of rainfall and/or <br />i rrigati on. <br /> <br />5. Corn responded well to three inseason irrigations, yielding <br />approximately 40 bushels per acre more than the mean of single <br />inseason irrigation applications at both Tribune and Manhattan. <br /> <br />It is evident that any water stress during the siUing stage shoul d <br />be avoided. It should be an irrigation management goal to have a <br />full soil reservoir prior to the silking stage. <br /> <br />The same type of experiment as desc ri bed above wa s done to detenni ne <br />the effects of irrigation timing on production yield in grain sorghum. <br />Tables 52 and 53 summarize the results of the grain sorghum experiment <br />for the Tribune and Manhattan stations, respectively. The conclusions <br />drawn from the grai n sorghum data are: <br /> <br />1. Grain sorghum yields from a single inseason irrigation water <br />application were approximately equal indicating no obvious critical <br />peri od. <br /> <br />2. The increase in grain sorghum yields for plots rece1v1ng three <br />inseason irrigations are insufficient to justify the two additional <br />i rri gati ons. <br /> <br />Depending upon planting dates, temperature, and precipitation variations <br />the maximum 5-day water usage from grain sorghum occurs slightly before <br />the boot stage. The 40-65 day period after emergence was defined as the <br />period of greatest water usage and includes the boot stage. A soil <br />water deficit occurring during this time would 1 ikely result in plant <br />water stress, thus having the greatest effect on yield. The severity of <br />the water stress is governed by the extent of the soil water deficit and <br />evaporative demand. <br /> <br />The results of the corn and grain sorghum data using one inseason <br />irrigation indicate that: <br /> <br />1. With no inseason irrigation, the 3-year average yield from <br />grain sorghum was greater than the corn yield at both Manhattan <br />and Tri bune. <br /> <br />21 <br />