Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Soybeans (Glycine max (L.) Merr.), grain sorghum (Sorghum bicolor (L.) Moench) and corn (Zea mays, L.) were planted on the same day in 1978. The crops were grown under field conditions, on Ida silt loam soil at the Western Iowa Research Center, Castana, Iowa, in order to determine the relationships among crops in actual evapotranspiration (AET), in plant rooting density profiles, in ratios of AET/open pan evaporation and in the dry matter produced per mm of water used;Soil matric potential, unsaturated hydraulic conductivity and the changes in gravimetric soil water contents throughout the soil profile as a function of time were measured to compute the water balance for each crop. Precipitation was measured at the Research Center weather station and runoff and deep drainage were estimated;Plant parameters such as leaf area index, stage of development, and dry matter production, including top and roots, were measured between 54 and 103 days after planting;The AET data showed no significant differences among crops from 35 to 99 days after planting with 280 mm of water used for soybeans, 277 mm used for grain sorghum and 301 mm used for corn;Although roots of the three crops reached about the same total depth during the season, the percentage of total root density decreased with depth (averaged over time) but soybean roots were 5% higher than sorghum and corn at the 30- to 60-cm depth;The maximum values for the ratio AET/open pan evaporation were about 1.0 and did not differ among crops;The total dry matter produced per mm of water used was highest for corn, followed by sorghum and finally by soybeans.



Digital Repository @ Iowa State University,

Copyright Owner

Afranio Almir Righes



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134 pages