AbstractRelationships between rooting depth, growth, and yields of corn and soil water availability in an Ultisol and an Oxisol are presented. Soil and crop management techniques considered to be adequate for maximum yield were used at the two experimental sites. At each site one treatment was irrigated as often as necessary to maintain a water tension of less than 1 bar. Soil properties, plant growth, effective rooting depth, soil water availability, plant water deficits, crop yields, and weather conditions were recorded. During a prolonged drought and at grain filling, corn growing in a typical Oxisol extracted soil water to a depth of 120 cm, and plants became water stressed after a soil water tension of 15 bars developed at 90 cm. In a typical Ultisol plants could not extract water effectively below 30 cm. Plants grew better in the Oxisol than in the Ultisol. Grain yields approached 9.4 tons/ha in the former but only 3.1 tons/ha in the latter.
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