Response of Three Corn Hybrids to Low Levels of Soil Moisture Tension in the Plow Layer

Fertilizer materials are generally mixed with the soil to plow depth and as a result, concentration of corn (Zea mays L.) roots is usually greatest in the surface soil; therefore, water demand is expected to be highest in the plow layer. The objective of these experiments was to evaluate the response of three corn hybrids to irrigation treatments that were designed to maintain soil moisture tension at low levels (less than 1-bar) in the plow layer rather than the entire root zone. Flowering date, plant height, and grain yield were used as indexes of response. Irrigation was applied at four levels (0.3, 0.6, 2.0, and 5.0 bars) of soil moisture tension in 1970 and at three levels (0.2, 0.4, and 0.6 bar) in 1971. Nitrogen was applied at 336 and 560 kg/ha, in 1971, to treatments irrigated at 0.2 bar of soil moisture tension. Each irrigation treatment was replicated four times and consisted of applying water at a selected value of soil moisture tension. A tensiometer was placed in each plot to he irrigated at soil moisture tensions below 1 bar in order to monitor soil moisture tension at a depth of 15 cm. Electrical resistance units were used in 1970 to monitor soil moisture tension in plots irrigated at tensions above 1 bar. Flowering occurred earlier and plant height increased as soil moisture tension at irrigation decreased. Grain yields were increased significantly (5% level) each year when plots were irrigated at 0.2 or 0.3 bar soil moisture tension instead of 0.6 bar. Irrigation at 0.6 bar did not increase grain yields in comparison with no irrigation in 1970. Each corn variety gave an inverse linear grain yield response to soil moisture tension values between 0.2 and 0.6 bar in 1971. There was a significant difference (5% level) between varieties in magnitude of grain yield response to irrigation in 1971. Highest grain yields were produced each year when soil moisture tension in the plow layer was maintained below 1/3 bar.