Influence of Row Spacing and Straw Mulch on First Stage Drying
1976
Adams, J. E. | Arkin, G. F. | Ritchie, J. T.
Evaporation during first stage drying was measured with evaporation plates on the soil surface in grain sorghum plots with 25-, 50-, and 100-cm row spacings, during several stages of grain sorghum [Sorghum bicolor (L.) Moench] development in 1972 and 1973. Evaporation during first stage drying was affected by row spacing, leaf area index (LAI), and soil shading. Both LAI and soil shading were related to row spacing and plant population. The more complete plant canopy of grain sorghum with narrow-row spacing decreased penetration of radiant energy to the soil surface and reduced the evaporation rate of soil water during first stage drying. Evaporation was greatest during the early part of the season when shading was least and lowest during boot stage and pollination, when all leaves were fully expanded and provided maximum plant canopy and soil shading. Narrow-row spacing established an earlier, and more complete plant canopy than conventional 100-cm row spacing and shaded more of the soil surface from early vegetative growth to maturity. Soil surface shaded near solar noon was a better indicator of first stage evaporation beneath a canopy than LAI. The combined effect of a mulched surface and a plant canopy on reducing evaporation was the product of the fractional reduction in potential evaporation resulting from the plant canopy and the evaporation resulting from the mulched surface with no canopy cover. An empirical equation was developed from the evaporation data for use in calculating first stage evaporation as related to potential evaporation, fraction of the soil surface shaded, and mulch rate.
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