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Effect of Gypsum and Deep-rooting Perennials on Subsoil Mechanical Impedance¹

ABSTRACT

Subsoil root growth in highly weathered southeastern soils is limited because of poor chemical conditions and high soil strength. Surface-applied gypsum can leach into the subsoil and amend the chemical properties of these soils. The objective of this study was to determine if gypsum also had a physical effect. Mechanical impedance was measured using a tractor-mounted penetrometer that gave values of cone index (CI) in gypsum-treated and nontreated plots of several ongoing experiments. Cone index was lower in the gypsum-treated plots where alfalfa (Medicago sativa L.) or peach trees [Prunus persica (L.) Batsch] had grown for several years, but there was no reduction in CI in fallow plots treated with gypsum. Samples from the alfalfa plots treated with gypsum had larger stable soil aggregates than samples taken from nontreated plots. We conclude that gypsum amendment increases subsoil root activity, which in turn reduces subsoil mechanical impedance.

¹ Contribution of the Agronomy Dep., Univ. of Georgia, Athens, GA 30602. Research supported by Florida Institute of Phosphate Research and Georgia Agricultural Experiment Stations.

² Assistant Professor, Dep. of Agronomy, Professor, Dep. of Agricultural Engineering, and Professor, Dep. of Agronomy, Univ. of Georgia, Athens, GA 30602.

Received for publication March 10, 1986.