Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 22, 1996
Publication Date: N/A
Technical Abstract: Water and chemical movement in soils are often investigated in the laboratory using columns of sieved, repacked soil. Frequently, a uniform water content and steady state infiltration are achieved and chemicals are applied as a pulse input with the water. In the real world, during the growing season, water usually comes as rain on unsaturated, aggregated soils. Conservation tillage encourages the development and preservation o macropores and agricultural chemicals are normally sprayed or broadcast on the soil surface without incorporation. We have attempted to simulate these conditions in the laboratory to determine how water and surface-applied chemicals move through macroporous soils in the field. Undisturbed 30 x 30 x 30 cm blocks of soil are encased in foam and simulated rain is applied using a motorized array of syringes. Percolate is collected at atmospheric pressure using a 64-cell grid lysimeter and pores > 2 mm in diameter are mapped with reference to the position of the grid lysimeter. Overall, the results indicate that water can enter and move through macropores in unsaturated soils in the absence of surface ponding. Earthworm-formed macropores are important in some soils, but other biologically formed macropores, structural pores, and cracks may play a similar role in other soils. As soil becomes wetter more flow occurs in smaller pores, but flow through the larger macropores may still dominate. Since soil samples measure solute retention, not solute transport, percolate samples are essential to study transport. Better methods to monitor and sample percolate movement in the field need to be developed.