|Casey, Francis - IOWA STATE UNIVERSITY|
|Horton, Robert - IOWA STATE UNIVERSITY|
Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: October 31, 1997
Publication Date: N/A
Technical Abstract: Two techniques that estimate field soil immobile water content (Theta im) and mass exchange coefficient (Alpha) have been compared. Both methods use the tension infiltrometer to apply nonsorbing anionic tracers to the soil surface. The first method uses a single tracer application and the second method applies a sequence of tracers. Five measurement positions in a Nicollet series soil (Fine-loamy, mixed, mesic Aquic Hapludoll) were chosen within a ridge tilled corn (Zea mays) field. The sequential tracer method gave immobile water fraction (Theta im/Theta) values that ranged from 0.45 to 0.98 and Alpha values ranging from 0.01 to 0.13 d-1, while the single tracer method gave (Theta im/Theta) values ranging from 0.03 to 0.16 and Alpha values ranging from 0.15 to 1.45 d-1. The estimated values for (Theta im/Theta) were less variable within a measurement area for the sequential tracer method than for the single tracer method. For a number of replications, the sequential tracer technique produced consistent values for Alpha at a single time, while the single tracer method produced highly variable Alpha values over a period of time.