Abstract
Compaction developed by agricultural practices may change water conducting soil pores. Compacted soil pores results in destruction of soil structure, reduces pore connection and hence reduction of soil quality which in turn affects the population of microorganisms in soils. A research was performed to study the pathways of water through the soil and quantify infiltration based on colored area at different levels of compaction in a loamy soil at Ahwaz University Compus in southern Iran. A completely randomized block design was used with five treatments: (blank with no passing, once, twice, three times, four times and eight times of tractor passings) with three replications. In the field, Brilliant blue CFC solution was used as a dye tracer and added uniformally to each treatment with a rate of 5 mm h^-1 for a period of 8 hours using a custom designed rain simulator. Colored flow paths were photographed by a digital camera. Digital pictures were analyzed with image processing techniques and surface distribution of dye tracer was quantitatively determined for each treatment. Our results showed that physical and hydraulic characteristics of soil was significantly affected by compaction. The highest impaction was observed at 0-20 cm. From this depth downward, no change was seen in soil physical characteristics due to compaction. The results of image processing also revealed that dye infiltration (as an index of water infiltration) had a 77.5 percent reduction at the highest compaction level (8 times tractor passing) when compared to blank. Dye tracer pattern was uniform in blank while in 4 and 8 times teraffic surface infiltration was little where as in lower depths dye transter was observed due to preferential flow. Although laboratory measurements indicated the compaction levels at different depths, it was not detected by dye tracer results. On the other hand, flow patterns show compaction effects and informations regarding changes developed in soil water infiltration.
 
Keywords: Brilliant blue CFC, Flow patterns, Rain simulator