Technical Abstract: This study investigates differences in the soil moisture product and brightness temperatures between 6 pm and 6 am local solar time, when the SMOS passes for a region in north-central Iowa. This region consists of 69 SMOS pixels and has uniform land-cover, consisting of maize and soybean row crops. The comparison was restricted to periods with no rainfall after noon prior to the evening pass, and no rainfall between the evening and morning passes. It was found that there was a significant difference in the soil moisture between evening and morning SMOS passes, with the soil moisture being lower in the morning for a majority of the days. The difference between the soil moisture measurements on some days exceeded the allowable error for SMOS of 0.04 m3/m3. In-situ and model results indicate this discrepancy, measured brightness temperature was converted to a polarization index (PI), and evening and morning values were compared. It was found that there is no signficant difference between evening and morning measurements of PI. We found that there was a large spread in data at low incidence angles. The PI values also indicate that there may be a decrease in soil moisture for the morning, but we suggest that given the in-situ and model measurement that this could be attributed to an increase in the volumetric water content of vegetation.