An environmental chamber was built to evaluate the effect of weather parameters and swath density that affect the drying rate of grass during field drying. A series of 52 drying experiments were conducted on corn stover of which 27 were used for model development and 25 were used for model validation. Both radiation and vapor pressure deficit improved the drying potential of corn stover, therefore drying in wide swaths is recommended to take advantage of solar radiation. The effect of wind speed was variable and was found to be dependent on solar radiation. During day time, an increase in wind speed removed the heat produced by radiation and thus decreased the drying rate. However at night time, the wind speed was positively correlated with drying rate. For this reason, separate drying rate models were developed for night time and day time conditions. Swath density was negatively correlated with drying rate which suggested that biomass should be dried in wide swaths if possible. This fact was confirmed with the field drying trials in which low density swaths reached safe storage moisture within a day or two after harvesting. Whereas, on most occasions, high density trays did not reached a safe storage level after 3 days of field drying. During drying, a rainfall event also affected the conditioned biomass more severely which was drying in wide swath than high density windrows. Therefore, an appropriate decision should be made based on the forecasted weather conditions to minimize the time spent by crop during the field drying period.