With the ability to monitor soil moisture in time comes the opportunity to develop ways to incorporate these measurements into predictive models, without compromising or overriding the model physics. The importance of soil moisture to the growth of crops is well understood and because of this it is recognized as one of the more important parts of crop modeling programs. This research focused on improvements to the Decision Support System for Agrotechnology Transfer -Cropping System Model (DSSAT-CSM) based on the accuracy of soil moisture estimates. To accomplish this, data assimilation techniques were implemented to process the uncertainty of the model related to state variables and the uncertainty found within in situ soil moisture measurements. Consideration of soil parameter uncertainty, which in?uences model estimates of soil moisture and model output, was taken into account using a Monte Carlo approach. A Kalman filter was used to combine the model estimates of soil moisture with in situ soil moisture measurements, while varying several important soil parameters in the model using a Monte Carlo approach. Covariances for the Kalman filter were calculated for the model and measurements based on the models standard deviation of soil moisture estimates and the standard deviation of the in situ soil moisture measurements. Data for this study was obtained from a research study conducted on irrigated wheat during the winters of 2003-04 and 2004-05 in Maricopa, Arizona in which thorough field and crop data were collected. The uncertainty of soil parameters was only moderately captured by the Monte Carlo approach for assimilation into the top layer of the soil profile. Improvement resulted for data assimilation of soil moisture through the reduction of the error between the measured and simulated grain yield and canopy weight for 47% and 37% of the simulations for the 2003-2004 and for 25% and 32% of the simulations for the 20042005 season, respectively. Assimilation was more effective for improving the model output of grain yield for the 2004-2005 than the 2003-2004 season and canopy weight for the 2003-2004 season than the 2004-2005 season. Further study is needed to fully understand the most desirable conditions for soil moisture assimilation and what other influencing effects data assimilation of soil moisture presents.