Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Agricultural and Biosystems Engineering


To improve the selection of farm machinery systems, a knowledge of time limitations is an important factor. The lack of accurate records of available field operation time can result in poor utilization of available time. When this occurs, the probability of profitable operation decreases. Delays due to wet field conditions may increase the fixed production cost per hectare, or may increase yield losses;The principal objective of this research was to develop a simulation model to predict the available field operation time as a function of weather and soil moisture conditions. To accomplish this objective, a soil moisture balance submodel to determine daily soil tractability conditions and a probability distribution submodel to predict the amount of time available for field work were developed. Tractability was a function of the moisture content in the top 30 cm of soil;The model was tested and validated by using 11 years of observed field workdays for central Iowa. The criterion used for assigning values to coefficients in the model was to minimize the difference between the observed and predicted tractability conditions. The agreement between the observed and predicted soil tractability conditions showed that the model was reasonably accurate in predicting tractability conditions;After validation of the soil moisture balance submodel, it was used to predict available workdays at various probability levels. A Markov chain method was applied to calculate the probability of having workable days in the Ames, Iowa, area.



Digital Repository @ Iowa State University,

Copyright Owner

Ahmed Saleh Babeir



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File Size

103 pages