Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Carl W. Mize


Wind may desiccate and cause direct mechanical injury to plants. Shelterbelts, which reduce wind speed, can be beneficial to crops grown near them. However, they are not often used in the United States because there is not adequate economic information that clearly shows their benefits. It is difficult to obtain the information because shelterbelts grow slowly, taking many years to show a yield improvement, and there are also an enormous number of combinations of crops, soil types and types of shelterbelts to consider. An alternative approach to evaluating the combinations is to develop a computer model that can simulate the production of crops grown under the influence of different shelterbelts on various soil types. Therefore, the primary objective of this study was to develop a ShelterBELT - Soybean (Glycine max L.) production model (SBELTS) by linking a microclimate model and a soybean production model with a tree foliage distribution model. The secondary objective was to develop a tree foliage distribution model for use with SBELTS;The tree foliage distribution model used the two parameter Weibull distribution to model crown surface area distribution curve. We found that the shape parameter of the Weibull distribution for a hybrid cottonwood clone (Populus euramericana, NC-5326) is close to a constant 2, and the scale parameter is strongly related to height for these trees. By combining the tree foliage distribution model that predicts tree height, shelterbelt width, and other characteristics, a micrometeorological model that predicts wind speed at various distances from a shelterbelt, and a soybean growth model that is sensitive to wind speed, SBELTS model was developed;No data were available to evaluate SBELTS so the model was evaluated by comparing predicted results with published information. SBELTS was used to predict soybean yield across a field with a shelterbelt. The predicted yield curve compared well with published yield curves. SBELTS was also used to predict yields for shelterbelts in wet, average, and dry years. The results showed no shelterbelt influence in wet years, some influence in average years, and a sizeable influence in dry years.



Digital Repository @ Iowa State University,

Copyright Owner

Xiaoming Qi



Proquest ID


File Format


File Size

75 pages