Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Ridge Tillage is a conservation tillage practice that is gaining popularity in the U.S. Ridge tillage allows earlier planting, rapid emergence, and accelerated seedling development. Ridge shape influences absorption of solar radiation, rainfall infiltration, and water drainage. The objectives of this study were to: determine the effects of the selected ridge construction factors of speed, depth adjustment, and tool type on ridge configuration; and, evaluate the impact of different ridge configurations on soil water content and soil temperature prior to planting, and soil physical properties that influence the ridged soil environment. Twenty-seven ridge building treatments were established with five replications. Ridges were constructed with three tool types (disk, shovel, and sweep), each operated at three speeds (5, 7, and 9 Km/hr) and three adjustment depths (50, 100, and 150 mm). The change of field configuration were used to quantify the ground surface-air interface, which directly and indirectly effects many soil physical properties (i.e. solar radiation absorption, evaporation, and gas exchange). Ridge height ranged from 87 mm to 220 mm, ridge cross-sectional area varied from 398 cm[superscript]2 to 822 cm[superscript]2, and ridge area index ranged from 1.12 to 1.32. Three shapes (convex, triangle, and concave-convex) were used to describe the resulting configurations. Ridge index, classified based on shape and size of the ridge, was then established. To evaluate soil environmental conditions, soil temperature and water content were measured from early spring to planting time each year. Soil temperature and water content are influenced by soil water desorption characteristics, soil air-filled porosity and soil penetration resistance. Three ridge shapes and three ridge sizes were determined based upon ridge index. All ridges were warmer and had higher soil growing degree days (GDD) than a flat surface. In moderately dry and warm conditions soil GDD are governed by the shape and size of the ridge; in wet and cool conditions all of the ridges, behaved similarly. Ridge configuration did have an effect on the initial water content. Drying patterns were similar for each ridge size and shape. Soil air-filled porosity and soil water desorption were not affected by tool type. Penetration resistance was significantly lower in the ridge top.



Digital Repository @ Iowa State University,

Copyright Owner

Mohammadreza Ghaffarzadeh



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101 pages