Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Agricultural and Biosystems Engineering

First Advisor

Rameshwar Singh Kanwar


The general purpose of this study was to investigate the effects of different degrees of stress due to excessive wetness on root and shoot growth, yield of corn, plant uptakes of nitrogen, phosphorous, and potassium; and on nitrogen leaching;Experiments were conducted in both environmentally controlled chambers and field lysimeters. Four stress levels due to excessive wetness, equivalent to 90, 180, 270 and 360 cm-days (Sieben's SEW[subscript]30 concept), were applied to growing corn by surface flooding for 3, 6, 9, and 12 days, and for 6, 12, 18, and 24 days when the water table was maintained at 15 cm below the soil surface;Results of this study indicated that the SEW[subscript]30 concept is not the best indicator of the relationship of soil wetness to crop response. Models were developed to predict shoot dry matter and yield as a function of SEW[subscript]30 values for each level of flooding. All growth parameters (plant height, leaf area, shoot dry matter and grain yield) were significantly related to the position of water table, either surface flooding or 15 cm below the surface;Surface flooding of corn reduced root dry weight significantly with the duration of flooding, a relation that did not hold for water table at 15 cm below the soil surface. Results of the root growth study also showed that root length and root dry weight were greater with water table at 15 cm below the soil surface than with surface flooding;Moreover, nutrient uptake (N, P, and K) decreased significantly with increased durations of surface flooding. But increases in the duration of water table at 15 cm below the soil surface did not decrease nutrient uptake. In comparison with surface flooding, water table at 15 cm below the soil surface resulted in less nitrate loss through drainage water;Another finding of this study was that the SDI (stress-day index) method was not able to predict yields accurately by use of stress factors calculated according to the SEW[subscript]30 concept. A technique was developed and evaluated to improve the relationship between corn yield and SDI values.



Digital Repository @ Iowa State University,

Copyright Owner

Niaz Ahmad



Proquest ID


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File Size

246 pages