Degree Type

Dissertation

Date of Award

1992

Degree Name

Doctor of Philosophy

Department

Agricultural and Biosystems Engineering

First Advisor

Rameshwar Singh Kanwar

Abstract

The goal of this study was to investigate the effect of various water-table management (WTM) practices on corn growth and yield and agricultural chemical concentrations in shallow groundwater. Field experiments were conducted for three years (1989-91) at the research sites near Ames and Ankeny. Water-table depths of 0.3, 0.6, and 0.9 m were maintained in field lysimeters at the Ames site, and variable water-table depths were maintained in a subirrigation field at the Ankeny site;Photosynthesis measurements were made regularly during the growing season, and yield data were collected at harvest. In 1989, a relatively dry year, photosynthesis rates were higher at shallow water-table depths than at deep water-table depths. In 1990, a very wet year, photosynthesis rates were not significantly different for water-table depths between 0.3 and 0.9 m, but rates decreased significantly for water-table depths shallower than 0.3 m. Water-table effects on photosynthetic water-use efficiency (PWUE) were highly significant in both dry and wet seasons. Corn yields increased with increasing water-table depths. Net radiation, leaf-air temperature differential, transpiration rate, stomatal conductance, and crop water stress index (CWSI) were strongly related to WTM practice during vegetative and flowering stages of corn growth. Results indicate that plant physiological parameters and CWSI could be used to develop the best WTM practices for corn growth in the humid region;Concentrations of NO[subscript]3-N in groundwater changed with WTM practices. The lowest NO[subscript]3-N concentrations were observed when water-table depths were maintained at 0.2 and 0.3 m from the soil surface. NO[subscript]3-N concentrations in groundwater also decreased with increased soil depth. Results showed that NO[subscript]3-N concentrations in groundwater could be significantly reduced by maintaining shallow water-table depths;Atrazine and alachlor concentrations in groundwater were significantly reduced by maintaining shallow WTD. Atrazine concentrations were higher than those of alachlor. Alachlor was not detected in many samples, however, atrazine was detected in all samples. Pesticide concentrations in groundwater decreased with soil depth and time. A subsurface water quality model ADAPT (Agricultural Drainage And Pesticide Transport) for the water table management system was used to simulate atrazine and alachlor concentrations in groundwater at various soil depths during the corn growing seasons of 1989 to 1991. Predicted values of atrazine and alachlor concentrations decreased with shallow water-table depths as was found from observed values. Observed and predicted results were compared and a good agreement was found between observed and predicted values.

DOI

https://doi.org/10.31274/rtd-180813-12442

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Prasanta Kumar Kalita

Language

en

Proquest ID

AAI9223935

File Format

application/pdf

File Size

224 pages

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