Water table management effects on photosynthesis, chlorophyll, crop yield, and water quality
This study was conducted to investigate the effects of different water table depths (WTDs) on plant physiological parameters, and on groundwater quality. Data for 1992 and 1993 were collected from field experiments conducted at two sites near Ankeny and Ames. At the Ankeny site, the water table depths were maintained at 0.2, 0.3, 0.6, 0.9, 1.1 m depths, and were maintained at 0.3, 0.6, and 0.9 m depths at the Ames site. Measurements on different physiological parameters were taken biweekly, whereas, water samples for NO[subscript]3-N and pesticide analysis were collected monthly;Analysis of the data show that photosynthesis rates, stomatal conductances, transpiration rates, and chlorophyll content were significantly affected at 0.2 and 1.1 m WTD treatments as compared to 0.3, 0.6, and 0.9 m WTD treatments. The 0.3 WTD treatment had higher values of these parameters, and values decreased with increased depth. The regression analysis showed strong positive relations between photosynthesis and leaf chlorophyll readings at both experimental sites. Results of these analyses reveal that leaf chlorophyll could be used as a good predictor of photosynthesis rates regardless of water table depth treatment;The average NO[subscript]3-N concentrations in groundwater were reduced by maintaining WTDs between 0.3 to 0.6 m compared to those at 0.2, 0.9, and 1.1 m WTD treatments. The average concentrations in groundwater generally decreased with increased depth and time during the growing season. The average NO[subscript]3-N concentrations, in most cases, were less than the 10 mg/L EPA standard with 0.3 m WTD treatment;The average atrazine and alachlor concentrations in groundwater were reduced by maintaining WTDs between 0.3 to 0.6 m compared to those at 0.2, 0.9, and 1.1 m WTD treatments during the two growing seasons. The average herbicide concentrations in groundwater generally decreased with increased depth and time. However, atrazine concentrations were significantly reduced after WTD treatments started which shows a positive influence of WTD practices in reducing pesticide concentrations;Corn yields significantly increased as water-table depths increased from 0.2 to 1.1 m in 1992 and 1993. A shallow water table depth of 0.2 to 0.3 m significantly reduced corn yield in the wet season of 1993 at the Ankeny site. Crop yields were maximum with a 0.9 m WTD at the Ames site and with a 1.1 m WTD at Ankeny.