Changes in Soil Properties and Corn Plant Parameters Due to Early Season Soil Waterlogging.

Corn (Zea mays L.) production losses due to temporarily flooded or saturated soils resulting from excessive precipitation are a persistent problem in Missouri and the Midwest Region of the United States. Application of different sources of nitrogen (N) fertilizer may promote increased flood tolerance and recovery in interaction with different corn hybrids. The objectives of this study were to: 1) assess the effects of waterlogging duration on soil properties through measurement of soil pH, temperature, bulk density and redox potential, and 2) determine the interactive effects of different pre-plant N fertilizer sources, corn hybrids, and waterlogging duration on plant parameters. A three-year field experiment with a randomized split-split-split plot design with three replications was established in 2013 in Northeast Missouri. Corn hybrids were subjected to seven days of soil waterlogging at the V3 growth stage. Fertilizer treatments used were urea (NCU), urea plus a nitrification inhibitor (NCU+NI), and polymer-coated urea (PCU) applied at a rate of 168 kg N ha^-1. No significant changes in soil bulk density to a depth of 30 cm were observed due to flooding in 2013 and 2014.  Soil surface pH measured during flooding increased significantly in 2014 by 0.4 units after 3 days of waterlogging and then decreased to its initial pre-flood value at the end of the flooding treatment. During the 2014 and 2015 growing seasons, soil redox potential decreased significantly by 0.015 units with each day of soil waterlogging showing the development of reduced and anaerobic conditions with time. Soil temperature was higher in waterlogged treatments compared to non-waterlogged treatments. In 2014, plant population was significantly decreased by 24% due to waterlogging.  Stomatal conductance varied depending upon the weather conditions each day during waterlogging. In 2013 and 2015, all three pre-plant fertilizer applications resulted in significantly higher leaf chlorophyll meter readings compared to the non-treated control. In 2015, leaf chlorophyll meter readings were significantly lower in waterlogged plots by 8% compared to non-waterlogged treatments.