Characterization of Grain Yield Under Drainage Water Management Practices Using Differences in Soil Moisture.

Subsurface drainage is an essential water management practice on many highly productive agricultural lands in the North Central, USA. Agricultural drainage improvement decreases year-to-year variability in crop yield, ensuring consistent production. We hypothesize that drainage water management practices as well as precipitations amount and frequency will affect the soil water regime and specifically the spatial and temporal changes in volumetric soil water content as controlled by root water uptake and leaching. In this research, we evaluate the impact of plant available soil moisture on crop yield for two contrasting drainage strategies: conventional free drainage and managed drainage. The data for this regional project come from four experimental sites located in Iowa, Indiana, Minnesota and Ohio. Unlike conventional free drainage systems that remove excess water to the design drain depth whenever it occurs, managed drainage conserves water by increasing the retention time of water in the soil profile. Availability of root-zone soil water is critical for plant growth and is a major determinant of crop yield. Yield benefits of managed drainage exist due to potential increased stored water in the soil profile that could be used by the crop if available at the right time. Continuous volumetric soil water content was collected during the growing season to assess temporal changes in excess and deficit soil water conditions and grain was harvested at the end of the growing season. This research will result in a better understanding of drainage water management affects on plant available soil moisture and crop yield. Moreover, the present research will provide an extensive database which can serve as input for analytical or numerical modeling of drainage water management.