Design drainage rates to optimize crop production for subsurface-drained fields

Abstract

Agricultural subsurface drainage is critical for crop production in temperate humid regions. With the heightened concern of its water-quality implications, we need a method to design drainage systems for both crop production and environmental protection. The objective of this research was to develop an empirical equation that estimates the design drainage rate (DDR) for local soil and weather conditions. This DDR can then be used in the Hooghoudt equation to estimate the optimum drain spacing that maximizes profit. We conducted DRAINMOD simulations for each combination of four factors: three drain depths, three effective radii, seven locations, and five soils. For each combination of factors, simulations were repeated for a range of drain spacing from 5 to 100 m using 30 years (1990–2019) of weather data planted with continuous corn (Zea mays L.). Simulations provided a 30-year average relative corn yield and drainage discharge for each combination of factors. The drain spacings that maximized annual economic return on investment were identified as optimum spacings and used to calculate the DDR for each combination of factors. Results were then used in a multiple linear regression to develop two empirical equations for northeast and southeast USA with DDR as the dependent variable. The independent variables were the long-term average growing-season precipitation, drain depth, equivalent saturated hydraulic conductivity, and depth to restrictive layer. The environmental value of the empirical equations is that they help avoid too narrow of a drain spacing, thereby preventing more drainage than is needed. In conclusion, application of these empirical equations is a means for estimating the site-specific optimum drain spacing that maximizes economic return on investment.