Long-term drainage experiment insights on crop yield, water flow, chemical transport, and soil improvement in southeastern Indiana.

A long-term subsurface drainage experiment was begun in 1983 at the Southeast Purdue Agricultural Center (SEPAC), to study the impacts of different drain spacings on crop yield, water flow, and chemical transport.  Additional studies assessed combinations of drainage intensity and agronomic management systems for improving soil physical and biological properties.  This presentation will highlight key findings from the 35-yr project.  In the drain spacing experiment, the four treatments were 5, 10, and 20 m spacings and a 40 m control spacing to represent “undrained.”  In the first 10 yr of continuous corn growth, yields were 157, 155, 152, and 147 bushels per acre for the 5-, 10- 20, and 40-m plots, respectively.   In the subsequent 25 yr of corn-soybean rotation, the corn yields among the 5-, 10-, and 20-m plots were similar to each other but significantly higher than the 40-m plots, in part due to more excessively wet years during the later period than in the earlier period.  Although yield differences were not as great as initially expected, farmers often see greater yield differences due to having poorer surface drainage leading to ponding and flooded areas in their fields, and due to timeliness benefits that were not applicable to our small research farm field.  Use of practices such as no-till, cover crops, manure, and rotation with hay crops were beneficial for soil physical properties when linked with drainage, but were not effective when the soil wasn’t drained.  Adequate drainage is a necessary first step for naturally poorly-drained soils, before other conservation practices can be effective.  Drainage flow and nitrate-N loss per hectare were greatest with the 5-m spacing and lowest with the 20-m spacing, and cover crops significantly reduced N losses in the drain.  Drainage flow response to precipitation has become more rapid over the life of the project.