| Abstrakt: |
Controlled drainage is the practice of using a water control structure to raise the outlet in agricultural fields during periods when drainage is unnecessary, with the primary purpose of reducing nitrate loss. The use of this practice may increase crop yields compared to free drainage because controlled drainage can capture water from precipitation as soil water and store it for crop use later in the growing season. However, results from published studies of controlled drainage have shown mixed impacts on crop yields, and the effects of field characteristics and annual weather variation on these impacts are not well understood. To analyze crop yield impacts, two controlled and two free draining plots in eastern Indiana were compared. A grid system consisting of 10 by 10 meter cells was created to obtain a balanced data set and used to analyze crop yield by year, annual wetness classification, soil drainage class, and elevation. Controlled drainage significantly increased the corn yield in six out of nine years, and the nine-year corn yield average increased by 2.3%. Soybean yield was significantly higher under controlled drainage in three out of four years, but there was no significant difference in the four-year soybean average. Years were further classified as wet, normal, or dry based on growing season precipitation, and results indicated controlled drainage had the greatest significant impact on corn yield in the dry years. Analyzing yield by soil drainage class determined that yield had the greatest response to controlled drainage on the very poorly drained soils. Controlled drainage had a significant yield benefit in corn during dry years in areas in which the elevation is more than 30 cm above the surface elevation at the outlet, and did not lead to significant differences in normal or wet years at any elevation. The grid-based analysis with a linear mixed model accounting for autocorrelation was useful for understanding within-field variability of yield response. [ABSTRACT FROM AUTHOR] |
