IMPACTS OF NO-TILL CORN PRODUCTION ON FIELD HYDROLOGY

In 2018, with funding through the Environmental Quality Incentives Program (EQIP) of the USDA-NRCS, we began a 6-year edge-of-field drainage water monitoring study on two of Miner Institute’s fields. The project was designed to investigate the impacts of no-till corn production on field hydrology and nutrient transport dynamics. Two 5-acre fields with similar management histories were selected for the project, and both had tile drainage installed approximately 4’ deep at 30’ lateral spacing in 2018 prior to the start of the project. Prior to the tile installation, the fields were both too wet too often to confidently plant corn, so both transitioned into their first year of corn at the start of the study. Both fields are also fairly flat and primarily composed of a very poorly drained silty clay (Adjidaumo series) with high organic matter contents (~5-6%).

The study employed a paired watershed design which utilizes a two-year calibration period, during which an initial relationship is developed between the two fields. Both fields were managed with conservation tillage practices during the calibration period. Each fall a manure application was incorporated with a single pass of a chisel plow. Spring tillage consisted of a disk harrowing to prepare the soil for planting. These practices left approximately 30% crop residue cover in the field during the nongrowing season. Treatments were randomly assigned and management in the treatment period remained unchanged for the control field (TILL), while the treatment field (NT) transitioned to no-till corn production and surface-applied manure with no incorporation in the fall of 2020.

There was substantial variation in annual precipitation across the study years, particularly during the treatment period years, which experienced a minimum of 21.95 inches in 2021 and a maximum of 46.24 inches in 2024 (see graph). Precipitation totals during the calibration period were both below the 30-yr mean, but only by 5% in 2019 and 13% in 2020.

Tile drainage was consistently the primary hydrologic pathway in both fields. Tile drainage represented 94% of the drainage from TILL during the calibration period and 95% during the treatment period. NT consistently generated more total drainage (surface + tile) and more tile drainage flow volumes than TILL during drainage events. During the calibration period, TILL generated an average of 18.55 in/yr of tile drainage and 1.19 in/yr of surface runoff, compared to 21.87 in/yr and 3.10 in/yr of tile drainage and surface runoff, respectively, in NT. During the treatment period when precipitation rates increased, the difference also increased between the two fields as TILL generated an average of 19.00 in/yr of tile drainage compared to 27.90 in/yr in NT.

The tile drainage peak discharges exhibited a 31% increase following the implementation of no-till, likely due to the formation of larger pores (macropores, aka preferential flow pathways). As the soil structure improves in the absence of tillage, these larger pores form and are much more effective at draining excess water rapidly through the subsurface. While the tile drainage discharge rates may increase with no-till management and improved soil structure, it is often at the expense of surface runoff due to the increased drainage capacity of the field. Reducing surface runoff may then potentially reduce peak discharge overall at the field-scale as it usually takes drainage water longer to move through it and into the tile lines than overland and immediately into a ditch. Additionally, reducing surface runoff will typically reduce the amount of erosion and phosphorus lost during drainage events.

Reducing the peak of the hydrograph is only one metric for characterizing the field’s hydrology, as total event flow is also important. Following the implementation of no-till during the treatment period, we observed similar changes in event drainage volumes at both the field-scale (17% reduction) and tile drainage alone (15% reduction) alone, though the magnitude of reduction varied across event sizes with the greatest differences (>15%) observed in smaller events. The similarity between the field-scale and tile drainage data indicates that the increase at the field scale was likely primarily driven by the increased tile drainage volumes.

Check out my article next month in which I’ll discuss how these hydrologic changes may have impacted the nitrogen dynamics in the soil.

— Laura Klaiber

klaiber@whminer.com