A study recently published in the 2023 Journal of the ASFMRA titled “Economic Analysis of Subsurface Tile Drainage Spacing” presents valuable insights based on data collected between 1984 and 2021 from a long-term drainage experiment in southeast Indiana. The study authored by Michael Langemeier, Eileen Kladivko and Edward Farris, compared four in-field drainage spacings: 16', 33', 66' and 133'.
The researchers evaluated various economic factors such as gross return per acre and net return per acre to determine the most profitable spacing option. As part of the analysis, the researchers also incorporated risk analysis using expected utility analysis and stochastic dominance.
The option for greatest return
The findings revealed the 16' spacing resulted in the highest gross return per acre. However, due to the high cost of tile installation associated with this spacing, the net return per acre was significantly lower compared with the other spacing options. Surprisingly, the 66' spacing emerged as the most economically viable choice because it yielded the highest net return per acre.
The 66' spacing not only offered a better net return per acre but also exhibited a higher certainty equivalent of net returns. The certainty equivalent represents a risk-adjusted return that considers average net returns and downside risk. The study employed second-degree stochastic dominance analysis, which showed that the 66' spacing was preferred by risk-averse decision-makers.
To account for variations in economic parameters, the researchers conducted sensitivity analyses. They tested different discount rates, tile installation costs and useful life assumptions for the drainage system. While these factors influenced the average net returns and certainty equivalents, the relative superiority of the 66' spacing remained consistent across the scenarios.
It is important to note this study focused primarily on economic aspects and did not extensively explore agronomic and water quality factors associated with tile drainage. However, previous research suggests tile drainage offers benefits such as improved timeliness of fieldwork, increased crop yields, enhanced infiltration and reduced sediment and nutrient losses in poorly drained soils.
What to learn from this study
The study’s findings provide valuable insights for farmers and land managers considering subsurface tile drainage in their fields. By considering the economic implications and incorporating risk analysis, decision-makers can make informed choices for drainage spacing.
Attendees of the ASFMRA’s Annual Conference in November will hear from Langemeier who will provide additional context and insight into these findings during a breakout session.
