Subsurface tile drainage is a farming practice utilized in various regions of the United States, primarily in the Midwest, that allows proper drainage of soils that do not naturally drain well. The practice involves a system of pipes and channels that allow water to flow out of an otherwise poorly drained field to a designated drainage outlet using gravity. Depending on the specific properties of the field such as soil type, field slope, and average precipitation, subsurface tile drainage can potentially greatly improve crop yields.
More cropland is tiled in Iowa than in any other state. Around 13 million acres in Iowa utilize subsurface tile drainage, which is around 4.2 million acres more than Illinois and 4.8 million acres more than Minnesota (Figure 1). Roughly half of all cropland in Iowa is tiled.
The yield increases resulting from tile drainage generate significant additional revenue. Additionally, crops planted in tiled fields require additional inputs to fully capture any potential yield improvements. Table 1 shows the estimated revenue and cost increases as calculated by Iowa State University Extension’s Farmland Tile Drainage Investment Analysis1.
Available here: https://www.extension.iastate.edu/agdm/wholefarm/xls/c2-90tilinganalysis.xlsx
This increase in crop production leads to a corresponding increase in broader economic activity throughout the state as farmers purchase the required additional inputs and spend their additional earned income. Additional revenue from tile drainage was estimated by allocating the 13 million acres drained by tile to corn and soybean acres according to the 2022 USDA Census of Agriculture corn/soybean split of harvested acres in Iowa (which is 57% corn and 43% soybeans) after first deducting 8% (roughly 1 million acres) of the total drained acres to account for idle cropland in Iowa.
These acreage values were then multiplied by the revenue per acre estimates in Table 1, resulting in an additional revenue of $628 million for tiled corn acres and $396 million for tiled soybean acres across the state. These values were entered into IMPLAN as an output increase for the corresponding industry (grain farming and soybean farming, respectively). Additional expenses were estimated with the same method and added to the events as an increase in intermediate expenses, with the production function adjusted to match the ratio of costs as shown above.
Table 2 shows the estimated total economic contribution of subsurface tile drainage to the Iowa economy on an annual basis. These values represent economic activity that already exists but would be lost if Iowa tile drainage was removed. The total contribution is estimated at 6,075 jobs, $499 million in labor income, $987 million in value added (equivalent to GDP), and $1.6 billion in output (sales). Around 60% of the total contribution comes from gains to corn production and 40% comes from gains to soybean production.
Gains from subsurface tile drainage have a significant effect on the Iowa economy. DIS recently conducted an analysis of the economic contribution of all agriculture in Iowa2, which estimated the contribution of all crop production in the state to be around 99,300 jobs, $7.0 billion in labor income, and $16.2 billion in value added, meaning that around 7% of Iowa’s crop contribution in terms labor income and 6% of crop contribution in terms of jobs and value added can be attributed to the presence of tile drainage in the state.
Full report available here: https://www.supportfarmers.com/iowaagintel/