The short answer is he or she doesn’t very often.
To a number of questioners in the Public Insight Network, it seems an anomaly that Minnesota experiences two things that seem contradictory: a lot of irrigation and a lot of land drained to dry it out. A caller to the Daily Circuit last week raised the same question: why would someone do that?
You asked, so we asked. Here’s Question 3 in our series of water-related Q and A’s.
FROM THE PUBLIC INSIGHT NETWORK: How can we reconcile the fact that farmers both tile land to cause it to drain and then irrigate the land? Would it be possible to regulate tiling more and prohibit irrigation on land that is tiled?
It would be possible to regulate these activities. A complicating issue is that both activities increase crop yields and the direct negative impacts on water resources is difficult to document at the farm-parcel scale. It is important to point out that, generally speaking, there are not many fields with both agricultural draining and irrigation. For the most part, heavy soils need drainage and sandy soils need irrigation. I’m sure that exceptions can be found, however.
Farmers drain land that has naturally poor drainage, and they irrigate land that typically lacks the ability to retain water well. As a result, the amount of overlap (land that is both drained and irrigated) is extremely small. In the future, small amounts of irrigation coupled with minor drainage may actually be one part of an overall strategy to reduce both the extent of drainage and irrigation.
It is unusual that an irrigation system and a tile-drainage system exist in the same field. Irrigation and tile-drainage are very important water management tools but they take place in very different regions of the state. Almost all irrigation takes place on soils that are very well drained already and on soils that typically can only hold 2-4 inches of available water in the root zone. Many of our tile drained soils are poorly drained and typically hold 4-8 inches in the root zone.