Hi George,

I don’t farm myself but I work with farmers and do some drainage design. Most tile in Iowa is at about 48 inches deep. Spacing is usually 30 – 40 ft for new pattern tile installations in tight soils. Most contractors are now running RTK guidance to install tile. We are encouraging people to consider shallower installation and/or controlled drainage due to our issues with high nitrate levels in drainage water. Controlled drainage might be a good fit if you are short of water certain times of the year and want to bring the water table up. We are just beginning to experiment with drainage water recycling, with holding ponds for irrigating the water back out during the summer. It’s still unknown whether it will pay economically, but with increasingly extreme weather it seems like the potential is there. Modeling suggests that the holding pond will need to sized be around ~4% of the drained area to hold enough water to be worth doing it, but that will vary with climate. Pumping irrigation water out of the drainage canals is workable if the distance is reasonable. I have seen it done in Ontario, Canada. We recommend a drainage coefficient (inches of water removed per day) of at least 0.5 for new installations. Some farmers are going even higher to prepare for the future. Having said all that, none of this will do much good if you can’t get the water to infiltrate to begin with. As you noted, keeping living roots in the ground, having lots of dead root channels, and building aggregation is the solution.