By Justin Isherwood

Field tile is a matter of routine for many farmers in the Midwest, the goal is better field drainage, the practice includes: Indiana, Iowa, Illinois and Minnesota.  With buried tile (porous pipes) farmers attempt to displace soil water in excess of the crop need.  As an agricultural practice, tiling has been around for a thousand years as agriculture utilized wetlands, by consequence some of the richest soil available.

In the Midwest tile drainage is most effective in the spring to remove snow melt and rain that can delay planting to the point of yield impact.  Modern seed varieties are designed for early planting and doing so can provide for  improved yields.  To adjust for the risk of high priced seed genetics, fields are “designed”/tiled to defray this risk.  Tiling plays a big role under some spring conditions, in other years tiling is a non-factor; for the Corn Belt, tiling is good crop insurance.

The risk of wet field/yield impact is so routine that many Midwest farmers tile fields as a matter of course.  The practice however is a double edged sword, while it may get a crop off to an early start, the down-side is the absence of this same moisture later in the season, and a crop that could do nicely without irrigation now needs irrigation.  With some 50 million tiled acres in America’s Corn Belt, the effect of tiling is greater than the number of tiled acres.  With surface drainage, tiling affects broad areas of landscape at the subsoil level, and the rate of soil moisture reduction through the growing season where inches, even fractional inches matter to the root zone in the surrounding landscape.

A notorious impact of field tile’s impact is the out-flow to streams and tributaries, delivering a disproportionate nutrient load direct from the Midwest to the Gulf Coast fishery at the cost to that fishery of 80% of its economic value.  Counterintuitive of the dietary value of fish and their health factor for most Americans, when this same Gulf region is the source of 40% of the nation’s ocean catch.  Since 1960, nitrate fertilizer use in the Midwest has increased six-fold.

Tiling is also something of a Corn Belt rage, as farm land values have sky-rocketed, tiling has been the means to bring more land into production.  From 2008-2011 Minnesota converted 1.3 million acres of grassland with tiling.  As farmers chase margins they do so at the price of downstream water quality and commodity surplus.

To the end the Corn Belt question becomes, can tiling be made an ecologically sound practice?  Springtime run-off has an inherent nutrient value gained from the decomposition of over-wintered plant cover as well as the soil solubles.  The spring soil profile is routinely saturated and tiling offers a place for the water to go.  As a way of solving the wet soil issue and the nutrient loss problem, some farmers are attempting center pivot irrigation despite irrigation isn’t strictly necessary, in order to reapply tile-water from impoundments where drainage water is held for later application, including its nutrient value.  The farmer gains early field use, an optimal planting date, and saves the otherwise lost fertilizer/pollutant, in some cases sufficient to grow the entire crop “fertilizer-free.”  Research suggests this fertility value begins as low as 20 ppm of nitrate.

An alternative being explored in Minnesota are tile systems designed to reapportion root zone water throughout the field using interconnected tiles with one-way valves.  To an end, the wet part of the field gets drier and the drier part gets wet.  Surplus water in this tile grid is directed by valves designed to redistribute the water more evenly in the field.  In effect, storing the water.  On heavy soils one inch increments of soil moisture adjustment have demonstrated to have a practical field margin.  Downstream nitrates show a 15-75% reduction with a 3-5 bushel increase in yield per acre.

Field drainage and agriculture’s role for downstream water quality is an increasingly important environmental subject.  The curse of field nitrates pits one sector of the economy against another, amounting to billions in lost revenue.  The ag sector and its Farm Bill cannot continue to balance 200 bushel corn at $4/bushel against red snapper at 16 dollars a pound with the nation’s health attached.

Nitrates are soluble, this how they work in nature by being readily soluble.  Nitrates are the life blood of photosynthesis and plant growth. At nitrates is the bottom-line Corn Belt question: Were a Farm Bill to restrict nitrate use by some meaningful percentage, could these nitrates be more completely utilized by the crops?  To the end reduce the nitrate loss to field drainage?  In doing so can the Corn Belt gain a market advantage?  A 150 bushel crop pencils out at 5 dollars the equal of 200 bushel at 3.75 while saving 50 units of NO₃  with the chance of a more complete utilization of the nitrate.

Perhaps it is time (again) for the ag-sector to retire problematic lands.  A new CRP Farm Bill adjusted for modern land prices, and downstream consequences.  Modern field practice tends to use all the field, to optimize the cultivation footprint.  Maybe it’s time for the farm sector saddled with marginless crops to reconsider their field practices and skip those wet places.  Per bushel price and water quality offer the chance for agriculture to give wetlands a break, as well as America’s watershed.