COMMENTS ON DRAFT PLAN OF ACTION FOR REDUCING, MITIGATING, AND CONTROLLINGHYPOXIA IN THE NORTHERN GULF OF MEXICO
From: Leslie A. Everett, Department of Soil, Water, and Climate, University of Minnesota July 25, 2000
As stated in the report, approximately 90% of the nitrate load is from non-point sources, primarily agricultural fields. Most of the nitrate from these fields is carried by water moving through the soil profile into tile drainage systems which are outletted directly to surface waters, including drainage ditches, streams, and rivers. In-stream denitrification is minimal in these drainage systems, especially at high flow, when most of the loadings occur.
The extent and density of subsurface drainage systems in the Upper Mississippi River Basin is being increased at a rapid pace because it provides economic returns through consistently improved crop yields. This trend will result in INCREASED nitrate loadings to surface water, because it allows more movement of water through the soil profile (away from surface runoff), and bipasses routes which would result in denitrification.
The principal sources of nitrate leached from the soil profile are nitrogen fertilizers and animal manure applied in excess of crop requirements and/or with incorrect timing, placement, and form of application. These management decisions, in the absence of regulatory constraints, are driven by economics, convenience, and risk avoidance factors.
Timing. Fall fertilizer (anhydrous ammonia) application reduces economic risk by avoiding wet spring conditions and allows the dealer-applicator to increase area covered with a fixed set of equipment. It also increases nitrate available for leaching, especially when applied at soil temperatures above 50 degrees F. Side-dressing after planting would provide N when the crop needs it most, however there is some risk of rain limiting field access at the appropriate time. Expected loss of N due to early application leads producers and dealers to apply excess N to compensate for the expected leaching and denitrification losses.
Amounts. No or inadequate 'credit' is given by the producer for nitrogen available in the field from previous legume crops, manure application, and organic matter mineralization. Factors include lack of trust of these credits by the producer, uneven N availablility from manure application, and economic pressure on fertilizer dealers to sell more product.
Cost. The cost of anhydrous ammonia and other nitrogen fertilizer is too low in relation to grain prices to be a constraint in rates of fertilizer applied or timing of application.
Regulatory constraints. There are no regulatory constraints on the amount of fertilizer nitrogen applied to farm fields in the Mississippi River Basin except where animal manure is applied (see Minnesota state feedlot rules). There is no requirement for crop nutrient management plans meeting state crop nutrient recommendations except in the case of large animal feedlot operations. Fertilizer dealers and crop consultants may recommend any rates which are considered in their own or the producers' economic interest, with no constraint on amounts delivered to drainage systems.
Finally, in the draft action plan, section titled "Adaptive Management: Action, Monitoring, and Research", I dispute the following statement. "Further it is clear that environmental responses to management actions in the basin likely will be slow, possibly requiring decades to demonstrate that remedial actions have helped the recovery of oxygen concentrations in the Gulf and have improved water quality in the Basin." There is nothing that I have seen, regarding nitrate nitrogen, which supports that statement. Changes in nitrate delivered to tile drainage systems move very quickly through the system, and are observed in the Gulf in the same season. That kind of language is appropriate for sediment and phosphorus, but not nitrate nitrogen. It does nothing but excuse ineffective mitigation actions.
Thanks for the opportunity to comment. Please confirm receipt of this comment by return email.
Les Everett, Education Coordinator
Dept. Soil, Water, & Climate, UM
439 Borlaug Hall
1991 Upper Buford Cr.
St. Paul, MN 55108
tel 612-625-6751; fax 612-625-2208