Tuesday, October 26, 2021

There was a terrible drought in Iowa in 1976 and 1977 and the only time Raccoon River nitrate (at Fleur Drive in Des Moines) measured greater than 20 ppm followed. The only time, that is, until the Raccoon peaked out at 24.7 ppm nitrate in 2013, immediately following the 2012 drought.

Now you may know that much of Iowa has been moderately dry, to severely dry, to popcorn fart dry in 2021. As a result, faculty at Iowa State University and staff at Iowa Corn Growers’ Association have been imploring farmers in the media (1-7) to be cognizant of nitrate left behind in their fields because of poor crop nitrogen uptake. Also, less has been lost to the stream network and aquifers so more will be vulnerable to loss when the rains return. It’s like when you forget to put the trash out, then next week you have twice as much. Surplus nitrogen, like your trash, doesn’t just disappear into the Milky Way. Ironically, there *are* a lot of reports of good crop yields this fall, so a reasonable person might ask why they applied so much in the first place. But hey, that’s just me. What do I know.

Not that it matters at all, but I commend ISU for proactively warning farmers that business-as-usual decisions on fertilization will pollute our water later. In fact, I would say this is a landmark event for a couple reasons. First, we have establishment agriculture admitting in the DES MOINES REGISTER no less that farmer decisions end up polluting our water, and secondly, that actual purchased fertilizer is part of the problem. Much of this discussion, after all, has focused on the idea that the pollution isn’t the farmers’ fault, it comes FROM THE SOIL. Big hitters in the legislature say this all the time. 

But I also decry the fact that, at this late date, we still need to tell farmers this. WE HAVE KNOWN THIS FOR 50 YEARS. I took about a 1-hour look at the scientific literature on this, and scientists and extension agents have been publishing stuff on this since at least 1983. I summarized some of the good ones and they are in the text box at the end of the post. 

Sitting in my boat recently, during an extended gap between caught fish, I thought about this and decided to have a little fun with it. Imagine, if you will, a scientist published a paper in 1983  that promised the magical “2-5 bushel yield bump” (ever notice how it’s always 2-5?) if farmers added a little porcupine piss to their fertility regimen. Replicated strip trials at Nashua, Gilmore City and Crawfordsville (now called Quillville by agronomy grad students) research farms show a 50.1% chance of returns on a $10/acre investment in this new, mysterious nutrient. “I’m getting an extra 0.8 kernels per ear”, reports Kossuth County farmer Harold Johnson, while holding up 4/5th of a kernel. He notes the effect may be less in southern Iowa counties. Farmers everywhere flood Iowa Ag retailers for requests to be first in line for the product, marketed by Agrichem Canada.

A cascade of events ensues. Cyclone basketball meets the Kansas Jayhawks, not in Hilton Coliseum, but in the Porcupine Palace where Quill Magic pops the 2nd-ranked Jayhawks’ hopes in the last second. On the gridiron, a little gold plate engraved with the word “Hawkeyes” is annually attached not to the Cy-Hawk Trophy, but the Porcupine Plaque. Ferentz gets another raise. Iowa State researchers plan proposal partnerships with Purdue University to investigate the synergies at the nexus of porcupine and pork, because USDA and NSF have millions to study the issue’s effect on distressed rural communities left behind by consolidation in agriculture. UI flood researchers want in, because, you know, porcupines can’t swim and they don’t know how to climb a levee, either. Iowa’s governor carves 10 days out of her busy schedule to hand out Porcupine On a Stick, I mean On a Quill, at the Iowa State Fair. Porc is the new pork, according to the governor. The other other white meat. Iowa billionaire schemes with has-been former governor to get taxpayers to pay for a Porcupine Pipeline (“it’s a win-win”, says ex-guv) that will pump the porcupine piss from the Boreal forests of northern Canada straight to Agribusiness Association of Iowa members, so their staff can promptly spray it onto the parking lot during a thunderstorm, where it runs off and kills some fish. “Porcupine piss just finds water and goes into it”, reports Iowa DNR.

The point here is that if something improves crop yields, well, there’s not much need for ISU researchers to implore farmers and agribusiness to embrace it. When it comes to YOUR water, we have to beg farmers for a half century (or more) to do it. The basic fundamentals of what is driving erosion and nutrient loss have been known for decades. DECADES. GENERATIONS.

Ted Corrigan, now CEO at Des Moines Water Works and my direct supervisor when I worked there, was fond of telling me that the best predictor of future behavior was past behavior. Tell me again why we don’t need regulation in agriculture.

Research discussing post drought nitrate:


Accumulation of NO3-N in agricultural soils resulting from the application of N fertilizer might occur during periods of less than normal precipitation because of fewer periods of runoff and decreased NO3-N transport.

Hagebro, C.L.A.U.S., Bang, S.E.S.S.E. and Somer, E.R.I.K., 1983. Nitrate load/discharge relationships and nitrate load trends in Danish rivers. Dissolved loads of rivers and surface water quantity/quality relationships, 141, pp.377-386.


The NO3-¬N soil test for N availability holds considerable promise for use with corn.

Magdoff, F.R., Ross, D. and Amadon, J., 1984. A soil test for nitrogen availability to corn. Soil Science Society of America Journal, 48(6), pp.1301-1304.


Nitrogen fertilizer not used due to drought conditions will be directly available for next year’s crop. The amount remaining can easily and accurately be measured with the nitrate soil test.

Gerwing, J.R., 1988. Fertilizer Carryover After Drought. Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange, South Dakota State University.


The best approach is to fertilize according to field-calibrated soil tests. Although an empirical approach, when restricted to the area from which the field calibration was derived, this approach can provide reasonable estimates of minimum fertilizer N requirements. Previous research has shown that fertilizer use based on such recommendations reduces production costs and nitrates leaching, while maintaining yields. With continued research, well calibrated soil test recommendations for fertilizer usage can provide the accounting of N needed to minimize nitrate leaching into ground water.

Power, J.F. and Broadbent, F.E., 1989. Proper accounting for N in cropping systems. In Developments in Agricultural and Managed Forest Ecology (Vol. 21, pp. 159-181). Elsevier.


The Magdoff Pre-Sidedress Nitrate Test (PSNT) is a soil test that provides more accurate fertilizer N recommendations for corn than previous N recommendation systems based on anticipated effects of manure and crop management. Using the test can result in significant reductions of fertilizer N use on high-N supplying soils.

Magdoff, F., 1991. Understanding the Magdoff pre‐sidedress nitrate test for corn. Journal of Production Agriculture, 4(3), pp.297-305.


Excessive quantities of N are added to crops when environmental factors (such as a drought) restrict crop yield.

Angle, J.S., Gross, C.M., Hill, R.L. and McIntosh, M.S., 1993. Soil nitrate concentrations under corn as affected by tillage, manure, and fertilizer applications (Vol. 22, No. 1, pp. 141-147). American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.


NO3-N accumulates in soil, not only from decreased transport to streams and uptake by plants, but also because of the existence of a greater thickness of unsaturated materials above the water table. As the water table declines during dry climatic conditions, the unsaturated zone becomes thicker, allowing increased accumulation and storage of NO3-N. When the water table rises with the onset of wetter climatic conditions (indicated by increased streamflow), the NO3-N stored in what was previously the unsaturated zone is mobilized and is available for transport by subsurface flow to the river.

These data indicate that during years of deficient precipitation, NO3-N accumulates in the soils, not only from decreased transport and uptake by plants, but also because of a greater thickness of unsaturated materials above the water table. As the water table declines during dry climatic conditions, a thicker unsaturated zone occurs allowing accumulation of NO3-N. When the water table rises during wetter climatic conditions, the NO3-N stored in what was previously the unsaturated zone is mobilized and is available for transport by subsurface flow to the river. Large NO3-N concentrations that persist for several months probably result from the mobilization of NO3- N that has accumulated in the drainage basin during periods of dry climatic conditions.

Land-management practices could help ameliorate the problem by decreasing N fertilizer application rates when warranted, to take into account residual NO 3- N concentrations in the soil profile.

Lucey, K.J. and Goolsby, D.A., 1993. Effects of climatic variations over 11 years on nitrate‐nitrogen concentrations in the Raccoon River, Iowa (Vol. 22, No. 1, pp. 38-46). American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.


Weather was a significant variable with two years of drought (1987-1988) followed by very wet years (1989-1990). There was significant carryover of nitrate in tile drainage from one year to the next.

Logan, T.J., Eckert, D.J. and Beak, D.G., 1994. Tillage, crop and climatic effects of runoff and tile drainage losses of nitrate and four herbicides. Soil and Tillage Research, 30(1), pp.75-103.


This data set also suggests the large effect of year or previous year's climate on residual N levels.  The test appears most helpful when corn is the previous crop, when the soil texture is either medium or fine, and when some carryover of residual nitrate is expected.

Schmitt, M.A. and Randall, G.W., 1994. Developing a soil nitrogen test for improved recommendations for corn. Journal of production agriculture, 7(3), pp.328-334.


Larger amounts of total and inorganic fertilizer derived nitrogen were left in the soil from the 1983 application than from 1982 due to the more severe drought conditions in 1983, which caused unusually low fertilizer derived nitrogen plant uptake.

Jokela, W.E. and Randall, G.W., 1997. Fate of fertilizer nitrogen as affected by time and rate of application on corn. Soil Science Society of America Journal, 61(6), pp.1695-1703.


These data indicate that nitrate concentrations in the tile water would be increased about 6 mg-N/L prior to the drought year and 20 mg-N/L after the drought year.

Mitsch, W.J., Day Jr, J.W., Gilliam, J.W., Groffman, P.M., Hey, D.L., Randall, G.W. and Wang, N., 1999. Reducing nutrient loads, especially nitrate-nitrogen, to surface water, ground water, and the Gulf of Mexico. National Oceanic and Atmospheric Administration National Ocean Service Coastal Ocean Program.


April–October rainfall was 35% below normal, and no samples were collected for nitrate N analyses. Under these dry conditions during the 3-yr period, corn yields and N uptake were low. However, residual soil nitrate nitrogen (RSN) continued to increase in the soil profile to levels as high as 259 kg/ha in the top 1.5-m profile. April–October precipitation in 1990 was 23% above normal, causing drainage volume to total >350 mm. Moreover, the annual flow-weighted nitrate N concentration averaged 35 mg/L, twice as high as during the dry years.

Randall, G.W. and Mulla, D.J., 2001. Nitrate nitrogen in surface waters as influenced by climatic conditions and agricultural practices. Journal of environmental quality, 30(2), pp.337-344.


Several methods for improving N management and reducing NO3 contamination of water resources have been previously proposed by others. Among them are recommendations for better use of soil tests to properly credit N sources.

Dinnes, D.L., Karlen, D.L., Jaynes, D.B., Kaspar, T.C., Hatfield, J.L., Colvin, T.S. and Cambardella, C.A., 2002. Review and interpretation: Nitrogen management strategies to reduce nitrate leaching in tile-drained Midwestern soils.


A severe drought in 1994 resulted in much reduced crop N uptake and unusually high residual nitrate in the autumn.

Soon, Y.K. and Clayton, G.W., 2003. Effects of eight years of crop rotation and tillage on nitrogen availability and budget of a sandy loam soil. Canadian journal of soil science, 83(5), pp.475-481.


Nitrate may also build up in the soil build up over several years of drought if crops have been fertilized for normally expected yields. Soil testing will detect this increase and enable fertilizer N recommendations to be reduced accordingly.

Hons, F.M., McFarland, M.L., Lemon, R.G., Nichols, R.L., Mazac Jr, F.J., Boman, R.K., Saladino, V.A., Jahn, R.L. and Stapper, J.R., 2004. Managing nitrogen fertilizer in cotton. Texas FARMER Collection.


In areas affected by last year’s drought, the University of Illinois recommends crediting back some of the nitrogen applied to last year’s crop if going back to corn. In severe drought areas, there may be enough carryover nitrogen to justify considering corn again in those fields.

Erickson, B., 2005. New Thinking Regarding Nitrogen Rates for Corn. Top farmer Crop.


Accounting for RSN (residual soil nitrogen) following dry years by using spring soil N tests (Magdoff et al., 1984 ; Blackmer et al., 1989 ; Bundy et al., 1993 ; Schmitt and Randall, 1994 ) could be quite helpful to growers. Unless the nitrate has been leached below the sampling zone, these tests should be able to provide information that would lead to reductions in the rate of fertilizer N recommended, resulting in lower nitrate-N losses in tile drainage water.

Randall, G.W. and Goss, M.J., 2008. Nitrate losses to surface water through subsurface, tile drainage. In Nitrogen in the Environment (pp. 145-175). Academic Press.


With drastic reductions in corn yield, N uptake would be low, and high carryover soil nitrate-N (NO3 -N) could be accounted for as an adjustment to 2013 rates. Carryover NO3 -N can be estimated by sampling the soil profile after harvest.

A concern relative to water quality following the drought may be the NO3 -N concentration and loading from agricultural landscapes. During the drought, soil NO3 -N can accumulate within the soil profile and then be lost during subsequent periods of excess precipitation.

Al-Kaisi, M.M., Elmore, R.W., Guzman, J.G., Hanna, H.M., Hart, C.E., Helmers, M.J., Hodgson, E.W., Lenssen, A.W., Mallarino, A.P., Robertson, A.E. and Sawyer, J.E., 2013. Drought impact on crop production and the soil environment: 2012 experiences from Iowa. Journal of Soil and Water Conservation, 68(1), pp.19A-24A.


These findings also suggest that precipitation events following periods of drought, like those observed after the 2012 growing season, can flush excess nutrients from the rooting zone further depleting the NO3-N pool and posing a risk to water quality.

Armstrong, J., 2015. Nitrogen availability and transport following drought in three agricultural watersheds in Central Illinois. Southern Illinois University at Carbondale.


The drought likely created highly N-enriched soils; this excess N mobilized during heavy spring rains (2013), resulting in a 34% increase (10.5 vs. 7.8 mg N L−1) in the flow-weighted mean annual nitrate concentration compared to recent years.

Loecke, T.D., Burgin, A.J., Riveros-Iregui, D.A., Ward, A.S., Thomas, S.A., Davis, C.A. and Clair, M.A.S., 2017. Weather whiplash in agricultural regions drives deterioration of water quality. Biogeochemistry, 133(1), pp.7-15.


At longer time scales, more intense, season-long droughts will have lagged effects on agricultural N losses. Long droughts lead to hydrologic disconnections and N retention in landscapes, resulting in higher N concentrations during subsequent flushing events.

Bowles, T.M., Atallah, S.S., Campbell, E.E., Gaudin, A.C., Wieder, W.R. and Grandy, A.S., 2018. Addressing agricultural nitrogen losses in a changing climate. Nature Sustainability, 1(8), pp.399-408.

  1. https://www.thegazette.com/guest-columnists/how-fertilizer-management-works-during-an-iowa-drought/

  2. https://www.desmoinesregister.com/story/opinion/columnists/iowa-view/2021/10/23/iowa-farmers-fall-nitrogen-fertilizer-management-options/6139787001/

  3. https://www.agupdate.com/midwestmessenger/news/crop/fertilizer-management-looks-different-in-times-of-drought/article_8d3ade94-31e6-11ec-800e-03dbda66a7cd.html

  4. https://www.no-tillfarmer.com/articles/10870-managing-nitrogen-application-during-a-drought

  5. https://www.farmprogress.com/crops/isu-research-suggests-reducing-fall-fertilizer-apps-during-drought

  6. https://www.agrimarketing.com/s/138147

  7. https://www.topyield.ag/app/posts/471/fertilizer-management-in-a-drought-new-research/