What’s ahead for fertilizer use considering what we see in the rearview mirror and the issues on the horizon? While it’s hard to say for certain, there are many factors at play that can give some insight.
Potassium (K) and phosphorus (P) application took big hits last year and will contribute to some very negative nutrient budgets (quantity applied minus quantity removed by crops) for key North American production areas. This red ink comes on top of rather precarious pre-existing nutrient budgets for the primary Corn Belt (see map). If we include recoverable manure nutrients, the eastern Corn Belt was applying about 10% more K than was being removed while the western Corn Belt was removing about 10% to 20% more than was being applied. Prior to the 2009 season, much of the Corn Belt was running a P deficit with crop removal in Iowa exceeding use by 20% to 30% and in Illinois by 50% to 60%. These were the budgets existing prior to the recent use reductions; the deficits will be much greater in 2009.
Conventional wisdom would lead us to at least two sets of agronomic impacts.
First, if fields experiencing significant use reduction were below critical soil test levels for these nutrients (roughly 40% of North American fields), some reductions in 2009 crop yields would be expected. The amount of this yield loss will be hard to determine this autumn due to the large impact weather always has on actual yields. However, the weather-induced delays in planting and the coolness of the season across much of the Midwest and northern Great Plains are conditions that typically translate into larger than normal nutrient responses — if the nutrients were applied. Date of crop maturity and grain moisture contents are likely also to be impacted by nutrient management, and these impacts are sure to be important to many regions. Then, there are the soil compaction issues created by traffic on wet soils this spring that often result in greater responses to application of K.
Looking forward, 2009 will stack up to be a year of significant mining of soil nutrients — on top of the nutrient budget scenario described earlier. We expect the result to be a reduction in soil P and K fertility levels. Aggregate data are not very useful in judging the impact of such reductions as the impact depends on the soil fertility levels you started with. So a premium exists this fall on knowing field or zone-specific soil fertility levels in order to determine adjustments in future fertilizer use. It is highly likely that the average soil test based P or K fertilizer recommendation will be higher next year than it was last year.
Beyond The Farm Gate
Leadership changes within elected government and agencies like EPA, and public statements made by those in authority, indicate that agriculture could be facing many new environmental hurdles. National science review committees have been or are developing reports that call for significant reductions (20% to 45%) in the release of nitrogen (N) and P into the environment. In years past, point source pollution (from identifiable pipes, smokestacks, etc.) was the largest target and focus of attention.
Today, nonpoint sources or diffuse losses of nutrients to the environment are considered the new regulatory and environmental policy “frontier.” As a consequence of these changes, few doubt that federal, state, and local authorities will be asking or requiring the agricultural community to ratchet down the loss of nutrients from our landscapes to fulfill their duties to protect our air and water resources.
Midwest farmers are keenly aware that hypoxia in the Gulf of Mexico has been largely blamed on N and P loss from agricultural lands. Spring (April-June) transport of N and P is believed to be one of the principal factors which fuel hypoxia development. In January 2008, the U.S. Geological Survey (USGS) identified N and P losses from farmland in Illinois, Iowa, Indiana, Missouri, Arkansas, Kentucky, Tennessee, Ohio, and Mississippi as the cause of over 70% of the hypoxic zone pollution.
In June, USGS reported that river flow this past spring (April-May) was up 17%, nitrite plus nitrate-N flux or discharge to the Gulf of Mexico was up 11%, and total N flux was up 5.5%, compared to the 1979 to 2008 averages. As a consequence of these increases, the predictive models used by some marine scientists were forecasting a record hypoxic zone size (8,456 square miles to 9,668 square miles) this summer. Somewhat surprisingly, the anticipated calamity did not happen and the hypoxic zone was much smaller than predicted (3,000 square miles; see figure below). Some are attributing the reduced size of the hypoxic zone this year to reduced fertilizer use by growers throughout the Mississippi River Basin. However, the supposition that less fertilizer use this year resulted in a smaller hypoxic zone does not jibe with the observed increase in spring transport of nitrite plus nitrate-N and total N to the Gulf, which were reported by USGS. Clearly, there are other factors which also influence hypoxia development.
Greenhouse Gas Challenges
Who among us has not heard about climate change and the influence of potent greenhouse gas (GHG) emissions on global warming? To curb the trend in global warming and climate change, reductions in carbon dioxide (CO2) emissions have been placed foremost among our society’s environmental goals now and into the future. Reductions in nitrous oxide (N2O) emissions are also being called for because N2O has a global warming potential about 300 times higher than CO2. Agricultural soil management, which includes inputs such as fertilizer and manure N, accounts for most of the world’s N2O emissions. Anything that can be done to improve crop recovery of applied N will likely result in significant reductions in N2O emissions, and help reduce other N losses that pose problems in the environment. When nitrate is abundant in the soil, creating a supply of readily available carbon (C) (i.e., adequate soil organic matter) and warm, moist soil conditions exist (i.e. at and above field capacity), there is a significant risk of N2O emissions.
However, well-managed fertilizer promotes plant growth and photosynthesis, during which CO2 is captured from the air. Increased plant biomass (both below and aboveground) helps sequestration of C in the soil, as soil organic matter, and therefore helps minimize atmospheric emissions of CO2 associated with land use and food production. Conservation practices like no-till and other management changes can help reduce soil disturbance, reduce the rate of soil organic matter decomposition, and help reduce CO2 emissions. When C is sequestered in soil organic matter, N as well as P and sulfur are also sequestered because these four nutrients are all essential components in soil organic matter. If crop production per existing land area can be increased, and the biomass production can also be increased, then many would suggest that crop agriculture can have a positive impact in helping lower GHG emissions and reducing the risks of global warming.
More Food, Fuel
The global food crisis has not gone away, it just left our headlines. The facts are that global cereal yields are currently increasing at a rate of 1.2% to 1.3% per year, based on 2007 yields, and food demand for decades to come is expected to increase at a rate in the vicinity of 2% per year. That gives a pretty clear picture of the importance of increasing productivity.
Use Our Tools
If there was ever a time for full throttle application of 4R nutrient stewardship, it’s now. Application of the right nutrient source, at the right rate, the right time, and the right place is the way forward. This simple concept brings together the science and practical application of nutrient management in a way that supports the economic, environmental, and social elements of sustainable crop production. The resulting site-specific nutrient best management practices become the in-field manifestation of the approach and the only rational means of attempting to meet the productivity, economic, and environmental demands mentioned above. All the science may not yet be done to fully address these issues, but much has been and is ready for more complete adoption. Implementing 4R nutrient stewardship and documenting the implementation are critical roles for agriculture and the fertilizer industry as we collectively address the issues of 2010 and beyond.