Perspective on Current and Future Agricultural and Environmental Need for Enhanced Efficiency Fertilizers

Search PMN

Paul E. Fixen, Senior Vice President, International Plant Nutrition Institute, Brookings, SD 57006

Abstract

The need for fertilizers with the potential for increasing nutrient use efficiency is great. Though nutrient use efficiency has been increasing in the USA, it is still often less than 50% for N in production fields. Improved short-term nutrient recovery by crops is needed. Improved crop recovery would reduce the contribution of crop production to the cascading of nutrients outside agroecosystems. To be adopted, efficiency enhancing approaches, including enhanced efficiency fertilizers, must be cost effective and fit into the total farm management system. They must also preserve the potential for cropping systems to become higher yielding to meet the anticipated increases in demand for food, feed, fiber and fuel.

The need is great for enhanced efficiency fertilizers for both economic and environmental reasons. Enhanced efficiency fertilizers include slow-release and controlled-release fertilizers, nitrification inhibitors, and urease inhibitors. Four needs to be filled by enhanced efficiency fertilizers follow.

Need 1: Improved Short-term Fertilizer Nutrient Recovery by Crops

The cost of fertilizer nutrients has undergone substantial recent increases due in part to increases in energy costs, especially natural gas. Declines in United States fertilizer use in 2006 of 2 to 9% compared to 2005 (11) were very likely related to higher fertilizer prices and reflect the interest of growers in controlling their fertilizer costs and in more efficient fertilizer use.

United States growers have gradually been increasing fertilizer use efficiency for several decades. For example, since the mid 1970s N fertilizer use per hectare on corn has increased 12% while corn yields have increased 60%, resulting in a 51% increase in partial factor productivity (Fig. 1). However, single-year recovery of N fertilizer is still nothing to brag about with typical levels in farm fields in the 20 to 50% range (7). Nitrogen not recovered during the year of application is not necessarily lost to air or water, but the risk of loss is certainly increased. Long-term recovery efficiency for P is higher ranging from 50 to 90% (9,10). However, single-year P recovery seldom exceeds 20% and is often less than 10%. Therefore, a significant portion of the benefit from the fertilizer investment is delayed.

Rising fertilizer costs, risk management issues, and the time value of money all support a need to increase short-term nutrient recovery by crops.

Fig. 1. Corn grain produced in the United States per unit of fertilizer N used, 1964 to 2005 [*Application rate for 2004 estimated as average of 2003 and 2005; updated from (2)].

Need 2: Reduced Contribution by Crop Production to the Cascading of N and P Outside Agroecosystems

As the total quantity of reactive N (all N other than N₂) increases on the planet due to increases in energy production, commercial fertilizer manufacture, and biological N fixation, concerns over the cascading of N lost from agro-ecosystems intensifies. The cascading of N through multiple ecosystems is illustrated in Figure 2. The primary response of agriculture to this concern has been to focus on increasing nutrient use efficiency, keeping N molecules cycling within the agroecosystems box in the diagram as long as possible. Nutrient use efficiency can have a major impact on fertilizer N creation at a global scale. The impact of assumed efficiency on global projections of N demand is illustrated in Table 1.

Fig. 2. The nitrogen cascade (3,14).

Table 1. Global projections of N demand to 2009-2010, 2020, and 2050.

Projection method		Year
Basis	NUE assumption	2000-2001 (6)	2009-2010 (5)	2020 (16)	2050 (16)
Basis	NUE assumption	N demand (Mt)
Regional fertilizer and crop production trends; soil rehabilitation beyond 2020^x	Constant at 10 to 20 kg cereal per kg N fertilizer^y	81.2	96.1	111.6	171.3
Food production predicted by IMPACT^z model	Constant at 1997 crop-specific levels	—	—	111.7	121.2
Food production predicted by IMPACT^z model	17% improvement over 1997 by 2020; 30% by 2050	—	—	96.2	106.6

^x The trend analysis assumed the N use would be higher in areas of significant soil degradation between 2020 and 2050.

^y NUE ranging from 10 to 20 were assigned to each global region based on a subjective interpretation of local agro-ecological and crop management conditions.

^z International Model for Policy Analysis of Agricultural Commodities and Trade.

Though not as complex as the N cascade, clear environmental justification exists for avoiding P losses from agroecosystems as well. A focus on both long-term and short-term nutrient use efficiency is warranted to protect water quality.

Need 3: A Cost Effective and Usable Efficiency Enhancing Approach

Greater synchronization of plant demand and N supply normally reduces the risk of N loss and improves nutrient use efficiency. Accomplishing that synchronization is a dynamic process influenced by seasonal weather and by changes in cropping systems. For example, use of conservation tillage in corn production has increased substantially in the last 30 years, a practice that could delay soil N mineralization compared to fall moldboard plowing and influence appropriate timing of N application. At the same time, research comparing older and newer hybrids has shown a trend of increased N uptake later in the season (12).

Spoon-feeding approaches employing split applications are frequently used in irrigated production but have had limited acceptance in rain-fed systems due in part to logistical challenges and costs. Timing of applications and time management on the farm can be at odds as competition exists from other fields or farms or from other farm enterprises. Many efficiency enhancing tools are never adopted by farmers because they either are not cost effective for the cropping system or they do not fit into the total farm management system. The application flexibility of enhanced efficiency fertilizers facilitates their adoption by crop producers.

Need 4: Increased Potential to Meet the Growing Demand for Food, Feed, Fiber, and Fuel

Estimates are that the world will need 50% more food by 2013 and twice as much within 30 years (4). World wheat plus coarse grain stocks for the 2007-2008 crop year are estimated at 14.5% of total use, a 30-year low, and part of a 10-year trend of steady declines is spite of several years with phenomenal crop growing conditions in major production regions of the world (15). The average decline in ending stocks during this 10-year period was 1.8% of total use. To put this trend in perspective, if it were to continue for another eight years, stocks would be totally depleted. Furthermore, expanding use of corn for ethanol production will put even greater pressure on grain stocks and production demand. The ethanol industry in the USA in 2007 used 18% of the United States corn crop to produce 25 billion liters of ethanol (8). Projections are for corn ethanol production to exceed 40 billion liters in the next couple years (13). Increased corn demand has lead to substantial increases in corn following corn production, where fertilizer N efficiency is a challenge.

A sobering illustration of the magnitude of the challenge agriculture faces is revealed by considering United States corn production over the last 43 years (Fig. 3).

Fig. 3. United States corn yields, 1964 to 2006 (after 1).

Over these four decades, in spite of major genetic improvement, considerable expansion of irrigation, increased N fertilizer rates, conservation tillage, integrated pest management and the advent of transgenic traits, the resulting yield increase was linear at 115 kg/ha/year. Breaking this line while meeting environmental expectations will be a huge challenge. Clearly, acceptable efficiency enhancing practices will need to maintain the potential for the cropping system to generate yield increases.

Conclusion

A schematic metaphor is helpful in illustrating the potential role of enhanced efficiency fertilizers and at the same time place them in appropriate context (Fig. 4). The "nutrient management genome" pictured here started as a DNA double helix. One of the strands represents productivity while the other represents environmental impact. The base pairs are the fundamental components of nutrient best management practices, source, timing, placement, and rate.

Fig. 4. The nutrient management genome.

Two main points are illustrated: the strands (productivity and environmental impact) must be linked through the base pairs (a proper set of best management practice (BMP) components) before the genome (nutrient management system) can have the desired impact on the organism (agroecosystem); and the impact of any base pair (i.e., fertilizer source) is dependent on the other base pairs (i.e., timing, placement, rate) it occurs with in the genome.

The metaphor conveys the strong message that for research to be most meaningful it must measure impacts on both productivity and the environment and appropriately manage or measure the interacting influences of other management practices.

More efficient fertilizers that better synchronize nutrient release and crop demand would be a great asset to crop producers as they strive to reduce nutrient losses while increasing productivity. However, they will only be effective if used in a system that recognizes the impact of enhanced efficiency fertilizers on rate, placement, and timing decisions.

Literature Cited

1. Cassman, K. G., Eidman, V., and Simpson, E. 2006. Convergence of agriculture and energy: Implications for research and policy. Commentary QTA 2006-3. CAST, Des Moines, IA.

2. Fixen, P. E., and West, F. B. 2002. Nitrogen fertilizers: Meeting contemporary challenges. Ambio 31:169-176.

3. Galloway, J. N., and Cowling, E. B. 2002. Nitrogen and the world. Ambio 31:64–71.

4. Glenn, J. C., Gordon, T. J., and Florescu, E. 2008. The Millenium Project: State of the Future. World Federation of UN Associations, Washington, DC.

5. Heffer, P., and Prud’homme, M. 2005. Medium-term outlook for global fertilizer demand, supply and trade: Summary report. Online. Int'l. Fertilizer Industry Assoc., Paris, France.

6. IFA. 2008. Statistics. Online. Int'l. Fertilizer Industry Assoc., Paris, France.

7. Mosier, A. R, Syers, J. K., and Freney, J. R. 2004. Nitrogen fertilizer: An essential component of increased food, feed, and fiber production. Pages 3-18 in: SCOPE 65: Agriculture and the Nitrogen Cycle: Assessing the Impacts of Fertilizer Use on Food Production and the Environment, A. R. Mosier, J. K. Syers, and J. R. Freney, eds. Island Press, Washington, DC.

8. Renewable Fuels Assoc. 2008. Changing the Climate: Ethanol Industry Outlook 2008. Online. Washington, DC. 9. Smil, V. 2000. Phosphorus in the environment: natural flows and human interferences. Annu. Rev. Energy Environ. 25:53-88.

10. Syers, J. K., Johnston, A. E., and Curtin, D. 2008. Efficiency of soil and fertilizer phosphorus use. FAO Fertilizer and Plant Nutrition Bulletin 18. Food and Agriculture Organization of the United Nations, Rome.

11. Terry, D. L., and Kirby, B. J. 2007. Commercial Fertilizers 2006. Association of American Plant Food Control Officials, Inc. (AAPFCO) and The Fertilizer Institute (TFI), Washington, DC.

12. Tollenaar, M. 1997. Yield response of old and new corn hybrids to nitrogen. Better Crops 81(4):3-5.

13. Tyner, W. E. 2008. The US ethanol and biofuels boom: Its orgins, current status, and future prospects. BioScience 58:646-653.

14. UNEP. 2003. GEO Year Book 2003. United Nations Environmental Program, Nairobi, Kenya.

15. USDA. 2008. Grain: World markets and trade, May 2008. Online. World Market and Trade Archives USDA Foreign Agric. Serv., Washington, DC.

16. Wood, S., Henao, J., and Rosegrant, M. 2004. The role of nitrogen in sustaining food production and estimating future nitrogen fertilizer needs to meet food demand. Pages 245-260 in: SCOPE 65: Agriculture and the Nitrogen Cycle: Assessing the Impacts of Fertilizer Use on Food Production and the Environment. A. R. Mosier, J. K. Syers, and J. R. Freney, eds. Island Press, Washington, DC.