Inorganic Nutrient Use in the United States: Past and Present - ACS

Chapter 11

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Inorganic Nutrient Use in the United States: Past and Present W . M. Stewart th

Great Plains Director, Potash and Phosphate Institute, 3206-B 66 Street, Lubbock, TX 79493

Inorganic nutrient use in the US is affected by many factors. The impact of some of these factors is more easily quantified than others. For example, the effect of factors such as crop and fertilizer prices and area in production can be evaluated using historical records and current statistics. Other factors such as changes in crop genetics and management practices are more difficult to quantify. A n evaluation of estimated nutrient removal/use ratio has revealed that the U S is currently depleting Ρ and Κ from soils on a national basis at an increasing rate each year. Over the 40-year period evaluated, soil Κ has been in the draw-down mode every year, and Ρ has been in the depletion mode since the early 1980s.

© 2004 American Chemical Society In Environmental Impact of Fertilizer on Soil and Water; Hall, William L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.

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Introduction Inorganic nutrient use in the U S has increased markedly over the past 40 years. Figure 1 shows total consumption of nitrogen (N), phosphate (P 0 ), and potash ( K 0 ) fertilizer from 1961 to 2000. The consumption curve in Figure 1 consists of three distinct segments. The first segment represents a period of linear increase in consumption from 1961 to about 1974. The next segment is a period of erratic consumption extending from about 1974 to 1986. Fertilizer use has been relatively flat in the final segment from about 1986 to 2000. Inorganic nutrient use in the US is influenced by many factors. Some of these factors are easily evaluated while others are not. Examples of factors that can be readily evaluated include area in production, fertilizer and crop price, government programs, and weather. Other factors affecting fertilizer consumption that may be more difficult to quantify include adoption of new technology, crop genetic improvements, and market development efforts. 2

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Selected factors affecting inorganic nutrient use The effect of crop acres (planted) on fertilizer consumption from 1961 to 2000 can be seen in Figure 2. Surprisingly, there was relatively little change in total area planted during the period of linear growth in fertilizer consumption (1961 to 1974). The relatively flat area planted from about 1961 to about 1972 suggests somewhat stable government programs in agriculture during this period. However, at the beginning of the period of erratic fertilizer consumption a more direct relationship between area in production and fertilizer use develops. The effect of area in production on fertilizer use is much more apparent in this period than previously. The largest shifts in area planted were in 1983 with the PIK (Payment in Kind) program and again from 1986 to 1987 with the C R P (Conservation Reserve Program). These government programs in turn had a substantial impact on N + P 0 + K 0 fertilizer use. Since the C R P program there has been relatively little change in area planted and in inorganic nutrient consumption. 2

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The impacts of the index of prices paid by farmers for fertilizer and the index of prices paid to farmers for crops on fertilizer consumption are shown in Figures 3 and 4. During the period of linear increased in fertilizer use (1961 to 1974) both crop and fertilizer prices were relatively stable. The stability in these factors and in crop acres during this period suggest a time of greater sense of security and confidence on the part of farmers to predict changes in factors affecting their operations (e.g., crop price, fertilizer price, and government programs). However, in the early to mid 1970s dramatic swings in both price indexes and consequently in fertilizer consumption were experienced. Factors

In Environmental Impact of Fertilizer on Soil and Water; Hall, William L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.


Figure 1. Consumption ο/Ν+Ρ2θ$+Κ2θ fertilizer in the U.S. from 1961 to 2000 (data source: USDA/ERS, 2000).



Figure 2. Area planted versus N+P2O5+K2O fertilizer use in the U.S. from 1961 to 2000 (data source for area planted: USDA/NASS, 2001. Historic Track Records, May 2001).


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Year Figure 3. Index offertilizer price paid by farmers versus N+P2O5+K2O fertilizer use in the U.S. from 1961 to 2000 (data source for price index: for 1961 to 1991, USDA/ERS, 1994. for 1992 to 2000, USDA/NASS, 2001).

Oil embargo and Price decontrol

Fertilizer use (N+P205+K20) Fertilizer price index



9SI In Environmental Impact of Fertilizer on Soil and Water; Hall, William L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.

157 such as the oil embargo and fertilizer price decontrol of 1973 and another oil embargo in 1979 dramatically affected fertilizer price. In the early 1990s the method of calculating both indexes was changed, therefore the peaks from the early 1990s forward are not on the same scale as those in previous years.


Nutrient removal/use ratio One way to gauge nutrient use is to consider it relative to nutrient removal. A n attempt to estimate yearly national Ρ and Κ removal/use ratio was made using production data from 18 crops in the U S . From these production data total nutrient removal was estimated for each of 40 years from 1961 to 2000. The 18 crops represented an average of 98 percent of acres harvested. Therefore, practically all Ρ and Κ removal nationwide was taken into account. Assumptions were made concerning the amount of Ρ and Κ removed per unit of production for each crop. The yearly inorganic nutrient use data was the same as was used in Figure 1. Figure 5 shows the estimated national removal/use ratio for both Ρ and Κ from 1961 to 2000. During the time of linear increase in fertilizer consumption (1961 to 1974) the ratios of removal/use declined for both Ρ and K , however during the period of erratic consumption (1974 to 1986) the ratios began to turn upward and have been steadily increasing since. This agrees with trends in yield of major crops and total Ρ and Κ use. Over the entire 40-year period yields of major crops have increased. Both Ρ and Κ consumption were increasing until around the mid 1970s. Phosphorus use in the U S began to flatten and even trend downward in the mid to late 1970s while Κ use began to flatten in the early 1980s. Therefore, since the mid 1970s to early 1980s the U S has been removing Ρ and Κ from its soils at a steadily increasing rate. In fact, considering the 1:1 line in Figure 5 the US has been in a depletion mode for soil Κ over the entire 40 years and has been depleting soil Ρ since the early 1980s. The removal/use ratios in Figure 5 do not take into account organic nutrient use. However, only a small percentage of cropland actually receives nutrients from manure. For the four major U S crops, the average percent of acres receiving manure from 1990 to 1997 was 17 for corn, 6 for soybeans, 4 for cotton, and 3 for wheat (USDA/ERS, 2000). Therefore, the increasing rate of depletion of soil Ρ and Κ across the nation applies to the majority of acres in production. The trends observed in Figure 5 are not sustainable. A s some point, i f these trends continue, a flattening and possibly a reduction in yields of major crops will be observed. While soils in many major production regions have tremendous capacity to buffer the effect of drawdown of soil Ρ and Κ on crop yield and performance, at some point even the most fertile soils will cease to produce increasing yields without adequate and balanced Ρ and Κ input. A case



Figure 5. Estimated total nutrient removal relative to inorganic nutrient use in the U.S. from 1961 to 2000 (removal values estimatedfrom yearly production data taken from: USDA/NASS, 2001. Historic Track Records, May 2001).

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in point involves the increased incidence of Κ deficiency in corn and soybean production in the Corn Belt and the North Central regions of the U S in recent years (Murrell, 2001). Another example is the increased occurrence of Κ deficiency in cotton throughout much of the cotton belt (Oosterhuis, 1994). These observations are likely a reflection of the increased removal relative to use of Ρ and K . A decline in removal/use ratios by increasing the use of Ρ and Κ relative to crop removal will avert the certain negative consequences of prolonged "mining" of these nutrients from US soils.

Conclusion Inorganic nutrient use in the U S is affected by many factors. The impact of some of these factors is more easily quantified than others. Fertilizer consumption in the US has dramatically increased over the past 40 years, however, this increase has not been consistent across years. From 1961 to about 1974 there was a period of linear increase in N+P+K consumption. From the mid 1970s until about 1986 there was a period of dramatic swings in fertilizer use. Finally, from 1986 to present consumption has been relatively flat. The effect of factors such as crop and fertilizer prices and area in production can be seen using historical records and current statistics. A n evaluation of estimated nutrient removal/use ratio has revealed that the U S is currently in the "mining" mode for both soil Ρ and K . According to this analysis the US is depleting Ρ and Κ from soils on a national basis at an increasing rate each year. Over the 40-year period evaluated, soil Κ has been in the draw-down mode every year, and Ρ has been in the depletion mode since the early 1980s. These trends cannot continue over the long term without consequences. These consequences will most likely come in the form of increased occurrence of Ρ and Κ deficiency symptoms and eventual flattening and/or reduction in average yields of major crops. To avoid these consequences the removal/use ratio for Ρ and Κ must be reduced. One method of achieving this, and thus avoiding eventual yield reductions, is to increase Ρ and Κ use relative to removal.

References Murrell, T.S. 2001. North Central Region Observations: Recognizing potassium deficiencies [Online]. Available at http://www.ppippic.org/ppiweb/usanc.nsf/$webindex/E536946145BEE7BF862569650064 5065 (verified 26 Sept. 2001)


160 Oosterhuis, K . M . 1994. Potassium nutrition of cotton in the U S A , with particular reference to foliar fertilization, p. 133-146. In G . A . Constable and N.W. Forrester (eds.) Challenging the Future: Proceedings of the World Cotton Research Conference-1. Brisbane, Australia. 1994.


U S D A / E R S . 1993. Agricultural Outlook Yearbook [Online]. Available at. http://usda.mannlib.cornell.edu/usda/ (verified 23 Sept. 2001). U S D A / E R S . 1994 Fertilizer Use and Price Statistics [Online]. Available at http://usda.mannlib.cornell.edu/ (verified 23 Sept. 2001). U S D A / E R S . 2000. Agricultural Resources and Environmental Indicators, 2000 [Online]. Available at http://www.ers.usda.gov/Emphases/Harmony/issues/arei2000/ (verified 23 Sept. 2001). U S D A / N A S S . 2001. Agricultural Prices 2000 Summary [Online]. Available at. http://usda.mannlib.cornell.edu/usda/ (verified 23 Sept. 2001). U S D A / N A S S . 2001. Historic Track Records [Online]. Available at http://www.usda.gov/nass/pubs/trackrec/track01d.htm (verified 23 Sept. 2001).


Inorganic Nutrient Use in the United States: Past and Present - ACS

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