Both organic and inorganic nutrient pools are important to the productivity, sustainability, and potential off-site environmental impacts associated with soil resource management. Organic carbon is that derived from plant, animal, and microbial material; and inorganic carbon is that present as minerals or salts. Soil nutrient management depends heavily on soil chemical, physical, and biological properties and processes; and environmental and management factors further influence nutrient cycling. In North America, soil organic matter has declined 30 to 60% in some soils since this land was first cultivated. Permanent removal of nutrients to support crop production and an insufficient nutrient release rate from mineral and organic sources has necessitated replacement of nutrients from concentrated fertilizer sources to increase and maintain adequate fertility and crop yields. Excessive application or low uptake efficiency of nutrients from concentrated inorganic fertilizers or renewable nutrient sources (e.g., animal manures, cover crops, or green manures) can result in the accumulation of nutrients in the soil. Nutrients not used by the plants may leach into groundwater or be transported in runoff or sediment to surface waters. In surface and groundwater, excessive concentrations of nutrients can make these water resources unacceptable for drinking, lead to nutrient enrichment known as eutrophication, sustain microorganisms from human or animal wastes, deplete the oxygen, or cause blooms of aquatic organisms that produce toxins. In soils with inherently low organic matter, maintaining adequate availability of all nutrients for crops is particularly difficult, especially where soils are dominated by complex exchange imbalances associated with acidity, salinity, sodicity or other chemical imbalances from secondary minerals.

In some production systems, chemical fertilizers can be a major expense, but in others it is a relatively small cost compared to other inputs. Uncertainty and a philosophy of fertilizer as insurance, coupled with historical experience, contributes to frequent fertilizer overuse. The ease of application and relative reliability and predictability of crop uptake of nitrogen and phosphorus from chemical fertilizers have decreased dependence on nitrogen-fixing crops and decomposition of manure or organic matter as nutrient resources. Fertilizer use-efficiency is commonly less than 50% in many agricultural systems, and application of excessive amounts of fertilizer contributes to agriculture being the largest nonpoint source of pollution to surface and groundwater. Economic utilization of renewable nutrient sources and poor nutrient use efficiency in agricultural systems are problems which must be addressed to reduce input costs and protect the environment.

Agricultural systems that efficiently utilize all nutrient resources; meet the food, feed, and fiber needs of society; and maintain or enhance the quality of our environment

To make agriculture an economically and environmentally sustainable enterprise by improving our understanding of nutrient cycling in agricultural settings; and by developing management practices that optimize nutrient availability, improve nutrient use efficiency, reduce reliance on nonrenewable nutrient sources, and reduce the potential for negative environmental impacts from all nutrient sources.

Table 1. ARS research locations conducting research contributing to specific problem areas within the Nutrient Management Component of the Soil Resource Management National Program.

State	Location	Problem Area
		Sustainable Systems	Fate and Transformation	On-site Retention	Soil Carbon
AL	Auburn	X			X
AR	Booneville	X		X	X
AR	Fayetteville		X	X
AZ	Phoenix				X
AZ	Tucson				X
CA	Davis
CA	Fresno
CA	Riverside		X	X
CA	Salinas
CO	Akron	X	X	X	X
CO	Ft. Collins	X	X	X	X
FL	Gainesville
FL	Miami			X
GA	Tifton		X	X
GA	Watkinsville	X	X		X
IA	Ames	X	X	X	X
ID	Kimberly		X	X	X
IL	Urbana
IN	West Lafayette		X		X
KS	Manhattan
LA	Baton Rouge			X
ME	Orono	X	X	X
MD	Beltsville	X	X	X	X
MN	Morris	X	X		X
MN	St. Paul			X	X
MO	Columbia
MS	Oxford
MS	Stoneville
MT	Sidney		X
ND	Mandan	X	X	X	X
NE	Lincoln	X	X	X	X
NM	Las Cruces				X
NY	Ithaca		X
OH	Columbus
OH	Coshocton	X	X	X	X
OK	El Reno		X
OK	Stillwater
OR	Corvallis	X		X
OR	Pendleton	X	X		X
PA	University Park	X	X	X	X
PA	Wyndmoor
SC	Florence		X	X	X
SD	Brookings	X			X
TX	Bushland
TX	Lubbock
TX	Temple		X	X	X
TX	Weslaco
WA	Prosser		X	X	X
WA	Pullman	X	X		X
WA	Wenatchee		X	X
WI	Madison		X	X
WV	Beaver		X	X	X
WV	Kearneysville
WY	Cheyenne	X	X		X