Joseph D. Cornell currently is a Postdoctoral Research Associate at Idaho State University where he is the Ecologist/Applied Mathematician for the Sanak Island Biocomplexity Project.Joseph studied with Dr. Charles Hall at the State University of New York, College of Environmental Science and Forestry (SUNY ESF) in Syracuse, New York where he received his PhD in Systems Ecology in 2003.
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Introduction
Fertilizers are human-made and natural products most often applied to soil to increase and maintain agricultural production. The practice of using natural fertilizers, particularly the feces and urine of humans and livestock, is probably as old as agriculture itself and may have developed as prehistoric humans practicing hunting and gathering noticed that not only did food plants grow where they had previously left food remains, but that those areas enriched with excrement produced more lush vegetation a and greater abundance of fruits and seeds.
Natural Fertilizers
Natural fertilizers include manure from livestock, post-harvest crop residues, “green manure” from surrounding fields and forests, composted plant and animal remains, and even human excrement. One of the major benefits of using these natural fertilizers is that often nutrients and organic matter are returned to the same fields from which they were previously harvested as food or fodder.
Another major benefit of using natural fertilizers is to convert what would often be a noxious agricultural by-product into a relatively inexpensive agricultural input. The economic return can therefore be two-fold; reduced costs of waste disposal and reduced costs of agricultural inputs. In rural areas which lack proper waste treatment and disposal facilities, the use of wastes as fertilizers is an elegant solution to both problems.
“Night Soil”
For example, the use of human wastes as fertilizer is still widely practiced in China where human “night soil” is collected and spread on local fields along with animal wastes. The use of human wastes as fertilizer however has a significant potential for transmitting human parasites and disease. Therefore, the historical use of human wastes as fertilizer greatly accounts for the culturally-derived practice in Chinese cuisine of cooking almost all vegetables.
Other Sources of Natural Fertilizer
A more common source of fertilizer is manure from livestock; primarily cattle, sheep, horses and other animals that feed on grasses and grains. In addition to manure from livestock, farmers throughout the world use “green manure” which is derived from vegetation cut from trees and other plants offsite, and then spread on fields. Often, green manure is obtained from various tree species and is considered a form of agroforestry. Post-harvest crop residues are also commonly plowed back into soils returning nutrients and organic matter to the soil. Other organic sources, most notably food wastes composed of plant and animal material may be converted into fertilizer by composting. Composting uses natural processes of decay and consumption by microorganisms and other creatures to break down the organic matter in food scraps creating a nutrient-rich mulch that can be added to soil or spread on fields and around plants.
In general, the use of natural fertilizers creates more tightly-linked and localized nutrient cycles. In contrast, the use of human-made fertilizers has steadily changed both the source of nutrients and the way that they cycle in (and out) of agricultural systems.