Organic Soil Amendments for Sustainable Agriculture: Organic Sources of Nitrogen, Phosphorus, and Potassium

Sustainable agriculture, which is characterized by farming profitably while minimizing damage to the environment, is not easy to practice. “Conventional” agriculture in the USA is commonly considered to involve practices that have potential to damage the environment. These include tilling the soil excessively, overapplying readily soluble inorganic fertilizers (“chemical fertilizers”), and overapplying pest-control formulations (herbicides, insecticides, fungicides, etc.). “Sustainable” agriculture attempts to find alternatives to such practices, alternatives that are economically feasible but have less potential to cause environmental damage. Switching from “conventional” to “sustainable” agriculture involves more than just simple substitutions, such as replacing an insecticide with a predator insect or replacing potassium chloride fertilizer with greensand. Because it attempts to be more “in tune with nature” than conventional agriculture, sustainable agriculture requires more information about environmental characteristics and the environmental impacts of agricultural practices. To the extent that agriculture incorporates environmental considerations, it becomes more complex and information-intensive, and it is considered to require greater levels of management effort and skill. For example, cultural and biological pest control requires detailed information about a pest’s life cycle and economic threshold levels of infestation of the crop. Similarly, using chicken manure to replace urea as an N source requires knowledge about the release pattern of organic N from the manure and synchronization of that release into the soil with the Ndemand pattern of the crop. Adequate levels of soil fertility and plant nutrients are important to farming, whether the practices are considered “conventional” or “sustainable.” A 1987 survey (WSARE 1995) showed that half of the farmers attempting to practice “sustainable agriculture” nationwide have experienced crop nutrient deficiencies. Although sustainable farming is often a much broader concept than “organic” farming, sustainable farming also emphasizes use of organic materials as soil amendments and sources of plant nutrients.