Both or organic and commercial fertilizers pose a potential risk to water quality. Proper planning and management will minimize the risk from both sources of crop nutrients. Traditional chemical fertilizers provide nutrients in forms that are highly water soluble so they will quickly move into the soil and be predictably available to the plant. Organic fertilizers typically will need to undergo some type of microbially mediated reaction and be converted to those same chemical forms to be available to the plant. Ultimately the plant takes up the nutrients in the chemical form whether they are applied as an organic or chemical fertilizer. Safety for the environment implies optimizing utilization of the applied nutrients by the crop and minimizing loss of the nutrients from the field. Losses occur from both sources with mismanagement. Mismanagement typically takes two forms, poor timing of application and applying too much fertilizer. Organic fertilizers typically fair better with a poorly timed application. There typically is less nutrient loss from poorly timed organic fertilizer applications because the organic form of the nutrient is typically less mobile and less prone to losses. The extra time needed to convert the organic form to the chemical form will slow losses from poorly timed applications. However, it is more difficult to predict the availability of organic nutrients so farmers are more prone to over-apply organic fertilizers potentially leading to greater losses. Another potential difference between chemical fertilizers and manure is uniformity. Quality control of commercial fertilizers is regulated in many states insuring fertilizers meet strict standards for uniformity and concentration. Some forms of manure are quite variable leading some farmers to apply more to insure all areas receive sufficent nutrients. This can lead to over-application in some areas of the field potentially leading to greater losses. One advantage of manure is the organic matter content. Organic matter improves soil quality including water infiltration thus reducing runoff from manured sites during precipitation events. For more information on the benefits of organic matter in manure, see the eXtension article "Environmental Benefits of Manure Application" Nutrient cycles in soil can be complex, particularly for nitrogen. What I have provided is a very general answer to which there are many exceptions and caveats. The forms and characteristics of fertilizers are quite variable for both chemical and organic fertilizers. The picture gets even more complicated when we also consider some of the treatments that are being added to chemical fertilizers to promote slow release similar to an organic fertilizer. And some organic fertilizers convert to chemical forms so quickly in soils to seem more like a chemical then an organic fertilizer. Some resources that detail some of the recommended practices for fertilizers all types are listed below: http://extension.missouri.edu/explorepdf/agguides/soils/g09221.pdf http://extension.missouri.edu/explorepdf/agguides/soils/g09220.pdf http://extension.missouri.edu/explorepdf/agguides/soils/g09218.pdf http://extension.missouri.edu/explorepdf/agguides/pests/ipm1027.pdf "http://extension.missouri.edu/explorepdf/regpubs/ncr187.pdf Dr. John Lory University of Missouri

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