The application of manure to soybeans has been identified as a potential environmental threat due to the fact that soybeans are legumes and do not require nitrogen supplementation. Thus, the application of animal manures may pose a risk to water quality. Our goal in this research project was to ascertain the actual risk of nitrogen loss by measuring nitrate-N accumulation in the soil and plant tissues throughout the growing season after a swine manure application (and corresponding commercial fertilizer treatments) and determine whether or not these applications present an environmental concern. Additionally, we were attempting to determine some potential guidelines in recommending a safe application rate of manure N. Our results indicate that application of manure N or commercial N at reasonable agronomic rates (<120 pounds of N per acre) should be of little environmental concern. This is supported by a lack of nitrate-N accumulation in the top 12” of soil, and a typical increase in tissue N accumulation when supplemental N is provided. Soybeans will accumulate soil N when it is supplied by manure or synthetic commercial sources. Higher rates of N (>180 pounds N per acre) from either source may pose an environmental risk in terms of excess soil nitrate-N and therefore should be discouraged.