Much of the research referenced here on the NutrientStar website was completed on small-plot trials. The majority of studies did not report sufficient information about environmental conditions and practices to enable a full assessment of the nutrient use efficiency (NUE) benefits possible from the use of each product. Consequently, NutrientStar reports results that suggest the effectiveness of the products based on yield only.

The intent of the NutrientStar program is to assess whether nitrogen stabilizers and decision support tools improve NUE. However, few of the trials applied more than one nitrogen rate, which prevented the calculation of NUE. NutrientStar also attempted to analyze the results of trials based on rainfall, but this was not possible because few of the trials reported daily rainfall before or after nitrogen application. Thus, yield results were averaged across all trials.

NutrientStar would be better able to assess the conditions under which assessed products might be effective as nitrification inhibitors and/or urea stabilizers if rainfall data is provided. When sufficient rainfall occurs in the 30 days after application to leach nitrate from the root zone, this would greatly increase the chance of products improving NUE as nitrification inhibitors. And when little to no rainfall occurs for two or more days after application, this greatly enhances the chances of urea stabilizers improving NUE. Therefore, an assessment including rainfall data could separate the trials into two or more categories, emphasizing the cases where sufficient rainfall occurred and where little or no rainfall occurred.

The NutrientStar program is committed to promulgating common standards for research and requirements for the minimum data required to allow products and tools to be fully assessed for their ability to improve NUE. Information about protocols required to fully assess products and tools is available here (PDF).