Assessing the Effects of Conservation Practices and Fertilizer Application Methods on Nitrogen and Phosphorus Loss from Farm Fields – A Meta Analysis

This project aims to use two tools of meta-analysis--propensity score and multilevel modeling--to quantify P loss reductions arising from soil and water conservation practices. It uses the MANAGE database, which provides field scale information on nutrient loss from agricultural land. Applied to the 2007 version of the MANAGE database, the two analytical tools each found that conservation practices (one or more of waterways, contour farming, terraces, and buffers) reduced total P loss by approximately 70%. In addition, they found that the conservation practices reduced the incremental increase in total P loss per unit increase in fertilizer application. These preliminary results have been summarized in a manuscript--essentially, a methods paper--submitted to the Journal of American Water Resources Association (Qian and Hamel, 2015).

Next steps include analysis of the 2014 version of the MANAGE database, which includes 65 peer-reviewed publications (ten more than the 2007 version) covering 1,980 watershed years. More than half of the observations in the database come from three states: Oklahoma, Texas and Ohio, with the remainder primarily from midwestern and southern states, California and Canada. A graduate student is reviewing the 65 publications for further background information of specific importance to elucidating the effect of source, rate, time, and placement of fertilizer application. The final analysis, likely to be available by mid-2015, aims to determine the influence of crop type, region, season, soil, and precipitation on conservation and fertilizer application practice effectiveness in reducing losses of total N and P.