Here is a very interesting paper about increasing nitrogen from crops into the Suwannee River Basin and its springs (promoting algae growth), with actual data on how well best management practices (BMPs) are containing the runoff: Environmental Nitrogen Losses from Commercial Crop Production Systems in the Suwannee River Basin of Florida, by Rishi Prasad, George J. Hochmuth, PLOSOne, Published: December 1, 2016, http://dx.doi.org/10.1371/journal.pone.0167558
Fig 3. Comparison of A) environmental nitrogen losses (Nenvloss) from three crops (potato, sweet corn and silage corn) during four growing seasons (2010 to2013) and B) relationship between seasonal total N rates and environmental nitrogen losses at the study farm in the Middle Suwannee River Basin, Florida. Silage corn was not studied during 2013. Mean values of Nenvloss (represented by individual bars and their standard errors for the three crops) followed by different letters indicate significant difference at α = 0.05 level
The springs and the Suwannee river of northern Florida in Middle Suwanee River Basin (MSRB) are among several examples in this planet that have shown a temporal trend of increasing nitrate concentration primarily due to the impacts of non-point sources such as agriculture. The rate of nitrate increase in the river as documented by Ham and Hatzell (1996) was 0.02 mg N L-1 y-1. Best management practices (BMPs) for nutrients were adopted by the commercial farms in the MSRB region to reduce the amounts of pollutants entering the water bodies, however the effectiveness of BMPs remains a topic of interest and discussion among the researchers, environmental administrators and policy makers about the loads of nitrogen entering into groundwater and river systems. Through this study, an initiative was taken to estimate nitrogen losses into the environment from commercial production systems of row and vegetable crops that had adopted BMPs and were under a presumption of compliance with state water quality standards. Nitrogen mass budget was constructed by quantifying the N sources and sinks for three crops (potato (Solanum tuberosum L.), sweet corn (Zea mays L.) and silage corn (Zea mays L.)) over a four year period (2010—2013) on a large representative commercial farm in northern Florida. Fertilizer N was found to be the primary N input and represented 98.0 ± 1.4, 91.0 ± 13.9, 78.0 ± 17.3% of the total N input for potato, sweet corn, and silage corn, respectively. Average crop N uptake represented 55.5%, 60.5%, and 65.2% of the mean total input N whereas average mineral N left in top 0.3 m soil layer at harvest represented 9.1%, 4.5%, and 2.6% of the mean total input N. Mean environmental N losses represented 35.3%, 34.3%, and 32.7% of the mean total input N for potato, sweet corn, and silage corn, respectively. Nitrogen losses showed a linear trend with increase in N inputs. Although, there is no quick fix for controlling N losses from crop production in MSRB, the strategies to reduce N losses must focus on managing the crop residues, using recommended fertilizer rates, and avoiding late-season application of nitrogen.
Thanks to WWALS Science Committee Chair Tom Potter for pointing out this paper.
-jsq, John S. Quarterman, Suwannee RIVERKEEPER®
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