Phosphorus fertilization, soil stratification and potential water quality impacts

Authors: Smith, Douglas; Huang, Chi Hua; Haney, Richard

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2016
Publication Date: 9/1/2017
Publication URL: http://handle.nal.usda.gov/10113/5852154
Citation: Smith, D.R., Huang, C., Haney, R.L. 2017. Phosphorus fertilization, soil stratification and potential water quality impacts. Journal of Soil and Water Conservation. 72(5):417-424. https://doi.org/10.2489/jswc.72.5.417.
DOI: https://doi.org/10.2489/jswc.72.5.417

Interpretive Summary: The current phosphorus fertilization strategies, particularly in no-till management, are leading to phosphorus stratification near the surface. While this is not solely responsible increased soluble phosphorus loss to Lake Erie, it is likely one contributing factor. We examined four potential strategies to minimize phosphorus loss from a corn-soybean rotation: 1) applying fertilizers annually instead of once during the rotation; 2) using alternate P sources commercially available in the region; 3) incorporating fertilizers; and 4) using cover crops to retain P. Three years into this study, none of the fertilization strategies appreciably diminished P stratification. The current commercially available dry phosphorus fertilizer sources in the region will not decrease soluble phosphorus loading. Cover crops will not decrease soluble phosphorus loading. Further, even though results from this study inconsistently showed that cover crops may increase phosphorus loading (i.e., with the high phosphorus rate), evidence from other studies indicate that cover crops may exacerbate soluble phosphorus loading problems. Thus cover crops may not be the go-to practice for resource managers where soluble phosphorus is the primary resource concern. The only practices that appear to improve soluble phosphorus loading in surface runoff was the incorporation of phosphorus and the use of liquid fertilizers. Incorporation of P fertilizers with tillage will likely result in greater erosion and total phosphorus losses, which must be taken into account with the relevant resource concerns by land managers and policy makers. We encourage the fertilizer industry to give strong consideration to use of less soluble P fertilizers or liquid fertilizers in sensitive watersheds, such as the Western Lake Erie Basin. Further, before firm recommendations can be made, other researchers are encouraged to perform field experiments on the use of liquid fertilizers or lower solubility phosphorus fertilizers at the field scale to ensure they do not decrease surface runoff dissolved P loading while increasing dissolved P discharge through subsurface tile.

Technical Abstract: Water quality experts have suggested that no-till induces phosphorus stratification, which may exacerbate soluble P runoff from agricultural fields, leading to eutrophication. The objectives of this study were to explore P fertilization strategies on P stratification and P runoff from a corn-soybean rotation. Plots were established with 9 treatments, including unfertilized, diammonium phosphate (DAP) applications, monoammonium phosphate (MAP) applications, injecting fertilizer or tilling fertilizer in, and the use of cover crops. Insofar as possible, fertilizer applications were made at 56 kg P/ha every other year or 44 kg P/ha every year. There were no differences in SP or TP between fertilizer source (MAP vs. DAP) or fertilizer rate (annual vs. biennial). The highest SP concentrations observed where from the high fertilizer rate (56 kg P/ha applied every other year) applied to cover crops. This may suggest cover crops are not the ideal practice to decrease SP losses from agricultural fields. Tilling fertilizer in reduced SP, but increased erosion and could potentially increase TP loss. Injecting liquid fertilizer (Polyphosphate) at the time of planting resulted in lower SP and TP loads than surface applied fertilizers. We encourage other researchers to confirm these results at the field-to-watershed scale, to ensure there are not unintended consequences of adopting this fertilization strategy. Further, fertilizer dealers, crop consultants and farmers should be encouraged to consider liquid fertilizer applications as one tool in the arsenal to minimize P losses from their fields.