Author
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Vadas, Peter |
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Jokela, William |
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Franklin, Dorcas |
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Endale, Dinku |
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Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/31/2011 Publication Date: 7/25/2011 Citation: Vadas, P.A., Jokela, W.E., Franklin, D.H., Endale, D.M. 2011. The effect of rain and runoff when assessing timing of manure application and dissolved phosphorus loss in runoff. Journal of the American Water Resources Association. 47(4):877-886. Interpretive Summary: Non-point source pollution of fresh waters by agricultural phosphorus can limit water use for drinking, recreation, and industry. One pathway of phosphorus loss is surface runoff, to which surface-applied manure can contribute. Increased time between manure application and the first rain-runoff event can reduce runoff phosphorus loss. Studies documenting such a decrease in runoff phosphorus often attribute the decrease to adsorption of manure phosphorus by soil, but this may not fully consider the effect of storm hydrology on runoff phosphorus. Since it is difficult to control real-life rain and runoff events, we ran a recently developed manure phosphorus runoff model with data from eight published studies and found the model successfully simulated the experimental conditions and predicted runoff phosphorus loss. Model results suggest soil adsorption of manure phosphorus is not a mechanism that will consistently decrease manure phosphorus loss in runoff. Rather, simulated results suggest that, regardless of when the first rain-runoff event occurs, manure phosphorus loss will be a function of storm hydrology, specifically the amount of rain that falls and the runoff-to-rain ratio. When drying conditions occur after manure application, changes in storm hydrology can decrease runoff phosphorus, but this may not happen when drying does not occur. Thus, our model suggests increasing the time between manure application and the first rain-runoff may not always decrease runoff phosphorus loss. This information can help producers understand the mechanisms controlling manure phosphorus loss in runoff, which can, in turn, help them decrease negative environmental impacts of their manure applications. Technical Abstract: Non-point source pollution of fresh waters by agricultural P can limit water use for drinking, recreation, and industry. One pathway of P transport is surface runoff, to which surface-applied manure can contribute. Increasing the time between manure application and the first rain-runoff event has been proposed as a practice to reduce runoff P loss. Few studies have specifically investigated this aspect of manure P loss in runoff, with mixed results. Studies documenting a decrease in runoff P with time after application often attribute the decrease to adsorption of manure P by soil, but may not fully consider the effect of storm hydrology on runoff P. We ran a recently developed manure P runoff model with data from eight published studies that investigated the effect of time after manure application on runoff P. Results show the model successfully simulated the experimental conditions in the eight studies and predicted runoff P loss. Given the model structure, successful simulations suggest interaction of soil and surface-applied manure and subsequent soil adsorption of manure P is not a mechanism that will consistently and significantly decrease manure P availability to runoff. Rather, results suggest that regardless of when the first rain-runoff event occurs, manure P loss in runoff will be a function of storm hydrology, specifically the amount of rain that falls and the runoff-to-rain ratio. When drying conditions occur after manure application, storm hydrology changes can result in decreased runoff P, but this may not happen under conditions when drying does not occur. Thus, increasing the time between manure application and the first rain-runoff may not always decrease runoff P loss. |
