Identification of mechanisms influencing nutrient transport on upland areas

Authors: Gilley, John

Submitted to: ASABE Annual International Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/17/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: An exercise was conducted to identify the mechanisms influencing phosphorus (P) and nitrogen (N) transport on upland areas using previously reported nutrient transport and runoff information. The data which was examined was obtained from field rainfall simulation studies evaluating the effects of varying runoff rates on P and N transport from either 2 or 4 m long plots located on cropland areas or beef cattle feedlots. In those studies, inflow was added to the top of experimental plots in four successive increments to simulate runoff rates occurring at greater downslope distances. Runoff rates on the sites where beef cattle manure or swine slurry was applied ranged from 2.20 to 22.9 L min-1 and maximum equivalent downslope distances varied from 22 to 108 m. The observations resulting from the field studies were first summarized. These observations resulted in the following question: What are the mechanisms influencing nutrient transport on upland areas? Hypotheses were then developed to answer this question. Nutrient transport on upland areas was thought to occur under two scenarios. For scenario 1, nutrient transport was influenced by: The quantity of P or N that was released by soil, manure, or slurry at a particular runoff rate and the amount of overland flow available to transport the released nutrients. For scenario 1, nutrient transport rates increased in a linear fashion with runoff rate. Under scenario 2, the maximum rate at which soil or manure can release P to overland flow had been reached and the P transport rate – runoff rate relation changed from a linear function to a constant value. Once the point of inflection occurred, P transport rates were constant.

Technical Abstract: An exercise was conducted to identify the mechanisms influencing phosphorus (P) and nitrogen (N) transport on upland areas using previously reported nutrient transport and runoff information. The data which was examined was obtained from field rainfall simulation studies evaluating the effects of varying runoff rates on P and N transport from either 2 or 4 m long plots located on cropland areas or beef cattle feedlots. In those studies, inflow was added to the top of experimental plots in four successive increments to simulate runoff rates occurring at greater downslope distances. Runoff rates on the sites where beef cattle manure or swine slurry was applied ranged from 2.20 to 22.9 L min-1 and maximum equivalent downslope distances varied from 22 to 108 m. The observations resulting from the field studies were first summarized. These observations resulted in the following question: What are the mechanisms influencing nutrient transport on upland areas? Hypotheses were then developed to answer this question. Nutrient transport on upland areas was thought to occur under two scenarios. For scenario 1, nutrient transport was influenced by: The quantity of P or N that was released by soil, manure, or slurry at a particular runoff rate and the amount of overland flow available to transport the released nutrients. For scenario 1, nutrient transport rates increased in a linear fashion with runoff rate. Under scenario 2, the maximum rate at which soil or manure can release P to overland flow had been reached and the P transport rate – runoff rate relation changed from a linear function to a constant value. Once the point of inflection occurred, P transport rates were constant.