Impact of flow path length and flow rate on phosphorus loss in simulated overland flow from a humic gleysol grassland soil.

In this overland flow simulation experiment, the relationships between flow path length, flow rate and the concentration of different P fractions were investigated. Overland flow was simulated using a 3 mx0.12 m laboratory flume. To remove the impact of rainfall on P lost in overland flow, simulated rainfall was not used during these experiments. Instead overland flow was generated by pumping water into the flume at the surface of the grass sod. The experimental setup allowed for the variation in flow path length and flow rate between and during experimental runs. The results demonstrated that an increase in flow path length caused an increase in Total Dissolved P (TDP), Dissolved Reactive P (DRP) and Total Reactive P (TRP) concentration in overland flow (p<0.01) while an increase in flow rate resulted in a decrease in the concentration of these P fractions in overland flow due to dilution (p<0.01). Total P (TP), Particulate P (PP) and Dissolved Organic P were not affected by the variables tested during this study. When flow path length was increased in conjunction with flow rate, there was an increase in TDP, DRP, and TRP concentrations despite the impact of greater dilution. The results indicate that variations in flow path length during a rainfall event may play a role in determining the concentration of dissolved P fractions in overland flow at field scale.

The impact of agricultural management practices on nutrient losses to water: data on the effects of soil drainage characteristics.

Against the background of increasing nutrient concentrations in Irish water bodies, this study set out to gain information on the potential of agricultural grassland to lose nutrients to water. Overland flow, flow from artificial subsurface drains and stream flow were gauged and sampled during heavy rainfall events. Dissolved reactive phosphorus (DRP), potassium (K), total ammonia (TA), and total oxidised nitrogen (TON) were measured in water samples. When the nutrient concentrations in water were examined in relation to the grassland management practices of the study catchments it emerged that soil P levels, the application of organic and inorganic fertilisers before heavy rainfall and the presence of grazing animals could all influence nutrient concentrations in surface and subsurface drainage water. Overall, the drainage characteristics of soil were found to have a considerable influence on the potential of land to lose nutrients to water.