Can foliar urea reduce nitrogen losses from potato production in Atlantic Canada?

In recent years it has become increasingly popular for potato producers in Atlantic Canada to include urea in the foliar applications of fungicides. Producers believe this practice sustains their potato crop through periods of water stress and allows for more rapid recovery following a precipitation event. This urea application is not considered as part of their nitrogen (N) fertility program and is applied in addition to the recommended rates of N fertilizer at planting. This project examines the potential to reduce the amount of N fertilizer added at planting in situations where foliar urea will be applied to the crop. The project evaluates whether using in-season foliar urea in combination with reduced N fertilizer rates at planting is an effective best management practice for sustaining potato yields, improving N use efficiency, and reducing nitrous oxide emissions and nitrate leaching.

An experiment at the Research Station in Harrington, Prince Edward Island, was conducted from 2013 through 2015. The treatments included five rates of N fertilizer application at planting (0, 120, 150, 180, 240 kg N/ha) as well as addition of 30 kg N/ha of foliar-applied urea on the 120 and 150 kg N/ha treatments. Marketable yield, growing season nitrous oxide emissions, soil nitrate concentration and nitrate flux (ion exchange membranes) were measured during the growing season.

Over the three years of the study, there was no yield benefit to N rates higher than 120 kg/ha, and application of foliar urea did not further increase yields. Nitrous oxide emissions were much higher in 2014 than in the other two years. In 2014, fertilizer-induced emissions of N₂O-N averaged 1.7% of the N applied, which was 4 times higher than in 2015 and 12 times higher than in 2013. There were no significant differences among N fertilizer application rates applied (other than compared to the zero rate check) and the application of foliar urea also had no effect on nitrous oxide emissions. Over the three years of the study, variation in nitrate adsorbed on ion exchange membranes (IEMS) explained 70% of the variation in nitrous oxide emissions. Therefore the use of IEMs might be a useful proxy measure for nitrous oxide emission.