Effect of Nitrogen Rate and Source On Nitrate Leaching Potential Under Potato Production.

Appropriate nitrogen (N) fertilization is essential to optimize potato yield and quality and to minimize environmental N losses. A combination of appropriate N rates and sources could be used to reach this goal. This study evaluated the effect of N fertilization on nitrate leaching potential under potato production using the two criteria: residual soil nitrate (RSN) and the soil solution nitrate (SWN) concentrations.The experiment was conducted in 2008 on an Orthic Humo-Ferric Podzol near Québec City, Canada using cultivar Russet Burbank. Treatments were four N rates (60, 120, 200 and 280 kg N ha^-1) for each of three sources of N [ammonium nitrate (AN), ammonium sulphate (AS) and a controlled-release N (CRF)] plus an unfertilized control. The CRF was applied 100% at planting and the AN and AS applied 40% at-planting and 60% at-hilling. Suction lysimeters were installed in all treatments except for 60 kg N ha^-1 to sample SWN at 18, 32, 44, 60, 74, 88, 100, 115, 115 130 days after planting (DAP). Soil was sampled to determine NO₃-N (0-0.9 m) at planting, at harvest, and in next spring.The SWN increase with N rates (N0<N120<N200<N280). At 18 DAP, the SWN followed the pattern AN>AS>CRF. At 32 DAP, the SWN followed the pattern AN, AS>CRF. At 44 DAP, the SWN of the CRF was lower than the AN, but was not different from the AS. These differences appeared even though all of the CRF was applied at planting. The low RSN found at harvest and in the next spring (1.3 and 2.5 kg NO₃-N ha^-1, respectively) demonstrates that RSN was not useful to evaluate nitrate leaching potential at this sandy site whereas the SWN highlighted the high potential for in-season leaching. The CRF was less susceptible to leaching which is advantageous for potato cultivated on sandy soils.