Agri-Environmental Effect of N Fertilizer On Potato Production.

Appropriate N fertilization is essential to optimize potato yield and minimize environmental N losses. This study evaluated the effect of fertilization with three N sources on tuber yield and plant N uptake, and on the risk of nitrate leaching, for potatoes grown in sandy soils in Quebec, Canada. Risk of leaching was assessed using residual soil nitrate (RSN) and the soil solution nitrate (SWN) concentrations. Treatments were four N rates (60, 120, 200, and 280 kg N ha^-1) for each of three N sources [ammonium nitrate (AN), ammonium sulphate (AS) and a controlled-release N (CRN)] plus an unfertilized control. The CRN was applied 100% at planting and the AN and AS applied 40% at-planting and 60% at-hilling. SWN was sampled biweekly from planting to harvest (nine sampling periods referred to as SP1-SP9) via suction lysimeters. Soil was sampled (0-0.9 m) to determine NO₃-N at planting, at harvest, and in next spring. Growing season precipitation was much higher in 2008 (712 mm) than 2009 (406 mm). Tuber yield increased with N rates up to 200 kg N ha^-1, but was not affected by N source. Plant N uptake was reduced under the wet conditions in 2008 for AN and AS but not for CRN. Even though all CRN was applied at planting, SWN was lower for CRN than AN or AS for SP1-SP3 in 2008 and for SP1 in 2009. However from SP7-SP9 in 2009, the SWN was higher for CRN than AN and AS. The low RSN at harvest and in the next spring (6.5 and 9.9 kg NO₃-N ha^-1, respectively) demonstrates that RSN was not useful to evaluate nitrate leaching at this sandy site. The CRN may be more advantageous in increasing plant N uptake and reducing the risk of early season leaching in a rainy season like 2008.