Residual Soil Nitrate and Potato Yield with Polymer Coated Urea (ESN).

Potato (Solanum tuberosum L.) requires steady, but not excessive, nitrogen (N) supply for maximum tuber yield, size, and solids, as well as minimal internal and external defects. Although more costly and labor intensive than dry broadcast applications, growers typically apply the majority of N through the irrigation water to maximize production. A controlled release N fertilizer, in the form of polymer-coated urea (PCU), is a possible alternative to this grower's standard practice. A newly formulated PCU may meet plant demand in a timely and efficient manner through temperature-controlled release of N into the soil solution. This improved efficiency could increase yield and tuber quality, prevent excess N loss from leaching and denitrification, and allow a more convenient and less labor-intensive fertilization system. The objectives of this study are to determine the effects of PCU on the yield and quality of Russet Burbank potatoes grown in Southeast Idaho during 2006-2007. Nitrogen was applied at four rates (33, 67, 100, or 133% of recommended) with three methods of application, namely: 1) urea at emergence, 2) PCU at emergence, and 3) split urea with half applied at emergence and the remaining applied in three in-season applications. Results showed significant increases in US No. 1, marketable, and total yield, as well as increases in crop value for PCU treatments over the other treatments. Post harvest soil analyses showed that nitrate levels in and below the rooting zone were reduced for PCU as compared to uncoated urea. The optimum rate of 67% PCU (based on net returns) had 5 Mg ha-1 increase in US No. 1 tubers and 62 kg ha-1 less nitrate-nitrogen in the subsoil, as compared to the grower’s standard practice at the full rate. These results suggest that this revised approach is an environmental and agronomic best management practice.