Nitrogen Use Efficiency and Potato Yield with Polymer Coated Urea.

Potato (Solanum tuberosum L.) requires a steady yet not excessive nitrogen (N) supply for maximum tuber size, yield, and solids while minimizing internal and external defects. Growers typically apply most N through fertigation to maximize production. However, this practice of fertigation is more costly and labor intensive than dry broadcast application. Polymer coated urea (PCU), a controlled release N fertilizer, is a possible alternative to this grower’s standard practice. Environmentally Smart Nitrogen (developed by Agrium Advanced Technologies) is a temperature controlled PCU designed to meet plant N demands in a timely and effective manner. Increased N use efficiency of potatoes improves tuber yield and quality, and decreases N loss from leaching, volatilization, and denitrification. The objectives of this study were to determine the effects of PCU on yield and quality of Russet Burbank potatoes grown in Southeastern Idaho. Nitrogen was applied at various levels of agronomic recommended rates. There were three methods of application; (1) urea at emergence, (2) PCU at emergence, (3) split urea with half applied at emergence and the remaining amount applied in three in-season applications. Results of the study showed significant increases in US no.1, marketable, total yields, and crop value for PCU treatments over other treatments. Post-harvest soil analyses showed that nitrate levels in and below the rooting zone were reduced for PCU as compared to urea. The optimum rate of 67% of recommended PCU (based on net returns) had 5 Mg ha^-1 increase in the US no.1 tubers, and 62 kg ha^-1 less nitrate-N in the subsoil, as compared to the grower’s standard practice at the full rate. These results suggest that temperature controlled diffusion PCU use is an agronomic and environmentally superior management practice.