Potato response to a polymer-coated urea on an irrigated, coarse-textured soil

Controlled release fertilizers, especially polymer-coated urea (PCU), have been shown to reduce nitrate (NO₃) leaching while maintaining potato (Solanum tuberosum L.) yields, but cost has been prohibitive. A new type of PCU (Environmentally Smart Nitrogen, Agrium, Inc., Calgary, AB) is less costly than previous PCUs, but its effectiveness on potato production has not been extensively studied. A 2-yr field study was conducted on loamy sand to evaluate the effect of this PCU on Russet Burbank tuber yield and to determine if it is economically comparable to soluble N sources. Several N rates of PCU applied at emergence were compared with two split applications of soluble N at equivalent rates. Additional treatments examined N application timing of PCU and a fertigation simulation with urea/ammonium nitrate. Petioles and midseason soil samples were collected to determine N status during the season. Overall, PCU and soluble N at equivalent N rates were found to have similar total and grade A yields and net monetary returns. The optimal N rate that resulted in maximum net returns was 251 and 236 kg N ha^-1 as soluble N and PCU, respectively. Petiole NO₃ concentrations were typically higher with soluble N early in the season and higher with PCU later in the season. Soil NO₃ determined in samples collected in late June was found to be a better predictor of yield and potential N need than those collected in mid- to late July. Overall, PCU may reduce or eliminate the need for split applications of N on coarse-textured soils.