Comparison of Asn-26 and Urea Fertilizers in Potato Production in Southeast Idaho.

Ammonium sulfate nitrate (ASN) fertilizer was used in 2014 to supply nitrogen (N) to a potato crop in a study conducted at the Brigham Young University – Idaho Agricultural Learning Laboratory, Rexburg, ID. Urea fertilizer was used in the study to provide a base comparison for the ASN. The objective of this study was to determine the effect of ASN fertilizer on Russet Burbank and Norkotah potato yield and tuber quality. The treatments included a control (0 kg additional N per acre) and three application levels of each fertilizer at 78, 157, and 235 kg N ha-1. The fertilizer was broadcast split applied with 20% applied immediately prior to planting on May 12, 20% applied each on July 10, 23, and 30, with remaining 20% applied August 15. Each plot was 12.2 m long with four rows, spaced 91 cm apart. The middle 6.1 m of the center two rows of each plot was mechanically harvested with tubers weighed to determine yield. The tubers were sorted and gravimetrically measured into weight/quality classifications.  A direct comparison of ASN to urea showed no differences between these two fertilizers at any N rate or when combined across rates, showing that ASN was equivalent to the traditional urea N source.  The ASN resulted in greater Norkotah yields than the control for the 170-285 and the > 400 g size at the 157 and the 78 kg N ha^-1 rates, respectively. However, only the urea at the 235 kg N ha^-1 rate resulted in greater US No. 1, Marketable, and Total yields than the control for both Russet Norkotah and Russet Burbank.  Multivariate analysis of variance was used to determine differences between treatments and Tukey’s mean difference test was used to determine differences between treatment and N source means at the alpha level of 0.05.   Although not statistically significant, an examination of the data suggests that the ASN reached its peak response with less N for the Norkotah than urea. For the Russet Burbank variety, it seemed that the response peaked at the low rate (78 kg ASN ha^-1 or urea + 112 kg ha^-1 base rate applied as urea = 190 kg N ha^-1) for both N sources. These finding may be a result of ASN containing S or ammonia volatilization of urea.