Are Post-Sidedress Nitrogen Applications Necessary for Potato Following Leaching Events?.

Nitrogen (N) management on potato typically includes two in-season side-dress applications and either planned or un-planned post-sidedress applicaitons. However, it is most often these post-sidedress applications that lead to overapplicaton of N and reduce the overall N use efficiency of the system. Thus, the objective of this study was to determine the effects of the later N applications on potato growth, nitrogen status, and yield. A three year study was conducted at the University of Wisconsin-Agricultural Research Station in Hancock, WI. The experimental design was a randomized complete block split plot, with four replications. The whole plot factor was the planned application of N (224, 280, or 336 kg-N ha^-1) as ESN (applied once) or as a split application of ammonium sulfate (at emergence) and ammonium nitrate (at tuberization). The split plot factor was post-sidedress N application and included 0, 1, 2, or 3 additional applications of 34 kg-N ha^-1 applied in July and August. In 2012, across both fertilizer sources, there was no apparent need for supplemental N, with the additional N increasing above ground biomass, but not increasing yield. Additinally, there is some indication that additional N led to lower yields. These results indicate the need for a continous assessment of the value of rescue N applications in this region to improve decision making by the potato farmers in order to protect water quality.