Potato is sensible to nitrogen (N) and optimal N fertilization improve the tuber yield and its quality. Potato crop N response varies widely within fields. It is also well recognized that significant spatial and temporal variation in soil N availability occurs within crop fields. However, uniform application of N fertilizer is still the most common practice under potato production. Management zone (MZ) approach can help growers to achieve a part of this. The goal of the project is to compare the uniform N application to variable rate N application based on MZs in a potato field.

In 2019, in partnership with a producer located in Kensington, Prince Edward Island, Canada, the spatial variability of the apparent electrical conductivity (ECa) and topography on a 8.6 ha field was addressed with soil sensing systems and the soil was sampled using an intensive grid of 30 m X 30 m. Then MZs were delineated with the ISODATA function of ArcGIS utilizing the ECa and the 2017 tuber yield data. Three MZs were judged optimal. The N fertilization strategy that the grower was welling to try was the variable N rate application (VRA) at pre-planting using a slow released N fertilizer (Agrotain, urease inhibitor). Three N rates were associated with the three MZs (referred as MZ₁, MZ₂, and MZ₃). When the highest ECa and yield were observed, the highest N rate was applied in the MZ₃ and where the lowest ECa and yield were observed, the lowest N rate was applied in the MZ₁. The pre-planting variable N rate applied in MZ₁, MZ₂, and MZ₃ was 20, 40, and 60 lbs acre^-1, respectively. The MZ₂ and the uniform treatment received the middle rate of 40 lbs N acre^-1. The rest of total N rate was uniformly applied at planting using urea at 110 lbs N acre^-1. The potato cultivar was Prospect. Experimental strip-treatments (30 rows X length of the field) were distributed in a RCBD with four replicates and across all the MZs. Before planting, the location of 35 sampling points (SP) were selected to represent all situations for the three MZs, treatments and the N rates. Nitrate and ammonium content before planting, in-season and at harvest were determined at the 35 SP. Nitrate petiole content and 3 m harvest tests were also done at the same SP.

Preliminary results indicated: 1- a significant correlation (r= 0.71) between the 3 m harvest test and the tuber yield monitor data; 2- increasing N rates (total N rate 130 vs. 150 vs. 170 lbs N acre^-1) significantly increased linearly the tuber yield monitor data; 3- the tuber yield monitor data in the VRA treatment at the N rate = 150 lbs acre^-1 was significantly higher than the one observed in the uniform treatment; 4- no effect of MZs or interaction between MZs and treatments were observed for the tuber specific weight. Additional results regarding petiole nitrate and soil nitrate and ammonium concentrations will also be presented.