Single-hole soil sampling for nitrogen in the potato hill

The nitrate distribution in the soil profile varies with fertilization and tillage practices in potato (Solanum tuberosum L.) production. Band-applied fertilizers localized near the seed at planting must diffuse through the bulk soil during the growing season. The hilling operation transforms soil surface into an undulating field landscape and redistributes the split-applied nitrogen fertilizers between the hill and the interrow. The soil sampling procedure during the growing season thus becomes extremely tedious when searching to quantify nitrate accumulation in the entire soil volume. The objective of this study was to assess seasonal nitrate accumulation in a soil volume from a single boring in the potato hill. An intensive sampling was conducted at four places in the 0- to 50-cm profile in potato fields receiving three rates of split-applied nitrogen (N) before hilling. Treatment and time effects provided a large range of nitrate concentrations throughout the soil profile. Nitrate content increased with N fertilization and organic-matter mineralization and decreased as a result of plant uptake and nitrate leaching. Averaged across the season, nitrate accumulation in the 0- to 50-cm profile represented 78% of that accumulated in the center of the hill on a per ha basis (r(2) = 0.90). A single boring in the center of the hill considerably reduced sampling time and cost and provided a fair estimate of seasonal nitrate accumulation in the 0- to 50-cm soil profile.