Petiole sap NO3-N testing as a method for monitoring nitrogen nutrition of potato crops
Petiole sap NO3-N concentrations were tested as a means for monitoring crop nitrogen (N) status and N fertilizer responses in potatoes. An ion specific electrode was used to monitor sap NO3-N concentrations of three varieties of potatoes grown with differing amounts of N fertilizer in 1993–1995. Plots provided with varying amounts of fertilizer N applied prior to planting or as a split application were sampled on six occasions through the growing season. Sap NO3-N levels were positively correlated with petiole dry matter NO3-N levels. Petiole sap NO3-N levels reflected rates and timing of N fertilizer application. Sap NO3-N levels in the three cultivars showed similar changes with time after planting and increasing N fertilizer rates. However, sap NO3-N levels measured under a particular set of conditions were unique for each cultivar. The correlation between yields and sap NO3-N levels varied with the sampling date and cultivar. Recommendations were developed for critical sap NO3-N concentrations at various stages in the development of the three cultivars. Key words: Ion specific electrode, nitrate, petiole, nitrogen, tissue testing, Solanum tuberosum