Nitrogen uptake efficiency by white cedar under different irrigation and fertilisation strategies on a sandy soil: model calculations

A combined conifer growth-soil water balance model was extended and parameterised to simulate the nitrogen (N) dynamics of a common nursery stock system [i.e., white cedar (Thuja occidentalis) grown for 2 years on a sandy soil]. The model was used to explore the effects on N uptake efficiency (Naue), N application rate (Nappl), and N loss (Nloss) of three irrigation strategies combined with a single, or a split fertiliser application at a recommended rate, without or with a correction for the mineral N content of the topsoil (Nmin,ts). Irrigation strategies used were: no irrigation, daily drip irrigation, or drip irrigation triggered by a pressure-head threshold value. Simulated N dynamics were in agreement with the measurements, but discrepancies were found between measured and simulated Nmin,ts. The simulated Naue was 29% in the first growing season, and 68% in the second growing season. Correcting for Nmin,ts reduced Nappl, especially in the non-irrigated strategy and in the threshold-irrigated strategy. Simulated Nloss during the 2-year growing period ranged from 79 kg N ha-1 for the non-irrigated strategy with a split-application, corrected for Nmin,ts, to 248 kg N ha-1 for the daily irrigated strategy with a split application. Simulated N concentrations in the percolating soil solution at a depth of 1 m exceeded the EU limit of 11.3 mg NO3-N l-1 in almost all simulations. In conclusion, additional measures are necessary to improve Naue, especially in the year of planting, to be able to reduce Nloss and meet the EU nitrate-N limit