Establishing the Nitrogen Dilution Curve for Potato Cultivar Bintje in Belgium

The nitrogen nutrition index (NNI) is recognized as a reliable plant-based
method for diagnosing the crop nitrogen status (CNS). The NNI is based on the concept
of critical nitrogen (Nc) dilution curve describing the Nc concentration in the whole
plant as a function of the total crop biomass (W). The objectives of this study were (i) to
establish the specific potato Nc dilution curve for cv. Bintje under Belgian growing
conditions; (ii) to assess if the established curve for cv. Bintje could be used for cv.
Charlotte; (iii) to compare the established curve with the existing Nc potato curves; and
(iv) to assess the possibility of using the obtained Nc curve to evaluate the potato CNS
and to predict the final yield. Field experiments studying increasing nitrogen (N) rates
were conducted at different locations in Belgium for several years. Biomass N concentration
and W production were determined at different sampling dates, and the final
tuber yield was determined at harvest. At a sampling date, the Nc was determined by
selecting the data point from the treatment presenting the highest W. The NNI was
calculated as the ratio between the measured N concentration inWand the predicted Nc
according to the Nc dilution curve. The Nc curve (Nc (%) = 5.37 W−0.45) was
developed for potato for cv. Bintje under Belgian conditions matching also for cv.
Charlotte. The Belgian Nc curve presented similar values as the curves developed
previously in Scotland and the Netherlands. NNI was related to relative tuber yield
(ratio between the tuber yield obtained for a given N rate and the highest tuber yield
obtained among all N application rates). The Nc curve and the NNI adequately
identified situations of limiting and non-limiting N nutrition and could be used to
establish the potato CNS and to predict the final yield.