Using crop reflectance to determine sidedress N rate in potato saves N and maintains yield

A low basal N application combined with in-season adjustment of the sidedress N rate has been proposed as a means to save N in growing potato (Solanum tuberosum L.). We hypothesize that a measurement of canopy reflectance provides information which can be used to adjust sidedress N rate. The objective of our work was to develop and test a canopy reflectance-based N sidedress system for potato in humid climates. In four years of experiments with ware potato on a sandy soil it was determined that the reflectance index WDVI correlates well with N uptake, that sidedress N should be applied at around the time of canopy closing, and that the sidedress N rate should be calculated as the difference between a (fixed) desired N uptake and a reflectance-based measurement of N uptake. The calculated N saving in these experiments was between 10 and 109 (average 56) kg N ha−1. The reflectance-based N sidedress system was tested at an additional two locations, with ware potatoes on a loamy soil and with starch potatoes on a sandy soil, in two further years of experiments. N saving in these experiments was between 8 and 88 (average 44) kg N ha−1. In both sets of experiments, yields with the sidedress system were generally at the same level as yields obtained with recommended N rates (basal N only). We conclude that the reflectance-based sidedress N system allows saving of N while maintaining yield.

► Canopy reflectance of potato (Solanum tuberosum L.) correlates well with N uptake.
► Insufficiency of N can be detected with a measurement of canopy reflectance.
► Sidedress N at around the time of canopy closure is timely to maintain yield.
► 44 kg N ha−1 saved on average with canopy reflectance-based N sidedress system.