Nitrogen efficiency indices of potato in response to nitrogen doses estimated by algorithms and applied as top-dressing

The objective of this study was to evaluate the effect of N doses estimated by algorithms and applied as top-dressing on different nitrogen (N) efficiency indices in Asterix potatoes. Two experiments were installed in the field. The experiments were conducted in the randomized block design, in split-plot scheme, with four replicates, whose treatments, in the plots, were determined by five N doses in pre-planting and, in the subplots, by three criteria (algorithms evaluated) of top-dressing N. At 21 DAE (days after an emergency), the fourth fully developed potato leaf was evaluated with the SPAD (Soil Plant Analysis Development) chlorophyll meter. This reading was used as an indicator of the need for top dressing. In harvesting the tubers, the following variables were determined: N content in shoots and tubers, amounts of N absorbed by shoots, tubers and total N, harvest index, N use efficiency, N agronomic efficiency and physiological efficiency of N. The application criteria did not significantly influence the variables related to the content and amount of absorbed N, except for the N content of the tubers in the 2018 experiment. Of N absorbed by shoots, tubers and plants and the agronomic efficiency of N were significantly influenced by the N dose applied pre-planting. The agronomic efficiency was significantly influenced by the N dose estimated by the N cover recommendation criteria. The highest values obtained for the variables related to the content and amount of N absorbed were those under application of 200 to 300 kg ha(-1) of N.