Chlorophyll Meter for the Evaluation of Potato N Status

Here, we propose a new approach to determine the level of plant N nutrition, based on the relationship between chlorophyll meter (CM) readings and total biomass in potato plants. The objectives of this work were i) to determine the critical curve CM (CM_c) readings; ii) to establish the relationship between N nutrition index of CM (NNI_CM), and relative tuber yields (RY), and iii) to establish the crop N required (NR). The experiments were carried out during four growing seasons. The cultivar Innovator was planted in a randomized complete block design with three replications and four N treatments (N0, N1, N2 y N3) to cover the range from deficient through surplus N. The CM reading was assessed with the Minolta SPAD 502 at different times during each growing season. The NNI_CM was determined as the ratio between the actual CM reading (CMa) and the CMc. The NR was determined as the difference between actual N uptake and the critical N uptake, divided the N utilization efficiency. The CMc for cultivar innovator was determined [CMc?=?51.4 W (Mg ha^_1)^?0.13; R²?=?0.83]. The NNI_CM ranged from 0.78 to 1.17. The relation between RY and NNI_CM was expressed as a linear-plateau function. For NNI_CM ≥0.9, the RY was near 98.0 %, whereas for NNI_CM below 0.9, the RY decreased [RY?=?7.73?+?100.0 NNI_CM; R²?=?0.55]. The relationship between the observed N uptake and the estimated N uptake values showed positive significant associations (p?