Non-invasive optical methods (spectrometry, thermal imaging) when determining nitrogen deficiency and the physiological state of wheat in the field conditions

The reflection spectra and leaf surface temperature were measured in a field experiment when growing wheat of the Daria variety in the field conditions of the Menkovo experimental station of the Agrophysical Research Institute. The plants were vegetated at different levels of nitrogen nutrition (0-200 kg/ha in increments of 40 kg/ha). Fertilizers were applied in 2 stages: 2/3 of the dose of nitrogen (nitrogen strip) before sowing and 1/3 (ammonium nitrate) at the stage of completion of tillering. The analysis of the diffuse reflection indices of the leaf surface revealed a close positive relationship between the chlorophyll index (ChlRI) and a close negative relationship between the photochemical reflection index (PRI) and the dose of nitrogen fertilizers applied at the early stages of nitrogen deficiency, when there are no visible symptoms of plant oppression. The reflection indices SIPI, R800, ARI and FRI, in addition to assessing the nitrogen supply of plants, can be useful in assessing the specific response of plants to the action of various stressors, for example, to a deficiency of soil moisture or a lack of soil nitrogen. The use of thermal imaging made it possible to assess the transpiration activity of wheat plants depending on the level of nitrogen nutrition and its change during the day.