Assessment of the Climatic Plasticity of the Perennial Grain Crop Kernza (Thinopyrum intermedium) under the Conditions of Southern Ukraine Based on Spectral Vegetation Indices
Abstract
Objective. To substantiate an approach for integrating Sentinel-2 spectral vegetation indices (NDVI, NDMI, NDRE) with agrometeorological indicators to assess the growth and development of Kernza under water and thermal stress conditions in southern Ukraine. Methods. Satellite image interpretation and field experiments were conducted in accordance with current standards of agronomic research and precision agriculture. Results. Weather conditions during both study years were characterized by pronounced variability and significant deviations from long-term climatic normals. In 2024, moderate spring temperatures and adequate moisture promoted active tillering and canopy formation, whereas anomalously high summer temperatures (up to 39–42 °C) combined with precipitation deficits led to soil– atmospheric drought and suppression of growth processes. In 2025, a mild winter ensured favorable overwintering, and spring conditions supported intensive biomass accumulation; however, a prolonged summer rainless period (over 68 days) resulted in severe water stress.
The temporal dynamics of NDVI, NDMI, and NDRE corresponded closely to crop phenological stages (BBCH scale) and prevailing weather conditions. Maximum NDVI values (0.628–0.691) were recorded during active tillering and stem elongation, while minimum values (down to 0.261) occurred during grain maturation under drought conditions. NDMI effectively reflected crop water status and the progression of water stress, whereas NDRE indicated generally sufficient nitrogen supply throughout the growing seasons.
Conclusions. The agrometeorological conditions of 2024–2025 in southern Ukraine were atypical and had a pronounced impact on the growth and development of Kernza. In 2024, favorable spring weather promoted intensive tillering (NDVI 0.628–0.646), whereas extreme summer heat (up to 39–42 °C) combined with precipitation deficits induced water stress, reducing NDVI to 0.468 and NDMI to −0.002. In 2025, a mild winter and favorable spring conditions enhanced biomass accumulation (NDVI 0.668–0.691); however, a prolonged summer drought (over 68 days) resulted in severe physiological stress (NDVI 0.261; NDMI −0.116). Autumn conditions in both years supported partial recovery of vegetation activity. A strong and consistent relationship was identified between agrometeorological drivers and derived spectral indicators of canopy condition. The findings demonstrate the suitability of spectral vegetation indices for operational crop monitoring and for quantifying the effects of hydrothermal variability on productivity formation.
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