Table 4 Relationship of vegetation indices in the tillering phase

The research was conducted in 2020–2022 on the territory of the Agricultural Company “Kolos” JSC, located in the Stavropol Territory. The soil of the experimental plot is represented mainly by common chernozem. Studies were conducted to determine the relationship of pigment indices (PSSRAa and PSSRb) in crops of soft winter wheat (variety Grom) and in the models “PSSRAa, PSSRb – VOG1” and “PSSRAa, PSSRb – SIPI” on different agricultural backgrounds in the unstable moisture zone. The study showed that chlorophyll indices (PSSRAa and PSSRb) are high in the seedling phase and markedly high in the tillering phase in all agricultural backgrounds. The models “PSSRAa, PSSRb – VOG1” and “PSSRAa, PSSRb – SIPI” showed high regression dependence of the variables in the seedling phase. Simultaneously, the model “PSSRAa, PSSRb – SIPI” is inversely proportional. During the tillering phase of “PSSRAa, PSSRb – VOG1” and “PSSRAa, PSSRb – SIPI,” the relationship between the variables decreased. However, the correlation in the “PSSRAa, PSSRb – SIPI” model improves, probably due to increased chlorophyll concentration (PSSRb). Consequently, the established relationship of the indices makes it possible to fix the vegetative phase of the development of winter wheat plants and display the state of the cultivated crop.