TY JOUR TI MULTISPECTRAL IMAGES OF AGRICULTURAL LANDSCAPES AS A TOOL FOR DETECTING HETEROGENEITY OF SOIL FERTILITY KW vegetation indices evi KW ndvi KW ndmi KW agriculture KW soil fertility KW steppe agricultural landscape KW salinity JO Vestnik of Omsk SAU AU BOROVKOV, A.A. AU AZARENKO, Y.A. PY 2023 IS 50 PB FSBEI HE Omsk SAU