There are stated methodic peculiarities of observations in field experiments with corn. There are presented observations and accounts in field experiments with corn by following indicators: plant structure, growth, and development; phenology and biometrics; diagnostics of mineral nutrition of corn; elements of yield structure; analytic observations in laboratory; yield account and the calculation of the nutrients consumption, protein yield. The article is based on a published book “Methodology of agricultural and technical investigations in experiments with main field crops” by Lukomets V.M., Tishkov N.M., and Semerenko S.A. (Krasnodar, 2022).