These are paintings of wheat fields Vincent creates throughout his lifetime.
“Drawn to Biblical parables, Van Gogh found wheat fields metaphors for humanity’s cycles of life, as both celebration of growth and realization of the susceptibility of nature’s powerful forces”.
Maurer, N; van Gogh, V; Gauguin, P (1999) . The Pursuit of Spiritual Wisdom: The Thought and Art of Vincent van Gogh and Paul Gauguin. Canbury and other locations: Associated University Press. p. 57. ISBN 0-8386-3749-3.