Crop art falls into several different categories, all of which employ land and/or what grows from it to create images.
Crop art Wikipedia
One version of Crop art is also called Seed art, a visual art created in mosaic-style. Mosaic is an ancient technique of making designs, often from bits of tile or glass. Mosaic is also a contemporary art form that is employed across many mediums. Seed pictures, or Crop art could also be seen as a technique of pointillism, like in painting, and as sharing design elements with textile arts such as needlepoint. Seed mosaic images are created by fixing vegetable matter, especially seeds, to a background. Coleen Sheehy, in Seed Queen quotes a classic text on the subject: Decorating with Seed mosaics, Chipped Glass and Plant materials (first pub.1960) by Elenor Van Rennslaer "...mosaics are tiles, glass, or stones set in mortar. Instead of these you can create a different kind of mosaic using such plant materials as seeds, tiny pods, and flowers" (Sheehy 49). The Corn Palace of Mitchell, South Dakota is one expression of this art. The Corn Palace was first built for the 1892 Corn Exposition. Outer walls of the building were -and still are- covered in murals made from multi-colored ears of corn (Sheehy 24); The seed mosaic portraits by Lillian Colton are also examples. Colton's name "became synonymous with the genre" (Sheehy 2). Colton made many seed portraits, especially of celebrities and she exhibited them in the strictly defined "Crop art" category at the Minnesota State Fair beginning in 1966, winning many prizes for her work. Rules for entry of Crop art allow "only seeds from Minnesota-grown farm crops or cultivated garden flowers, fruits, and vegetables" with no wild plant seeds permitted. Colton continued to teach and make Crop art until her death at age 95 in 2007 (Sheehy 2). A new generation of Crop, or Seed artists, known as the "Postmodern School of Minnesota Crop Art" (Sheehy 90) is continuing this folk tradition. Some of these artists are "Cathy Camper, Alan Carpenter, Kim Cope, Linda Koutsky, Nancy Loung, Suzy Mears, Laura Melnick, and David Steinlicht" (Sheehy 90). There is a custodial aspect and preservation ethic associated with this plant-based art form; Making Crop art is not only a way preserving and rejuvenating a vibrant folk craft but its practice foregrounds the need to collect, store, and value the lore and varieties of seeds.
The Rose Bowl Parade floats employ the flowers of plants in a similar collage or mosaic style.
Other views of Crop art are only obtained from the air. Land art, Earth art, and Environmental art are similar in scale; in Crop art the canvas is the size of the fields it stretches over. A major practitioner of this type of Crop art, Earthwork, or Living sculpture is Stan Herd. Herd says an early inspiration for his art was the ancient earth drawings called Nazca Lines after the Nazca people of Peru (Herd 14). One of his first works was the 160-acre (0.65 km2) portrait of "Kiowa War Chief Satanta" (1981) in southwest Kansas. Herd's work reflects a spiritual connection with the land, and respect for Native American culture (Herd 9). "Little Girl in the wind" (1992, Salina Kansas) was a portrait of an indigenous woman; Carole Cadue, a Kickapoo was the subject of this Earthwork. This portrait was made by burning and mowing, but without plowing the land. (Herd 56) His  includes photos of his work and lists some publications where his work has appeared, including a Smithsonian magazine article by Jim Robbins, July, 1994. In Crop Art Herd mentions installation artist Christo observing that "Christo's success hinged on his ability to communicate with people outside the art world" (Herd 16). Herd's work is related to the wider arc of the Prairie Renaissance Movement, a loose grouping of people in the Midwestern United States focused on the preservation and restoration of prairie ecosystems, arts, and culture. From the Prairie Plains Resource Center in Nebraska website to the University of Wisconsin-Madison's Arboretum website to Minnesota's Prairie Renaissance Cultural Alliance website to The Native Prairies Association of Texas website concern with the preservation and restoration of prairies ties into the larger categories of prairie preservation and environmental ethics; efforts to preserve these prairie ecosystems are a version of In-situ conservation of the plant genetic materials which make up the palettes of all crop artists.
The term crop art can also stretch to cover formations known as crop circles. Crop Circles first came to mass media attention during the 1980s after they were noticed in some agricultural fields in southern England (Ency Rel/Spir). Most often the images consist of very large and intricate series of rings and lines formed when standing crops, such as wheat and rye are flattened into patterns. Some attribute these designs to the marks left by landings of extra terrestrial craft because the images are usually very large, appear over a short period of time, and some do not show any visible tracks into or out of the design. These same type of figures are found all over the world; though many do not attribute their manifestation to visitations by alien beings. Crop Circles are sometimes called crop formations, agroglyphs, or pictograms. Some are also created by recognized "landscape artists" for commercial purposes.