This article proposes the concept of genome network, describes different variations of the somatic genome network, and reviews the agricultural implications of such variations. All genetic materials in a cell constitute the genome network of the cell and can jointly influence the cell's function and fate. The somatic genome of a plant is the genome network of cells in somatic tissues and of nonreproductive cells in pollen and ovules. Somatic genome variation (SGV, approximately equivalent to somagenetic variation) occurs at multiple levels, including stoichiometric, ploidy, and sequence variations. For a multicellular organism, the term "somatic genome variation" covers both the variation in part of the organism and the generation of new genotype individuals through somatic means from a sexually produced original genotype. For unicellular organisms, genome variation in somatic nuclei occurs at the whole organism level because there is only a single cell per individual. Growth, development and evolution of living organisms require both stability and instability of their genomes. Somatic genome variation displays many more attributes than genetic mutation and has strong implications for agriculture.