Botanical: Daniel Ludlow notes:
"Although the equivalent of the word corn is used in some Semitic languages to refer to various types of cereals, including wheat, Joseph Smith would probably translate it here so it would be clear to the understanding of his readers in the United States. Thus, the "corn" here is probably maize, which is frequently called corn in the Americas. It is not clear what crops are referred to by the titles of "neas" and "sheum." (Ludlow, Daniel L. A Companion to Your Study of the Book of Mormon. Deseret Book, p. 181).
Sorenson does offer a possiblity for "sheum":
"Two other puzzling plants are mentioned in Mosiah 9:9, among those cultivated by the Zeniffites: "sheum" and "neas." The former word has recently been identified as "a precise match for Akkadian s(h)e'um, 'barley' (Old Assyrian 'wheat'); the most popular ancient Mesopotamian cereal name." The word's sound pattern indicates it was probably a Jaredite term. This good North Semitic word was quite at home around the "valley of Nimrod," north of Mesopotamia, where the Jaredites paused and collected seeds before starting their long journey to America (Ether 2:1, 3). (Incidentally, the form of the word as the Book of Mormon uses it dates to the third millennium B.C., when the Jaredites left the Near East. Later, it would have been pronounced and spelled differently.) Apparently the Nephite scribe could not translate it to any equivalent grain name, nor could Joseph Smith do so when he put the text into English. The plant and its name no doubt were passed down to the Nephites/Zeniffites through survivors from the First Tradition, just as corn itself was. Since the words barley and sheum were both used in the same verse (Mosiah 9:9), we know that two different grains were involved, but what "sheum" might specifically have been in our botanical terms we cannot tell at this time. Perhaps this was amaranth? (Sorenson 1985, p. 186).
Social: The statement of planting is not only important as an indication of the important labor that was begun, but a statement of the continuation of a lifestyle. Zeniffites were agriculturalists. As with much of Mesoamerica, their social model was developed around the central services of the town and the surrounding farming areas.