The printer’s manuscript does not have the word about between digged and it. Although the original manuscript is not extant for the word about, the nearby fragments that do exist suggest that there is no room for about except by insertion. But if it had been supralinearly inserted in 𝓞, it most likely would have been copied into 𝓟. In other words, if the about was accidentally lost here in Jacob 5:47, it probably occurred as Oliver Cowdery took down Joseph Smith’s dictation.
In his editing for the 1837 edition, Joseph Smith supplied the word about for Jacob 5:47, which is consistent with all other usage in the olive tree allegory:
As David Calabro notes (personal communication), the same language referring to digging about a tree is found in Christ’s parable of the fig tree in the Lord’s vineyard, a parable that clearly parallels the olive tree allegory here in Jacob 5:
Thus in the olive tree allegory, we expect trees to be “dug about”. In the example from Jacob 5:47, the preposition about was probably accidentally omitted from the original manuscript because the surrounding transitive verbs (nourished, pruned, and dunged ) are all immediately followed by the pronoun it. Notice, however, that in the other examples (in verses 4, 5, 27, and 76), the pronoun it directly follows other conjoined verbs, but that does not prevent the about from occurring between the verb dig and the it.
Summary: Accept Joseph Smith’s emendation “digged about it” in Jacob 5:47; for this passage the word about was apparently lost during the dictation of the text; usage elsewhere consistently supports the use of about in the expression “to dig about a tree”.