The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
12. The earth (is meant by the word 'anna'), on account of the subject-matter, the colour, and other passages.
We read, 'Water thought, may I be many, may I grow forth. It sent forth food (anna)' (Kh. Up. VI, 2, 4).--Here a doubt arises, whether the word 'anna' denotes things fit to be used as food, such as rice, barley and the like; or cooked food; or else the earth.
The pûrvapakshin maintains that the word is to be understood in the former sense; for, he says, the word 'anna' means 'food' in ordinary language, and is moreover confirmed in that sense by the complementary passage, 'Therefore whenever it rains anywhere, most food is then produced;' for when it rains, rice, barley and the like, but not earth, are produced in abundance.
To this we reply that by the word 'anna' we have to understand earth as being produced from water.--Why?--On account of the subject-matter, on account of the colour, and on account of other passages.--The subject-matter, in the first place, is clearly connected with the elements, as we see from the preceding passages, 'it sent forth fire, it sent forth water.' It would therefore be improper to pass over a further element, viz. earth, when its turn has come, and to assume without reason that rice and the like are meant by the word 'anna.'--In the second place, we find that in a complementary passage there is mentioned a colour which agrees with earth, 'the black colour (of fire) is the colour of anna.' Eatable things on the other hand, such as cooked dishes, and rice, barley and the like, are not necessarily black.--But earth too is not necessarily black; for the soil of some fields has a whitish colour like milk, and that of others looks red like glowing coals!--True, but that does not affect our argument, since what we have to look to is the predominant colour. Now the predominant colour of earth is black, not either white or red. The Paurânikas also designate the colour of the earth by the term 'night'
[paragraph continues] (sarvarî); now the night is black, and we therefore conclude that black is the colour of earth also.--In the third place other scriptural passages also, which refer to the same subject, declare that 'from water (sprang) earth' (Taitt. Up. II, 1), and that 'what was there as the froth of the water, that was hardened and became the earth' (Bri. Up. I, 2, 2). On the other hand the text declares that rice and the like were produced from the earth, 'From earth sprang herbs, from herbs food' (Taitt. Up. II, 1).--As, thus, the general subject-matter as well as other arguments clearly proves that the word 'anna' here denotes earth, we can in no way accept the view that rice and the like are referred to. The common use of language to which the pûrvapakshin appeals is of no avail against the arguments favouring our interpretation. The complementary passage also ('whenever it rains,' &c.) is to be viewed as pointing out that, owing to the earthy nature of food (rice, &c.), earth itself mediately springs from water.--For all these reasons the word 'anna' denotes this earth.