Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
Culture of Grain
Their husbandry was mainly occupied with the culture of the cereals. The usual grain was spelt (-far-);(8) but different kinds of pulse, roots, and vegetables were also diligently cultivated.
8. Perhaps the latest, although probably not the last, attempt to prove that a Latin farmer's family might have subsisted on two -jugera- of land, finds its chief support in the argument that Varro (de R. R. i. 44, i) reckons the seed requisite for the -jugerum- at five -modii- of wheat but ten -modii- of spelt, and estimates the produce as corresponding to this, whence it is inferred that the cultivation of spelt yielded a produce, if not double, at least considerably higher than that of wheat.
But the converse is more correct, and the nominally higher quantity sown and reaped is simply to be explained by the fact that the Romans garnered and sowed the wheat already shelled, but the spelt still in the husk (Pliny, H. N. xviii. 7, 61), which in this case was not separated from the fruit by threshing. For the same reason spelt is at the present day sown twice as thickly as wheat, and gives a produce twice as great by measure, but less after deduction of the husks. According to Wurtemberg estimates furnished to me by G. Hanssen, the average produce of the Wurtemberg -morgen- is reckoned in the case of wheat (with a sowing of 1/4 to 1/2 -scheffel-) at 3 -scheffel- of the medium weight of 275 Ibs. (= 825 Ibs.); in the case of spelt (with a sowing of 1/2 to 1 1/2 -scheffel-) at least 7 -scheffel- of the medium weight of 150 lbs. ( = 1050 Ibs.), which are reduced by shelling to about 4 -scheffel-.
Thus spelt compared with wheat yields in the gross more than double, with equally good soil perhaps triple the crop, but--by specific weight--before the shelling not much above, after shelling (as "kernel") less than, the half. It was not by mistake, as has been asserted, but because it was fitting in computations of this sort to start from estimates of a like nature handed down to us, that the calculation instituted above was based on wheat; it may stand, because, when transferred to spelt, it does not essentially differ and the produce rather falls than rises.
Spelt is less nice as to soil and climate, and exposed to fewer risks than wheat; but the latter yields on the whole, especially when we take into account the not inconsiderable expenses of shelling, a higher net produce (on an average of fifty years in the district of Frankenthal in Rhenish Bavaria the -malter- of wheat stands at 11 -gulden- 3 krz., the -malter- of spelt at 4 -gulden-30 krz.), and, as in South Germany, where the soil admits, the growing of wheat is preferred and generally with the progress of cultivation comes to supersede that of spelt, so the analogous transition of Italian agriculture from the culture of spelt to that of wheat was undeniably a progress.
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Reference address : https://www.ellopos.net/elpenor/rome/1-13-agriculture-trade-commerce.asp?pg=6