Caewil

A good modern source would be Kurt A. Raaflaub. If you can, get the whole blackwell companion to the Roman Republic. Very well researched and not dry at all.

According to archaeological sources, there was no serious decline in the number of smaller tenants. While the larger landed estates would have been run primarily by slaves, there is no evidence that they were used to grow grain or other staple crops. Furthermore, since more labour is necessary at harvest than at other times, the most cost-effective method of farming would have been to hire labour from the smaller estates during harvests, rather than having to provide for a larger number of slaves. Perhaps the reason the Marian reforms were necessary was that none of the later wars were of direct consequence to the republic's security, thus making it difficult to convince small tenants to leave their homes for foreign wars of agression. Especially if such wars took place in relatively poor, inland areas such as the interior of spain and africa where there was little to plunder and wars tended to drag on.