I can't see the benefits here over The Bountiful Feast.
- Magic to keep the soil healthy (most likely CrHe Base 1) - All instant Creo rituals need Vis to make their effects permanent, and as this is soil then it's a Terram base not a Herbam base. If you're spending Vis anyway, why not just create the food directly?
- Magic to insure enough water (ReAq) - This is much easier with Creo Aquam unless you're diverting an existing water source. Whilst this would cost Vis, it would produce a spring rather than a set amount of water, so it could be used for all future farming projects.
- Magic to prepare the fields (ReTe) - Most of the other steps are far easier to accomplish with mundane workers.
- Magic to grow the plants to maturity (CrHe Base 15+) Legitimate, it's a duration spell not a ritual so doesn't need Vis.
You could also just use Rego Herbam or Rego Terram to magically animate farming tools to move at your direction if you really didn't want to bother with human grogs.