1. Weregild: In order for the magic to work, Eorde requires either a sacrifice of bread and/or herbs placed into the earth, or something else worth at least 1d3 gold pieces per HD of the spell’s target.
2. Weoh: Be it one of the nine herbs, the proper leys, or the local landwights, the magic requires the priestess be in a natural place. If not, then the spell will only occur at 1/2 strength.
3. Folde: It is now touching the bare, natural earth that's needed, otherwise the spell's effects happen 1d6 turns later instead.
4. Beorgan: Warded, if the priestess has allies on either side, then she gains a +2 bonus to her AC and saves until they fall or depart. If not, then she suffers the reverse. In either case, the effects last for 3d4 rounds.
5-8. Earth Sign: The spell works without side-effect this time, except for a 33% chance of some subtle, earthy, and/or agricultural indication showing too.
9. Landwihta: The landwights aid the magic for a 50% bonus to its effect, range, or duration, but if the priestess hasn’t been respectful to them (or to the land itself) then she suffers a -4 penalty to all rolls for the next 2d4 hours instead.
10. Wassail: If the spell is cast with the priestess touching bare, natural earth, then its effect, range, or duration can be increased by 50%.
11. Hearg: Being at a place especially sacred to Eorde, one of great, natural beauty and fertility, where it is loved by the sky, allows the spell's effect, range, or duration to be doubled.
12. Erce Eorþan Modor: The magic works for two-fold its usual effect, range, or duration, as well as it not being expended so it can be cast again that day. What is more, if wholesome things are gathered, sown, and prayed over the ground where the magic is to occur (usually taking 1d3 turns), then all those aspects may be tripled.
Folk Variations
Some requirements can instead be for the spell's target...
Jord/ Fjörgyn (Norse): (if meant to be beneficial) or the priestess (if not) to take either 1d3 hit points or 1d3 damage to a random ability score instead.
Airtha (Gothic): (if there is one) or the priestess (if there isn't) to save vs. death/ make a Will save DC 10 or be scared (-2d3 to all rolls) for the next 2d3 rounds instead. Gothic clerics have their own magical side-effect table too (link).
Nerthus/ Erda (Germanic): (if there is one) or the priestess (if there isn't) to ride or see someone in a cart, or to be immersed in water, earth, or the like.
