ORIGINAL: farm hunter
1-1/2" sounds deep to me for buckwheat.
Personally I'd be happy with 1/2". Soil to seed contact is the most important consideration. Drag something around if you dont have a set of disks. Then roll it flat or drive over it repeatedly to assure good soil firmness and seed to soil.
FH
I was thinking the same thing. A general rule of thumb when planting something is to go no deeper than 4x the diameter of the seed.
Make sure you have a nice, uniform seedbed. You don't want a lot of big clods. When the seed germinates, any roots that hit large pockets of air will die.