Tractate Sheviit - Chapter 5 - Mishnah 2 שביעית פרק ה׳ משנה ב׳

One who buries luf (a type of onion) in the soil during the sabbatical year:Rabbi Meir says: it must be not less than two seahs in quantity, three handbreadths in height, and covered with earth one handbreadth deep. The sages say: it must be not less than four kabs in quantity, one handbreadth high, and covered with earth one handbreadth deep. And he should bury it in a place where people walk.