Chullin 88: Covering the Blood of a Slaughtered Animal, Cases of Ashes and Dirt

What is used in kisuy hadam, covering the blood when animals are slaughtered?  A new Misha teaches that beyond the dirt noted in the Torah, lime, fine sand, fine granulated manure, crushed potsherd, crushed brick, or crushed earthenware are all options.  Rabban Shimon ben Gamliel notices that as long as plants can grow in it, it is valid.  The Gemara adds that ashes are another option.

We learn about other mitzvot that use dirt or ashes.  Rava teaches that as a reward for saying "I am but dust and ashes" (Bereishit 18:27), Avraham's children merited the mitzvah of para aduma, the red heifer and the mitzvah of the dust used in the ceremony of the sota, the wife accused of adultery.  And why not use the example of the dirt used for kisuy hadam?  The Gemara explains that dirt serves only the purpose of covering the blood in kisuy hadam, whereas in para aduma and sota, the dirt and ashes are central in purifying what is defilied and establishing a woman's innocence.

The Gemara continues to discuss why these mitzvot are connected to Avraham's statement when they would be required in any case given these situations.  Perhaps the rituals surrounding the para aduma were simplified because of Avraham's merit.  And perhaps Avraham's merit allowed a sota to be permitted to her husband again, promoting shalom bayit.