Gemara

(R. Yishmael): "(If one slaughters a Chayah (wild animal) or bird, he must cover the blood) in Afar (soil)." A tradition from Sinai uproots the verse. The Halachah is, it may be covered with anything.

Chulin 88a (Mishnah): One may cover the blood with fine manure, fine sand, plaster, or ground up pottery, bricks or cork. One may not cover with coarse manure or sand, nor with bricks or cork that were not ground up, or a Keli;

R. Shimon ben Gamliel permits only with things in which vegetation grows.

Version #1 (Rabah bar bar Chanah): Fine sand is sand that a potter does not need to crush.

Version #2 (Rabah bar bar Chanah): Coarse sand is what a potter must crush.

The two versions argue about sand thatneeds (to be crushed,) and does not need (a Kli). It can be crushed by hand.

(Beraisa) "Be'Afar" disallows covering with rocks or a Keli. V'Chisahu" allows anything, e.g. fine manure, sand, pulverized rocks or pottery, stubble of flax, sawdust, plaster, crushed bricks or cork. "Be'Afar" excludes coarse manure or sand, ground up metal, bricks or cork that were not ground up, flour, or bran, for these are not kinds of Afar.

(Rav Nachman bar Rav Chisda): We may use only something in which seeds can be planted, and they will sprout.

Rava denounced this, and Rav Nachman bar Yitzchak said that he derived it from a Beraisa.

(Beraisa): If one in the Midbar has no Afar, he can grind up a gold coin and use the pieces. If he is on a ship, he can burn a garment and use the ashes.

(R. Zeira): Pulverized gold may be used, for it is called Afar - "v'Afros Zahav."

(Beraisa - Beis Hillel): We may cover with ashes, for they are called Afar - "me'Afar Sereifas (ha'Chatas)".

Beis Shamai: No. Ashes are called Afar Sereifah, not (plain) Afar.

Pesachim 47a - Question: Rabah should exempt for plowing on Yom Tov, Ho'il (since) the dirt could be used for Kisuy if he will slaughter a bird on Yom Tov!

Answer: The ground is wet.

Rishonim

Rif and Rosh (Chulin 29b): Fine sand is sand that a potter need not crush. We cover only with something in which seeds can sprout.

Ran (DH u'Makshu (2)): Why do we allow ground up gold? It does not sprout seeds! Afar Midbar shows that something called Afar that cannot sprout seeds is invalid! It is difficult to say that it is not called (Stam) Afar. The She'altos explains that Rav Nachman held that Chachamim agree with R. Shimon. Rava refuted this, for a Beraisa permits ground up gold! This shows that they argue, and the Beraisa is like Chachamim. He cannot use Afar Midbar, for it is coarse, and he has nothing to grind it up. The Halachah follows them. It seems that the Rambam agrees.

Note: The text of the Rif, Ran and Rosh said that one in the Midbar burns his cloak, and one on a boat grinds a gold coin. Perhaps this hints that the one in the Midbar has nothing to grind up a coin or Afar Midbar. According to our text, why were the two cases taught separately?!

Beis Yosef (YD 28 DH ul'Iyan): Something that is not Afar, but the Torah calls it Afar, is better than an inferior Afar that does not make seeds sprout, even if vegetation grows in it.

Rosh (Chulin 6:10): R. Shimon explains the first Tana. They do not argue. Vegetation can grow in everything listed in the Mishnah. The two versions argue about sand that needs and does not need to be crushed. Rashi says that Version #1 calls this fine, for it need not be crushed; Version #2 calls it coarse. The Rif brought only Version #1. This suggests that he explains oppositely.

Ma'adanei Yom Tov (50): According to Rashi, Version #1 is lenient. It is unreasonable for the Rif to rule leniently, therefore the Rosh says that the Rif explains oppositely. Only what need not be crushed at all may be used.

Rambam (Hilchos Shechitah 14:11): One may cover the blood with Afar, plaster, gypsum, fine manure, fine sand that a potter need not crush, or ground up rocks or pottery, fine stubble of flax, fine sawdust, and crushed bricks,clay or cork. All of these are Afar. Kisuy with a Kli or rocks is not Kisuy, for it says "be'Afar."

Rambam (12): Therefore, one may not cover with coarse manure or sand, flour, bran, ground up metal, for these are not kinds of Afar. The only exception is ground up gold, for it says "v'Afros Zahav" and "Ad Asher Dak le'Afar."

Tosfos (Avodah Zarah 44a DH Nachal) Why is ground metal invalid? One may not grind up idolatry (of any metal) and strew the ashes in the air, for this fertilizes (43b)! Perhaps ground metal helps, but by itself it cannot grow things. Alternatively, ground metal fertilizes only when it is burned, like the golden calf.

Tosfos (Chulin 88b DH Matzinu): In Beitzah (2a), Beis Shamai agree that oven ashes may be used to cover! R. Tam says that oven ashes, from wood, sprout seeds. Ashes of food and clothing do not sprout seeds. The Rashbam says that the Seifa, which permits oven ashes, is only Beis Hillel's opinion.

Poskim

Shulchan Aruch (YD 28:23): Anything that sprouts seeds is called Afar and may be used for Kisuy. If seeds cannot sprout in it, if it is called Afar it may be used.

Beis Yosef (DH Ein): Perhaps the Tur holds that something is called Afar only if seeds can sprout in it.

Beis Yosef (DH u'Mah she'Chosav v'Chol): Rashi says that 'something in which we can plant seeds, and they will sprout' excludes salty Afar.

Shulchan Aruch (ibid.): Therefore, one may use manure, very fine sand that a potter need not crush at all, plaster, Charsis, bricks or earthenware plugs that were crushed, ground up rocks or pottery, fine stubble of flax, food or clothing that was burned to Afar, Shichur, eye powder, and stubble that is extracted from a grinder. One may not use coarse manure, sand that a potter must crush, flour, bran, ground metal that was not burned, excluding ground gold, which is called Afar - "v'Afros ha'Zahav." Ashes are called Afar - "me'Afar Sereifas ha'Chatas."

Shach (35): All of these may be used after they were burned.

Beis Yosef (DH u'Mah she'Chosav Rabeinu uv'Sid): Rashi says that Shichur is crushed coals. The Rambam says that it is oven soot.

Shulchan Aruch (24): We may not cover with Afar Midbar, for it is salty and does not sprout seeds.

Rema: Therefore, one may not cover with Afar wet from water, nor with snow.

Beis Yosef (DH Kosav Ba'al): Rashi explains that wet land sprouts seeds, but it cannot be crushed; it sticks together. Semag says that 'Afar' denotes fine grains that one can count - "Im Yuchal Ish Limnos Es Afar ha'Aretz."

Shach (36): The text should not say 'therefore', rather, 'similarly.' It is clear from Pesachim 47b that wet Afar sprouts seeds.