Permissibility of Turbah

What is the ruling on the permissibility of using the Turbah for salah. 
If one does not use a Turbah Karbala and has no belief in any redemptive qualities of such soil. Does prostrating on a Turbah fulfill the sunnah of prostrating on the earth?

Imam Qasim (AS) and Imam Ahmed bin Isa (AS) encouraged people to pray on soil, right?

As salamu alaikum,

According to the Madhab of Imam Qasim Ibn Ibrahim alayhi salam it is mustahab to place your forehead in sujood on soil or something grown out of soil. But there is no problem in itself by praying On a prayer rug.

قال إمام زيد ابن علي عليه السلام لا بأس بالصلاة على البيات و المسوح.

حدثنا محمد بن منصور قال و اخبرني جعفر عن قاسم ابن إبراهم في الصلاة على المسوح و اللبود و البسط و أشباهها: يستحب لكلي مصلي ان يضع جيبه على التراب و حضيض الأرض فإنه كان لا بد مما يتوفى به الأرض كان مما تنبت الأرض إلا ان يخشى ضرر الحر و البرد فيتوقى بما يوقيه و يسجد من ذلك على ما أحب

Translation:

Imam Zaid ibn Ali, peace be upon him, said: “There is no harm in praying on coarse cloth and felt.”

Muhammad ibn Mansur narrated to us, saying, and Ja’far informed me from Qasim ibn Ibrahim regarding prayer on coarse cloth, felt, rugs, and similar items: “It is recommended for every person praying to place their forehead on the soil and the ground itself. If it is necessary to use something between oneself and the ground, it should be something that the earth produces unless one fears the harm of heat or cold. In such cases, one may use what protects them and prostrate on what they prefer from that.”

It should be added to this that What is meant by making sujood on soil is not what the imamiyya practice with turbah. I know of no one of our scholars holding such a position, what is meant by this is making sujood on soil altogether not on some small part of soil which is only for the forehead. If you actually look up the texts in the book of our great Imam Ahmad ibn Isa alayhi salam you will see that the wording is about praying on soil or prayer rug or such things.

Wa salamu alaikum

Asalamu Alaykum
I found this:

The following was sent to me by the Imam Rassi Society about a question asked by a brother why non-Ja’fari Muslims don’t use the turba (i.e. rock from Karbala).

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Allama al-Hussein bin Yahya al-Houthi, may Allah preserve him, responded to this question in one of his texts. The translation of his answer is as follows:

If one were to consider it as a sunnah, it is impermissible. Furthermore, it is a heretical innovation because there is no proof that establishes such. If one were to consider it a good thing because of its blessings, we do not hold it to be a good thing. This is because it is clay (turba) of sadness, not a clay of blessings! How can we consider it a clay of blessedness when the best of all men on earth was killed on it unjustly by his enemies?!
And Allah knows best!