COMPOST is the best material that conserves moisture, and with multiple benefits i.e. nutrient supply, promote growth of beneficial soil fauna and economical as well as ecologically beneficial. YES enough organic material is available the only need is efficient use. Adding synthetic chemical may never be a sustainable practice at least for drylands.

I agree with the answer of Dr. Sharma.

Compost is the best material that acts as hydrogel and can be used as moisture retaining material in dry land ecosystem. Also, compost is prepared from agricultural waste and kitchen waste which helps in reducing the municipal and household waste problem. It also acts a natural fertilizer to crops that provides nutrients for their growth and improves soil fertility.

compost is right material no doubt about it but its undergo decomposition in faster rate. So i thought that adding biochar one of the option and anyone can idea about other material may be added with biochar to retain soil moisture in the soil for long time

On a small scale, calcined clays (e.g., kitty litter, Turface, etc.) retain soil moisture and are stable for long periods of time. For reclamation efforts, calcined clays are a viable option, but if you are looking for an amendment for thousands of acres this is not it.

"Like hydro-gel"? This may be tangential to your research: I agree that hydro-gel holds lots of water but at what rate does it release that water? Some hydro-gels may actually sequester water at the expense of other organisms that depend upon soil moisture. A study of water holding hysteresis will be in order for the use of any material, natural or otherwise .