They should be enough but depends upon what you want to analyze particularly how many parameters you want do? You can go for basics pH, Moisture, available N and P, total C,N,P

you can get all of these done by using less than 20 gms of soil.

Hope this helps

@ Mirza, I think you should check the soil physical parameter like organic matter, oxygen and carbon dioxide concentration, porosity, soil pH and EC. I think 20 g soil is enough for your work.

Hi Mirza, for metagenomics analysis the required edaphic properties may vary based on your specific research question as also mentioned by Pankaj Kumar Singh . Physical parameters such as soil pH, soil moisture or soil water content, bulk density, texture, porosity, water holding capacity, aggregate stability, electric conductivity etc. may be investigated. Further, Soil nutrients in terms of C (organic and inorganic carbon, dissolved organic carbon, total carbon, labile and recalcitrant carbon), N (organic and inorganic, total nitrogen), Phosphorus etc. may be determined. I also suggest to analyze soil microbial biomass carbon to understand the variabilities in the metagenomic data better.

If you want help on how to understand the correlations of these parameters with the metagenomic data please check the following article:

Article Edaphic factors override temperature in shaping soil bacteri...

Thanks and all the best in exploring your research.