Hi Baskaran. You can use PVPP or CTAB method to get rid of humic acid contaminants. If it doesn't work out well, then try to include these two chemicals in the agarose gel and then run your sample. But my suggestion would be to use commercially available kits to get your work done in a short time.
One of my friend is extracting of DNA from marine sediments. Initially she tried conventional techniques to get rid of humic acid but failed. Once she started using kits she got good results. In my opinion, buying a commercial kit would help you save a lot of time. Good luck.
Hi, sorry for late reply as I recently joined RG, however find various protocol suggest different additives to be used (find attached article) along with my own protocol, which worked good in my case. But a key point you may dilute DNA to get rid of interference of Humic in PCR.