No don't use soil!.. do you not have some gravel substrate or a neutral sand? that's all your plant needs to grow in with the aid of some aquatic plant fertilizers and a light source. The plants will also help deal with the excess waste that will fall between the gravel bits. Make sure you choose a substrate that is neutral and will not affect your PH drastically. You can test this by placing a sample in some white vinegar, if it effervesces, then it will disrupt your chemical balance in your tank. Make sure you don't use coral based substrate (most sands) as this will cause your PH to spike and can actually kill your fish if it happens quickly enough.
