I see someone use it as an organic fertilizer for their plants.

Potassium humate is a soil supplement, so yes, it is good for plants.

Potassium humate is one important humic acid salt,could efficient optimize nitrogen phosphorous in soil, also optimize micro element absorption and create a suitable environment for microbial. Main function & benefits:
1. increase the efficiency of fertilizers,especially Urea,ammonium sulfate,DAP,MAP;
2. promote the buffering power and fertility of soil by improving the structure;
3. neutralize both acidic and alkaline soil to release the beneficial metal ions, thus promote absorption by plants;
4. optimized the absorption of beneficial ion by plants thus increase plants growth accordingly increase the yield and fruits quality;
5. enhance plants’ ability to counter stressed conditions.

Here is a link: http://www.greenagrosource.com/our-products/humic-acid/potassium-humate hope it helps