They used concrete as a reagent.
Your use of "concrete" threw me off. Just a translation problem. In English (American English, anyway), concrete=cement+sand+rocks, either semi-fluid or hardened. I take it you meant a box of unhardened dry cement. If they are using cement to seed clouds, I can see your concern. I wonder if you would have to drill holes in the top layer of your dirt in order to plant seeds.