Xiaoling found that the rice grown at home was slender and prone to lodging after returning home, so she suggested applying one of the following fertilizers to change this growth.

Potassium fertilizer can make crops resistant to lodging and diseases and insect pests, and the planted rice is slender and prone to lodging, so potassium fertilizer should be used;

A, urea contains nitrogen, which belongs to nitrogen fertilizer, so the option is wrong;

B, ammonium nitrate contains nitrogen, which belongs to nitrogen fertilizer, so the option is wrong;

C, potassium chloride contains potassium, which belongs to potash fertilizer, so the option is correct;

D, ammonium chloride contains nitrogen, which belongs to nitrogen fertilizer, so the option is wrong;

So choose C.