I believe the answer is wind I'm not sure..Hope this helps!!
Simple your answer is going to be wild fire.
Grass would be a producer since it uses Photosynthesis to make its own food and a cow would be a consumer
A soil can be low in ammonium and potassium ions because of increased acidity of the soil. The acidity is caused by hidrogen (H) and Al (alluminuim) ions. There few causes: acid rain, nitrate leaching, rainfall, decompositions of organic matter (leaves, corps etc) due to microorganism activity.