“Because nitrogen is used as a fertilizer for plants, we expected additional nitrogen would promote plant growth as well as microbial activity, thereby increasing carbon put into soils,” said Peter Homyak, study co-author and assistant professor in UCR’s Department of Environmental Sciences.

In dryland soil, the type that covers much of Southern California, this is not what they saw.

Instead, the team found that under certain conditions, extra nitrogen causes dryland soil to acidify and leach calcium. Calcium binds to carbon, and the two elements then leave the soil together. This finding is detailed in the journal Global Change Biology.

To obtain their results, the research team sampled soil from ecological reserves near San Diego and Irvine that have been fertilized with nitrogen in long-term experiments. This allowed them to know precisely how much nitrogen was being added, and account for any effects they observed.