PLYMOUTH — One of the world’s largest fertilizer makers says it plans to cut 500 jobs globally as it deals with a significant decline in earnings.

The Plymouth-based Mosaic Co. is reporting that its first-quarter earnings are down 40 percent compared to a year ago. The fertilizer business has been plagued by low prices for several quarters.

Mosaic plans to cut 50 jobs at its Plymouth headquarters, which employs about 300. Mosaic’s five-year plan is to cut $500 million in costs, including reducing its workforce of about 8,200 by 6 percent.