(Adds fertilizer prices, expansion update, Street expectations)
Nov 4 (Reuters) - U.S. fertilizer producer CF Industries Holdings Inc reported a 31 percent drop in third-quarter profit on Wednesday after markets closed, pressured by weakening prices.
Nitrogen fertilizer prices have fallen sharply year over year, weighed down by excessive global production and soft demand. CF and other North American producers, however, benefit from low costs of natural gas, a key ingredient in nitrogen fertilizer production.
CF's net earnings fell to $91 million or 39 cents per share from $131 million or 52 cents per share a year earlier, missing expectations. Net sales for the quarter totaled $927.4 million, up slightly due to a recent acquisition.
Analysts, on average, had expected the world's third-largest maker of nitrogen fertilizer to earn 73 cents a share on sales of $887 million, according to Thomson Reuters I/B/E/S.
The average selling price for ammonia fell 15 percent from a year earlier to $446 per ton, while the price of UAN (urea ammonium nitrate) dipped nearly 7 percent year over year to $242 per ton.
CF said its expansions at nitrogen plants in Louisiana and Iowa were on schedule for start-up between the fourth quarter of this year and mid-2016.
Illinois-based CF was involved in three of four deals in summer in the nitrogen fertilizer sector, including a $6-billion purchase of Netherlands-based rival OCI NV's North American and European plants. (Reporting by Rod Nickel in Winnipeg, Manitoba; Editing by Chris Reese and Andrew Hay)