Monsanto Co , the world's biggest seed company, posted better-than-expected profit on Thursday as revenues grew in its key corn and soybean seed businesses and it benefited from a low tax rate.

Monsanto, a leader in the development of genetically altered crops, said net income was $1.092 billion, or $1.97 a share for the second quarter, which ended February 28, down from $1.129 billion, or $2.02 a share a year ago, due in part to a slide in its herbicide business.

Excluding items, earnings rose to $2.16 a share from $1.77. Analysts on average were expecting $2.07.

Soleil Securities analyst Mark Gulley said the results were helped by several variables, including a low tax rate, but pure fundamentals were strong.

Corn and soy remain the foundation of the company, and that continues to do well, said Gulley, who has a buy rating on the shares, which were up 2.2 percent before the market opened.

Monsanto said the second quarter saw revenue jump both in its U.S. branded corn seed and traits business and in its U.S. soybean seed and traits business, while fewer planted acres for corn in Brazil was noted because of drought conditions.

Seed and genomics sales were $3 billion for the second quarter, up 20 percent from a year earlier. At the same time, sales of Roundup and other herbicides dropped 21 percent.

Company officials said last year, U.S. volume of the Roundup herbicide was up in the second quarter ahead of an anticipated price increase, but this year sales returned to more historical patterns.

Overall, St. Louis-based Monsanto reported record net sales of $4 billion for the second quarter, up 8 percent from a year earlier.

Monsanto said its results were impacted by $162 million, or 19 cents per share, in charges attributable to in-process research and development tied to the acquisitions of a sugarcane breeding and technology company in Brazil.

The company said its full-year earnings should be in the range of $4.23 to $4.33 per share on a reported basis and in the range of $4.40 to $4.50 per share on an ongoing basis. Analysts are looking for $4.72 a share.

(Reporting by Carey Gillam)