Monsanto Co , the world's biggest seed company, said on Thursday that quarterly profit fell 3 percent due in part to lower volume sales of its key herbicide products.

St. Louis-based Monsanto, a leader in the development of genetically altered crops, said net income was $1.09 billion, or $1.97 a share in the second quarter ended on February 28, down from $1.13 billion, or $2.02 a share, a year earlier.

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

Monsanto reported record net sales of $4 billion for the second quarter, up 8 percent from a year earlier, but lower volumes of Roundup herbicide limited results.

The company left unchanged its full-year 2009 forecast for adjusted earnings of $4.40 to $4.50 a share on an ongoing basis. Analysts are looking for $4.72.

Monsanto shares rose 5.3 percent to $86.11 in trading before the market opened.

(Reporting by Carey Gillam; Editing by Lisa Von Ahn)