Monsanto Posts Loss, Herbicide Sales Drop  KANSAS CITY, Mo. (Reuters) - Agricultural chemicals maker  Monsanto Co. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=MON.N target=/stocks/quickinfo/fullquote"&gt;MON.N&lt;/A&gt; posted a quarterly net loss on Wednesday  as a drop in Roundup herbicide sales in the United States more  than offset increased demand for its specialty seed technology.