I recently received a copy of a paper published by CropLife Foundation entitled "The Importance of Herbicides for Natural Resource Conservation in the U.S.".   Publication date: January 2012.

I thought the paper had some interesting data on how herbicidal weed control has reduced the amount of tillage-based weed control and contributes to reductions in soil erosion, water concervation, and energy use in agriculture. 

The article is available along with a number of other publications at the CropLife Foundation home page (here), direct link to the pdf (here), or attached below with permission of the authors.

Take care,
Brad

From the introduction of the paper:
Herbicides are used to reduce weed populations on approximately 220 million acres of U.S.
cropland [1]. More than 90% of the acreage of most field crops as well as vegetable, fruit, nut, and specialty crops are treated with herbicides annually. Herbicides were first introduced in the 1940s and by the 1970s had achieved a dominant role in managing weeds in crop fields. Prior to the introduction of herbicides, the dominant methods of weed control were cultivation and hand weeding. Although still practiced, cultivation and hand weeding have been greatly reduced in U. S. crop production.

The use of herbicides has had major impacts on the conservation of soil, water and energy
resources in the U.S. These impacts occurred largely due to the replacement of tillage with
herbicides for weed control. Weed control methods used by organic growers also impact natural resource, even though they do not include herbicides, which furthers our understanding of the role of herbicides in conservation.