some excerpts:
Losing Farmland That Is Essential to Food Security
Of the 2.5 million hectares of farmland that Japan has lost over the past 50 years-equivalent to the total area of rice paddies in Japan today-about half has been converted for residential or industrial use.
...
The end result of this situation is that town halls, pachinko parlors, and other buildings are constructed in the middle of rice fields, leaving Japan's farmland riddled with holes like a moth-eaten dress. Developments like this not only do nothing to lower costs by enabling farmers to consolidate; they even block the sun from surrounding farmland.
France has secured its farmland resources by clearly delineating urban areas from agricultural areas through zoning and by limiting the benefits of agricultural policies to full-time farmers who derive at least half of their income from farming and expend at least half of their labor in farming, thus actively concentrating farmland in the hands of these farmers. These policies have enabled France to raise its food self-sufficiency ratio from 99% to 122% and the average size of its farms from 17 hectares to 52 hectares (as of 2005).
(note: you can collect your farmer's subsidy by being a "part time" farmer and using your land very unproductively. Productivity doesn't matter to these people since they just want to hit the bare minimum requirement to get their handout. My own maternal grandfather was one such part time farmer -- though not as unproductive as some.)
The Issue of Corporate Involvement
Farmers' groups strongly oppose the acquisition of farmland by joint stock companies, claiming that it would encourage land speculation. It is not joint stock companies but farmers themselves, however, who have profited by converting half of the 2.5 million hectares of lost farmland to other uses-equivalent to the total area of rice paddies in Japan today.
Corporate ownership allows for legal structures and arrangements that introduces flexibility into this traditionally all-or-nothing arrangement. [2]
Also, corporate ownership structures allow farm operators to pool the risk and capital requirements of a larger scale operation. Business loans that limit personal liability in the event of insolvency is greatly preferable to personal loans when undertaking expansion and improvement towards the preexisting operation.
I'd appreciate it if you could explain to me how corporate ownership of farmland by virtue of corporate ownership alone would reduce land productivity, as you have asserted. While I certainly agree that factory farming methods have created problems with antibacterial and hormonal health, greenhouse gas production, etc., I have a difficultly seeing how such abusive practices would decrease land productivity, separate from the other problems they cause.
[1] http://www.maff.go.jp/j/pr/aff/1207/spe1_02.html
[2] "Creating Jobs Through the Specified Corporation Lease Program" http://www.tokyofoundation.org/en/articles/2008/let-corporat...
Japan already has such laws. They simply circumvent them and build more and more seven-elevens on agricultural land.
In the US, corporate farms = animal abuse, complete indifference to pollution, and a general lack of accountability to the communities the farms are a part of. Furthermore, it has decimated rural communities across the US.