http://www.economist.com/news/science-and-technology/21717351-fruits-de-mer-plucking-minerals-seabed-back-agenda?fsrc=scn/fb/te/bl/ed/pluckingmineralsfromtheseabedisbackontheagenda
One of the things farmers have learned through years and years of plowing is that it destroys the microbial communities in the soil. While they can come back, it takes years.
This will do more harm than good, I believe.