Organic farming indeed reduces the amount of nutrient runoff, there is no doubt about that. But then the question is, do we want to deal with periodical algae blooms, or sacrificing additional land as large as Mexico in order to produce the same amount of food?
There are already many initiatives and techniques to reduce runoff as much as possible, while increasing organic productivity to the same level won't be achieved in the near future with the techniques we have today (Especially when we keep blocking GMO's). So Better education and usage of chemicals seems like a better alternative for a long term sustainable solution. But that's my opinion.