Peak Soil

Hello all, I just returned from a farming conference in Virginia where I where I was studying GROW BIOINTENSIVE agriculture under its inventor, John Jeavons (author of "how to Grow More Vegetables.") I heard something there I'd never heard before which is that we have reached a time of "peak farmable soil." Basically, Mr Jeavons has run his numbers on a 'farm-able space per person' basis. Apparently it takes around 30,000 square feet to grow all of one person's food per year using conventional agriculture and this type of agriculture is depleting the soil at an extremely fast rate- 6 pounds of soil is depleted for every 1 pound of food created.
Mr Jeavons pointed out that even Organic Farming isnt sustainable because usually much of the fertilizers used to build up the soil are coming from somewhere else, depleting the soil they come from. (However because they are organic they are still better for the environment than conventional farm practices.)
The Biointensive method of farming includes dedicating a high percentage of one's farming area to "compost crops", crops that will replenish the soil. I'm glad at least this method exists cause it started to feel like we were otherwise doomed. Biointensive farming is the type they used in the Bioshere II experiment, where 6 people were able to to survive with only around 3,500 square feet dedicated to growing food per person. A marked difference to the 30,000 sq ft needed in conventional agriculture.
Mr Jeavons also mentioned that 213,000 people are born every day (births - deaths) and by 2014, 90% of the population of the world will be living in the developing world. We all know that there is plenty of famine in the developing world and that much of it is more of a result of political barriers rather than an actual lack of food on the planet at this time, but if what Jeavons claims about Peak Farmable Soil is correct, there will not actually be enough soil/food to support the number of humans of the very near future even if those political barriers were down- UNLESS we change our agricultural practices.
I personally am still promoting gardening of any kind (mostly through my website WorldFoodGarden.org,) even if many kinds of gardening are not sustainable. I feel that if we are ever going to reach a place of total sustainability for the planet we need to take all the steps to get there- the first one being to reintroduce the west to where food comes from and connecting them to the power of growing it. Only then can we start to introduce a holistic case to policy makers for how nature works and have it be really understood to the point of effecting agricultural policies.
Any thoughts?