The German term "Nachhaltigkeit" meaning sustainability was first used by Hans Carl von Carlowitz his 1713 book about forestry "Silvicultura oeconomica", while thinking about how to achieve an efficent and profitable use of the forest, while maintainig its healthy existence for future generations.

The ecological agriculture itself is of course the natural form of agriculture, so every kind of pre-modern subsistence economy without components from the modern chemical and biological(genetic) industries was/is basically ecological.

So the idea of going "back to nature" came hand in hand with the industrial revolution, it's urbanisation and it's alienation of the people from nature. The earliest ideas i could find regarding an ecological agriculture begins in the 1920's in Germany and Switzerland with the Lebensreform movement which intended a "back to nature"-lifestyle in all areas of life, including food.

I hope i could help anwser your question.