The Living Soil (1943) by Lady Eve Balfour is considered a seminal classic in organic agriculture and the organic movement. The book is based on Balfour's agricultural and medical research, and the initial findings of the first three years of the Haughley Experiment, the first scientific, side-by-side farm trial to compare organic and chemical-based farming.
The Living Soil was also published as The Living Soil and the Haughley Experiment.
Currently out of print, the full text is available online in the Agriculture Library at http://www.soilandhealth.org.