1. Contributions to Our Knowledge of the Aeration of Soils.;Government Printing Office Bureau of Soils Bulletin,1904
2. A laboratory study of the diffusion of oxygen through pasture topsoils.;Gradwell;N Z J Sci,1961
3. The importance of long-term experiments for soil science and environmental researchA review.;Plant Soil Environ,2006
4. Estimating soil bulk-density from particle-size analysis and organic-matter content.;Rawls;Soil Sci,1983
5. Long term research on agricultural systems.;Available at: (verified December,2011