Pathak, P and Sahrawat, K L and Rego, T J and Wani, S P  (2005) Measurable biophysical indicators for impact assessment: changes in soil quality.   In:  Natural resource management in agriculture: methods for assessing economic and environmental impacts.   CAB International Publishing, Wallingford Oxfordshire, UK, pp. 53-74.  ISBN 0-85199-828-3