... Biological Factors 20 2. 2 .2 Physical and Chemical Interactions 21 2. 2.3 Root Development and Nutrient Access 22 2. 3 Managing Soil Systems for Tropical Agriculture 22 2. 3.1 Agroforestry 23 2. 3 .2 Weed Management ... Properties of Soils, 12th ed., Prentice Hall, Upper Saddle River, NJ, 20 02, 523 . With permission.q 20 06 by Taylor & Francis Group, LLC Biological Approaches to Sustainable Soil Systems3 2 2 Soil System ... Can. J. Soil Sci., 48, 323 –330, 1968. With permission.q 20 06 by Taylor & Francis Group, LLC Biological Approaches to Sustainable Soil Systems3 6 biological activity are low or nil due to suboptimal...