@INBOOK {LAL:1979, title = {The role of soil physical properties in maintaining productiviity of soils in the tropics}, author = {Lal, R. }, editor = {Lal, R. and Greenland, D. J}, year = {1979}, type = {Soil Physical Properties and Crop Production in the Tropics edited by R. Lal and D.J. Greenland}, pages = {3--6}, publisher = {J. Wiley & Sons}, address = {U.K}, }