Vieira, S.R., Castro, O.M. de and Topp, G.C. (1992) “Spatial variability of some soil physical properties in three soils of São Paulo, Brazil”, Pesquisa Agropecuaria Brasileira, 27(2), pp. 333–341. doi:10.1590/S1678-3921.pab1992.v27.3654.