Prado, R. de M., Roque, C.G. and de Souza, Z.M. (2002) “Resistance to penetration and density of a soil submitted to different systems of tillage and cultivations”, Pesquisa Agropecuaria Brasileira, 37(12), pp. 1795–1801. doi:10.1590/S1678-3921.pab2002.v37.6533.