Estudo comparativo de alguns solos típicos do Planalto Central Brasileiro

Resumo

            Twenty-five cuttings have been made with gimlet until 220 cms depth during the exploring excursion promoted, in 1948, by Conselho Nacional de Geografia, in the States of São Paulo, Mato Grosso, Goiás and Minas Gerais, comprising a total of ninety-two samples of soil. The points, where the cuttings have been made, were chosen in such a way that the represent areas geographically and ecologically well defined.

            The samples were analyzed in the laboratories of the Agricultural Chemistry Division of the Department of Agriculture of the State of Rio de Janeiro, in duplicate, and the determination of the following characteristics have been made: real specific mass; apparent specific mass; moisture equivalent; mechanical analyses; pH in water; exchangeable calcium, magnesium and potassium; available phosphate and total phosphate; loss of ignition; carbon; total nitrogen and silica, alumina and sesquioxide of iron of the weathering complex.

            Were also made calculations of: pore space; texture classification; exchangeable hâdrogen; total of exchangeable bases; percentage has saturation (index of Hissink); organic matter (%C X 1,724); relation C/N; index of silica/alumina ("ki") and index of silicasesquioxides ("kr").

            With the result of the analyse of the weathering complex has been made the pedological classification of Vageler, but that classification does not correspond well enough to the universal concept already adopted of the division of soils in sialitical and alitical.

            It has been suggested to introduce a modification in that classification in order to put it in harmony with the baste concept of the pedological classification, giving at the same time a quantitative interpretation.

            The author proposes a new symbolic representation for the different types of soil, which gives the total of the percentages of silica, alumina and sesquioxide of iron of the weathering complex referred to 100 grams of fine earth, the name of the texture and color, (representation of the I.Q.A.) thus specified:

          -Sample n.° 105 1-Feralito-1,3-R-Vm

          -Sample n.° 112 6-Feralito-0,7-TRG-Vm

            A comparative study has shown that the index "kr" is more significant than the "ki", for, this one, in some cases, shows too high values, in discordance with what could be expected having in consideration the climatic zone in which are those soils.

            The comparison of the data obtained has been only possible after the establishment of the indexes of fertility, prosed by the author, based on the statistical method, known as index of concentration. Instead of using variable mean values, for each determination a standard central value has been chosen, what can be justified by the fact that it makes easier the comparison inside and outside of the group analyzed.

            The index of fertility proposed is the. arithmetic mean of the indexes of each determination representing graphical conditions of direct influence on the life of the plants, computed proportionally to the depth, until 50 em. Its general expression is the following:

1. F. ( Ipo + Ieu + IpH + Ica + IMg + Ik + Ipa + Ipt + Imo +Ix + ... ) / n;

            and the one used is this study is the following:

            I.F = 50/po + UE/20 + Ph/5 + Ca + Mg/10 + K/0,5 + T/15 + Pt/50 + MO/2 + N/0,1 / 10

             The degree of fertility will be the index of fertility expressed in percentage (G.F.% = 50 x I.f.). The maximum value for each index in the computation of the mean value is 2.