Arsenicais e inseticidas orgânicos sôbre o algodoeiro em terras roxa e arenosa

Resumo

The authors carried out a series of pots and plots experiments applying arsenical and organic insecticides to cotton plants cultivated in "terra roxa" and in a sandy soil. The first results were presented in 1947, to the la. Reunião Brasileira de Ciência do Solo (First Brazilian Congress of Soil Science); they pointed out the danger resulting from the accumulation of arsenic in soils due to the constant applications of arsenicais to control cotton pests; in the course of the time, the amount of residual arsenic in the soil would determine a decrease in cotton yield caused by its toxic effect on the crop. The following conclusions were drawn from the last three experiments: 1) the field experiment conducted in a sandy soil to which lead arseniate was applied in increasing rates produced a reduction of 50 per cent in the yield (the three highest doses were responsible for this result); by this way, the pot experiment published in 1947 was confirmed); 2) in the pot experiment with "terra roxa" toxic effects appeared only in the plants receiving the last dosis of lead arsenate; this result is explained quite naturally by a considerable absorption of the AsO4 --- ion by "terra roxa" colloidal material; furthermore the CaO, P2O5 and Fe2O3 content and the pH value (higher) would decrease the arsenate solubilization in the soil considered; 3) the pot experiment with organic insecticides applied in the rates usually employed in the control of cotton pests, showed that 10% D.D.TD. and 2.5% Rotenone did not affect cotton plants cultivated in a sandy soil; however we agree with FOSTER (1951), in the point that both mineral and organic insecticides must be applied in the minimum amount as possible; we also think that experiments like those should be carried out with the known insecticides, in several soil conditions and with many crops in order to determine the maximum limits of tolerancy.