Fertilizer experiments with corn: XXII - Trials with various phosphorus sources (8th series)

Three experiments comparing superphosphate with Olinda and Araxa phosphates (ground phosphorite of the state of Pernambuco and ground apatite of the state of Minas Gerais, respectively) were carried out in 1958-59 at three different locations in the state of São Paulo. Superphosphate was applied at three rates, the highest of which was 80 kg per hectare; the other two phosphate sources were employed only in the amount corresponding to the highest rate of superphosphate. The responses to phosphorus were very good in two of the trials, but only fair in the third. Although the results were obtained in but one year, the natural phosphates proved fairly effective in the two first trials, the average yield increases due to Olinda and Araxa phosphates being respectively 71 and 56 per cent of that of superphosphate. In the third triad, located on an acid soil high in organic matter. Olinda-phosphate was a little superior to superphosphate. Under the conditions of this trial the addition of a small dosis of available phosphorus was safficient to promote the attainable yield. It seems. therefore, that Ohnda-phosphate could provide the required phosphorus supplement and the application of 80 kilograms of P2O5, per hectare as superphosphate was excessive. However, even under the mentoned condition; the response to apatite was much inferior to those of the other phosphates.