Additions to the characterization and mapping of soils deficient in phosphorus and potassium, for corn, in the physiographic region of Northeast Brazil

Abstract

The present study was conducted to evaluate soil analysis with respect to the response of corn to applications of phosphorus and potassium fertilizers. Results from thirteen experiments, in diverse physiographic areas of Northeast Brazil were correlated with chemical soil analysis using the North Carolina State University method. The objective of the study was to develop a rapid method of interpreting soil analysis for the "soil-climate-plant" conditions of the Northeast and to determine the chemical-fertility factors that may be limiting agricultural production. The relationship between available phosphorus and exchangeable potassium and corn production was studied using treatments in which either phosphorus or potassium was omitted. Statistical analysis indicates that this procedure offers a means through which the chemical analysis of these elements can be better used as a measure of their availability in the soil. In addition it will allow, through continual interpretation of chemical analysis of the soil sample, the characterization and mapping of areas deficient in phosphorus and potassium. Results have established as critical, levels of 10.5 ppm for available phosphorus and of 45.0 ppm for exchangeable potassium in the soil. Based on these critical levels, the following suggestions were made: 1. From 0 to 10.5 ppm of P indicates low phosphorus soil. A high probability of response of phosphorus fertilization may be expected. The estimated average increase in production should be about 47%. 2. Above 10.5 ppm P indicates high phosphorus soil. The probability of response to phosphate fertilizer would be low. 3. Below 45 ppm K indicates low potassium soil. Probability of response to potassium fertilization would be high.