MODELS TO DETERMINE PHOSPHORUS AND NITRATE CONCENTRATION IN QUARTZARENIC NEOSOL AND RED LATOSOL USING TDR

Abstract

TDR (Time domain Reflectometry) allows monitoring soil ions in real time using the soil water content (?) and the bulk electric conductivity (CEs), which allows estimate electric conductivity of the soil solution (CEss) and the nutrient ionic concentration (Ci). This study was done to adjust and test models that estimate the concentrations of nitrate and phosphorus using data of soil water content and bulk electric conductivity of Quartzarenic Neosol (RQ) and Red Latosol (LV) using a TDR. The study was done in soil columns. Phosphorus and calcium nitrate solutions were applied in five different concentrations to soils at five different water contents. Based on determination coefficient (r2), the model of Vogeler et al. (1996) followed by that of Rhoades (1976) best adjusted the CEss, CEs and ? for both soils and fertilizer concentrations. Through the model of Vogeler et al. (1996), the phosphorus Ci as the function of CEs and ? was estimated by combining a potential model, that correlated the data of CEss and the phosphorus content at low concentration of Ci in RQ and for the full range Ci in LV. On the other hand, a linear model was used for nitrate in both soils and for phosphorus at high concentrations in RQ. In RQ, the models overestimated low concentrations of phosphorous and underestimated high concentrations, and all concentrations studied in LV. The nitrate concentration was underestimated in RQ and overestimated in LV.