Predição da mineralização de nitrogênio pelo método Direct Steam Distillation (DSD) em solos aptos ao cultivo de arroz irrigado

Abstract

Nitrogen (N) fertilization management in the states of Rio Grande do Sul (RS) and Santa Catarina (SC), Brazil, is performed using interpretation tables of soil organic matter (SOM) in which we obtain the interpretation ranges of N availability and therefore N rates. However, the productivity of flooded rice is highly variable according to the SOM content, resulting low and high relative grain yields regardless of the SOM content or N fertilization. Soil analysis methods estimate the labile organic N, which is mineralizable and may be available during the crop cycle. Moreover, these methods have the potential to obtain a better correlation between the amount of soil analysis and crop productivity. Therefore, this study aims to evaluate the ability of alkaline hydrolyzable N content extracted by Direct Steam Distillation (DSD) method of analysis to predict N mineralization in paddy soils from RS state. We collected 32 soil samples (0-20 cm layer) in the five rice production areas of RS state, which presented some contrasting texture and SOM content. The DSD method was used to obtain the mineralizable N content in the soil samples. We carried out a laboratory experiment to determine the N mineralization in anaerobic incubation, and another greenhouse experiment to determine the content and the accumulation of N by rice plants. We evaluated the Pearson linear correlation coefficient (r) (P <0.05) between the N content available after 28 days of anaerobic incubation and the N accumulation by rice plants with the N content obtained by DSD, SOM, total N and clay contents. The results of N estimated by DSD, N mineralized under anaerobic incubation and N accumulated by plants showed high amplitude, which was linked to the attributes of the soil samples. Results have shown that the evaluation of a more labile fraction of N by the DSD method improves the estimation of N availability when compared to the methods that assess the total SOM. This method has the potential to be used as indicator of the N availability in paddy soils in the RS state. The soil clay content influenced mineralization, availability and accumulation of N by rice plants, suggesting the necessity to include this soil parameter in the calibration, interpretation and/or recommendations of N fertilization for flooded rice.