Predicting N Mineralization Using the Direct Steam Distillation Method in Flooded Soils
Flooded rice is a highly relevant in the State of Rio Grande do Sul (RS) where 1.07 million hectares were cropped in 2012/13 season producing 8 million tons, which represented 69% of the national production. Nitrogen recommendation for upland or flooded rice in RS is based on soil organic matter (SOM) content but, nevertheless, yield has not presented high correlation with SOM recently. Therefore, studies are in place to develope methods and plant/soil parameters more efficient to predict N availability along the crop cycle or even prior seeding time. This project aims to evaluate the ability of the Direct Steam Distillation method in predicting N mineralization in flooded soils of RS.
IPNI-2014-BRA-64
29 Apr 2016
2015 Annual Interpretive Summary
Predicting the amount of N released during soil organic matter (SOM) mineralization is important to evaluate N availability for crops, as well as in the development of best management practices to maximize N use efficiency and minimize adverse environmental impacts. The objective of this study was to evaluate the extraction capacity of alkaline hydrolyzable N from soils by the method entitled “Direct Steam Distillation“ (DSD) in flooded soils of Rio Grande do Sul, Brazil. Twenty-two soil samples from areas representing rice cultivation in the state were collected and used in the experiments. A first experiment was conducted to predict the N mineralization capacity of such soils by the DSD method. A second experiment was set to evaluate the N mineralization of the same soils by anaerobic incubation at 40oC for four weeks. A third experiment intended to evaluate the N accumulation by plant tissues.
The estimated values for the DSD methodology presented a large range, varying from 55 to 317 mg N/Kg of soil, as a result of the wide range in SOM, mineralogy and clay content of soils in the study. The N estimated by the DSD showed similar trends when compared to the N mineralized for the different soils, independent of soil properties. A more adequate relationship with N mineralized was found when correlating with the extraction of labile SOM fractions by the DSD than with extractants with higher intensity, such as SOM or total N in the soil. A good correlation was found between the DSD method and the N uptake by the plants, which seems adequate for the goal of evaluating this method in routine analysis for flooded soils.