Nitrate and ammonium in soil solution in tobacco management systems

Douglas Rodrigo Kaiser,José Miguel Reichert,André Pellegrini,Carlos Arnoldo Streck,Dalvan José Reinert

doi:10.1590/s0100-06832010000200011

Abstract

Tobacco farmers of southern Brazil use high levels of fertilizers, without considering soil and environmental attributes, posing great risk to water resources degradation. The objective of this study was to monitor nitrate and ammonium concentrations in the soil solution of an Entisol in and below the root zone of tobacco under conventional tillage (CT), minimum tillage (MT) and no-tillage (NT). The study was conducted in the small-watershed Arroio Lino, in Agudo, State of Rio Grande do Sul, Brazil. A base fertilization of 850 kg ha-1 of 10-18-24 and topdressing of 400 kg ha-1 of 14-0-14 NPK fertilizer were applied. The soil solution was sampled during the crop cycle with a tension lysimeter equipped with a porous ceramic cup. Ammonium and nitrate concentrations were analyzed by the distillation and titration method. Nitrate concentrations, ranging from 8 to 226 mg L-1, were highest after initial fertilization and decreased during the crop cycle. The average nitrate (N-NO3-) concentration in the root zone was 75 in NT, 95 in MT, and 49 mg L-1 in CT. Below the root zone, the average nitrate concentration was 58 under NT, 108 under MT and 36 mg L-1 under CT. The nitrate and ammonium concentrations did not differ significantly in the management systems. However, the nitrate concentrations measured represent a contamination risk to groundwater of the watershed. The ammonium concentration (N-NH4+) decreased over time in all management systems, possibly as a result of the nitrification process and root uptake of part of the ammonium by the growing plants.

Highlights

The States of Southern Brazil account for 96 % of the nation’s tobacco production and the main production regions are found on basaltic slopes and crystalline shield rocks (SCP, 2003)
The study was conducted in the watershed Arroio Lino, in Agudo, Rio Grande do Sul, Brazil
The soil retains a high water content in periods of greater rainfall and fertilizer solubilization, water flow and nitrate leaching to positions below the tobacco root system may be favored

Summary

Introduction

The States of Southern Brazil account for 96 % of the nation’s tobacco production and the main production regions are found on basaltic slopes and crystalline shield rocks (SCP, 2003). Incompatible agricultural practices with the land use capability of these regions and the application of high fertilizer and pesticide rates make tobacco cultivation an activity with a high contamination risk for water resources in watersheds. These factors result in a rapid decline of the productive capacity of the soil (Minella et al, 2007) and local water quality (Gonçalves, 2003; Pellegrini, 2005; Becker et al, 2009). Nitrogen and K are the nutrients most demanded by tobacco for high productivity and quality. High ammonium concentrations reduce K uptake by tobacco plants (Scherer et al, 1984)

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