Long-term vinasse application enhanced the initial dissipation of atrazine and ametryn in a sugarcane field in Tucumán, Argentina.

The production of sugarcane bioethanol generates large volumes of vinasse, an effluent whose final disposal can produce an environmental impact that is of concern. The long-term disposal of vinasse in sugarcane fields could challenge crop management, such as the performance of traditional herbicides, by changing soil properties. This study aimed to evaluate the effect of long-term vinasse application on the field and the dissipation of atrazine and ametryn herbicides in a subtropical sugarcane agroecosystem, and to discuss the potential processes involved in it. Vinasse affected soil properties by increasing pH (12%), electrical conductivity (160%), and soil organic carbon (25%) at 0-10 cm depth of soil. Differences in the herbicide calculated sorption coefficient (Kd) varied according to the pedotransfer function applied and the herbicide type (atrazine or ametryn). During the first seven days after herbicide application, the soil underwent long-term vinasse application and increased atrazine and ametryn dissipation 45% and 33%, respectively, compared with the conventional fertilization scheme (control). The Pesticide Root Zone Model revealed that dissipation was mediated mainly by the degradation process rather than transport or other processes. The long-term application of vinasse in a typical sugarcane field of Tucumán, Argentina decreased the potential groundwater pollution of triazines and, adversely, reduced their bioavailability for weed control. For this, the present study presents original information about how long-term treatment with vinasse may require an adaptation of conventional management practices such as the application of herbicides in Argentina and other sugarcane-producing regions. Integr Environ Assess Manag 2023;00:1-12. © 2023 SETAC.

Integrating critical values of soil drivers for mitigating GHGs: An assessment in a sugarcane cropping system.

Agricultural practices can reduce emissions of greenhouse gases (GHG). The definition of management practices toward mitigating GHG emissions could gain accuracy by integrating critical values of soil variables related to GHG fluxes. The aim of this study was to combine critical values of soil variables determining groups of GHG fluxes with similar and/or opposite direction of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). We determined CO2, N2O, CH4 fluxes, soil temperature, gravimetric soil moisture (GSM), soil inorganic nitrogen (SIN), soil bulk density (SBD), soil porosity (P), and water-filled pore space (WFPS) monthly in three consecutive growing seasons in a sugarcane agroecosystem. The regression tree method defined groups of emission. Six terminal groups of CO2, N2O fluxes, and four for CH4 fluxes were determined. The critical values of soil variables that defined the terminal groups with the highest fluxes were soil temperature (>19 °C) and GSM (>35.2%) for CO2, GSM (>29.2%) and SIN (≤1.1 ppm) for N2O, and GSM (>24.9 °C), SBD (>0.98 g cm-3) and SIN (>1.82 ppm) for CH4. Trade-offs were found among GHGs: N2O emissions were high and CO2 emissions were low when GSM and soil temperature ranged from 29 to 35% and 14-19 °C, respectively (moderate values). CO2 emissions were high and N2O emissions were the lowest when GSM was equal or lower than 29.2% and soil temperature ranged from 19 to 21.3 °C. In this study, we highlight that management practices aimed to mitigate GHG fluxes should consider the integrated analysis of critical values of soil variables for GHGs together in order to avoid trade-offs.

To burn or not to burn: The question of straw burning and nitrogen fertilization effect on nitrous oxide emissions in sugarcane.

Nitrous oxide (N2O) is the main greenhouse gas emitted from farming systems and is associated with nitrogen (N) fertilizer application as well as decomposition of organic matter present in the environment. The objective of this study was to determine the effect of post-harvest straw burning and synthetic N fertilization on the dynamics of N2O emissions in the sugarcane-soil system in Tucuman, Argentina, compared with a native forest. Close-vented chambers were used to capture N2O during three consecutive growing seasons. The highest N2O emissions from the sugarcane-soil system coincided with the period of high soil and air temperatures, rainfall and soil N content. The effect of synthetic N fertilization on annual cumulative N2O emission was 7.4-61.5% higher in straw burned than in unburned treatments, especially during a wet growing season. There was a significant effect of treatments on N2O emission factors among growing seasons: 0.58-1.67% and 0.94-3.34% in the unburnt and burnt treatments, respectively. The emission factors for sugarcane are highly dependent on rainfall, temperature and crop management practices; regarding the latter, avoiding straw burning and reducing N soil availability, assessing alternative N fertilizers or new application modes such as split rates, seem to be the key for mitigating N2O emissions from the sugarcane-soil system in Tucumán, Argentina.