Effects of herbicides on urea nitrogen transformation and greenhouse gas emission of soil in citrus orchards with different planting years
A 2018 laboratory experiment compared woodland soil with 10- and 30-year citrus orchard soils to test how glyphosate and butachlor altered urea transformation and greenhouse gas emissions.
What the study did and found
The 2018 article “Effects of herbicides on urea nitrogen transformation and greenhouse gas emission of soil in citrus orchards with different planting years” by Zheng Xiangzhou, Wang Yasa, Zhang Yushu, Zhang Jing and Ding Hong used a two-factor, three-level laboratory block design. The herbicide treatments were no herbicide, glyphosate at 10 mg kg-1 active ingredient and butachlor at 10 mg kg-1 active ingredient. Soil history was represented by woodland, a 10-year citrus orchard and a 30-year citrus orchard; every treatment received 200 mg N kg-1 dry soil as urea. Relative to woodland, the 10- and 30-year orchard soils had 5.12- and 4.30-fold higher total denitrification loss, 7.80- and 2.74-fold higher total N2O emission, and 19.62% and 39.64% higher total CO2 emission, respectively. The 30-year orchard also emitted 16.74% more CO2 than the 10-year orchard. Butachlor increased N2O emissions by 56.27% in the 10-year soil and 85.41% in the 30-year soil versus no herbicide, while glyphosate did not significantly change total CO2 or N2O emissions in any planting-year treatment.
Why it is cited
The paper is useful when discussing how herbicide effects depend on both soil management history and the nitrogen cycle. Its design separates orchard age from herbicide treatment, allowing later authors to distinguish background differences between long-cultivated orchard soils from treatment-specific responses.
Later research supports the broader premise that herbicides can alter soil microbial communities and nutrient-cycling processes, but the magnitude and even direction of effects vary with compound, dose, exposure time and soil properties. Reviews of herbicide-microbiome interactions describe consequences for nutrient cycling and plant-soil processes, while more recent meta-analytic work on glyphosate reports strongly context-dependent effects on soil respiration and carbon cycling. These findings are compatible with the 2018 study’s treatment- and soil-specific responses, but they do not justify generalizing its exact citrus-orchard percentages to other soils, herbicides or field conditions.
The topic today
Current work increasingly combines greenhouse-gas measurements with microbial-community profiling, functional genes and soil physicochemical data to explain why herbicide responses differ among systems. Studies of nitrogen-cycle herbicide effects now examine microbial pathways directly, and management research also evaluates ways to reduce both pesticide residues and N2O emissions. The 2018 citrus experiment therefore remains most informative as a controlled comparison showing that orchard history and herbicide identity can interact with urea transformation and gas fluxes. Field-scale risk assessment still requires site-specific evidence, realistic application patterns and longer-term measurements.