Wood Vinegar Mitigates Herbicide Impact in Rice Paddies

Introduction

The widespread use of herbicides in paddy fields has raised concerns over soil health, microbial diversity, and nutrient availability. A study published in the *Journal of Agricultural Science* investigated how the application of pyroligneous acid (PA), also known as wood vinegar, affects the chemical and biological properties of paddy soil, particularly when combined with the herbicide bentazone cyhalofop-butyl (BCB).

Experimental Design and Application Method

The study was conducted under greenhouse conditions using paddy soil mixed with sandy soil in a 1:1 ratio. Researchers tested seven treatments:

  • T1: Control (no treatment)
  • T2: 100-fold diluted wood vinegar (100 WV)
  • T3: 50% BCB (half the recommended herbicide dose)
  • T4: 100% BCB (full herbicide dose)
  • T5: 50% BCB + 100 WV
  • T6: 50% BCB + 250 WV (250-fold diluted wood vinegar)
  • T7: 50% BCB + 500 WV (500-fold diluted wood vinegar)

The wood vinegar was obtained from a local distributor and applied via spraying at the 2–3 leaf growth stage of barnyard grass (*Echinochloa crus-galli*), approximately 6–8 days after transplanting. The experiment lasted 10 days after treatment application, during which soil samples were analyzed for chemical and microbial changes.

Key Findings

Soil Chemical Changes

  • pH Levels: Treatments with PA showed a slight reduction in soil pH, maintaining a near-neutral to slightly alkaline condition. The greatest pH decrease occurred in the 50% BCB + 250 WV treatment.
  • Nutrient Availability: The control group had the highest levels of total carbon, available phosphorus, exchangeable calcium, magnesium, sodium, and potassium. All PA-treated soils had slightly lower nutrient levels, likely due to enhanced microbial activity accelerating nutrient cycling.
  • Electrical Conductivity (EC): The highest EC was recorded in soils treated with 100% BCB, indicating increased ion concentration. However, the addition of PA at higher dilutions helped stabilize EC levels.

Microbial Activity and Soil Health

  • Increased Microbial Diversity: The 50% BCB + 500 WV treatment significantly enhanced microbial activity, as measured using the Biolog EcoMicroPlate™ system.
  • Carbon Utilization Patterns: Principal Component Analysis (PCA) indicated that different PA treatments altered microbial communities, increasing the use of various carbon sources such as D-mannitol and α-D-lactose.
  • Reduced Microbial Inhibition: While 100% BCB decreased microbial richness and activity, combining BCB with PA at higher dilutions (500 WV) helped mitigate this negative impact, supporting beneficial soil microbes.

How Pyroligneous Acid Works

The efficacy of PA in soil management can be attributed to its composition:

  • Organic Acids: Acetic and propanoic acids lower pH slightly, influencing nutrient solubility.
  • Phenolic Compounds: These compounds have antimicrobial properties that regulate microbial populations.
  • Carbon Sources: PA provides readily available carbon that stimulates beneficial microbial activity.

Implications for Sustainable Rice Farming

This study highlights the potential of pyroligneous acid as an amendment to mitigate herbicide impacts on soil health. By combining PA with lower herbicide doses, farmers may achieve effective weed control while preserving beneficial microbial diversity and soil fertility.

Future research should explore long-term effects, field-scale applications, and interactions with different soil types. As sustainable agriculture gains momentum, PA emerges as a promising tool for improving paddy soil health and productivity.

Article based on: Chemical and Biological Properties of Paddy Soil Treated with Herbicides and Pyroligneous Acid