2,4-Dichlorophenoxy acetic acid mineralization in amended soil

Area of Science:

• Environmental Science
• Soil Science
• Microbiology

Background:

• The fate of herbicides in soil is crucial for agricultural sustainability.
• Municipal biosolids and livestock manures are common soil amendments.
• Understanding how these amendments affect herbicide degradation is important for risk assessment.

Purpose of the Study:

• To investigate the impact of municipal biosolids and hog manure on the degradation of the herbicide 2,4-D in soil.
• To determine how the timing of herbicide application relative to amendment application affects 2,4-D fate.
• To explore the mechanisms behind observed changes in 2,4-D mineralization.

Main Methods:

• Laboratory incubation of a coarse-textured soil at 20°C.
• Application of municipal biosolids and liquid hog manure to soil.
• Addition of the herbicide 2,4-D at agronomic rates at different time points after amendment application.
• Measurement of 2,4-D mineralization and soil respiration over 100 days.

Main Results:

• Immediate application of biosolids or manure with 2,4-D increased 2,4-D mineralization by approximately 47% compared to controls (31%).
• This enhancement was linked to increased heterotrophic microbial activity, particularly soil respiration, with biosolids showing the greatest effect.
• Delayed application of 2,4-D (1-4 weeks after amendments) generally reduced mineralization, especially with manure, suggesting diminished amendment effects over time.
• Manure's negative impact on 2,4-D mineralization was comparable to soil texture effects and was not due to altered sorption, possibly involving preferential microbial consumption of manure's organic carbon or sorption of transformation products.

Conclusions:

• The timing of 2,4-D application relative to soil amendment with biosolids or manure significantly influences its degradation rate.
• Biosolids and manure can initially enhance 2,4-D microbial breakdown, but this effect is transient and can be reversed, particularly with manure.
• Further research is needed to elucidate the mechanisms, such as microbial competition or transformation product sorption, responsible for the observed effects of manure on 2,4-D fate.