In-field variation in 2,4-D mineralization in relation to sorption and soil microbial communities.
This study was undertaken to assess 2,4-D mineralization in an undulating cultivated field, along a sloping transect (458 m to 442 m above sea level), as a function of soil type, soil microbial communities and the sorption of 2,4-D to soil. The 2,4-D soil sorption coefficient (Kd) ranged from 1.81 to 4.28 L kg(-1), the 2,4-D first-order mineralization rate constant (k) ranged from 0.04 to 0.13 day(-1) and the total amount of 2,4-D mineralized at 130 days (M(130)) ranged from 24 to 39%. Both k and M(130) were significantly negatively associated (or correlated) with soil organic carbon content (SOC) and Kd. Both k and M(130) were significantly associated with two fatty-acid methyl esters (FAME), i17:1 and a18, but not with twenty-two other individual FAME. Imperfectly drained soils (Gleyed Dark Grey Chernozems) in lower-slopes showed significantly lesser 2,4-D mineralization relative to well-drained soils (Orthic Dark Grey Chernozems) in mid- and upper-slopes. Well-drained soils had a greater potential for 2,4-D mineralization because of greater abundance and diversity of the microbial community in these soils. However, the reduced 2,4-D mineralization in imperfectly drained soils was predominantly because of their greater SOC and increased 2,4-D sorption, limiting the bioavailability of 2,4-D for degradation. The wide range of 2,4-D sorption and mineralization in this undulating cultivated field is comparable in magnitude and extent to the variability of 2,4-D sorption and mineralization observed at a regional scale in Manitoba. As such, in-field variations in SOC and the abundance and diversity of microbial communities are determining factors that require greater attention in assessing the risk of movement of 2,4-D by runoff, eroded soil and leaching.
Farenhorst
A
A
Department of Soil Science, University of Manitoba, Winnipeg, Canada. farehor@ms.unimatoba.ca
Londry
K L
KL
Nahar
N
N
Gaultier
J
J
D015084:2,4-Dichlorophenoxyacetic Acid / Q000032:analysis / Q000737:chemistry*; D000327:Adsorption; D002244:Carbon / Q000737:chemistry; D004784:Environmental Monitoring; D006207:Half-Life; D006540:Herbicides / Q000032:analysis / Q000737:chemistry*; D007700:Kinetics; D008350:Manitoba; D008903:Minerals / Q000032:analysis / Q000737:chemistry*; D012987:Soil / Q000032:analysis; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis; D014877:Water Pollution, Chemical / Q000517:prevention & control
D006540:Herbicides; D008903:Minerals; D012987:Soil; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; D015084:2,4-Dichlorophenoxyacetic Acid; D002244:Carbon