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Mineralization of Norflurazon in a Cranberry Bog Soil: Laboratory Evaluations of Management Practices

Dep. of Natural Resources Science, 121 Greenhouse, Univ. of Rhode Island, Kingston, RI. 02881.

^* Corresponding author (hgc103{at}uriacc.uri.edu).

ABSTRACT

Norflurazon (4-cldoro-5-(methylamino)-2-(,,-trifluoro-m-tolyl-3(2H)-pyridazinone) is a pre-emergent herbicide used in cranberry (Vaccinium macrocarpon Air.) cultivation to control annual grasses, sedges, and broadleaf weeds. Cranberries are an economically important crop in New England, Wisconsin, and other parts of the northern USA. The biodegradation of norflurazon in the high organic matter, acidic soil characteristic of cranberry bogs has been shown to proceed slowly (Savin and Amador, 1998). The potential effects of cranberry cultivation practices—soil moisture control, fertilization, sand addition, and herbicide application rate—on mineralization of norflurazon in a bog soil were evaluated in a laboratory study. Optimal soil moisture for norflurazon mineralization was between 80 and 90% of water-holding capacity (WHC) in soil from the Oi and A horizons. Saturating the soil reduced the rate of norflurazon mineralization significantly. By contrast, soil respiration was maximal at 25% of WHC in both horizons. Addition of inorganic P increased soil respiration, but did not affect norflurazon mineralization significantly. Addition of inorganic N plus P increased soil respiration in the A, but not Oi, horizon and significantly decreased norflurazon mineralization in the Oi horizon. Sand addition had no significant effect on norflurazon mineralization. Mineralization was affected by herbicide application rate, with the rate of mineralization increasing proportionally with increasing concentration from 0.75 to 7.5 mg norflurazon kg^–1 soil. The mineralization of ¹⁴C-norflurazon was slow for all of the agronomic practices evaluated, indicating that the potential for norflurazon to accumulate in cranberry bog soils may be high.