Nitrogen Transformations in Soil as Affected by the Fungicides Benomyl, Dyrene, and Maneb¹

Abstract

The frequency and extent of fungicide use on putting green turfgrasses prompted investigations to determine the effect of three commonly used fungicides on N transformations in soil. Laboratory and field studies were conducted to study the effect of the following fungicides on nitrification and N mineralization in soil: benomyl [(methyl l‐(butylcarbamoyl)‐2‐benzimidazolecarbamate)], rene [(2,4‐dichloro‐6‐(0‐chloranilino)‐s‐triazine)], and rnaM‐7 neb (manganese ethylenebisdithiocarbamate). In laboratory studies, the three fungicides were added at rates of 0, 25, 75, and 150 ppm and the soil incubated at 21±1 C and moisture content of 30±1%. Analyses for NH+4‐N and (NO‐2 + NO‐3)‐N were conducted at various times during a 16‐week incubation period. Almost no effect was detected for benomyl, but a complete blockage occurred at the 150 ppm rate of maneb. Dyrene had an intermediate effect. Based on concentrations of (NH+,4 + NO‐2 + NO‐3)‐N in the untreated control as compared to treated soil, benomyl was stimulatory to N mineralization. Inhibitory effects were observed for both Dyrene and maneb after 4 weeks of incubation, but these effects had disappeared after 16 weeks. In the field, 14 weekly applications of benomyl, Dyrene, and maneb at 90, 90, and 135 g active ingredient/are were made to a ‘Penncross’ creeping bentgrass, Agrostis palustris Huds., golf green. Soil samples were taken from a depth of 0 to 2.5 cm (excluding thatch) and determinations of NH+4‐N and (NO‐2 + NO3‐)‐N concentrations were made at weekly intervals during a 5‐week incubation. There was no effect of any of the fungicides on nitrification but enhanced N mineralization occurred with application of all three of the fungicides. The differences in the effects of these fungicides on nitrification and N mineralization in laboratory as compared to field applications were considered to be the result of lower rates of application associated with more rapid rates of degradation under field conditions as contrasted with the high single rates of application under laboratory conditions.

Response of mycorrhizal western red cedar to organic phosphorus sources and benomyl

“…(The ATP-fed plants received an additional 1.51 mg N per pot at each feeding at the low rate, and 7.53 mg N per pot at each feeding at the high rate.) Although it is not known how plant-available the N in benomyl is, Mazur and Hughes (1975) also report increased N after benomyl treatment, and believe the source of this N to be the fungicide.…”

Fungicides in Kentucky Bluegrass Turf: Effects on Thatch and pH1

“…Organic acids were not considered important in this study because the most acid soils were in treatments where thatch mineralized very slowly. Mazur and Hughes (1975) reported that nitrification was not generally inhibited with applications of benomyl, maneb, and anilazine in turfgrasses grown in the field. In their studies, the application rates were I. I to 1.2 times as high as used in our study, and 14 applications were made as compared to our nine.…”

Effect of Nitrapyrin on Mineralization of Urea and Isobutylidene Diurea in a Highly Organic Medium

“…Flasks were placed in a growth chamber and incubated at 30° ± 1°C; this temperature is considered to be the optimum temperature for nitrification to occur in soil and is commonly found in container plants (2). Nitrogen was extracted from medium samples with 2 m KC1 as described by Mazur and Hughes (12). Analyses for urea, NH4 and NO2 + NO3 were by methods de scribed by Bremner (3).…”