Field Experiments to Investigate Long‐term Effects of Repeated Applications of McPa, Tri‐allate, Simazine and Linuron: Report After 6 Years

Abstract

Summary. In five long‐term field experiments begun in 1963, each of four herbicides was applied to plots either planted with the same crop each year or uncropped. The following treatments were applied annually: MCPA at 24 oz/ac to barley at the 5‐leaf stage, triallate at 24 oz/ac to barley pre‐emergence, simazine at 24 oz/ac to maize pre‐emergence, linuron at 12–24 oz/ac to carrots preand post‐emergence. The main assessments reported in this paper are crop yield and persistence of herbicide residues. In the fifth experiment, these herbicides were applied twice each year at about double the above these to plots kept as far as possible free from all vegetation. MCPA did not affect the yield of barley and disappeared from the soil within 2–3 weeks of each application. In the uncropped plots, the time for the applied dose (3 lb/ac) to reach the limit of detection was reduced from 3 weeks in 1964 (after three previous applications) to 4 days in 1968 (after ten previous applications). Tri‐allate did not affect the yield of barley. Soil residues could be detected for 5–6 months following each dose of 24 oz/ac. When applied at 48 oz/ac twice yearly, a residue persisted but with no progressive build‐up during the 6‐year period. Agreement between bioassay and CLC methods of determining residues varied from good to a factor of 4, with CLC usually, but not always, providing a higher figure. No residues of pre‐allate could be detected in the barley straw or grain. Simazine did not influence the yield of maize during 1963–67. In 1968 there was a significant reduction in yield of foliage and stems but not in grain yield. Simazine applied to maize disappeared from the soil rapidly during the first 6 weeks; after this period 20–25% of the applied dose could be recovered. The remaining residues declined slowly and 1–2 oz/ac could be detected 23–50 weeks after application. No residues were found below the 0–2 in. soil level. When 48 oz/ac was applied twice annually a residue persisted varying from 8 to 27 oz/ac/6 in. There was no accumulation from year to year and no evidence that repeated treatment influenced breakdown rate. Most of the simazine remained in the 0–2 in. soil level. In three out of four determinations there was good agreement between CLC and bioassay results. Linuron reduced the yield and % dry matter content of carrot roots in 1965 and 1966 probably because of exceptional short‐term phytotoxicity, otherwise there was no effect. Half the applied dose of 8–16 oz/ac disappeared from the soil within 8 weeks and residues were undetectable after 6 months. The residues in the uncropped plots did not fall below 11 oz/ac. Most remained in the 0–2 in. layer of soil but some herbicide was found in the 2–4 and possibly 4–6 in. layers. Progressive build‐up of residues did not occur and repeated treatment did not influence breakdown rate. No linuron could be detected in carrot roots in 1965; in 1966, following an abnormally late application, 05 ppm was found. Chemical analyses of soil samples taken at regular intervals during 1...

Elucidating the Key Member of a Linuron-Mineralizing Bacterial Community by PCR and Reverse Transcription-PCR Denaturing Gradient Gel Electrophoresis 16S rRNA Gene Fingerprinting and Cultivation

“…The rates of dissipation in agricultural soils determined by laboratory and field experiments are highly variable, with values ranging from days to several years (2,8,9,11,16,23). Linuron is frequently detected in surface and ground waters near or below areas with intensive use, and in one extreme case, linuron was detected in a drinking-water well in concentrations up to 2,800 g liter Ϫ1 (2).…”

Persistência de linuron e orizalina em latossolo roxo sob cultivo de soja

“…A partir de então, houve sintomas ocasionais na planta-teste. Fryer & Kirkland (1970) observaram que a maior quantidade de linuron é encontrada nos primeiros 5cm do solo; portanto, a perda da atividade do produto não pode ser devida à percolação à camada mais profunda. A rápida degradação, segundo Walker (1978), também não se deve à temperatura.…”

“…(1985) e Fryer & Kirkland (1970), sob certas condições, quando repetidas aplicações de pesticidas são feitas no mesmo local, a persistência e a eficiência do produto diminuem, havendo ausência de uma lag fase mais longa no processo de degradação de alguns pesticidas de solo.…”

Simazine and Linuron Residues in Peach Orchard Soil After Repeated Annual Applications

“…Residues of both herbicides have been found in the soil 1 yr after treatment in quantities sufficient to damage susceptible crops (Roadhouse and Birk l96l; Morris and Penney 1971;Ragab 1974;Smith and Emmond 1975). Despite this potential for persistence, no large accumulations of simazine have been found in cases where relatively high rates were applied for up to 9 yr to the same soil, although carry-over ofresidues from year to year occurred (Dawson et al 1968;Fryer and Kirkland 1970;Bowmer 1972; Leonard et al 1974). In a previous study on residue accumulation after long-term linuron application, no significant buildup was observed (Fryer and Kirkland 1970).…”

“…Despite this potential for persistence, no large accumulations of simazine have been found in cases where relatively high rates were applied for up to 9 yr to the same soil, although carry-over ofresidues from year to year occurred (Dawson et al 1968;Fryer and Kirkland 1970;Bowmer 1972; Leonard et al 1974). In a previous study on residue accumulation after long-term linuron application, no significant buildup was observed (Fryer and Kirkland 1970). Movement of these herbicides into the soil profile was restricted essentially to the top l5 cm, with the majority of herbicide being found in the top 5 cm (Roadhouse and Birk 1961;Dawson et al 1968;Fryer and Kirkland 1970 At moderate rates simazine has generally been observed to persist longer than linuron (Kearney et al 1969;Fryer and Kirkland 1970) although Fryer and Kirkland (1970) found that when rates of these herbicides high enough to cause carry-over were applied, the residues of linuron were usually greater than those of simazine.…”