Persistência e lixiviação do herbicida simazina em solo barrento cultivado com milho

Abstract

RESUMOForam determinadas, em experimento de campo, a persistência e a lixiviação do herbicida si mazina na dose de 3 kg/ ha i. a. em um so lo pod zol ver mel ho -ama rel o de textu ra bar renta plantado com milho, por meio do monitoramento de se us re sí duos , dura nt e um an o ap ós a su a a p l i c a ç ã o , e m 1 4 d e j a n ei r o d e 1 9 9 2 . 0 e x p e r i m e n t o f o i c o n d u z i d o n a E s t a ç ã o Experime ntal do Instit uto Bioló gico, Campin as, SP, ut ilizan do -se o mét odo de croma to gra fia gasosa para a determinação analítica de resíduos. Em pr eg ou -se o fa to ri al 8 X 5, "é po ca s de amostragem do solo" X "profundidades de a mo s t r a ge m" , qua t r o r e pe t i ç õe s pa r a o s procedimentos experimentais no campo, reduzidas pa ra du as na s de te rm in aç õe s an al ít ic as . Os r e s u l t a d o s d e m o n s t r a r a m q u e a m a i o r concentração do herbicida localizou-se na camada supe rfi cial do solo (0-10 cm de profundidade), onde persistiu até 360 dias após o tratamento na concentração de 0,08 mg/kg de solo. A curva de persistência do produto, para a profundidade de 010 cm , foi re pr es en ta da po r um a eq ua çã o exponencial do terceiro grau. Foram encontrados resíduos de simazina nas camadas de solo à pro fun did ade s de 10 -20, 20 -30 e 30 -40 cm até 1 8 3 , 6 5 e 6 5 d i a s a p ó s o t r a t a m e n t o , respectivamente.Palavras chave: Resíduo, solo, herbicida, ecotoxicologia. ABSTRACTPersistence and leaching of simazine in soil planted with corn.The soil persistence and leaching of simazine were investigated under field conditions at Campinas, SP, Brazil in a loamy podzol redyellow soil planted with corn crop. Simazine was applied at the rate of 3,0kg/ha a.i. at preemergence of weeds and corn on january, 14 1992. Gas chromatography analysis of soil samples taken at five different depths (0-10cm, 10-20cm, 20-30cm, 30-40cm and 40-50cm), eight times after simazine application over the year showed that the highest herbicide concentra tion was found at the 0-10cm layer; simazine residues we re no t fo un d be lo w 40 cm so il de pt h an d persistence curve of the herbicide was accounted for a 3 rd . gra de reg res sio n. One yea r aft er the treatment simazine residues were found in the soil (0,08 mg/kg).

Sorption and leaching potential of herbicides on Brazilian soils

“…(1995) estimated simazine t 1/2 to be 28 d in a sandy soil (pH 5.3 and 0.53% OC). Recently, Blanco et al . (1997) have assumed a t 1/2 of 22 d in surface samples (0–10 cm) of a loamy‐sand soil (17.3% clay, pH 5.8 and 0.69% OC) in Campinas, SP (Brazil).…”

Herbicide — Soil Interactions, Applied to Maize Crop Under Brazilian Conditions

“…In this experiment, [37] observed that the soil solution pH varied from 6.8 to 5.3 in soil samples; and the simazine pK (21°C) = 1.7 indicated that, under these conditions and despite simazine being a weak base, most herbicide molecules would be in the molecular form (only 0.006% would be ionized). According to [45,46], simazine presents log Kow = 1.51 characterizing its lipophilic property, and increasing the chances of herbicide molecule sorption by soil colloids.…”

“…Blanco [37], determined herbicide persistence and lixiviation up to 50 cm soil depth, using gaschromatography, in a field experiment with simazine applied as a pre-emergent herbicide in maize at the rate of 3 kg ha -1 (a.i. = active ingredient), in the State of São Paulo, Brazil.…”

“…Blanco et. al [37,47] carried out field experiments in the same period and edaphoclimatic conditions, allowing the comparison between simazine and metolachlor results: metolachlor presented higher persistence (380 DAT) than atrazine (184 DAT), and this latter showed lesser lixiviation (until 20 cm depth), once metolachlor and simazine lixiviated until 30 and 40 cm depth, respectively. From these results it might also be inferred that when these herbicides are sequentially used in successive crops, undesirable product residue amount might accumulate in the soil.…”

“…Simazine residue means determined in several soil depth samples (layers from 0-10 until 40-50 cm), collected in different sampling dates[37].…”