Persistence of auxinic herbicides applied on pasture and toxicity for succeeding crops

Anais da Academia Brasileira de Ciências (2018) 90(2): 1717-1732 (Annals of the Brazilian Academy of Sciences) Printed version ISSN 0001-3765 / Online version ISSN 1678-2690 http://dx.doi.org/10.1590/0001-3765201820170134 www.scielo.br/aabc | www.fb.com/aabcjournal Persistence of auxinic herbicides applied on pasture and toxicity for succeeding crops* ARNON H.C. ANÉSIO1, MÁRCIA V. SANTOS1, RAUL R. SILVEIRA1, EVANDER A. FERREIRA2, JOSÉ B. DOS SANTOS2 and LEANDRO D. DA SILVA1 1 Departamento de Zootecnia, Universidade Federal dos Vales do Jequitinhonha e Mucuri, Campus JK, Rodovia MG 367, 5000, Alto do Jacuba, 39100-000 Diamantina, MG, Brazil 2 Departamento de Agronomia, Universidade Federal dos Vales do Jequitinhonha e Mucuri, Campus JK, Rodovia MG 367, 5000, Alto do Jacuba, 39100-000 Diamantina, MG, Brazil Manuscript received on February 23, 2017; accepted for publication on November 22, 2017 ABSTRACT The aim of this work was to determine the persistence of auxinic herbicides applied on tropical pasture and toxicity for succeeding crops. The herbicides were applied in an area of dystrophic red‒yellow latosol with pasture infested of weeds. At 40, 80, and 280 days after application of herbicide, the soil samples were collected at depths of 0 to 20 cm. Soil with residues of 2,4-D, 2,4-D + picloram, triclopyr, and a soil without herbicide application were analyzed with six replicates. Seven crops were cultivated in these soils: cucumber (Cucumis sativus L.), velvet bean [Mucuna pruriens (L.) DC.], pigeon pea [Cajanus cajan (L.) Millsp.], alfalfa (Medicago sativa L.), lablab bean [Lablab purpureus (L.) Sweet], corn (Zea mays L.), and sorghum [Sorghum bicolor (L.) Moench]. The plants of cucumber, pigeon pea, and alfalfa were the most susceptible to the auxinic herbicide residues. However, the lablab bean was the only one among the dicot evaluated that showed tolerance to the 2,4-D + picloram residual when cultivated in soils at 280 days after application of herbicide. Corn and sorghum showed lower chlorophyll content in soils with 2,4-D + picloram residual up to 80 days after application of herbicide. Key words: growth regulator, herbicide residue, 2,4-D, picloram, triclopyr. INTRODUCTION Auxinic or auxin‒mimetic herbicides represent the oldest and possibly the most widely used herbicide to control weeds in pastures (MacDonald et al. 2013). However, some of these herbicides have residual activity in the soil and can become undesirable, because they can result in damage to succeeding crops, contamination of water sources Correspondence to: Leandro Diego da Silva E-mail: *This work is part of the dissertation of the first author - PPGZOO/UFVJM. by leaching, and toxicity to non‒target organism (Braga et al. 2016). The herbicides 2,4-D, picloram, and triclopyr are synthetic auxins which have the highest number of commercial products registered in Brazil (MAPA 2015). In addition, these herbicides are acidic and have great mobility in soil solution. However, mainly the soil characteristics and the rainfall after application will determine the leaching index of these herbicides (D’Antonino et al. 2009a). The soil persistence of 2,4-D and triclopyr, when applied in commercial dosages, is around An Acad Bras Cienc (2018) 90 (2) 1718 ARNON H.C. ANÉSIO et al. four weeks in clayey soils and warm climate. While the picloram has a long persistence in the soil, it can be found up to two or three years after application depending on soil and environmental conditions (Deubert and Corte-Real 1986, Santos et al. 2006). However, there are few studies addressing the soil persistence of these herbicides and the intoxication of plants in systems with succession of crops. Knowledge about crop responses to herbicide residual enables the development of strategies for more intensive use of the area, in addition to the possibility of discovering crops with potential phytoremediation, bioindicators, and the best variables for evaluating crops in soils contaminated by herbicides. Therefore, based on the hypothesis that the herbicide persistence in the soil depends on several factors and the crops have a differentiated sensitivity to the auxinic herbicides. Thus, was proposed the present work with the objective of evaluating the persistence of auxinic herbicides applied on tropical pasture and toxicity for succeeding crops. MATERIALS AND METHODS The experiment was carried out in two stages. In the first stage, the herbicides were applied in a pasture of bahia grass (Paspalum notatum Flüggé) infested with siamweed [Chromolaena odorata (L.) King & H.E. Robins] and sicklepod [Senna obtusifolia (L.) H.S. Irwin & Barneby] in “Couto de Magalhães de Minas”, MG, Brazil. The herbicide was applied under suitable environmental conditions by using a sprayer with constant pressure coupled to a bar with nozzle-type range TT11002 with 3 bar pressure and volume sprayed of 150 L ha‒1. At 40, 80, and 280 days after application of herbicides (DAA), the soil samples were collected at depths of 0 to 20 cm, in representative sites of the area and in an area without herbicide application (control). The second stage of the experiment was conducted in a greenhouse at the “Universidade An Acad Bras Cienc (2018) 90 (2) Federal dos Vales do Jequitinhonha e Mucuri” in Diamantina, MG. The soil was classified as dystrophic red‒yellow latosol with clay-sandy texture and the chemical characterization described in Table I. The rainfall and temperature averages during the 280 DAA is represented in Figure 1. Four treatments with six replicates were analyzed; soil with residues of 2,4-D (1340 g a.e. ha‒1), 2,4-D + picloram (720 + 192 g a.e. ha‒1), triclopyr (960 g a.e. ha‒1), and a soil control without herbicide application. Seven crops were cultivated in these soils: cucumber (Cucumis sativus L.), velvet bean [Mucuna pruriens (L.) DC.], pigeon pea [Cajanus cajan (L.) Millsp.], alfalfa (Medicago sativa L.), lablab bean [Lablab purpureus (L.) Sweet], corn (Zea mays L.), and sorghum [Sorghum bicolor (L.) Moench]. The evaluations were performed at 20 and 40 days after sowing (DAS). The soil was sieved and the equivalent to 3 t ha‒1 of dolomitic limestone was applied. The substrates were fertilized with equivalent to 400 kg ha‒1 formulated at 8‒28‒16 (N‒P2O5‒K2O) and 100 mg dm‒3 of urea 20 days after plant emergence. Ten seeds per pot of each crop species were sown and then later thinned and two plants left per pot. Watering was done daily to keep the soil moisture with 80% field capacity. The crops grew for a period of 40 days in polyethylene pots of 7 L volume, coated with polyethylene film to avoid herbicide loss by leaching. At 20 and 40 DAS the plants intoxication were visually evaluated using a scale of 1 to 4 (EWRC 1964). Where 1 represents no toxicity (normal plants), 2 mild intoxication (intoxication evident only in the leaf blade, with folds at the edges), 3 moderate intoxication (plants with more intense folds, increase o (...truncated)