Sulfentrazone leaching potential is dependent on soil properties such as strength and type of clay, organic matter content and pH, and may result in ineffectiveness of the product and contamination of groundwater. The objective of this study was to evaluate sulfentrazone leaching in five soils of the sugarcane region in the Northeast Region of Brazil, with different physical and chemical properties, by means of bioassay and high-performance liquid chromatography (HPLC) resolution. The experiment was conducted in a split plot in a completely randomized design. The plots had PVC columns with a 10 cm diameter and being 50 cm deep, filled with five different soil classes (quartzarenic neosol, haplic cambisol, yellowish-red latosol, yellowish-red acrisol, and haplic gleysol), and subplots for 10 depths in columns, 5 cm intervals. On top of the columns, sulfentrazone application was conducted and 12 hours later there was a simulated rainfall of 60 mm. After 72 hours, the columns were horizontally placed and longitudinally open, divided into sections of 5.0 cm. In the center of each section of the columns, soil samples were collected for chromatographic analyses and sorghum sowing was carried out as an indicator plant. The bioassay method was more sensitive to detect the presence of sulfentrazone in an assessment for chromatography soil, having provided greater herbicide mobility in quartzarenic neosol and yellowish-red latosol, whose presence was detected by the indicator plant to a depth of 45 and 35 cm, respectively. In the other soils, sulfentrazone was detected up to 20 cm deep. The intense mobility of sulfentrazone in quartzarenic neosol may result in herbicide efficiency loss in the soil because the symptoms of intoxication and the amount of herbicide detected via silica were highest between 15 cm and 35 cm depth regarding the soil surface layer (0-10 cm), indicating that sulfentrazone should be avoided in soils with such characteristics.

A B S T R A C TSunflower is a crop that has aroused the interest of farmers because of its adaptability to wide climatic conditions and for its use in biodiesel production. However, there are only a few studies on sunflower fertilization in alkaline soils. This study aimed to evaluate nitrogen (N) and phosphorus (P) fertilization in sunflower (Helianthus annuus L.) cultivated in alkaline soil. A field experiment was carried out in Baraúnas-RN, Brazil, in a Haplic Cambisol derived from calcareous rock, where the sunflower H-251 hybrid was cultivated. The treatments were a combination of four doses of N (30, 60, 90 and 120 kg ha -1 ) and four doses of P 2 O 5 (30, 60, 90 and 120 kg ha -1 ). Sunflower growth and yield increased with the doses of N and P 2 O 5 . Doses of 30 kg ha -1 of N and 30 kg ha -1 of P 2 O 5 were more economical, corresponding to grain yield of 2378 kg ha -1 . Critical levels associated with these doses of N and P 2 O 5 were 28.2 g kg -1 for N leaf content, 2.84 for P leaf content, and 6.75 mg dm -3 for soil available P extracted by Mehlich-1.Adubação nitrogenada e fosfatada na cultura do girassol em Cambissolo alcalino R E S U M O O girassol é uma cultura que tem despertado o interesse dos produtores por sua adaptabilidade a diferentes condições climáticas e pela possibilidade de produção de biodiesel. Porém, pesquisas sobre adubação de girassol em solos alcalinos são escassas. Neste trabalho, objetivou-se avaliar a resposta da cultura do girassol (Helianthus annuus L.) à adubação nitrogenada e fosfatada em solo alcalino. O experimento de campo foi conduzido no município de Baraúnas, RN, em um Cambissolo Háplico eutrófico, onde se plantou o híbrido de girassol H-251. Os tratamentos resultaram da combinação de quatro doses de N (30, 60, 90 e 120 kg ha -1 ) e quatro doses de P 2 O 5 (30, 60, 90 e 120 kg ha -1 ). O crescimento e a produtividade do girassol aumentaram com o incremento das doses de N e de P 2 O 5 . As doses de 30 kg ha -1 de N e 30 kg ha -1 de P 2 O 5 se mostraram mais econômicas, correspondendo à produtividade de 2.378 kg ha -1 de grãos. Os níveis críticos associados a essas doses econômicas de N e de P 2 O 5 foram 28,2 g kg -1 para o teor de N na folha, 2,84 g kg -1 para o teor de P na folha, e 6,75 mg dm -3 para o P disponível no solo pelo extrator Mehlich-1.

-Ametryn is one of the most widely used herbicides in the sugarcane culture. Little is known about the interactions between this herbicide and the attributes of soils in the sugarcane region of northeastern Brazil. This knowledge, before recommending herbicide, will minimize the negative effects on the environment, particularly on water resources, and will ensure weed control efficacy. In this work, ametryn leaching potential was estimated through bioassays and chromatography, in five soils from the sugarcane region in northeastern Brazil: Quartzarenic Neosol (Entisol); Red Argisol (Ultisol); Ferrihumiluvic Spodosol (Spodosols); Red-Yellow Acrisol (Oxisol) and Haplic Cambisol (Inceptisols). To achieve this, columns were prepared with samples of the respective soils. On top of these columns ametryn was applied and, 12 hours later, a 60 mm rainfall was simulated. After water draining (72 hours after herbicide application), the columns were longitudinally opened to withdraw samples of each soil, every 5 cm. On some of these samples, ametryn quantification was performed by high-performance liquid chromatography and, on the others, biological assays were performed to confirm the results. Ametryn mobility was influenced by the physical-chemical characteristics of soils, mainly by organic matter content, texture and cation exchange capacity (CEC). However, this cannot be considered for Ferrihumiluvic Spodosol, whose cementing characteristics restrict the infiltration of water and organic compounds. Increased leaching ametryn occurred in Quartzarenic Neosol (Entisol), with higher herbicide concentration in the 5 to 10 cm depth layer, in relation to the 0 to 5 cm surface layer, indicating possible agronomic efficiency loss and higher risk of groundwater contamination.Keywords: herbicide, liquid chromatography, bioassay, mobility. RESUMO -O ametryn é um dos herbicidas mais utilizados na cultura da cana-de-açúcar, e pouco se conhece sobre as interações desse herbicida com os atributos dos solos da região canavieira do Nordeste brasileiro. Esse conhecimento antes da recomendação do herbicida permite minimizar os efeitos negativos ao ambiente -em especial, aos recursos hídricos -e garantir a eficiência no