1975 AJCS 12(12):1975-1982 (2018) ISSN:1835-2707 doi: 10.21475/ajcs.18.12.12.p1405 Effect of Boron (B) and lime on production of watermelon in dystrophic yellow latosol soil Raquel Sobral da Silva¹, Marileia Barros Furtado¹, Nítalo André Farias Machado*², Hosana Aguiar Freitas de Andrade¹, Analya Roberta Fernandes Oliveira¹, Maryzélia Furtado de Farias¹, Luisa Julieth Parra- Serrano¹, Jomar do Livramento Barros Furtado¹, Raissa Rachel Salustriano Silva-Matos¹, Marcos Renan Lima Leite¹ 1 Center of Agrarian Sciences and Environmental, Federal University of Maranhão (UFMA), Chapadinha, Brazil ²Technological and Exact Sciences Center, State University of Western Paraná (UNIOESTE), Cascavel, Brazil *Corresponding author: nitalo-farias@hotmail.com Abstract The low concentration of boron in the soil is one of the main challenges for the cultivation of watermelon in regions of the Cerrado biome, due to the appearance of rot apical which may occur due to the lack of boron in the soil or due to boron toxicity by the use of fertilizers without recommendation. There is a narrow range between the appropriate and toxic level pf boron. Therefore, the objective of this study was to evaluate the effect of boron doses on watermelon production in the soils with and without liming. The experiment was carried out in a dystrophic yellow latosol soil, in a randomized block design in subdivide plots: plots (i) liming or without liming and subplots: (ii) boron (0, 2, 4 and 5 kg.ha -1 ), with 8 treatments and 5 replicates. The data were analyzed by regression analysis. The maximum point of the equation was estimated by equating the first derivative of the equation to zero. The diameter, length, weight, number of commercial fruits, bark thickness, percentage of fruits with apical rot, commercial fruits, female flowers, total soluble solids, productivity and profitability were evaluated. The use of boron provided positive effects on the analyzed variables. However, in concentrations higher than 4 kg ha -1 its behavior was fitted with a quadratic model (R²: 0.77 to 0.99). The range was equivalent to 2 to 4 kg ha -1 of boron with a specific level of 2.4 kg.ha -1 , whereas the base saturation rose to 70%, promoted greater productivity for watermelon cultivated in dystrophic yellow latosol under conditions of the closed biome. Keywords: Fertilization, Citrullus lanatus L, Apical rot, Calcium. Abbreviations: IAA_ indoleacetic acid; B_Boron; Ca_Calcium. Introduction The cultivation of watermelon (Citrullus lanatus L.) is widespread in countries with high temperatures due to its nutritional value, succulence and good flavor. Moreover, the easy handling combined with the lower cost of production, make watermelon one of the most cultivated fruits in the world, compared to other crops (Oliveira et al., 2012; Bhosale et al., 2017). In Brazil, watermelon cultivation has been extended to the areas of the Cerrado (Carmo et al., 2015), especially due to the high profitability in the off- season period of grain cultivation. One of the main obstacles to the production of watermelon in the Cerrado is related to the impact of the apical rot caused by calcium (Ca) deficiency and boron (Ferreira et al., 2013), which is related to the low content of organic material in the soil and the reduced amount of B in the mineralogical composition of them. In addition, as the Cerrado soils are acidic, the use of liming is indispensable and has the consequence of raising the pH, culminating in the higher concentration of B in the form of borate anions, which implies a greater adsorption, and consequently less availability to cultures. B is an essential micronutrient for the cultivation of watermelon because it is related to physiological processes essential for production, such as the formation of the pollen tube, favoring fertilization and fruit formation (Ferreira et al., 2013; Farag et al., 2017). However, the lack of elucidation on the requirement of boron, the adequate dose and the response of the watermelon to its application are still unknown because of the narrow range between the appropriate level and the toxic, which makes the recommendations based on empirical methods of dose response triggering productive impacts such as toxicity or physiological disturbances. On the other hand, Ca is a nutrient of extreme importance for proper formation of the cell wall (Zeist et al., 2016) and, similarly to B, it is found in deficient amounts in the mineralogical composition of soils of the Cerrado, being supplied by liming. Ca and B present strong soil interaction, and Ca content decreases when there is excess B in the soil, while low Ca contents cause B deficiencies (Malavolta, 1997). The interactions between B and Ca increase the margins of error dose-responses based on recommendation