Journal of Agricultural Science; Vol. 11, No. 2; 2019 ISSN 1916-9752 E-ISSN 1916-9760 Published by Canadian Center of Science and Education 465 Determination of Basal Temperature and Its Relationship With Jatropha Crop in Irrigated and Non-irrigated System Diogo H. M. Moraes 1 , Derblai Casaroli 1 , Adão W. P. Evangelista 1 , José Alves Júnior 1 , Rafael Battisti 1 & Marcio Mesquita 1 1 College of Agronomy, Federal University of Goiás, Goiânia, Brazil Correspondence: Diogo H. M. Moraes, College of Agronomy, Federal University of Goiás, Goiânia, Brazil. Tel: 55-649-9243-3948. E-mail: diogo.slmb@gmail.com Received: October 30, 2018 Accepted: November 30, 2018 Online Published: January 15, 2019 doi:10.5539/jas.v11n2p465 URL: https://doi.org/10.5539/jas.v11n2p465 Abstract Full plant growth and development require, among others, air temperatures and water availability at levels appropriate to each crop. The effect of temperature on plant development can be represented by the thermal sum, which requires the lower basal temperature for each plant species. However, plant responses may be different when associated with different soil water contents. This work determined the lower and upper basal temperature of Jatropha curcas L. and verified the relationship between thermal sum and crop development under different water regimes, in the climatic conditions of Goiânia, GO, Brazil. We evaluated twenty-four plants cultivated at the planting density of 2,222.2 plants ha -1 . Of these, twelve plants were irrigated from October 2010 to October 2012, whereas the other twelve remained unirrigated. Basal temperatures were estimated by four different methods described in the literature, in two phases of observation, maturity and total cycle. From the results, regression analysis was performed. The lower basal temperature was 4.9 and 7.2 °C, and upper basal temperature was 38.8 and 36.8 °C, respectively, for the maturity and total cycle stages. The accumulated thermal sum for the complete plant development of jatropha was 10,314.55 DD (±1574.73) for the non-irrigated treatment, and 9,260.67 DD (±735.06) for the irrigated treatment. The results of plant development showed good coefficient of determination in relation to the accumulated thermal sum. Keywords: Jatropha curcas L., temperature, degree-days, growth and development 1. Introduction Jatropha curcas L. is a perennial monoic species belonging to the family Euphorbiaceae, which also includes species of castor bean (Ricinus sp.), manioc (Manhiot sp.) and rubber tree (Hevea spp.). Regarding production, its main characteristic is to supply raw material for Biodiesel generation. It is considered a rustic, sunlight-demanding crop with high resistance to drought. Jatropha presents great adaptability to diverse edaphoclimatic and low soil fertility conditions (Arruda, Beltrão, De Souza, Jamil Marur, & Severino, 2004; Freitas, Missio, Matos, Resende, & Dias, 2011). Pena, Evangelista, Casaroli, and Alves Júnior (2016) determined the temperature range suitable for the development of jatropha: between 15 and 28 °C. Moreover, the authors observed that there are no regions unfit for crop development in the state of Goiás. The water demand of jatropha, for its full development, is 1,200 mm annual water. Tolerant to drought, jatropha also tolerates rainfall between 360 and 2,400 mm. However, so as not to affect production, ideal cultivation would be in regions where the deficit does not exceed 720 mm (Yamada & Sentelhas, 2014). Temperature is one of the main environmental parameters delimiting environmental conditions for the development of a plant species. In plants, metabolic processes are highly dependent on the temperature of the site where they grow. Environmental temperature exerts a great impact on plant photosynthesis and respiration, since it influences several biochemical reactions related to these two physiological processes (Taiz & Zeiger, 1998; Beltrão & De Oliveira, 2008). Extreme air temperatures do not favor the development of certain enzymatic reactions in plants. For this reason, each plant species develops best within a certain air temperature threshold (Bonhomme, 2000).