32 AJCS 11(1):32-37 (2017) ISSN:1835-2707 doi: 10.21475/ajcs.2017.11.01.pne180 Growth and biomass of sunflower under different nitrogen levels and available water in the soil of a semi-arid region Samuel Silva 1 , José Alberto Ferreira Cardoso 2 , Hallyson Oliveira 2 , Ronaldo do Nascimento 2 , Rafaela Félix Basílio Guimarães 2 , Armindo Bezerra Leão 2 1 Federal Institute of Alagoas (IFAL) Campus Piranhas, Alagoas, Brazil 2 Federal University of Campina Grande, Academic Unit of Agricultural Engineering, Campina Grande, 58.109- 970, Paraíba, Brazil *Corresponding author: hallysonoliveira_@hotmail.com Abstract The adequate water supply and nitrogen in the soil is essential for the growth and development of plants. Sunflower is the target of several studies of such factors due to the economic importance and the needs to expand in the semi-arid regions of Brazil. This work aimed to evaluate the growth variables, measured at 80 days after sowing (DAS), and the biomass obtained at 100 DAS of the Helio 253 sunflower hybrid under the effect of nitrogen and water levels. The experiment was conducted in a greenhouse in the city of Campina Grande- PB, in split-plot of a completely randomized design with four moisture levels in the soil (50, 75, 100 and 125% of available water) and four nitrogen rates (30, 60, 90 and 120 kg ha -1 ). Among all levels of available water in the soil, the stem diameter (SD) ranged from 13.6 to 19.6 mm and the plant height (PH) from 93 to 107 cm. Plants with 100% AW showed a leaf area (LA) 45% greater than the treatment with higher water stress. The heads had an average diameter between 83 and 98 mm, the dry biomass of the heads (DBC) and total dry biomass (TDB) ranged from 45 to 55 g and of 65 to 101 g, respectively. The weight of a thousand seeds per head (W1000) obtained minimum and maximum of 49 and 66 g. The stem diameter ranged between 14.4 to 18.3 mm and the minimum and maximum plant height values were 93 and 110 cm, using applied N levels. The leaf area varied from 22 to 36 dm 2 and the heads had average diameter of 86 to 99 mm. With respect to the dry biomass of the heads, there was a variation of 38 to 68 g and TDB of 68 to 107 g and W1000 valued between 52 and 65 g under doses of N. There is considerable variation in all variables mainly due to increased water level in the soil and nitrogen fertilization. Keywords: Helianthus annuus L., irrigation, nitrogen fertilization. Abbreviations: DAS_days after sowing; N_nitrogen; WRC_water retention capacity; ETo _ reference evapotranspiration; AW_available water; SD_stem diameter; PH_plant height; LA_leaf area; CD_head diameter; DBC_dry biomass of the head; TDB_total dry biomass; W1000_thousand seed weight; ABA_abscisic acid. Introduction Sunflower is native to North America and currently is grown on every continent, as it has wide adaptability to different environmental conditions and its income is little influenced by latitude, altitude and photoperiod (Zobiole et al., 2010). In Brazil, sunflower is an option preferred as the second crop in the summer (off-season). There are many prospects of cultivation and growth of sunflower in the country. It is mainly due to the production of biofuels and also to serve as a noble edible oil in the market, confectionery, bird foods, silage, meal for animal feed, ornamental production, honey production, and the possibility of export of grain and oil (Person, 2013; Silva et al., 2014). The need to increase production to meet Brazil's domestic demand requires not only the expansion of the agricultural area, but also increase of the crop productivity, depends to several factors such as adequate mineral nutrition of plants and favorable water conditions (Oliveira et al., 2010). In Brazil, there are problems that limit the productivity of sunflower such as the irregular distribution of rainfall during the year (Silva et al., 2015) and the lack of nutrients in the soils, mainly nitrogen (Faria et al., 2015). The sunflower accumulates large amounts of nutrients, in which the nitrogen (N) is the major one. However, its response to fertilization is limited (Jardini et al., 2014), due to its deep root system which increases the operating capacity and utilization of natural soil fertility and also the fertilizing of the previous crop, with absorption of nutrients from deeper layers (Santos et al., 2013a). Moreover, Santos Jr. et al. (2014) reported that N is the largest nutritional limiting factor on sunflower productivity and absence of N provides a reduction of up to 60% in the potential for sunflower production. The maximum production of sunflower has been achieved with N rates between 80 to 90 kg ha -1 . However, with doses of N between 40 and 50 kg ha -1 it is possible to obtain 90 % of maximum relative production, which is equivalent to the amount of the nutrient economically efficient (Lobo et al., 2013). Santos et al. (2010) observed that the sunflower exported 71 % of N of the cumulative total. Santos et al. (2013b) reported that the excess of nitrogen is also harmful, as it causes excessive growth of sunflower, causing sensitive leaves, favorable for the incidence of pests and diseases. In turn, this affects production of grains, as well as problems with lodging and decrease in percentage of oil. Therefore, the amount of N to be applied needs to be determined for each type of soil, area and crop. The amount of water required for the crop is also not well-defined, but in the majority of the