Behavior of Sunflower Irrigated With Salt Water and Nitrogen Fertigation

The sunflower (Helianthus annus L.) crop has been gaining prominence in wastewater research due to its relevance to the production of edible oil, biodiesel and ornamental and decorative material. In the field of floriculture, the crop has been emerging as an alternative offer of a short-cycle product, with contrasting colors and easy identification by the consumer. The objective of this work was to evaluate the different electrical conductivities of water associated with nitrogen fertigation rates on the vegetative, physiological and productive behavior of ornamental sunflower. The experimental design was completely randomized, in a factorial scheme 6x4, referring to six levels of electrical conductivity of water (ECa of 0.5, 1.5, 2.5, 3.5, 4.5 and 5.5 dS m-1) and four nitrogen fertigation rates, with one control and the other three applications performed every 10, 20 and 30 days after emergence (DAE), with five replications, totaling 120 experimental units. The variables analyzed were: stem diameter, root length, chlorophyll a, b and total chlorophyll content, fresh and dry phytomass of shoots, roots and total phytomass, seed mass and capitulum mass. The salinity negatively affected the physiological variables, growth and productivity evaluated, decreasing with increasing electrical conductivity of irrigation water (dS m-1). Nitrogen fertigation at 10 days after emergence resulted in an increase in the stem diameter of sunflower plants.


Introduction
Sunflower (Helianthus annuus L.) is an annual dicotyledon belonging to the family Asteraceae, originating in North America (Zobiole et al., 2010).This species, besides being an important option for the agricultural producer in systems involving crop rotation or succession, presents excellent oil quality and yield, much appreciated in animal feed as a source of protein, as well as in the production of biofuels, being a crop which also aims at the commercialization of flowers (Silva et al., 2011).
The ornamental sunflower can be grown in any region of the Brazil, presenting it self as an alternative to the floriculture sector, for being a crop without great management difficulties.The crop has broad climatic irrigation, aiming at mitigating and correcting the problems arising from inadequate water supply in agriculture (Silva et al., 2011), increasing the productivity of grains, oil or dry mass in crops under irrigation.
Notwithstanding, in the Brazilian semi-arid region, due to the scarcity of surface water sources, the water used for irrigation purposes by rural families is obligatorily of subterranean origin (crystalline basement), which in most cases presents restrictions of use for having high salt concentration, especially sodium, determining production limitations, with damaging effects to plants in their different phases, in addition to causing problems of edaphic and environmental degradation, leading to problems of great proportions in the productivity of agricultural crops (Andrade et al., 2012;Costa et al., 2013).The saline water as well can to change the soil aggregate structure, reduce the permeability, increase the salinity and restrict the water, nutrients and oxygen availability (Russo, 2005;Wong et al., 2008).
Nitrogen (N) is the most required nutrient for the greatest diversity of cultivated plants, because the development is highly dependent on the availability of this nutrient due to its functions in plant metabolism, participating as a constituent of the molecule of chlorophyll, nucleic acids, amino acids and proteins (Taiz & Zeiger, 2012).
In view of the above, the objective of this work was to evaluate the different electrical conductivities of irrigation water associated with nitrogen fertigation rates on the vegetative, physiological and productive behavior of ornamental sunflower.

Materials and Methods
The experiment was conducted in a screened greenhouse, between October 2014 and February 2015, in the Agricultural Sector of the Center for Human, Social and Agrarian Sciences (CCHSA) of the Federal University of Paraíba (UFPB), Campus III, in Bananeiras-PB, located in the microregion of Brejo Paraibano, at 6º45′ S latitude and 35º37′ W longitude, with a hot and humid (tropical rainy) climate.
The experimental design was completely randomized, in a factorial scheme 6 × 4, referring to the irrigation water salinity in six electrical conductivities of water (ECa of 0.5, 1.5, 2.5, 3.5, 4.5 and 5.5 dS m -1 ) and four fertigation times with nitrogen in the amount of 60 kg ha -1 , being one control (without fertigation) and fertigation performed at 10, 20 and 30 days after emergence (AED), with five replications.The source of nitrogen was utilized by urea.
The experimental units were composed of pots with a volumetric capacity of 1.3 dm 3 (15 cm high), filled by a substrate formed by vegetal soil and bovine manure, in the ratio of 3:1 (v/v), (Table 1).The seeding was carried out in October 2014, and the seeds were sown directly in the pot.The seeds began their emergence 5 days after sowing.When they reached 10 cm in height, thinning was performed, leaving a single plant per experimental unit.The variety used in the experiment was the cultivar "Sol Noturno".
During the experimental period, the temperature and humidity of the air were measured daily with a digital termo-hygrometer installed in the experimental area, at the height of the benches (Table 2).

Table 1 .
Chemical and fertility characterization of the substrate used in the experimental units

Table 2 .
Average of the temperature e humidity maximum and minimum of the conduction environment of the experiment t stem diamete ertigation (Fig addition of nitr lants.These re owers bottled i d Santos Júnio meter of the ave ans higher sto being desirabl also emphasiz ong intensity o ma savanna, o the nutritiona dard by Grieve al sunflower p to the 20 (•••••) a on of the electr observed that t on at 10 DAE le those found se verified the 6) in experime 7.7 mm for the hat contribute ms have suffici gical function, off et al. (201 n values of 12.2 n tested, are w 010).d with saline w (-••-••) days aft