Abstract
Water deficit is one of the limiting factors of agricultural production, especially in semi-arid regions. In this sense, the aim of this study was to evaluate the growth and the physiological characteristics of sunflower cv. Helio 251 at different levels of water replacement and potassium doses in an experiment conducted in the greenhouse of the Center for Technology and Natural Resources of UFCG, Campina Grande, PB. The experiment was laid out in randomized complete block design, by studying five levels of water replacement (40, 60, 80, 100 and 120% of actual evapotranspiration - ETr) associated with potassium fertilizer levels (50; 75; 100; 125 and 150% of the indication for assays). The increase of water replacement levels promoted increase in plant height, stem diameter, number of leaves per plant, leaf area, and dry biomass of leaves, and dry biomass of the stem. The level of 75.25% of ETr provided the highest leaf dry weight (0.88 g). The increase in water replacement from 51.33% of ETr provided a reduction in the SPAD index. Water replacement lower than 100% ETr affected gas exchange of sunflower plants, reducing rate of the rate of the photosynthesis by 66% by the water deficit in the soil. The potassium doses had no effect on sunflower growth at 45 DAS neither they altered gas exchange in sunflower plants in the grain filling stage. Key words: Helianthus annuus L., water stress, SPAD index, gas exchange, rate of the photosynthesis.
Highlights
The increase in water replacement from 51.33% of ETr provided a reduction in the SPAD index
The potassium doses had no effect on sunflower growth at 45 days after sowing (DAS) neither they altered gas exchange in sunflower plants in the grain filling stage
It can be observed that the higher values of % ETr (100 and 120) presented the highest mean values for plant height (PH), stem diameter (SD), NL, leaf area (LA), dry biomass of leaves (DBL) and dry biomass of the stem (DBS); on the other hand, the lowest values of % ETr (40, 60 and 80) presented the highest values for SPAD (%)
Summary
Sunflower (Helianthus annuus L.) is a very important crop for the Brazilian semiarid region because of its broad climatic adaptability, high drought tolerance and yield (Prado and Leal, 2006), providing a greater competitive advantage over other crops such as soybeans, because it has higher yield per hectar in oil production (Zobiole et al, 2010). In this sense, sunflower can be used to meet the noble edible oils market, feeding birds, silage production, meal and cake for animal feed, ornamental production as well. Sunflower accounts for about 13% of all vegetable oil produced in the world, with in recent years, increase in cultivated area (Nobre et al, 2011)
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