The effect of chemical, biological and organic nutritional treatments on sunflowers yield and yield components under water deficit stress

To achieve the higher economic yield of crop plants, supplying enough nutrients to plants is very important. Moreover, nutrient uptakes by plants is influenced by the soil water contents. However, nowadays chemical fertilizer application is important agronomic factor that has significant effects on growth and quantity and quality of final yield, but traditional nutrient management and excessive use of chemical fertilizers may cause the environmental problems such as contamination of soil and water resources, low quality of agricultural products and reduction of soil fertility. These factors have drawn attention to health and ecological sustainable farming systems (Sharma, 2002). In this context, usage of organic and biological products for plant nutrition is considered as one of the solutions to achieve the goals of sustainable agriculture.
To evaluate the effect of various feeding systems on yield and yield components of sunflower (Helianthus annuus L.) under the influence of water deficit stress, a split-plot experiment based on randomized complete block design with three replications, was carried out in the Agricultural Faculty of Bu-Ali Sina University during the growing season of 2013-2014. Main plots consisted of two irrigation levels: optimum irrigation and deficit irrigation stress (irrigation after 60 and 120 mm evaporation from evaporation pan, class A, respectively) and sub-plots included of nine nutrition systems: 1- no bio or chemical fertilizer application, 2- 100% of the recommended chemical fertilizer , 3- vermicompost, 4- phospho nitro kara, 5- vermicompost phospho nitro kara, 6- vermicompost ½ chemical fertilizer, 7- phospho nitro kara ½ chemical fertilizer, 8- vermicompost phospho nitro kara ½ chemical fertilizer, 9- ½ proposed chemical fertilizer. Phospho-nitro-kara which contains phosphate solubilizing and nitrogen fixing bacteria (Bacillus coagulans, azotobactr chroocuccum and Azospirilium lipoferum) was impregnated with seeds. Vermicompost was mixed with the soil before planting based on the recommendation of the producer company (15 t.ha-1). After determining evapotranspiration of the reference plant (ET0) by FAO- Penman-Monteith method and crop coefficients (Kc) in different stages of crop growth, plant water requirement was determined (Allen et al., 1998). Finally, the irrigation water volume was estimated according to the effective rainfall, irrigation efficiency (60%) and 45% depletion of soil moisture in the root zone (Doorenbos & Kassam, 1979).
Water deficit stress and nutrient treatments significantly affected all measured traits except the harvest index. Water deficit stress significantly reduced head diameter by 24% in comparison with optimum irrigation. The maximum diameter (17.03 cm) was obtained in vermicompost treatment. One thousand seed weight of sunflower under optimum irrigation was 1.3 times as much as water deficit treatment. Combined treatment of vermicompost and half of recommended chemical fertilizer yielded maximum 1000- seed weight (56.67 g). Under optimum irrigation, the highest weight of the head was achieved from 100% chemical fertilizer application, while under water stress, maximum head weight (830.67 g) was obtained in vermicompost treatment and the minimum value (485.33 g) was obtained from chemical fertilizer vermicompost phospho nitro kara. In both irrigation levels, the highest biological yield was obtained from full application of chemical fertilizer, but this treatment in stress condition did not have significant difference with combined application of vermicompost and half of chemical fertilizer, vermicompost and 50% of chemical fertilizer. 100% recommended chemical fertilizer in optimum irrigation, had a maximum grain yield (693.67 g.m-2).
Organic fertilizers by increasing soil organic matter, improving soil chemical properties such as pH and CEC, increasing the activity of microorganisms and nutrient accessibility led to increase soil fertility. In this study, especially under stress condition, it was observed that vermicompost by increasing water holding capacity and nutrients availability, improvement of plant growth, increasing assimilation and transmission of assimilates to seeds, led to increase the economic yield of sunflower.
In conclusion, although chemical fertilizers play an important role in enhancement of crop yield, though may cause some environmental problems too. In addition,biological fertilizers alone can not provide nutrient requirements of crops. Generally, in order to achieve sustainable agriculture, especially under the influence of water stress condition, it seems that reduction of chemical fertilizers and replacing them with vermicompost can be an effective method.