Effect of Irrigation with reclaimed water on fruit characteristics and photosynthesis of olive trees under two irrigation systems
Gheisari, M., N. Ashrafi, A. Maleki and A. Nikbakht. 2015. Effect of Irrigation with reclaimed water on fruit characteristics and photosynthesis of olive trees under two irrigation systems. Journal of Water and Soil. 29: 569-577(In Persian with Eng. Abstract)
Introduction: Olive (Olea europaea L.) trees are mainly cultivated in the Mediterranean area and are grown for their oil or processed as table olives. Despite the fact that olive is known to be resistant to drought conditions due to its anatomical, physiological, and biochemical adaptations to drought stress, reports indicate that the olive can be adversely affected by drought stress, which has a negative effect on the growth of olive trees. In the absence of adequate supplies of water, the demand for water can be met by using improved irrigation methods or by using reclaimed water (RW). Reports have shown that recycled water has been used successfully for irrigating olive orchards with no negative effects on plant growth.Attention has been paid to reclaimed water as one of the most significant available water resources used in agriculture around large cities in arid and semi-arid regions. On the other hand, irrigation efficiency is low and does not meet the demands of farmers.In order to investigate the possibility of irrigating olive orchards with subsurface leakage irrigation (SLI) in application of reclaimed water, an experiment was carried out with the aim of investigating the effect of reclaimed water on photosynthetic indices and morphological properties of olive fruit.
Materials and Methods: Research was conducted using a split-plot experimental design with two factors (irrigation system and water quality) on the campus of Isfahan University of Technology in Isfahan, Iran, on a sandy-clay soil with a pH of 7.5 and electrical conductivity (EC) of 2.48 dSm-1.PVC leaky tubes were used for the SLI system. The SLI system was installed 40 cm from the crown of each tree at a depth of 30 - 40 cm.At the end of the experiment fruit yield, weight per fruit, volume, length and firmness were calculated. A portable gas exchange system (Li-6400., LICOR, Lincoln, NE, USA) was used to measure the net rate photosynthesis (A), the internal partial pressure CO2 (Ci), and stomatal conductance (gs) between (09.30 – 11.30 h) on a fully expanded current season leaves situated at mid canopy height. Statistical assessments of differences between mean values were performed by the LSD test at P = 0.05.
Results and Discussion The results revealed that reclaimed water enhanced fruit yield, weight (15%), volume (23%) and leaf photosynthesis (22%) in plants compared with clear water. Recycled water was found to supply more nutrients than clear water. High nutrient concentrations in RW, compared to those in clear water, result in nutrient accumulation in the soil, making them available to plant roots to promote overall plant growth and fruit production. Improved N, P, K nutrition of wastewater-irrigated plants has been reported (Farooq et al, 2006). Olive leaves and stems represent storage organs for N and release it in response to the metabolic demands of developing reproductive and vegetative organs (Fernandez-Escobar et al., 2004). However, Al-Abasi et al. (2009) found no statistical differences. Irrigation with SLI systems increased the photosynthesis (33%), and stomatal conductance (57%) when compared with surface irrigation systems. The results showed that reclaimed water had a significant effect on photosynthesis and stomatal conductance. However, fruit length and firmness had no significant difference. Substomatal CO2 decreased when the SI systems were used for irrigation. Also SLI system could enhance fruit yield (65%), weight (17%), photosynthesis (32%) and chlorophyll Fluorescence (Fv/Fm) (18%). The SLI systems with recycled water induced greater shoot growth, total leaf surface area, and transpiration during the entire growing period. This led to an overall positive effect on mean fruit weight and total fruit production per tree. The SLI system applying RW led to more photosynthesis by 34% as compared to the SI system. In the present study, the SLI system delivered water directly in the root zone and improved water availability, which enhanced photosynthetic assimilation rates and plant growth to a great extent. David et al. (2003) showed that subsurface drip irrigation versus other irrigation methods reduced evaporation and improved growth and production in peach trees.