Crop yield response to water - Cra

clayey soils. If supply is very limited, and a new irrigation system is going to be installed, oneoption would be to use subsurface drip as E losses would then be negligible.The goals of water saving using RDI in olive orchards appear particularly interesting. Mostdocumented evidence indicates that RDI strategies supply only 30 to 70 percent of the volumeneeded for fully-irrigated trees. Seasonal water volumes of as little as 50 mm are sufficient toincrease yields significantly in subhumid climates, whereas about 100 mm are needed in drierclimates. These amounts are definitely much less than that used in most other crops.Today, an important issue is the use of RDI to optimize oil quality. Recent evidence shows thatthe concentration of phenolic compounds and volatile compounds with sensory impact can beoptimized using RDI strategies rather than by applying full irrigation or under rainfed (Gomez-Rico et al., 2007; Motilva et al., 2000 and Servili et al., 2007). The beneficial effects of moderatewater deficits that are imposed by RDI on olive oil composition stemmed the term ‘qualitativeirrigation’, an aspect which will probably be more important. There are some reports thatrecommend restricting irrigation before harvest to limit or avoid trunk damage during mechanicalharvesting by trunk shakers and/or problems of oil extractability during processing in the mill.Deficit irrigation appears to be beneficial for optimizing the pulp-to-pit ratio in of table olives(Gucci et al., 2009).Additional considerationsIntroducing irrigation to rainfed olive growing involves a number of potential side effects.Increasing incidence of Verticillium wilt (Verticillium dahliae) disease has been reported,especially for young orchards. There is documented evidence that inoculum density of thepathogen is higher in wet areas than in dry. Although the cause of greater incidence ofVerticillium wilt in irrigated orchards is unclear, it is likely that susceptible secondary oliveroots increase close to the drippers where the soil may be quite wet favouring infection, weedssurvive longer and temporarily host the pathogen, and infected leaves decompose quickerunder high humidity conditions (Lopez-Escudero and Blanco-Lopez, 2005). The Verticilliumwilt disease is a limiting factor for irrigated orchards in some areas where localized, lowfrequencyirrigation is recommended as a management technique.Further, reportedly here is an increasing damage by the olive fruit fly (Bactrocera oleae Gmel.)in irrigated orchards, but supporting evidence is not strong. The olive fruit fly preferablydamages large fruit (cultivars of large fruit size and olive fruit with high water content aremore susceptible than small), so its effect may be indirect because irrigation increases fruit size.However, it is likely that the fruit fly also enjoys more favourable conditions when humidity ishigher because of irrigation in the olive orchard.Problems of the low oil yield of fruit from fully-irrigated, very high density orchards of somecultivars have been reported, but they appear to be related to technological problems in oilextraction when fruit is highly hydrated rather than to less oil in the fruit itself. Because of therelatively high resistance to salinity, olive trees yield well when irrigated with saline waters(Gucci and Tattini, 1997).312crop yield response to water