Environmental impact of (olive) irrigation. Luca Testi IAS-CSIC Córdoba

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1 Environmental impact of (olive) irrigation Luca Testi IAS-CSIC Córdoba 1

2 This talk is NOT about the environmental impact of olive growing. Olive growing in general has environmental impacts like any other human activity when exerted massively reduction of biodiversity pesticides erosion...etc... 2

3 We will only try to answer two questions: What are the additional potential risks that are generated on the environment by switching from rainfed to irrigated olive farming? How can they be reduced or avoided? 3

4 The rainfed Mediterranean tree crop 4000 BC 5 min in a day: a short story today modern olive irrigation practice 4

5 Leaching Solutes stripped from the soil by water flowing through it Environmental damage: Non-point pollution of underground waters, rivers, lakes and sea Eutrophication (fertilizers) Increased by irrigation (overirrigation, enhanced drainage) MODIS - Terra satellite 11 June

6 Leaching Specifically for olive irrigation: Localized irrigation (drip/microsprinkler..) minimize drainage (small water amounts applied frequently) The volume of soil constantly wet is relatively small, leaves plenty of volume free to retain rainfalls Comparatively, the risk of nonpoint pollution generated by irrigated olive farming is small 6

7 Leaching Strategies for risk reduction and sustainability: Avoiding drainage (overirrigation): assessing precisely the olive water requirements use of water balance in irrigation scheduling Avoiding excess of solutes (overfertilization): correct fertilization plan: soil and leaf analisys correct application timing Responsible use of herbicides and pesticides - CONTROL 7

8 Salinization Salts accumulation in the soil Dangerous in dry areas and closed watersheds Bad quality irrigation water Environmental damage: Stress on plants Reduction of soil fertility Soil physical degradation (Na) Desertification 8

9 Salinization Specifically for olive irrigation: Olive is resistent to salinity, can be irrigated with bad quality water with small effects on yield; drip irrigation helps Irrigating with saline water in dry areas where rainfalls are not capable to flush the soil periodically has little visible effect in the short term, but may be unsustainable in the long run Salinization may be a big environmental risk in dry areas with bad quality water supply 9

10 Salinization Strategies for risk reduction and sustainability: close monitoring of soil and water salinity in vulnerable areas use of water balance to control the periodical occurrence of adequate drainage caution in wastewater supplied irrigation schemes Expect a decrease in the the average quality of water due to its increasing scarcity Also, the global change won t help... 10

11 Runoff and Erosion Surface water flow on sloping terrain drags the soil downhill, thinning the profile Environmental damage: Reduced soil fertility Reduced soil water retention Agrochemicals and fertilizers are dragged to rivers and lakes Soil particles increase the turbidity of rivers and water bodies (can be filled-up) Courtesy prof. J.V. Giraldez 11

12 Runoff and Erosion Specifically for olive irrigation: High frequency, localised irrigation is unlikely to increase runoff even in the more unfavourable terrain The wetted soil (with low infiltration rate) is a small fraction of the total when a rain occurs during the irrigation season Localised irrigation does not increase the risk of runoff and erosion In irrigated olive groves more soil is protected by the canopy and cover crops are easier to establish than in dry farming 12

13 Excessive water use The practice of irrigation can draw water off a watershed above the sustainable rate Environmental damage: Depletion of acuifers Reduction of river flow Disappearance of springs Destruction of wet ecosystems Door open to desertification 13

14 Excessive water use PD-USGOV-NASA 14

15 Excessive water use It is a global risk associated to irrigation in general I s going to be worse, because: the increasing competence with other (stronger) sectors the global climate change perspective (Mediterranean area seems to become hotter and drier) great number of unregulated water sources difficult control 15

16 Excessive water use Specifically for olive irrigation: Olive is a great water saver: it closes considerably the stomata at high evaporative demand, even when irrigated Olive is resistant to drought: water shortages in dry years almost never kill the groves (but super high density?) Olive uses irrigation water more efficiently than other crops: Guadalquivir valley, Andalusia, Spain Crop Area Requirement Unit Req. (ha) (hm 3 ) (m 3 /ha) rice others olive (47.4%) 860 (24.7%) 2260 Total

17 Excessive water use Specifically for olive irrigation: 17

18 Excessive water use Strategies for risk reduction and sustainability: the magnitude of the irrigated area must be limited according to the basin rate of recharge accurate calculation of olive water requirements and irrigation scheduling we have the tools always consider the soil water storage when accounting for seasonal irrigation amounts: let olive use the rain! improve and extend deficit irrigation strategies 18

19 Excessive water use Deficit irrigation and water productivity: Yield, olives (t / ha) Olive evapotranspiration (mm) Fully irrigated marginal productivity: 0.1 kg oil / m 3 water 50 mm less: marginal productivity 0.34 kg oil / m 3 water Rainfed: marginal productivity 0.65 kg oil / m 3 water Olive can be very productive even with small irrigation amounts 19

20 Concluding: The irrigation of olive has a negligible impact on erosion and solute leaching, if it is localised and if the irrigation scheduling and requirements are correctly calculated. Salinisation is a risk only with bad quality water and where the rainfall regime can t clean the soil frequently. We need to match the magnitude of irrigated olive farming with the basins recharge capability (valid for every crop...). In comparison with other crops, olive needs less water, and uses it more efficiently: under limited water supply it should have a comparative advantage over all the alternative crops. 20

21 A last remark: A water stressed plant reduces the photosynthesis rate, and assimilates less CO 2. Irrigation by avoiding or reducing water stress increases the carbon gain of the ecosystem, thus it helps in contrasting the CO 2 concentration increase in the atmosphere. How much? Thank you. 21