1 : Unité Eau et climat Centre National d Énergie des Science et Techniques Nucléaire, Rabat, Maroc. * amenzou@cnesten.org.ma 2 : Université Cady Ayyad, Marrakech, Maroc 3 : IRD Maroc Isotopic and conventional techniques to improve the irrigation practice in order to enhance agriculture production under water limiting conditions in morocco N. AMENZOU(1,*), H. MARAH(1), F. RAIBI(1), J. EZZAHAR(1), S. KHABBA(2), S. ERRAKI, J. Lionel (3)
PLAN Problematic Study site Field installation Laboratory works Results Conclusions
Drought meteoric Principal data of Moroccan agriculture, Specially in this area The irrigation of agriculture remains the only possible way to improve the production. The evapotranspiration and deep percolation constitute the most important factor of water losses, whose, its determination is capital for a well control for water resources management.
Objectives Quantification of loss by deep percolation. Determination of evapotranspiration components flow by using isotopic methods (Keeling plot) ; Validation of use isotopic techniques in our conditions
Tow studies cases Orange tree Wheat crop Drip irrigation Flood irrigation
Study site The study area, Tensift catchment (N9.30, N7.15 and W30.45, W32.15) lying in the middle of Morocco. Tensift has a semiarid climate; with 253 mm average annual precipitation falls during winter and spring (November April). Very little precipitation falls between May and October. The principal economic activity is agriculture and it s based on irrigation practices
study site equipped with : Standard meteorological instruments to measure: -Wind speed and direction ; -Air temperature and humidity ; -ET by Eddy covariance system ; -Soil humidity was measured at different depth.
Sampling Water vapor was collected from 5 heights at same time. For each group vapour was collected during 1hour with a flow rate of 250 ml min-1 using a vacuum pump - Soil Surface (0-5cm) ; - ¼ of the vegetation ; - ½ of the vegetation ; - Maximal of vegetation ; - 1 m up the vegetation.
Soil and vegetation Using a hand-auger, soil was sampled from the surface to 80 cm. In the objective to determine the evaporation front Stem water extracted by hand vaccum pump from stem.
Laboratory works In the laboratory the water of soil and stem are extracted by vacuum distillation, during 2 hours at 100 C Cryogenic distillation ligne Stable isotope analysis Uncertainties by LASER (DLT-100) (± 1 standard deviation) - δ 18 O ~ 0.2 SMOW - δd ~ 1 SMOW
Orange study
The crop planted since 2000 with medium density and irrigated with drip irrigation system, the distance between dripper is 1 m Soil type : The soil has high sand and low clay contents (18% clay, 32% silt, and 50% sand).
Flux meter installation - Flux meter is Installed at 80 cm depth, under the ground which correspond to the roots zone.
Results 1 10 19 28 37 46 55 64 73 82 91 100 109 118 127 136 145 154 163 172 181 190 199 208 217 226 235 244 253 262 271 280 289 298 307 316 325 334 343 352 361 400 0 350 300 5 250 200 150 10 15 Irrigation rain Humidity tem solar radation W S 100 50 20 0 25 The environmental condition during the growing season of 2009 Precipitation temporal patterns over the growing season of citrus trees were characterized by low and irregular rainfall events, with a total precipitation amount of about 295 mm. The amount and timing of irrigations applied by the farmer are presented also in this figure
ET0 of well-watered grass calculated following the FAO-Penman- Monteith equation during 2009 This Figure shows the seasonal variations of the reference Evapotranspiration ET0 of well-watered grass calculated using the The FAO Penman Monteith equation for the meteorological forcing parameters collected over our study site. The ET0 pattern is characteristic of semi-arid continental climates. with an average accumulated annual ET0 of 1355 mm. The lowest values of ET0 occurred during the winter and autumn (0.05 mm/day) and the highest values occurred in the summer (11.07 mm/day).
H+ET (wm-2) The energy balance closure is an important indicator of the performance of an Eddy Covariance system. 600 500 400 y = 0,7469x R 2 = 0,7287 300 200 100 0 0 100 200 300 400 500 600 Rn-G (wm-2) Validation of EC data This figure presents a cross plot between measured (Rn-G) and the sum of the turbulent fluxes (H+ET). We can concluded that the ET measured by EC was acceptable with a slope 0,74 and R2 0,728.
Water balance cumul mm 1 13 25 37 49 61 73 85 97 109 121 133 145 157 169 181 193 205 217 229 241 253 265 277 289 301 313 325 337 349 361 The use of water balance equation allows to determine the rate of infiltration cumul ET mm irrigation and rainfall 1400 1200 1000 495 mm 800 600 400 200 0 Day 2009 Cumulative Evapotranspiration (ET) measured by Eddy covariance, compared to sum cumulative precipitation (mm) and irrigation amount (mm). For this case the difference between cumulative ET and the sum of cumulative irrigation and rain is about 495 mm corresponding to 38% of amount irrigation and rain
Direct measurement (fluxmeter) cumulative water (rain irrigation and infiltration) 84 95 106 117 128 139 150 161 172 183 194 205 216 227 238 249 260 271 282 293 304 315 326 337 348 359 fluxmeter measurment mm irrigation and rainfall mm 1400 1200 1000 425 mm 800 600 400 200 0 Day 2009 Cumulative drainage compared to sum cumulative precipitation (mm) and irrigation amount (mm) 425 mm represented 32% of the sum of cumulative rain and irrigation. This result confirms the obtained result by using the water balance equation The difference between direct measurement of percolation and that derived from the water balance can be explained by Surface runoff of rain
Isotopic data δ 2 H 0 y = 6,3937x - 4,4308 R 2 = 0,8859-20 -40-60 irrigation water LMWL All samples GMWL Linéaire (All samples) -80-12 -10-8 -6-4 -2 0 δ 18 O δ18 O versus δd in precipitation, atmospheric water vapor, soil water and stem water All samples ( vapor, soil water, stem water, irrigation water) are situated around the LMWL. The regression line of all samples intersect the LMWL at the point that presents the origin of all samples
Keeling plot δd δd -30,00 y = -77,15x - 63,464 R 2 = 0,0156-30,00 T y = -392,5x - 46,348 R 2 = 0,4577-50,00 T -50,00-70,00-70,00 ET -90,00 ET -90,00-110,00-110,00-130,00-150,00 E 0,000 0,010 0,020 0,030 0,040 0,050 0,060 0,070 0,080 0,090 1/[H2O] -130,00 E -150,00 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 1/[H2O] δs δa h T δt δ ET R 2 α εk δe FT 16-41,4-65,08 0,43057 29,084-44,63-46,30 0.457 1,0750 1,0250-140,50 0,982 17-46,14-68,53 0,3363 28,942-45,15-63,464 0.015 1,0751 1,0250-134,861 0,795 δ ET intercept of keeling plot δe calculated by Craig and Gordon model (1965) δt measured * E h atm eq 1 1 h 1 h / 1000 surface k h k
Contibution of transpiration and evaporation on evapotranspiration The fractional contribution of transpiration to the total ET fluxes (FT) were calculated from: 120 100 F T ET T E E 80 60 40 E T 20 0 16/07/2009 17/07/2009 Considering orange crop transpiration as one source and soil evaporation as another one, the fractional contribution of plant transpiration to total ET (T/ET) is 79,5% for δd July. Therefore the transpiration dominates the evaporation.
δ 2 H 0 P1: y = 4,5493x - 14,145 R 2 = 0,8592-20 P2: y = 3,489x - 21,081 R 2 = 0,8978-40 -60 soil water 16 soil water 17 irrigation water LMWL Soil water 16/07/2009 soil water 17/07/2009-80 -12-10 -8-6 -4-2 0 δ18 O The figure shows that the profile extract at midday on 16/07/2009 have a slope 4.648, but the second profile extracted on 17/07/2009 have a slope 3.489. That shows high evaporation during the second day compared to the first one. That confirms the results obtained by keeling plot.
Wheat study
Wheat study Superficie : 5ha Irrigation type : flood Soil type : Clay Silt sandy % 40 42.1 26.9
Isotopic data δ²h LMWL: δ²h = 8,11δ 18 O + 13,5-10 -20-30 -40-50 Wheat study 22/02/12-10 δ²h -20 23/02/12-30 -40-50 -60-70 -80-90 -100-20,0-15,0-10,0-5,0 δ 18 O soil water irrigation atmospheric vapor -60-70 irrigation p2-80 Atmaspheric vapor -90 δ 18 O -100-15,0-13,0-11,0-9,0-7,0-5,0-3,0 0 δ 2 H 24/02/12 All samples for three day of sampling ( vapor, soil water, irrigation water) are situated around the LMWL the regression line of the all samples intersect the LMWL at point that present the origin of all samples -20-40 -60-80 irri 24 p2 Atmospheric vapor -100-15 -13-11 -9-7 -5-3 -1 δ 18 O
Wheat study Keeling plot -10.00-20 y = -239.55x - 52.954-20.00-30.00 T y = -214.24x - 57.579 R 2 = 0.5303-30 -40 T ET R 2 = 0.562-40.00 ET -50-50.00-60.00-60 -70.00-70 -80.00 E -80-90.00-90 E -100.00 0.000 0.020 0.040 0.060 0.080 0.100 0.120 0.140 0.160 0.180-20 -30-40 T -100 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 y = -218.95x - 59.751 R 2 = 0.3905-50 -60 ET -70-80 -90-100 -110 E 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
% Contribution of E and T Wheat study δs δa h T δt δ ET R 2 α εk δe FT 22/02/12-27,26-73,46 0,43 24.11-34,55-57,58 0,530 1,08 1,03-119,28 0,73 23/02/12-5,72-68,22 0,46 23.87-27,29-52,95 0,562 1,08 1,03-90,09 0,59 24/02/12-26,05-71,36 0,45 23.06-37,44-59,75 0,39 1,08 1,03-122,06 0,74 The fractional contributions of plant transpiration to total ET (T/ET) is 68 % for three day. This may can explain by height canopy cover 77 % at this growing stage. 120 100 80 60 40 E T 20 0 1 2 3 Day Contribution of transpiration
Wheat study Partitioning of the evapotranpiration components by Aquacrop model 24/02/2012 22/02/2012 Isotope Model Model Isotope By analysing this figure we can conclude that the model gives an acceptable estimate of plant transpiration and soil evaporation. The differences between isotopic and aquacrop estimation, were 5 and 12% for 22/02/2012 and 24/02/2012 respectively.
Wheat study Estimation of the Yield Yield (t/ha) Measured Simulated 5,1 4,98 In this table we present a comparison between simulated and measured yield using the quantity of irrigation applied by the farmer. As we show, It s clear that the model simulate reasonably the yield. We can conclude that the Aqauacrop model still the more accurate model for estimation the Yield under semi-arid climate
Accumulated (mm) Wheat study Irrigation efficiency assessment 600 500 Irrigation + Rainfall Transpiration Aquacrop 400 300 P (67% of total irrigation) 200 100 0 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 DAS By evaluating the water balance equation using the model outputs, a large quantity of water is lost through soil evaporation and infiltration (67% of total irrigation).
Conclusions This region Characterised by low and irregular rainfall events. Very little precipitation falls between May and October This region Characterised by a high climatic demand The water balance equation and direct measurements (fluxmeter) give the same results for the percolation loss For the orange crop irrigated with drip irrigation the loss by percolation is 32% of sum amount of irrigation and rain The loss by surface runoff is 6% of the sum accumulative amount irrigation and rain Keeling plot technique shows that transpiration dominates the evaporation for orange crop irrigated with drip irrigation system this result is confirmed by analysis of stable isotope profiles
Keeling plot technique for wheat culture give a good result for the partitioning of Evapotranspiration components with high R 2. The high contribution of transpiration may can explained to high canopy cover The comparison of % of the contribution of transpiration on ET calculated by isotopic technique and Aquacrop model are similar Aquacrop model still the more accurate model for estimation the Yield and Irrigation efficiency under semi-arid climate The comparison between flood irrigation and drip irrigation shows that the losses by evaporation and infiltration is higher for flood irrigation than loss by infiltration for drip irrigation It was found that the visual observation of the physical conditions of the plant is not sufficient to efficiently manage the irrigation
Acknowledgments Soil and Water Management and Crop Nutrition (SWMCN) Section of the Joint FAO/IAEA CRP member