Mohamed Moncef Masmoudi

Sap flow measurement by a single thermal dissipation probe: exploring the transient regime

Abstract• In thermal dissipation method the stationary regime is used to estimate sap flow density from the temperature difference between a heating probe and a non-heating one.• A new approach, based on the non-stationary regime of a single heating probe, is investigated on an olive tree branch. Probe temperature is monitored for different flow densities and for heating and cooling modes. Measurement sequences of 10 min using 5 s time steps are made just after the heating is switched on or off.• Results show that temperature variation has a quasi-exponential phase whose duration decreases for increasing flow densities. Thermal indices using temperature of the probe measured at initial, final, and intermediate times ti were developed. Relationships between sap flow density and thermal indices were found to be linear for ti = 10 s−60 s with better coefficients of determination in cooling mode (R2 = 0.94–0.96) than in heating (R2 = 0.83–0.93). Validation tests confirmed the robustness of the single probe method with lowest error obtained for ti = 20 s.• Single probe method seems to be a promising technique to measure tree sap flow. Its application could be considered under cooling mode using ti = 20 s and relatively short measurement sequences e.g. 5–10 min.Résumé• La méthode de dissipation de chaleur utilise le régime stationnaire pour estimer la densité de flux de sève à partir de la température d’une sonde chauffée et une sonde non chauffée.• Une nouvelle approche exploitant le régime transitoire d’une seule sonde est testée sur une branche d’olivier. Des séquences de mesure de la température de la sonde sont réalisées pour différentes densités de flux. Les mesures sont effectuées toutes les 5 s pendant les 10 min qui suivent la mise en route ou l’arrêt du chauffage.• La variation de la température présente une phase quasi-exponentielle de durée inversement proportionnelle à la densité de flux. Des indices thermiques utilisant les températures de la sonde aux instants initial, final et intermédiaire ti ont été développés. Les relations entre les densités de flux et ces indices sont de type linéaire pour ti = 10 s−60 s avec des coefficients de détermination plus élevés en refroidissement (R2 = 0.94−0.96) qu’en chauffage (R2 = 0.83–0.93). Un travail de validation a confirmé la robustesse de la méthode, l’optimum étant ti = 20 s.• La méthode de la sonde unique semble être une technique prometteuse pour mesurer le flux de sève des arbres. Son application est envisageable en mode refroidissement avec ti= 20 s et des séquences de mesure relativement courtes : 5–10 min.

Measuring Crop Evapotranspiration Over Hilly Areas

Agricultural production systems around the Mediterranean basin rely mostly on rainfed agriculture in hilly watersheds, although some irrigation is sustained downstream of water reservoirs. With climate change and increasing demand for water, most commonly cultivated species, particularly cereals, are exposed to high risks of water shortages during the growing season. Under such threats, managing agricultural activities, for optimum water use, requires a good assessment of crop actual evapotranspiration (ET), a major term of both land surface energy and water balances.

Evapotranspiration of Wheat in a Hilly Topography: Results from Measurements Using a Set of Eddy Covariance Stations

Several methods allow the determination of evapotranspiration (ET), either by direct measurement or by estimation from weather data. The most used estimation method is the FAO56 (FAO-PM), based on the concept of reference evapotranspiration (ETo) and crop coefficient (Kc). The eddy covariance technique (EC) developed for measurement of convective fluxes between land surface and the atmosphere is commonly used to estimate ET. However, these methods were established under standard conditions in flat terrain, and their use in hilly areas is questionable. In this work, the variability of ETo and ET measured by EC and energy balance (EB) in a hilly area of northern Tunisia is studied for different relief configurations. The experiment was conducted using a meteorological (M), and three EC-EB measurement stations in three wheat fields. Two stations were installed on opposite slopes of a ridge with apposing aspects and moderate slopes (A, B), and one station was installed in a flat site (C). Results of monitoring during the mid-season of wheat growth showed similar ETo levels in all sites for hourly and daily time steps with relative RMSE in the range 0.03–0.08 compared to M. Average ET values in sloping fields (A, B) were, respectively, 15% and 10% lower than in (C). However, hourly values of ET/ETo obtained from EC measurements were smaller than FAO-Kc, contrarily to those based on the EB method.

Effect of High Temperature Stress on Wheat and Barley Production in Northern Tunisia

Increasing temperatures due to global warming have raised concerns about food security in the southern Mediterranean region. This work attempts to study the limitation to cereal production in Tunisia. Data from six governorates were used to develop relationships between cereal yields and the sum (STx) of maximum temperatures over the threshold of 15 °C. The data envelopment analysis method was used to identify the attainable regional production among seasons having a total rainfall over 350 mm. Results showed that yields of bread wheat, durum wheat and barley decreased, respectively, by 0.4, 0.26, and 0.32 t ha−1 for each 100 °C-day increase in STx, over the 1973–2013 period. An increasing trend in STx was observed for the major synoptic stations of the studied areas over the last 40 years but with different speeds. Future projections to 2050 showed a 15% rise for STx with a low radiative forcing scenario resulting in cereal yield gaps up to 0.26 t ha−1.

Calibration of AquaCrop Salinity Stress Parameters for Barley Under Different Irrigation Regimes in a Dry Environment

In the arid environment of southern Tunisia, FAO’s AquaCrop model version 4.0 has been calibrated to evaluate the effect of irrigation strategies with saline water on barley yield. Data sets during barley cropping seasons 2012 and 2013 in Medenine, southern Tunisia, were used to calibrate and evaluate this model. Barley canopy cover, grain yield, biomass production, and soil salinity and water content were simulated under three irrigation regimes. The RMSE, Willmott index of agreement (d), and r2 analysis showed good agreement between the simulated and observed data, especially for the biomass production and grain yield. The difference between observed and simulated grain yield under full irrigation was only 1% for the first and second seasons. The difference for biomass was around 2%. The trend of canopy cover was well simulated with slight over estimation in the beginning of the season for both seasons. Salinity stress parameters were adjusted to simulate the combined effect of drought and salinity stress where the electrical conductivity of water (ECw) was used as the indicator threshold of salinity instead of the saturated soil-paste extract (ECe) in this case. The model tended to overestimate the soil water content and the ECe but with reasonable statistical indices for total root zone soil water content (RMSE: 8.6–11 mm, d: 0.78–0.98) and for ECe (RMSE: 1.35–0.94 dS/m, d: 0.63–0.88).

Response of Vegetable Crops to Irrigation Regimes Using Saline Waters

Field studies were conducted to examine the response of potato, carrot, fava bean, and pepper to irrigation regimes using saline water in a commercial farm. The irrigation regimes were full (FI100) and deficit (DI70) irrigated with levels of 100 and 70% of crop evapotranspiration (ETc) when the readily available water, 40% of total available water (TAW), in the FI100 treatment was depleted, and traditional farmer practice (FM). For all experiments, the largest soil salinity values were observed under the farmer treatment compared to the FI100 and DI70 treatments. The highest mean yields of potato (24.4–27.5 t/ha), carrot (28.4–30.3 t/ha), fava bean (19–21.3 t/ha), and pepper (10.9–12.5 t/ha) were recorded for the FI100 treatment. Compared with FI100, significant reductions in potato, carrot, fava bean, and pepper yields were observed under the DI70 treatment, with only a few exceptions, resulting from a reduction in yield components. The farmer’s method not only caused significant reductions in yields but also resulted in an increase of water usage of 14–22%, 18–21%, 12.5–19%, and 13.9–15.5% for potato, carrot, fava bean, and pepper, respectively, and increased soil salinity. Water productivity (WP) values reflected the differences in yields and varied between 4.3 (farmer) and 13.7 kg/m3 (DI70) for potato, 4.4 and 11.7 kg/m3 for carrot, 4.8 and 13.7 kg/m3 for fava beans, and 0.8 and 2.6 kg/m3 for pepper across different years and treatments. The FI100 scheduling technique with variable water amounts was more efficient and provided significant advantage in yield, water productivity and net income, compared to the FM treatment in potato, carrot, fava beans, and pepper yields under arid environment. FI100 scheduling technique is suggested for vegetable crops in the arid environment. Under water restriction conditions, adoption of the DI70 strategy allows 30% water saving compared with FI100 with relatively small impact on soil salinity and some reductions in yield and net income.

Performance of Saxton and Rawls Pedotransfer Functions for Estimating Soil Water Properties in the Cap Bon Region-Northern Tunisia

Appropriate land use and management requires a good knowledge about the main hydraulic properties of the soil, in particular soil moisture at field capacity (FC), permanent wilting point (PWP), and water holding capacity (HC). In the absence of direct measurements, these characteristics could be estimated from data on texture and organic matter content, using pedotransfer functions (PTFs). In this study, FC, PWP, and HC of predominant soil types in Cap Bon (Vertisols, Cambisols, and Calcisols), are estimated using Saxton and Rawls (Soil Sci Soc Am J 70:1569–1578, 2006) PTFs and complete sets of soil analysis data. Results show that when all soil samples (61) are taken together, obtained estimations were well correlated with measured values for FC (R2 = 0.72) and PWP (R2 = 0.72). Similar correlations were observed for Cambisols and Calcisols taken separately (R2 = 0.65–0.70.); but there was an overestimation of FC and PWP for Vertisols (percentage of clay > 50%). However, relatively weak relationships were observed between estimated and measured values for HC in all cases (R2 = 0.15). PTFs seem appropriate to be used in combination with remote sensing methods for generation of soil FC and PWP maps needed in irrigation and agriculture efficient management.

Studying the effects of deficit irrigation as an on-farm strategy on carrot yield in arid environment

Limited supply of good quality water is a major constraint to crop production in the Mediterranean region of Tunisia. Presently, there is an increasing pressure to use saline water to intensify agriculture in the arid part of Tunisia. Irrigation of a wide range of crops such as potatoes, lettuces, fava beans and carrots is increasing around shallow wells having a salinity more than 3 dS/m. Production systems based on crops that are not tolerant to salinity in arid regions would not be sustainable without proper management of both water and salt. Good management of irrigation water is required for farmers seeking a viable mean to maximize water use. Many studies have reported substantial increases in crop yields

Phenology and Yield Efficiency of Early, Mid-, and Late-Maturing Cultivars of Peach in Irrigated Orchards under Mediterranean Climate

ABSTRACT Productivity of peach cultivars with different ripening seasons was studied under the growers’ conventional conditions of Tunisia. Experiments were performed in northern Tunisia (36° 41ʹ N, 10° 15ʹ E). Performances of Flordastar, Royal Glory, and Carnival as respectively early, mid-season, and late ripening cultivars were evaluated under the grower’s conventional irrigation programs. Fruit growth, yield, water supply, and water productivity were determined through four years. For the three cultivars, Flordastar, Royal Glory, and Carnival, fruit maturity was achieved at 650, 1100, and 2200 GDD, respectively. Average yields were 17.4, 29.8, and 41.1 t ha–1 and mean values of water productivity were 1.9, 3.1, and 3.6 kg fresh yield m–3 for early, mid-season, and late cultivars, respectively. Results of agronomic performances evaluation at the farm scale provided a reference on the behavior of early, mid-season, and late cultivars of peach in irrigated orchards in semi-arid conditions.