Effects of different on-farm management on yield and water use efficiency of Potato crop cultivated in semiarid environments under subsurface drip irrigation

In Tunisia the amount of water for irrigated agriculture is higher than about 80% of the total resource.The increasing population and the rising food demand, associated to the negative effects of climate change,make it crucial to adopt strategies aiming to improve water use efficiency (WUE). Moreover, the absence of an effective public policy for water management amplifies the imbalance between water supply and its demand. Despite improved irrigation technologies can enhance the efficiency of water distribution systems, to achieve environmental goals it is also necessaryto identify on-farm management strategies accounting for actual crop water requirement. The main objective of the paper was to assess the effects of different on-farm managementstrategies (irrigation scheduling and planting date) on yield and water use efficiency of Potato crop (Solanumtuberosum L.) irrigated with a subsurface drip system, under the semi-arid climate of central Tunisia. Experiments were carried out during three growing seasons (2012, 2014 and 2015) at the High Agronomic Institute of ChottMariem in Sousse, by considering different planting dates and irrigation depths, the latter scheduled according to the climate observed during the season. All the considered treatments received the same pesticide and fertilizer management. Experiments evidenced that the climatic variability characterizing the examined seasons (photoperiod, solar radiation and average temperature) affects considerably the crop phenological stages, and the late sowing shortens the crop cycle.It has also been demonstrated that Leaf Area Index (LAI) and crop yield resulted relatively higher for those treatments receiving larger amounts of seasonal water. Crop yield varied between 16.3 t/ha and 39.1 t/ha, with a trend linearly related to the ratio between the seasonal amount of water supplied (Irrigation, I and Precipitation, P) and the maximum crop evapotranspiration (ETm). The maximum crop yield was in particular obtained for a value of this ratio equal to 1.45. Moreover, when increasing the seasonal pluviometric deficit (P-ETm) and therefore the irrigation depth (I), standard deviations of crop yield tended to decrease, as a consequence ofthe more uniform soil water content in the root zone. In terms of agronomic water use efficiency (AWUE),differences among the investigated treatments varied in a quite narrow range,due to thecombined effects of seasonal precipitation and atmospheric water demand on irrigation depths and crop yield.On the other hand, when considering irrigation water use efficiency (IWUE), more relevant differences between treatments were observed,being the higher values of IWUEgenerally associated to the lower irrigation depths. However, to define the best irrigation management strategy it is necessary, from one side, to consider the availability of water and from the other, to perform aneconomic analysis accounting for the cost of water and the related benefits achievable by the farmer

Irrigation management strategies to improve Water Use Efficiency of potatoes crop in Central Tunisia

In Tunisia, the expansion of irrigated area and the semiarid climate make it compulsory to adopt strategies of water management to increase water use efficiency. Subsurface drip irrigation (SDI), providing the application of high frequency small irrigation volumes below the soil surface have been increasingly used to enhance irrigation efficiency. At the same time, deficit irrigation (DI) has shown successful results with a large number of crop in various countries. However, for some crops like potatoes, DI is difficult to manage due to the rapid effect of water stress on tuber yield. Irrigation frequency is a key factor to schedule subsurface drip irrigation because, even maintaining the total seasonal volume, soil wetting patterns can result different during the growth period, with consequence on crop yield. Despite the need to enhance water use efficiency, only a few studies related to deficit irrigation of horticultural crops have been made in Tunisia. Objective of the paper was to assess the effects of different on-farm irrigation strategies on water use efficiency of potatoes crop irrigated with subsurface drip irrigation in a semiarid area of central Tunisia. After validation, Hydrus-2D model was used to simulate soil water status in the root zone, to evaluate actual crop evapotranspiration and then to estimate indirectly water use efficiency (IWUE), defined as the ratio between crop yield and total amount of water supplied with irrigation. Field experiments, were carried out in Central Tunisia (10◦ 33’ 47.0” E, 35◦ 58’ 8.1◦ N, 19 m a.s.l) on a potatoes crop planted in a sandy loam soil, during the growing season 2014, from January 15 (plantation of tubers) to May 6 (harvesting). Soil water status was monitored in two plots (T1 and T2) maintained under the same management, but different irrigation volumes, provided by a SDI system. In particular, irrigation was scheduled according to the average water content measured in the root zone, with a total of 8 watering, with timing ranging between one and three hours in T1, and between about half-an-hour and one-hour and a-half, in T2. The validity of Hydrus-2D model was initially assessed based on the comparison between measured and estimated soil water content at different distances from the emitter (RMSE values were not higher than 0.036). Then, model simulations allowed to verify that it is possible to enhance irrigation water use efficiency by increasing the frequency of irrigation even maintaining limited water deficit conditions during the full development stage subsequent the crop tuberization. Experimental results, joined to model simulations can therefore provide useful guidelines for a more sustainable use of irrigation water in countries characterised by semi-arid environments and limited availability of water resources

Impacts of different tillage practices on soil water infiltration for sustainable agriculture

Over the years, cultivation using sustainable tillage practices has gained significant importance, but the impact of tillage on soil water infiltration is still a concern for landowners due to the possible effects on crop yield. This study investigates the impact of different tillage managements on the infiltration rate of sandy clay loam soil under a semiarid environment. Field experiments were conducted in Chott Mariem Sousse, Tunisia. The tillage practices consisted of three treatments, including a tine cultivator (TC, 16 cm), moldboard plows (MP, 36 cm) and no-tillage (NT). Three infiltration models, Kostiakov, Philip and Horton, were applied to adjust the observed data and evaluate the infiltration characteristics of the studied soils. Comparison criteria, including the coefficient of determination (R2 ), along with the root mean square error (RMSE) and mean absolute error (MAE), were used to investigate the best-fit model. The results showed that moldboard plowing enhanced soil infiltration capacity relative to tine cultivation and no-tillage treatments. The mean saturated hydraulic conductivity was highest under MP, while it was lowest in NT, with 33.4% and 34.1% reduction compared to TC and MP, respectively. Based on the obtained results, Philip’s model showed better results with observed infiltration due to a higher R2 (0.981, 0.973 and 0.967), lower RMSE (3.36, 9.04 and 9.21) and lower MAE (1.46, 3.53 and 3.72) recorded, respectively, for NT, MP and TC. Horton’s model had a low regression coefficient between observed and predicted values. It was suggested that the Philip two-term model can adequately describe the infiltration process in the study area

Evaluation de l’effet de nutrition azotée sur la productivité de l’eau de quelques variétés de blé dur

Le blé dur a besoin d’énergie pour accomplir les principales fonctions métaboliques et physiologiques, cette énergie est fournie principalement par l’azote qui est en outre un constituant fondamental de la plante. Malgré son importance et à cause de sa forte solubilité, l’azote est classé un polluant potentiel pour l’environnement. L’objectif de ce travail est d’étudier la réponse de quatre variétés de blé dur (Karim, Razzak, INRAT100 et Dhahbi) au traitement azoté. Les résultats ont montré que nouvelle obtention (Dhahbi) a donné le meilleur rendement et les efficiences d’utilisation de l’eau les plus élevées que ce soit avec ou sans fertilisation grâce à l’impact d’amélioration génétique. Ainsi, Il est recommandé de planter la variété Dhahbi pour limiter l’utilisation des engrais azotés, protéger l’environnement et maximiser le revenu brut surtout des petits exploitants.

Effet de l’application du fongicide sur la productivité de l’eau du blé tendre

En Tunisie, le secteur céréalier joue un rôle socio-économique important. Le présent travail est réalisé dans l’objectif d’étudier l’effet d’un fongicide sur l’efficience de l’utilisation de l’eau des anciennes variétés et des nouvelles obtentions de blé tendre. Les composantes finales du rendement ainsi que les efficiences de l’utilisation de l’eau des anciennes et nouvelles variétés ont été statistiquement analysées à la fin de la compagne expérimentale. Les résultats ont montré que les variétés Kodss et Maktarus ont présenté des performances meilleures même en absence du traitement fongicide. Ceci confirme leurs capacités de résistance à la rouille jaune la plus dévastatrice de la culture du blé tendre. Néanmoins, le fongicide utilisé (ogame) a prouvé son efficacité à protéger les cultures contre les stress biotiques et à améliorer les rendements et la qualité de la production. Ainsi, il est recommandé d’éviter les traitements fongiques sur les nouvelles variétés

Discussion on "Modeling Approaches for Determining Appropriate Depth of Subsurface Drip Irrigation Tubing in Alfalfa"

The discussed paper deals with the quite interesting topic of design and management of subsurface drip irrigation (SDI), with the aim to identify the appropriate depth at which to install driplines to avoid wetting the soil surface. The study proposes the results of simulations, obtained with the well-known HYDRUS 2D/3D model version 2.x, and considering three different irrigation management strategies applied on alfalfa crop cultivated in two different soil types in Holtville, California

Potential of thermal images and simulation models to assess water and salt stress: Application to potato crop in central Tunisia

The growing water scarcity is a real concern in Mediterranean countries characterized by semi-arid or arid climate such as Tunisia, where it is crucial to improve water use efficiency without affecting agricultural productivity. The importance of identifying methods and technologies to optimize water use in agriculture has been recognized worldwide, in response to the limited water availability. Objective of the paper was to verify the potential of the combined use of infrared thermography and simulation models to assess the effects of water and salt stress on potato crop parameters and crop yield, under the environmental conditions of central Tunisia. The database collected with field experiments allowed the application of Hydrus-2D model to simulate water and salt stress. The achieved results evidenced that water savings are possible in Tunisia if irrigation is scheduled based on the climate and/or plant water status. Experiments showed that the high variability on crop yield within the treatments was mainly associated to possible clogging phenomena, rather than emitters' quality or deficiency in distribution uniformity. When considering the thermal image analysis, it was demonstrated that the crop water stress index (CWSI) is strongly related to soil matric potential, so that handled infrared thermography can be considered a powerful tool for irrigation scheduling of potato crop. Moreover, the rate of maximum evapotranspiration reduction estimated by model simulations, resulted fairly well correlated with the corresponding CWSI obtained by thermal images, thus evidencing the suitability of the model to assess the effects of water and saline stress on crop transpiration and to identify irrigation scheduling parameters aimed to optimize water use efficiency

Using HYDRUS-2D model to assess the optimal drip lateral depth for eggplant crop in a sandy loam soil of central Tunisia

The main objective of the work is to assess the optimal drip lateral depth for Eggplant crop (Solanum melongena L.) irrigated with a drip system in a sandy loam soil by means of field measurements and simulation models. Initially, the performance of Hydrus-2D was assessed based on the comparison between simulated soil water contents (SWC) and the corresponding measured in two plots, in which laterals with co-extruded emitters were laid on the soil surface (drip irrigation, DI-0) and at 20 cm depth (subsurface drip irrigation, SDI-20), respectively. In order to identify the optimal position of the lateral, the results of different scenarios, obtained by changing the installation depth of the lateral (5 cm, 15 cm and 45 cm) were compared in terms of water use efficiency (WUE), expresses as the ratio between actual transpiration and the total amount of water supplied during the entire growth season. Simulated SWCs resulted fairly close to the corresponding measured at different distances from the lateral and therefore the model was able to predict SWCs in the root zone with values of the Root Mean Square Error generally lower than 4%. According to the examined scenarios, soil evaporation decreases at increasing drip lateral depth, while the associated WUE tends to increase when the depth of the lateral rises from 0 to 20 cm. Depth installation greater than 20 cm involve a higher loss of water to deep percolation with consequent decrease of WUE

Optimizing subsurface dripline installation depth with Hydrus 2D/3D to improve irrigation water use efficiency in the central Tunisia

The main objective of the work is to optimize drip installation depth for Eggplant crop irrigated with surface or subsurface drip irrigation systems to improve irrigation Water Use Effeciency (WUE), by means of field measurements and simulations carried out with Hydrus-2D model. Initially, a comparison between simulated Soil Water Contents (SWC) and the corresponding measured in two plots, in which laterals with coextruded emitters are laid on the soil surface (T0) and at 20 cm depth (T20), respectively. In order to choose the best position of the lateral, the results of different simulation run, carried out by choosing a deeper installation (T45) depth. Simulated SWC’s resulted fairly close to the corresponding measured at different distances from the emitter and therefore the model was able to predict SWC’s in the root zone with values of the Root Mean Square Error generally lower than 4%. This result is consequent to the appropriate schematization of the root distribution, as well as of the root water uptake. The values of WUE associated to the different examined installation depths tend to a very slight increase when the position of the lateral is situated on 20 cm and start to decrease for the higher depths

Potential of Thermal Images and Simulation Models to Assess Water and Salt Stress: Application to Potato Crop in Central Tunisia

The growing water scarcity is a real concern in Mediterranean countries characterized by semi-arid or arid climate such as Tunisia, where it is crucial to improve water use efficiency without affecting agricultural productivity. The importance of identifying methods and technologies to optimize water use in agriculture has been recognized worldwide, in response to the limited water availability. Objective of the paper was to verify the potential of the combined use of infrared thermography and simulation models to assess the effects of water and salt stress on potato crop parameters and crop yield, under the environmental conditions of central Tunisia. The database collected with field experiments allowed the application of Hydrus-2D model to simulate water and salt stress. The achieved results evidenced that water savings are possible in Tunisia if irrigation is scheduled based on the climate and/or plant water status. Experiments showed that the high variability on crop yield within the treatments was mainly associated to possible clogging phenomena, rather than emitters’ quality or deficiency in distribution uniformity. When considering the thermal image analysis, it was demonstrated that the crop water stress index (CWSI) is strongly related to soil matric potential, so that handled infrared thermography can be considered a powerful tool for irrigation scheduling of potato crop. Moreover, the rate of maximum evapotranspiration reduction estimated by model simulations, resulted fairly well correlated with the corresponding CWSI obtained by thermal images, thus evidencing the suitability of the model to assess the effects of water and saline stress on crop transpiration and to identify irrigation scheduling parameters aimed to optimize water use efficiency