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

Atténuation de l'impact du déficit hydrique sur une culture de petit pois par la combinaison d'amendements organiques et de systèmes d'irrigation localisés

Cette recherche visait à évaluer l’impact de deux systèmes d'irrigation combinés à un amendement organique du sol, sur les paramètres hydrodynamiques et chimiques du sol et sur la productivité d'une culture de petit pois "Pisum sativum L. " soumise à des conditions de stress hydrique. Les résultats obtenus ont montré que les rampes poreuses permettent une meilleure stabilité du stock d'eau avec une amplitude de 30 mm contre 50,7 mm pour le système au goutte à goutte et un développement racinaire de petit pois plus intéressant avec une différence d'environ 2,5 cm par rapport au système de goutte à goutte. Le rendement n'a pas été significativement affecté et nous avons enregistré une différence de 3,43% en faveur des rampes poreuses. En revanche, la nodulation des racines et la fixation symbiotique de l'azote dépendaient du système d'irrigation, et nous avons trouvé une teneur en azote total plus élevée pour les sols irrigués par des rampes poreuses qui a atteint 1,4 g/kg. Les amendements organiques ont augmenté la teneur en humidité du sol à 24 et 25% pour la tourbe et le biochar respectivement par rapport au témoin. La croissance végétative de la plante a également été améliorée avec les amendements

Atténuation de l'impact du déficit hydrique sur une culture de petit pois par la combinaison d'amendements organiques et de systèmes d'irrigation localisés

Cette recherche visait à évaluer l’impact de deux systèmes d'irrigation combinés à un amendement organique du sol, sur les paramètres hydrodynamiques et chimiques du sol et sur la productivité d'une culture de petit pois "Pisum sativum L. " soumise à des conditions de stress hydrique. Les résultats obtenus ont montré que les rampes poreuses permettent une meilleure stabilité du stock d'eau avec une amplitude de 30 mm contre 50,7 mm pour le système au goutte à goutte et un développement racinaire de petit pois plus intéressant avec une différence d'environ 2,5 cm par rapport au système de goutte à goutte. Le rendement n'a pas été significativement affecté et nous avons enregistré une différence de 3,43% en faveur des rampes poreuses. En revanche, la nodulation des racines et la fixation symbiotique de l'azote dépendaient du système d'irrigation, et nous avons trouvé une teneur en azote total plus élevée pour les sols irrigués par des rampes poreuses qui a atteint 1,4 g/kg. Les amendements organiques ont augmenté la teneur en humidité du sol à 24 et 25% pour la tourbe et le biochar respectivement par rapport au témoin. La croissance végétative de la plante a également été améliorée avec les amendements

Application of STICS model in assessment of the effects of irrigation practices and soil properties on yield of a durum wheat (Triticum durum Desf.) cultivar in the irrigated area of Oued Rmel in Tunisia

International audienceThe progress in computer technology has enabled the development of crop models reproducing the behavior of a crop in a wide range of pedoclimatic conditions and technical itineraries. This work aims to study the impact of total available soil water in the root zone (TAW) on durum wheat yield (Triticum durum Desf.) as affected by irrigation regime in Mediterranean climatic conditions of Tunisia. In this work, STICS model was used to simulate effects of farmer’s irrigation practices in wheat in the pedoclimatic conditions of the irrigated area of Oued Rmel in Tunisia over a 20-year period. Assessment of irrigation practices in the study area was performed, compared to rainfed system, in terms of yield Original Research Article Annual Research & Review in Biology, 4(5): 747-765, 2014 748 and produced biomass at harvest. The model was calibrated to simulate the growth and development of winter wheat using the field observed crop data collected from three growing seasons in two locations in Tunisia. To carry out the study, three types of soil (S1, S2 and S3) in the Oued rmel irrigation scheme were chosen on the basis of their available soil water in the root zone (TAW). The study showed that the model adequately predicts crop yield and biomass. Simulation results showed that the farmers’ irrigation practice results, in higher grain yield and dry matter at harvest as compared to rainfed system. Simulated grain yield was significantly higher in soil with high TAW than in the other soils. Results showed that the highest difference (30%) in simulated grain yield, between the two water regimes, was obtained in soil having high TAW. Depending on the soil type, simulated dry matter at harvest increased from 4% to 12% compared to rainfed system

Application of STICS model in assessment of the effects of irrigation practices and soil properties on yield of a durum wheat (Triticum durum Desf.) cultivar in the irrigated area of Oued Rmel in Tunisia

International audienceThe progress in computer technology has enabled the development of crop models reproducing the behavior of a crop in a wide range of pedoclimatic conditions and technical itineraries. This work aims to study the impact of total available soil water in the root zone (TAW) on durum wheat yield (Triticum durum Desf.) as affected by irrigation regime in Mediterranean climatic conditions of Tunisia. In this work, STICS model was used to simulate effects of farmer’s irrigation practices in wheat in the pedoclimatic conditions of the irrigated area of Oued Rmel in Tunisia over a 20-year period. Assessment of irrigation practices in the study area was performed, compared to rainfed system, in terms of yield Original Research Article Annual Research & Review in Biology, 4(5): 747-765, 2014 748 and produced biomass at harvest. The model was calibrated to simulate the growth and development of winter wheat using the field observed crop data collected from three growing seasons in two locations in Tunisia. To carry out the study, three types of soil (S1, S2 and S3) in the Oued rmel irrigation scheme were chosen on the basis of their available soil water in the root zone (TAW). The study showed that the model adequately predicts crop yield and biomass. Simulation results showed that the farmers’ irrigation practice results, in higher grain yield and dry matter at harvest as compared to rainfed system. Simulated grain yield was significantly higher in soil with high TAW than in the other soils. Results showed that the highest difference (30%) in simulated grain yield, between the two water regimes, was obtained in soil having high TAW. Depending on the soil type, simulated dry matter at harvest increased from 4% to 12% compared to rainfed system

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

Assessing Hydrus-2D Model to Investigate the Effects of Different On-Farm Irrigation Strategies on Potato Crop under Subsurface Drip Irrigation

The objective of this paper was to assess the performance of Hydrus-2D model to simulate the effects of different on-farm irrigation strategies applied on potato crop. The ability of the model to simulate the stress coefficient (Ks), obtained as the ratio between actual and maximum transpiration, and to define the productive function of potato crop under the semi-arid conditions of central Tunisia were also evaluated. Experiments were carried out on potato crop under full (FI) and deficit irrigation (DI) and two different water qualities supplied by means of a subsurface drip irrigation system. Results evidenced that the model, despite some discrepancies locally observed, can fairly accurately predict soil water contents and electrical conductivity around buried emitters. Furthermore, under water and salt stress conditions, “measured” Ks, based on crop water stress index (CWSI) obtained on thermal images, resulted in a good correlation with the corresponding estimated by the model (R2 = 0.8). The database collected during the three growth seasons also allowed the definition of the crop productive function represented by a linear relationship between the relative yield loss and Ks. This function represents a useful guidelines for the sustainable use of irrigation water in countries characterized by a semi-arid climate and a limited availability of water for irrigation

Effects of Saline and Deficit Irrigation on Soil-Plant Water Status and Potato Crop Yield under the Semiarid Climate of Tunisia

Water supplies have been decreasing in several semi-arid regions, and it is therefore necessary to adopt irrigation strategies aimed at maximizing water use efficiency. In this paper, the effects of saline and deficit irrigation on water use efficiency and on potato crop response, based on observations of soil and plant water status, were investigated. Experiments were carried out in Central Tunisia, by monitoring potato crop growth during two seasons in four distinct treatments (T1–T4), represented by two different irrigation doses and two water qualities. For irrigation scheduling purposes, thresholds of soil matric potential, soil water content and Crop Water Stress Index (CWSI) were identified with the aim to quantify the effects of water and/or salinity stress on the achievable yield. Experiments allowed verifying that crop yield is strongly affected by the seasonal amount and quality of applied water. Despite differences of crop yield between treatments T2, T3 and T4 not being statistically significant (P < 0.05), crop yield varied between 26.3 t/ha (T3 in 2015) to 16.3 t/ha (T4 in 2015). However, crop yield decline of 17.0 t/ha and 12.0 t/ha per each 100 mm decrease of applied water were observed under the application of water electrical conductivity of 1.6 dS/m and 4.1 dS/m respectively. On the other hand, an increase of 1.0 dS/m in water electrical conductivity caused a yield decline rate of about 10%. The results achieved showed that under the semi-arid climate of Tunisia, potato crop irrigation should be scheduled to avoid water deficit; however, the possibility to reduce water supply can be envisaged when water availability is limited, but with the awareness to accept the shortage of production. Finally, when saline water is the only source available to the farm, it is necessary to avoid the reduction of irrigation doses, to prevent excessive salt accumulation in the root zone with unavoidable effects on crop yield