International audiencePredicting soil hydraulic properties and understanding their temporal variability during the irrigated cropping season are required to mitigate agro-environmental risks. This paper reports field measurements of soil hydraulic properties under two drip irrigation treatments, full (FT) and limited (LT). The objective was to identify the temporal variability of the hydraulic properties of field soil under high-frequency water application during a maize cropping season. Soil hydraulics were characterized using the Beerkan infiltration method. Seven sets of infiltration measurements were taken for each irrigation treatment during the cropping season between June and September 2007. The first set was measured two weeks before the first irrigation event. The results demonstrated that both soil porosity and hydraulic properties changed over time. These temporal changes occurred in two distinct stages. The first stage lasted from the first irrigation event until the root system was well established. During this stage, soil porosity was significantly affected by the first irrigation event, resulting in a decrease in both the saturated hydraulic conductivity Ks and the mean pore effective radius ξm and in an increase in capillary length αh. These hydraulic parameters reached their extreme values at the end of this stage. This behavior was explained by the “hydraulic” compaction of the surface soil following irrigation. During the second stage, there was a gradual increase in both Ks and ξm and a gradual decrease in αh when the effect of irrigation was overtaken by other phenomena. The latter was put down to the effects of wetting and drying cycles, soil biological activity and the effects of the root system, which could be asymmetric as a result of irrigation with only one drip line installed for every two plant rows. The processes that affected soil hydraulic properties in the two irrigation treatments were similar. No significant change in ξm and αh was observed between FT and LT. However, as a result of daily wetting and drying cycles, which were strongest in LT, the soil in this treatment was found to be more conductive than that of FT. This showed that most of the changes in pore-size distribution occurred in the larger fraction of pores. The impact of these temporal changes on the dimensions of the wetting bulb was studied using a simplified modeling approach. Our results showed that there were marked differences in the computed width and depth of wetting bulb when model input parameters measured before and after irrigation were used. A temporal increase in capillary length led to a more horizontally elongated wetting bulb. This could improve both watering and fertilization of the root zone and reduce losses due to deep percolation. As a practical result of this study, in order to mitigate agro-environmental risks we recommend applying fertilizers after the restructuration of tilled soil. Further studies using improved models accounting for temporal changes in soil hydraulic properties are needed

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International audienceThe management of irrigated agricultural fields requires reliable information about soil hydraulic properties and their spatio-temporal variability. The spatial variability of saturated hydraulic conductivity, Ks and the alpha-parameter αvG-2007 of the van Genuchten equation was reviewed on an agricultural loamy soil after a 17-year period of repeated conventional agricultural practices for tillage and planting. The Beerkan infiltration method and its algorithm BEST were used to characterize the soil through the van Genuchten and Brooks and Corey equations. Forty field measurements were made at each node of a 6 m × 7.5 m grid. The soil hydraulic properties and their spatial structure were compared to those recorded in 1990 on the same field soil, through the exponential form of the soil hydraulic conductivity given by the Gardner equation, using the Guelph Pressure Infiltrometer technique. No significant differences in the results obtained in 1990 and 2007 were observed for either particle-size distribution or dry bulk density. The mean value of αvG-2007 was found to be identical to that of αG-1990, while that of Ks-2007 was significantly smaller than that of Ks-1990. In contrast to the Gardner equation, the van Genuchten/Brooks and Corey expression was found to be more representative of a well-graded particle-size distribution of a loamy soil. The geostatistical analysis showed the two parameters, Ks and αvG-2007, were autocorrelated up to about 30 and 21 m, respectively, as well as spatially positively correlated within a range of 30 m. Despite the difference in the mean values of Ks between the two studies, the spatial structures were similar to those found in the 1990 experiment except for the covariance sign. The similarity in autocorrelation ranges indicate that the spatial analysis of soil hydraulic properties is independent of the infiltration methods (i.e., measurement of an infiltration flux) used in the two studies, while the difference in the covariance sign may be linked to the use of two different techniques of soil hydraulic parameterization. The covariance values found in the 2007 campaign indicates a positive relationship between the two parameters, Ks and αvG-2007. The spatial correlations of soil hydraulic parameters appear to be temporally stabilized, at least within the agro-pedo-climatic context of the study. This may be attributed to the soil textural properties which remain constant in time and to the structural properties which are constantly renewed by the cyclic agricultural practices. However, further experiments are needed to strengthen this result

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Enhancing water productivity for sustainable crop production and water savings represents a major challenge for agricultural water management. Pot experiments under open field conditions were conducted for two years, 2016 and 2017, to assess the effects of regulated deficit irrigation under mulch on onion crop production, following a 2 × 3 factorial experiment with two soil cover systems (wheat straw mulch and no-mulch) and three irrigation levels (100%, 80%, and 60% of crop evapotranspiration), with six replications.The results indicated that onion plants were responsive to straw mulching. Bulb diameter, total yield, dry matter, and water productivity were significantly enhanced under mulch whatever the irrigation level used. The seasonal crop water requirements also considerably decreased (about 33%). The results also showed the sensitivity of onion to water stress. Yield, dry matter, and water productivity were higher under full irrigation compared to the deficit irrigation. However, when mulch was used, regulated deficit irrigation highly significantly improved water productivity and onion crop quality and quantity; and this approach could be a promising management practice to meet water shortage consequences in the dry Mediterranean region.

Direct seeding into mulch (DSM) reduces soil evaporation. Therefore DSM can decrease the crop water demand. Furthermore DSM provides a favorable food source for soil microorganisms which can enhance the degradation of organic matter and improve nitrogen (N) availability for crops. Nowadays, a major challenge in irrigation is to increase irrigation water productivity (WP). This study assessed the impact of DSM on the N balance and WP according to experimental results compared with conventional tillage (CT). The results showed that DSM could mitigate N losses and improve WP for corn and sorghum. Because of field experimental limitations PILOTE, an operational model, was employed to test the hypothesis that DSM can be more efficient in water use. PILOTE was adapted and then calibrated and validated in the same experimental station. Taking into account the cover crop season, the model simulated the irrigation amount for a corn crop with a target yield of 14 t/ha during the long climatic series of 1991-2007. The results showed a WP increase from 77 with CT to 102 kg/mm with DSM. DSM can improve WP and save a water application depth of 40 mm compared to CT, which is interesting in a context with water scarcity.

Direct seeding into mulch (DSM) is a cropping system that is increasingly used in the world. The major concern among producers is the possible yield penalties associated with DSM compared to conventional tillage (CT). The aim of our study was to assess the effects of DSM on the yields of corn, sorghum and durum wheat, as well as water use efficiency (WUE) and nitrogen dynamics. An experimental study was carried out at the Lavalette experimental station from 2001 to 2007. Corn, sorghum and durum wheat were sown in two tillage treatments (CT and DSM). Yield and some yield components, nitrogen dynamics and WUE were determined. The results showed that DSM could maintain the crop production of corn and sorghum, however, for durum wheat, CT performed better. DSM improved WUE and irrigation water use efficiency (IWUE) of corn and sorghum and decreased crop evapotranspiration from 5 to 27%. These results suggest that DSM is a relevant alternative to the CT system for corn and sorghum in the SE of France. Adopting DSM with a relevant crop rotation and cover crop resulting in a better IWUE for this system compared with CT can effectively address water scarcity issues in this region. RÉSUMÉLe semis direct en paillis (DSM) est un système de culture qui est de plus en plus utilisé dans le monde. La préoccupation majeure des producteurs est la pénalité possible de rendement associée à DSM par rapport au labour conventionnel (CT). Le but de notre étude était d'évaluer les effets de la DSM sur le rendement du blé de maïs, de sorgho et de blé dur ainsi que l'efficacité d'utilisation de l'eau (WUE) et la dynamique de l'azote. Une étude expérimentale a été réalisée à la station expérimentale de Lavalette de 2001 à 2007, où maïs, sorgho et blé dur ont été semés dans des traitements de labour et DSM. Le rendement et certaines composantes du rendement, la dynamique de l'azote et WUE ont été déterminés. Les résultats ont montré que DSM pourrait maintenir la production des cultures de maïs et de sorgho, cependant, pour le blé dur, CT a obtenu de meilleurs résultats. DSM améliore WUE et l'efficacité d'utilisation de l'eau d'irrigation (IWUE) de maïs et de sorgho et diminue l'évapotranspiration des cultures de 5 à 27%. Ces résultats suggèrent que DSM est une alternative pertinente au système de CT pour le maïs et le sorgho dans le Sud Est de la France. Adopter DSM avec une rotation culturale adaptée et des cultures couvrantes donne une meilleure IWUE dans ce système par rapport à CT, et peut aider à résoudre la pénurie d'eau dans cette région.

Introduction: Minimizing production costs for drip-irrigated crops by reducing the number of driplines per unit-area is an urgent need to address the sustainability of the present production system. Materials and Methods: A two-year field experiment (2017 and 2018) was carried out to assess the effects of twin-row crop production system on two sweet corn varieties (Zea mays L.: an introduced variety “Silver Queen” and a local variety “White Kokab”) grown in a clay loam soil in the dry Mediterranean region. Three-row crop/dripline spacing configurations for each variety with three replicates were tested as: (i) single-row system at 75-cm crop row spacing with 75-cm dripline spacing (a dripline for each crop row), (ii) single-row system at 75-cm crop row spacing with 150-cm dripline spacing (a dripline for two crop rows), and (iii) twin-row system, 37.5 cm apart, on 150-cm centers, with 150-cm dripline spacing (a dripline for each twin-rows). Results and Conclusion: The local variety was better than the introduced variety in husked cop yield (13.93 t ha-1) and irrigation water use efficiency (IWUE, 1.92 kg m-3). Results also showed that the twin-row system with 150-cm dripline spacing provided similar husked cop yield and IWUE as the conventional 75-cm dripline spacing due to the more favourable rootzone soil water status; and both were higher in the two attributes than the single-row 150-cm dripline spacing. With 50% less unit-area driplines, twin-rows with 150-cm dripline spacing was considered to be more productive, economical and environmentally friendly.