Soil salinization is a global phenomenon that affects large tracts of arid farmland worldwide. It contributes to the loss of soil fertility, declining yields, and – in the most severe cases – land unsuitability for cultivation. Irrigation water applications are both the main cause of and the solution to, anthropogenic (or ‘secondary’) salinization because salt typically enters the soil column as dissolved in irrigation water and leaves it through excess water applications (e.g., leaching). Excess leaching, which places additional water costs in areas affected by water scarcity, can be achieved with different irrigation techniques and practices. Here, by complementing a process-based crop water model with a salt balance of the shallow soil, we investigate the tradeoff between root zone salinization and water conservation to limit withdrawals from the water source. We evaluate how such a tradeoff is achieved under different irrigation technology and excess leaching practices. Considering as a case study the cultivation of tomatoes in Egypt, we find that drip and furrow irrigation allows for better control of salt accumulation, thus preventing crop exposure to salt stress. Drip irrigation achieves this goal with minimal water applications because it maintains the soil wetter. Thus, the (rare) rainfall events find more suitable conditions to drain the excess moisture. Conversely, by using more irrigation water (and ‘less efficiently’), furrow irrigation allows for higher rates of soil drainage and salt leaching. The irrigation schedule typically adopted with sprinkler irrigation allows for soil drying, thus limiting the ability of rainfall events to drain the soil and leach its salts. Collectively, these results highlight the key role of irrigation technology and practices in the management of secondary salinity in dryland agriculture. Specifically, there is a tradeoff between minimizing water use and preventing salt accumulation in the root zone. Drip irrigation exhibits the co-benefit of achieving both goals, while furrow irrigation limits soil salinity at the cost of requiring greater volumes of applied irrigation water.

The appearance of the regular vegetated ridge patterns observed in some ephemeral rivers of semi-arid regions (Nanson, Tooth, & Knigthon 2002) has previously been explained by hydraulic arguments (optimization of the bed load transport capacity, see Huang & Nanson (2007)) without including the role of vegetation in the process. Those arguments provide neither the conditions under which the more efficient anabranching system can be realized nor a description of the dynamics leading to anabranching. As an alternative, we propose a simplified model accounting for the flow-mediated interactions between riparian vegetation located at different points of the river channel. Classically, the appearance of river morphologic features is explained by the equations of morphodynamics. However, due to the complexity of the action of vegetation on the flow and on sediment transport, a complete physically-based set of coupled ecomorphodynamic equations is not available yet. We propose an effective model for the interactions between vegetated obstacles. Depending on the relative position of the obstacles, one observes either positive or negative feedbacks: on the lee-side of a permeable obstacle, flood sheltering may occur and favor deposition that helps in turn the establishment of biomass, conversely scouring is increased laterally due to obstacle-induced flow diversion (Zong & Nepf 2010). In the situation where the hydrological timescale (flooding frequency for a given effective magnitude) and the biological timescale (vegetation development rate) are comparable, the spatially inhomogeneous feedbacks can result in the appearance of organized regular structures. Aerial photographs give us the characteristic morphological scale of patterns. We then perform a stability analysis of our model and derive a set of conditions under which the combination of hydrological, ecological and pedological factors allows the formation of anabranching patterns. We discuss the role of the different ingredients in relation to the fluvial environments in which such patterns typically emerge. Finally, we conjecture on the relevance of the proposed mechanism to explain ubiquitous vegetated scroll bars that are observed on the interior of meander bends.