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Population growth and changes in climate and diets will likely further increase the pressure on agriculture and water resources globally. Currently, staple crops are obtained from annuals plants. A shift towards perennial crops may enhance many ecosystem services, but at the cost of higher water requirements and lower yields. It is still unclear when the advantages of perennial crops overcome their disadvantages and perennial crops are thus a sustainable solution. Here we combine a probabilistic description of the soil water balance and crop development with an extensive dataset of traits of congeneric annuals and perennials to identify the conditions for which perennial crops are more viable than annual ones with reference to yield, yield stability, and effective use of water. We show that the larger and more developed roots of perennial crops allow a better exploitation of soil water resources and a reduction of yield variability with respect to annual species, but their yields remain lower when considering grain crops. Furthermore, perennial crops have higher and more variable irrigation requirements and lower water productivity. These results are important to understand the potential consequences for yield, its stability, and water resource use of a shift from annual to perennial crops and, more generally, if perennial crops may be more resilient than annual crops in the face of climatic fluctuations. [ABSTRACT FROM AUTHOR]

Farm specialization and associated simplification of the crop rotation raise concern about the ability of cropping systems to deliver high and stable yield in the long-term. Exploiting data from 52 years of a long-term experiment in Southern Sweden, we investigated impacts of three conventional cropping systems (‘crop-livestock’, ‘specialized’, and ‘diverse’) on yield levels and stability of winter and spring wheat. For winter wheat, the ‘diverse’ and ‘crop-livestock’ systems enhanced yields by 15% compared to the ‘specialized’ system. For spring wheat, the ‘crop-livestock’ system tended to show higher yield than the ‘diverse’ one. The stability analysis showed that in winter wheat the three systems lead to equally stable yields considering year-to-year variability. For spring wheat, the ‘crop-livestock’ system tended to perform better in favorable years relative to the other systems. Overall, the results revealed that for winter wheat cultivation, stockless diverse cropping provides an valid alternative to crop-livestock in the context of specialized farming where crop and livestock are separated. [ABSTRACT FROM AUTHOR]

Highlights: [•] Stomatal optimization theories have neglected the effect of dynamic soil moisture. [•] Here soil moisture is considered to provide a closure for the optimization problem. [•] The new solutions link marginal water use efficiency to air [CO2] and soil water. [•] Previously inconsistent theoretical results and data are generalized and explained. [Copyright &y& Elsevier]

Abstract: An effective description of water transport in the soil–plant–atmosphere continuum (SPAC) is needed for wide-ranging applications in hydrology and climate-vegetation interactions. In this contribution, the theory of water movement within the SPAC is reviewed with emphasis on the eco-physiological and evolutionary constraints to water transport. The description of the SPAC can be framed at two widely separated time scales: (i) sub-hourly to growing season scales, relevant for hydro-climatic effects on ecosystem fluxes (given a set of plant hydraulic traits), and (ii) inter-annual to centennial scales during which either hydraulic traits may change, as individuals grow and acclimate, or species composition may change. At the shorter time scales, water transport can be described by water balance equations where fluxes depend on the hydraulic features of the different compartments, encoded in the form of conductances that nonlinearly depend on water availability. Over longer time scales, ontogeny, acclimation, and shifts in species composition in response to environmental changes can impose constraints on these equations in the form of tradeoffs and coordinated changes in the hydraulic (and biochemical) parameters. Quantification of this evolutionary coordination and the related tradeoffs offers novel theoretical tactics to constrain hydrologic and biogeochemical models. [Copyright &y& Elsevier]

Abstract: The optimality of irrigation strategies may be sought with respect to a number of criteria, including water requirements, crop yield, and profitability. To explore the suitability of different demand-based irrigation strategies, we link the probabilistic description of irrigation requirements under stochastic hydro-climatic conditions, provided in a companion paper [Vico G, Porporato A. From rainfed agriculture to stress-avoidance irrigation: I. A generalized irrigation scheme with stochastic soil moisture. Adv Water Resour 2011;34(2):263–71], to crop-yield and economic analyses. Water requirements, application efficiency, and investment costs of different irrigation methods, such as surface, sprinkler and drip irrigation systems, are described via a unified conceptual and theoretical approach, which includes rainfed agriculture and stress-avoidance irrigation as extreme cases. This allows us to analyze irrigation strategies with respect to sustainability, productivity, and economic return, using the same framework, and quantify them as a function of climate, crop, and soil parameters. We apply our results to corn (Zea mays), a food staple and biofuel source, which is currently mainly irrigated through surface systems. As our analysis shows, micro-irrigation maximizes water productivity, but more traditional solutions may be more profitable at least in some contexts. [ABSTRACT FROM AUTHOR]

Abstract: With vast regions already experiencing water shortages, it is becoming imperative to manage sustainably the available water resources. As agriculture is by far the most important user of freshwater and the role of irrigation is projected to increase in face of climate change and increased food requirements, it is particularly important to develop simple, widely applicable models of irrigation water needs for short- and long-term water resource management. Such models should synthetically provide the key irrigation quantities (volumes, frequencies, etc.) for different irrigation schemes as a function of the main soil, crop, and climatic features, including rainfall unpredictability. Here we consider often-employed irrigation methods (e.g., surface and sprinkler irrigation systems, as well as modern micro-irrigation techniques) and describe them under a unified conceptual and theoretical framework, which includes rainfed agriculture and stress-avoidance irrigation as extreme cases. We obtain mostly analytical solutions for the stochastic steady state of soil moisture probability density function with random rainfall timing and amount, and compute water requirements as a function of climate, crop, and soil parameters. These results provide the necessary starting point for a full assessment of irrigation strategies, with reference to sustainability, productivity, and profitability, developed in a companion paper [Vico G, Porporato A. From rainfed agriculture to stress-avoidance irrigation: II. Sustainability, crop yield, and net profit. Adv Water Resour 2011;34(2):272–81]. [ABSTRACT FROM AUTHOR]

• On-farm ponds can sustainably provide water for irrigation, but impose trade-offs. • A minimalist model coupling soil water, crop and pond water storage is developed. • We identify the best pond size for different climates, soils and irrigation strategies. • Production maximization and low yield risk minimization require different pond sizes. • Future more extreme climates will make these goals even harder to reconcile. In many regions precipitation does not reliably meet crop water demands – a situation that climate change will likely exacerbate. Supplemental irrigation can help enhance and stabilize crop yields, but the need of water for irrigation has often led to groundwater over-exploitation. On-farm ponds can provide a more sustainable water source. Their use has often been promoted by local authorities, but, by converting a portion of cultivated area to water storage and reducing water availability downstream, on-farm ponds also imply constraints and trade-offs. For an effective exploitation of their potential benefits, they must be carefully designed and managed based on the local edaphic and climate conditions – a non trivial, task because of the cascading effects of rainfall unpredictability. Here we identify the most suitable on-farm pond size, according to two criteria: maximization of average yield (i.e., production maximization) and achievement of a minimum acceptable yield (i.e., risk minimization, accounting for the farmer's risk aversion). To this aim, we develop a minimalist model, requiring few, physically based parameters, coupling crop biomass, soil moisture, and water stored in the pond. While general, the model is here applied to a case-study in the Lower Mississippi River Basin (USA). Simulations show that yield maximization and risk minimization are goals hard to reconcile, regardless of climatic conditions, soil type and irrigation strategy, with smaller ponds allowing the maximum average yield at the cost of reducing its stability from year to year. Stress avoidance irrigation ensures higher yields than deficit irrigation, even if it implies a faster use of the stored water. Future, more extreme climates will result in lower maximum average yields and narrower ranges of pond sizes ensuring desirable minimum yields. [ABSTRACT FROM AUTHOR]

One of the most important resources within agriculture is nitrogen (N), and depletion of N resources is an important element in the evaluation of sustainability in agriculture. Therefore, identifying crops with high nitrogen use efficiency (NUE) is important for the sustainability of the system. In an energy crop context, sustainability in crop production could aim at enhanced energy output with maintained or reduced depletion of N resources. Crops with different photosynthetic pathways (C 3 vs. C 4 ) and life histories (perennials vs. annuals) are expected to differ in NUE and also energy harvest per unit N lost from the system. The aim is to characterize the growth, NUE and energy output per unit N lost for three common crops frequently used for energy; maize, winter wheat and perennial grassland (ley). These crops differ in photosynthetic and life history strategies. Above ground biomass of wheat, grassland ley and maize was sampled within a long-term experiment in Central Sweden. The experiment has a split-plot design with four replicates. Four aboveground harvests were conducted during the growth period and plant N contents were determined. Biomass growth, yield (above ground biomass in ley and maize, grain biomass in wheat) and some functional traits were assessed, and the NUE components N uptake efficiency, yield-specific N efficiency and yield N concentration were calculated according to Weih, et al. (2011). Energy output per N lost with the harvested product was calculated assuming crop-specific higher heating values for biofuel use. The N uptake efficiency and yield-specific N efficiency were higher in maize than wheat and ley. The yield N concentration was higher in the perennial ley than the annual crops, and lowest in maize. Energy output per N lost in the harvested product was greater in maize compared to wheat and ley. The results are discussed in a agricultural sustainability perspective. [ABSTRACT FROM AUTHOR]

• Non-dimensional combinations of soil, plant, and climate variables reduce the complexity of plant water use strategies. • Plant water flux control relative to demand is the non-dimensional group that primarily influences plant water use performance. • Plant water use strategies that maximize long-term mean transpiration weighted by risks of water stress match soil moisture observations. • Combining non-dimensional groups and ecohydrological optimality offers constraints to quantify and understand plant water stress responses. Plant responses to water stress influence water and carbon cycles and can lead to feedbacks on climate yet characterizing these responses at ecosystem levels remains uncertain. Quantifying ecosystem-level water use strategies is complex due to challenges of upscaling plant traits and disentangling confounding environmental factors, ultimately limiting our ability to understand and anticipate global change in ecosystem dynamics and ecohydrological fluxes. We reduce the dimensionality of this problem and quantify plant water use strategies by combining plant traits with soil and climate variables into parameter groups that synthesize key eco-physiological tradeoffs. Using a parsimonious soil water balance framework, we explore variations in plant water uptake capacity, water stress responses, and water use performance via these non-dimensional parameter groups. The group characterizing the synchronization of plant water transport and atmospheric water demand emerges as the primary axis of variation in water use strategies and interacts with the group representing plant hydraulic risk tolerance, especially in arid conditions when plant water transport is limiting. Next, we show that specific plant water use strategies maximize plant water uptake (leading to carbon gain benefits) weighted by risks of water stress (leading to higher costs of water use). A model-data comparison demonstrates that these ecohydrologically optimal parameter groups capture observed soil moisture variability in 40 ecosystems and beyond aridity, rainfall frequency is an important environmental control for plant water use strategies. The emerging parsimonious link between ecohydrological performance and non-dimensional parameters provides a tractable representation of plant water use strategies, relevant to parameterize global models while accounting for ecological and evolutionary constraints on the water cycle. [ABSTRACT FROM AUTHOR]

• The ecological niche space for nitrogen (N) use traits was defined via n -dimensional hypervolumes. • Trait space was influenced more by the cultivar identity than crop mixing. • High N uptake was associated with a reduced overlap in niche-space in the mixtures. • Initial seed N pools contributed to N accumulation, shoot and tiller production. More efficient resource use, especially nitrogen (N) in agricultural fields could considerably reduce the losses and spillover effects on the environment. Cereal-legume mixtures can lead to more efficient uptake of growth-limiting resources, and increase and stabilize yields, due to the variation in functional traits that facilitate partitioning of niche space. Here we identify crop mixtures with functional traits that facilitate optimal N resource use in two selected cereal-legume mixtures by using the multi-dimensional trait space concept. Combinations of pea-barley and faba bean-wheat crops were grown in the field as pure cultures and mixtures in Central Sweden, during two years with contrasting weather. The ecological niche space was defined via the n -dimensional hypervolumes represented by N pool, tiller/branch number, shoot biomass, and grain yield functional traits. Regressions and correlations allowed quantifying the relations between functional traits and plant N pools. Differences in trait space were not a result of crop mixing per se , as similar hypervolumes were found in the pure culture and mixture-grown crops. Instead, the trait space differences depended on the cultivar identities admixed. Furthermore, cereals increased their efficiency for N uptake and therefore benefitted more than the legumes in the mixtures, in terms of accumulated N and grain yields. Tiller and shoot biomass production in cereals was positively correlated to N pool accumulation during the season. Resource acquisition through increased N uptake in the mixture was associated with a reduced overlap in niche-space in the mixtures, and initial seed N pools significantly contributed to within-season N accumulation, shoot and tiller production. [ABSTRACT FROM AUTHOR]

• APSIM was calibrated and validated for pure cultures of wheat and faba bean. • APSIM was evaluated for wheat-faba bean pure cultures and intercrops in Europe. • APSIM reproduced pure culture aboveground dry matters and, for wheat, yields. • APSIM overestimates faba bean performance relative to wheat in intercrops. • APSIM must incorporate an alternative approach to simulate height growth. Cereal-legume intercropping can increase yields, reduce fertilizer input and improve soil quality compared with pure culture. Designing intercropping systems requires the integration of plant species trait selection with choice of crop configuration and management. Crop growth models can facilitate the understanding and prediction of the interactions between plant traits, crop configuration and management. However, currently no existing crop growth model has been calibrated and tested for cereal-legume intercrops throughout Europea. We calibrated the Agricultural Production Systems sIMulator (APSIM) for pure cultures of wheat and faba bean using data from Dutch field trials, and determined the phenological parameters to simulate pure cultures and intercrops from seven field experiments across Europe. APSIM successfully reproduced aboveground dry matters and, for wheat only, grain yields in pure cultures. In intercrops, APSIM systematically overestimated the aboveground dry matter and grain yield of faba bean and underestimated those of wheat. APSIM was reasonably capable of simulating plant heights in pure cultures, but respectively overestimated and underestimated the height of faba bean and wheat in intercrops. In order to simulate wheat-faba bean intercrops better, APSIM should be improved regarding the calculation of biomass partitioning to grains in faba bean and of height growth in both species. [ABSTRACT FROM AUTHOR]

• Comprehensive review about the water and carbon cycles in perennial Kernza plants. • Kernza has a relatively high water-use efficiency through the whole growing season. • Kernza tends to have higher evapotranspiration rates when compared to annual counterparts. • Kernza has shown to act as carbon sink on a long-term basis. Perennial crops have been proposed as a more sustainable alternative to annual crops, because they have extended growing seasons, continuous ground cover, reduced nutrient leakage, and sequester more carbon in the soils than annual crops. One example is intermediate wheatgrass (Thinopyrum intermedium), a perennial crop that has been used as a cool-season forage throughout the USA and Canada and also across its native range in Eurasia. Since the 1980′s, intermediate wheatgrass has been under domestication to improve seed fertility and grain yield. Commercial products are being sold under the trade name Kernza, owned by The Land Institute, located in Salina, Kansas, USA. This review provides a comprehensive framework about the physical and biological aspects involving the water and carbon cycles in Kernza plants. The main aspects we highlight here are based on previous findings regarding Kernza: i) the ability of maintaining a relatively high water-use efficiency throughout the whole growing season, which is beneficial to mitigate water stress, representing an important physiological mean to acclimate under severe, unfavorable weather conditions, and ii) its higher evapotranspiration (ET) and net carbon uptake rates, particularly when compared to annual counterparts. Only a thorough multifaceted assessment of the repercussion for carbon and water fluxes of a shift from annual crops to Kernza will allow assessing the perspectives of such novel perennial crop to support food security and a number of ecosystem services, particularly under future climates. [ABSTRACT FROM AUTHOR]