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To understand how climate change affects crop yields, we need to identify the climatic indices that best predict yields. Grain yields are most often predicted using precipitation and temperature in statistical models, assuming linear dependences. However, soil water availability is more influential for plant growth than precipitation and temperature, and there is ecophysiological evidence of intermediate yield maximizing conditions. Using rainfed maize and soybean yields for 1970–2010 across the USA, we tested whether the aridity index, that is, the ratio of precipitation and potential evapotranspiration seasonal totals and a proxy of soil water availability, better predicts yield than growing season precipitation total, average temperature and their interaction. We also tested for non‐monotonic responses allowing for intermediate yield‐maximizing conditions. The aridity index alone explained 77% and 72% of maize and soybean yield variability, compared with 78% and 73% explained by temperature, precipitation and their interaction. Yield responses were non‐monotonic, with yields maximized at intermediate precipitation and temperature as well as at intermediate aridity index of 0.79 for maize and 0.98 for soybean. The yield maximizing precipitation also increased with growing season average temperature, faster in maize than soybean. The intermediate yield maximizing conditions show that rainfed maize and soybean yields could both increase and decrease depending on whether climatic conditions come closer to or deviate from the yield maximizing conditions in the future. In most counties, during 1970–2010, the precipitation and aridity index were lower and temperature higher compared with those maximizing yields, suggesting that climate change will reduce yields. [ABSTRACT FROM AUTHOR]

Climate change is predicted to hamper crop production due to precipitation deficits and warmer temperatures inducing both water stress and increasing herbivory due to more abundant insect pests. Consequently, crop yields will be impacted simultaneously by abiotic and biotic stressors. Extensive yield losses due to such climate change stressors might, however, be mitigated by ecosystem services such as insect pollination. We examined the single and combined effects of water stress, insect herbivory and insect pollination on faba bean yield components and above‐ and belowground plant biomass under realistic field conditions. We used rainout shelters to simulate a scenario in line with climate change projections, with adequate water supply at sowing followed by a long period without precipitation. This induced a gradually increasing water stress, culminating around crop flowering and yield formation. We found that gradually increasing water stress combined with insect herbivory by aphids interactively shaped yield in faba beans. Individually, aphid herbivory reduced yield by 79% and water stress reduced yield by 52%. However, the combined effect of water stress and aphid herbivory reduced yield less (84%) than the sum of the individual stressor effects. In contrast, insect pollination increased yield by 68% independently of water availability and insect herbivory. Our results suggest that yield losses can be greatly reduced when both water stress and insect herbivory are reduced simultaneously. In contrast, reducing only one stressor has negligible benefits on yield as long as the crop is suffering from the other stressor. We call for further exploration of interactions among ecosystem services and biotic and abiotic stressors that simulate realistic conditions under climate change. [ABSTRACT FROM AUTHOR]

When rainfall does not meet crop water requirements, supplemental irrigation is needed to maintain productivity. On-farm ponds can prevent excessive groundwater exploitation – to the benefit of the whole community – but they reduce the cultivated area and require investments by each farmer. Thus, choosing the source of water for irrigation (groundwater vs on-farm pond) is a problem of collective action. An agent-based model is developed to simulate a smallholder farming system; the farmers' long-/short-view orientation determines the choice of the water source. We identify the most beneficial water source for economic gain and its stability, and how it can change across communities and under future climate scenarios. By using on-farm ponds, long-view-oriented farmers provide collective advantages but have individual advantages only under extreme climates; a tragedy of the commons is always possible. Changes in farmers' attitudes (and hence sources of water) based on previous experiences can worsen the economic outcome. [ABSTRACT FROM AUTHOR]

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]

Autumn-sown field crops have important agronomic advantages (e.g., reduction of soil erosion and nutrient leaching, maximizing the use of spring moisture) and have the potential to be highly productive even though adverse winter conditions can negatively affect crop viability and yield. In the face of the unpredictable weather patterns and the expected shifts in climate in the near future, there is an imperative to develop methods to quantify both the risk of winter damage and how it is affected by altered climatic conditions and crop variety. We propose a set of indices to characterize synthetically the risk of crop damage stemming from cold spells, extended periods at low temperature, frequent occurrence of freeze-thaw cycles, and prolonged snow cover. An existing model of crop hardening and dehardening is further developed to account in full for the variability of lethal threshold temperature among individual plants. This model is coupled to a simple yet realistic description of crop-sensed temperature, so that required inputs are limited to crop-specific responses to low temperature and standard meteorogical data (average daily temperature and snow depth). This framework is applied to winter wheat under the current climatic conditions for central and southern Sweden. The roles of variety-specific hardening ability, temperature, and snow are assessed separately, thus obtaining indications of the potential impacts of variety selection and future predicted changes in temperature and snow cover in the region. Variety-specific hardening ability and response to exposure to low temperature may drastically alter the extent of winter damage. The most prevalent damaging mechanism depends on the climatic regime, with crops in colder areas benefiting from extended snow cover. A tradeoff between temperature (and hence latitude) and snow emerges, with locations at intermediate latitudes subjected to the highest risk of crop damage from exposure to low temperature and frequent freeze-thaw cycles. The same locations are also characterized by the highest inter-annual variability in the extent of winter damage - a fact that has potential implications for yield reliability. [ABSTRACT FROM AUTHOR]

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]