Yield stability is fundamental to global food security in the face of climate change, and better strategies are needed for buffering crop yields against increased weather variability. Regional- scale ...analyses of yield stability can support robust inferences about buffering strategies for widely-grown staple crops, but have not been accomplished. We present a novel analytical approach, synthesizing 2000-2014 data on weather and soil factors to quantify their impact on county-level maize yield stability in four US states that vary widely in these factors (Illinois, Michigan, Minnesota and Pennsylvania). Yield stability is quantified as both 'downside risk' (minimum yield potential, MYP) and 'volatility' (temporal yield variability). We show that excessive heat and drought decreased mean yields and yield stability, while higher precipitation increased stability. Soil water holding capacity strongly affected yield volatility in all four states, either directly (Minnesota and Pennsylvania) or indirectly, via its effects on MYP (Illinois and Michigan). We infer that factors contributing to soil water holding capacity can help buffer maize yields against variable weather. Given that soil water holding capacity responds (within limits) to agronomic management, our analysis highlights broadly relevant management strategies for buffering crop yields against climate variability, and informs region-specific strategies.
Agriculture in 2050 HUNTER, MITCHELL C.; SMITH, RICHARD G.; SCHIPANSKI, MEAGAN E. ...
Bioscience,
04/2017, Volume:
67, Issue:
4
Journal Article
Peer reviewed
Open access
The prevailing discourse on the future of agriculture is dominated by an imbalanced narrative that calls for food production to increase dramatically—potentially doubling by 2050—without specifying ...commensurate environmental goals. We aim to rebalance this narrative by laying out quantitative and compelling midcentury targets for both production and the environment. Our analysis shows that an increase of approximately 25%–70% above current production levels may be sufficient to meet 2050 crop demand. At the same time, nutrient losses and greenhouse gas emissions from agriculture must drop dramatically to restore and maintain ecosystem functioning. Specifying quantitative targets will clarify the scope of the challenges that agriculture must face in the coming decades, focus research and policy on achieving specific outcomes, and ensure that sustainable intensification efforts lead to measurable environmental improvements. We propose new directions for research and policy to help meet both sustainability and production goals.
To fuel their activities and rear their offspring, foraging bees must obtain a sufficient quality and quantity of nutritional resources from a diverse plant community. Pollen is the primary source of ...proteins and lipids for bees, and the concentrations of these nutrients in pollen can vary widely among host-plant species. Therefore we hypothesized that foraging decisions of bumble bees are driven by both the protein and lipid content of pollen. By successively reducing environmental and floral cues, we analyzed pollen-foraging preferences of Bombus impatiens in (i) host-plant species, (ii) pollen isolated from these host-plant species, and (iii) nutritionally modified single-source pollen diets encompassing a range of protein and lipid concentrations. In our semifield experiments, B. impatiens foragers exponentially increased their foraging rates of pollen from plant species with high protein: lipid (P:L) ratios; the most preferred plant species had the highest ratio (∼4.6:1). These preferences were confirmed in cage studies where, in pairwise comparisons in the absence of other floral cues, B. impatiens workers still preferred pollen with higher P:L ratios. Finally, when presented with nutritionally modified pollen, workers were most attracted to pollen with P:L ratios of 5:1 and 10:1, but increasing the protein or lipid concentration (while leaving ratios intact) reduced attraction. Thus, macronutritional ratios appear to be a primary factor driving bee pollen-foraging behavior and may explain observed patterns of host-plant visitation across the landscape. The nutritional quality of pollen resources should be taken into consideration when designing conservation habitats supporting bee populations.
Interest in planting mixtures of cover crop species has grown in recent years as farmers seek to increase the breadth of ecosystem services cover crops provide. As part of a multidisciplinary ...project, we quantified the degree to which monocultures and mixtures of cover crops suppress weeds during the fall-to-spring cover crop growing period. Weed-suppressive cover crop stands can limit weed seed rain from summer- and winter-annual species, reducing weed population growth and ultimately weed pressure in future cash crop stands. We established monocultures and mixtures of two legumes (medium red clover and Austrian winter pea), two grasses (cereal rye and oats), and two brassicas (forage radish and canola) in a long fall growing window following winter wheat harvest and in a shorter window following silage corn harvest. In fall of the long window, grass cover crops and mixtures were the most weed suppressive, whereas legume cover crops were the least weed suppressive. All mixtures also effectively suppressed weeds. This was likely primarily due to the presence of fast-growing grass species, which were effective even when they were seeded at only 20% of their monoculture rate. In spring, weed biomass was low in all treatments due to winter kill of summer-annual weeds and low germination of winter annuals. In the short window following silage corn, biomass accumulation by cover crops and weeds in the fall was more than an order of magnitude lower than in the longer window. However, there was substantial weed seed production in the spring in all treatments not containing cereal rye (monoculture or mixture). Our results suggest that cover crop mixtures require only low seeding rates of aggressive grass species to provide weed suppression. This creates an opportunity for other species to deliver additional ecosystem services, though careful species selection may be required to maintain mixture diversity and avoid dominance of winter-hardy cover crop grasses in the spring.
Cover crop mixtures can provide multiple ecosystem services but provisioning of these services is contingent upon the expression of component species in the mixture. From the same seed mixture, cover ...crop mixture expression varied greatly across farms and we hypothesized that this variation was correlated with soil inorganic nitrogen (N) concentrations and growing degree days. We measured fall and spring biomass of a standard five-species mixture of canola (Brassica napus L.), Austrian winter pea (Pisum sativum L), triticale (x Triticosecale Wittm.), red clover (Trifolium pratense L.) and crimson clover (Trifolium incarnatum L.) seeded at a research station and on 8 farms across Pennsylvania and New York in two consecutive years. At the research station, soil inorganic N (soil iN) availablity and cumulative fall growing degree days (GDD) were experimentally manipulated through fertilizer additions and planting date. Farmers seeded the standard mixture and a "farm-tuned" mixture of the same five species with component seeding rates adjusted to achieve farmer-desired services. We used Structural Equation Modeling to parse out the effects of soil iN and GDD on cover crop mixture expression. When soil iN and fall GDD were high, canola dominated the mixture, especially in the fall. Low soil iN favored legume species while a shorter growing season favored triticale. Changes in seeding rates influenced mixture composition in fall and spring but interacted with GDD to determine the final expression of the mixture. Our results show that when soil iN availability is high at the time of cover crop planting, highly competitive species can dominate mixtures which could potentially decrease services provided by other species, especially legumes. Early planting dates can exacerbate the dominance of aggressive species. Managers should choose cover crop species and seeding rates according to their soil iN and GDD to ensure the provision of desired services.
Strategies for conserving plant diversity in agroecosystems generally focus on either expanding land area in non-crop habitat or enhancing diversity within crop fields through changes in within-field ...management practices. In this study, we compare effects on landscape-scale species richness from such land-sharing or land-sparing strategies. We collected data in arable field, grassland, pasture, and forest habitat types (1.6 ha sampled per habitat type) across a 100-km
2
region of farmland in Lancaster County, Pennsylvania, USA. We fitted species-area relationships (SARs) for each habitat type and then combined extrapolations from the curves with estimates of community overlap to estimate richness in a 314.5-ha landscape. We then modified these baseline estimates by adjusting parameters in the SAR models to compare potential effects of land-sharing and land-sparing conservation practices on landscape richness. We found that species richness of the habitat types showed a strong inverse relationship to the relative land area of each type in the region, with 89 species in arable fields (66.5% of total land area), 153 in pastures (6.7%), 196 in forests (5.2%), and 213 in grasslands (2.9%). Relative to the baseline scenario, major changes in the richness of arable fields produced gains in landscape-scale richness comparable to a conversion of 3.1% of arable field area into grassland habitat. Sensitivity analysis of our model indicated that relative gains from land sparing would be greatest in landscapes with a low amount of non-crop habitat in the baseline scenario, but that in more complex landscapes land sharing would provide greater gains. These results indicate that the majority of plant species in agroecosystems are found in small fragments of non-crop habitat and suggest that, especially in landscapes with little non-crop habitat, richness can be more readily conserved through land-sparing approaches.
•We estimated the temporal dynamics of ecosystem services provided by cover crops.•Cover crops increased 8 of 11 ecosystem services in a 3-year grain rotation.•Estimates of cover crop benefits were ...sensitive to the point in time analyzed.•Trade-offs occurred between ecosystem benefits, profitability, and management risks.•This type of framework can improve agroecosystem management for multiple ecosystems services.
Cropping systems that provide ecosystem services beyond crop production are gaining interest from farmers, policy makers and society at large, yet we lack frameworks to evaluate and manage for multiple ecosystem services. Using the example of integrating cover crops into annual crop rotations, we present an assessment framework that: (1) estimates the temporal dynamics of a suite of ecosystem services; (2) illustrates ecosystem multifunctionality using spider plots; and (3) identifies key time points for optimizing ecosystem service benefits and minimizing trade-offs. Using quantitative models and semi-quantitative estimates, we applied the framework to analyze the temporal dynamics of 11 ecosystem services and two economic metrics when cover crops are introduced into a 3-year soybean (Glycine max)–wheat (Triticum aestivum)–corn (Zea mays) rotation in a typical Mid-Atlantic climate. We estimated that cover crops could increase 8 of 11 ecosystem services without negatively influencing crop yields. We demonstrate that when we measure ecosystem services matters and cumulative assessments can be misleading due to the episodic nature of some services and the time sensitivity of management windows. For example, nutrient retention benefits occurred primarily during cover crop growth, weed suppression benefits occurred during cash crop growth through a cover crop legacy effect, and soil carbon benefits accrued slowly over decades. Uncertainties exist in estimating cover crop effects on several services, such as pest dynamics. Trade-offs occurred between cover crop ecosystem benefits, production costs, and management risks. Differences in production costs with and without cover crops varied 3-fold over 10years, largely due to changes in fertilizer prices, and thus cover crop use will become more economical with increasing fertilizer prices or if modest cost-sharing programs are established. Frameworks such as that presented here provide the means to quantify ecosystem services and facilitate the transition to more multifunctional agricultural systems.
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