Increasing the quantity and quality of plant biomass production in space and time can improve the capacity of agroecosystems to capture and store atmospheric carbon (C) in the soil. Cover cropping is ...a key practice to increase system net primary productivity (NPP) and increase the quantity of high-quality plant residues available for integration into soil organic matter (SOM). Cover crop management and local environmental conditions, however, influence the magnitude of soil C stock change. Here, we used a comprehensive meta-analysis approach to quantify the effect of cover crops on soil C stocks from the 0–30 cm soil depth in temperate climates and to identify key management and ecological factors that impact variation in this response. A total of 40 publications with 181 observations were included in the meta-analysis representing six countries across three different continents. Overall, cover crops had a strong positive effect on soil C stocks (P < 0.0001) leading to a 12% increase, averaging 1.11 Mg C/ha more soil C relative to a no cover crop control. The strongest predictors of SOC response to cover cropping were planting and termination date (i.e., growing window), annual cover crop biomass production, and soil clay content. Cover crops planted as continuous cover or autumn planted and terminated led to 20–30% greater total soil C stocks relative to other cover crop growing windows. Likewise, high annual cover crop biomass production (>7 Mg·ha−1·yr−1) resulted in 30% higher total soil C stocks than lower levels of biomass production. Managing for greater NPP by improving synchronization in cover crop growing windows and climate will enhance the capacity of this practice to drawdown carbon dioxide (CO₂) from the atmosphere across agroecosystems. The integration of growing window (potentially as a proxy for biomass growth), climate, and soil factors in decision-support tools are relevant for improving the quantification of soil C stock change under cover crops, particularly with the expansion of terrestrial soil C markets.
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.
Aims
Half of field crop nitrogen (N) is often derived soil organic matter (SOM) mineralization, yet we do not fully understand the extent to which plant genotypic differences influence SOM ...mineralization dynamics across different soil N contexts. We explored the effects of rapeseed (
Brassica napus
) genotypic diversity on N uptake from organic and inorganic N sources.
Methods
In a greenhouse study, we applied dual
15
N labeled ammonium-nitrate fertilizer to examine N uptake patterns of rapeseed in different N environments. Ten varieties were grown in a full factorial experiment with four treatments, including combinations of high and low N fertilizer and SOM.
Results
We found limited varietal differences in total biomass or N uptake across soil environments. Across all varieties, SOM was an important, additive N source even as N fertilizer availability increased. High SOM/High Fertilizer treatment plants obtained 64% of N from SOM, while plants grown with High SOM/Low Fertilizer obtained 89% of total N from SOM. Under low SOM availability, the high fertilizer addition increased overall N uptake from SOM by 42% relative to the low N fertilizer treatment.
Conclusions
Integrating plant reliance on SOM-N sources into crop breeding and NUE estimates has potential to improve crop productivity and improve overall system N use efficiency.
A global transformation in semi-arid cropping systems is occurring as dryland (non-irrigated) farmers in semi-arid regions shift from crop rotations reliant on year-long bare fallows, called summer ...fallow, to more intensively cropped systems. Understanding the rate of cropping system intensification at the landscape scale is critical to estimating the economic and environmental implications of this movement. Here, we use high-resolution satellite data to quantify dryland cropping patterns from 2008 to 2016 in the US High Plains. We use these estimates to scale up our previous field-level research in this region on soil carbon, herbicide use, yields, and profitability. Over the nine year study period, the High Plains witnessed a profound shift in cropping systems, as the historically dominant wheat-fallow system was replaced by more intensified rotations as the dominant systems by land area. Out of the 4 million hectares of non-irrigated cropland in the study area, this shift coincided with a 0.5 million-hectare decline in summer fallow and a concurrent increase in alternative (non-wheat) crops. We estimate that, from 2008 to 2016, these patterns resulted in a 0.53 Tg (9%) increase in annual grain production, 80 million USD (10%) increase in annual net farm operating income, substantial reductions in herbicide use, and an increase in C sequestration that corresponds to greenhouse gas reductions of 0.32 million metric tons of CO2 equivalents per year (MMTCO2e yr−1). We project each of these implications to a scenario of potential maximum 100% intensification and estimate that, relative to 2016 levels, herbicide use would be reduced by more than half, grain production would increase by 25%, net operating income would increase by 223 million USD (26%), and greenhouse gases would be reduced by an additional 0.8 MMTCO2e yr−1. The scale of cropping intensification in the High Plains and its environmental and economic impacts has important implications for other regions undergoing similar transformations, and for policy that can either support or hinder these shifts toward more sustainable cropping systems.
Trends of increasing agricultural trade, increased concentration of livestock production systems, and increased human consumption of livestock products influence the distribution of nutrients across ...the global landscape. Phosphorus (P) represents a unique management challenge as we are rapidly depleting mineable reserves of this essential and non-renewable resource. At the same time, its overuse can lead to pollution of aquatic ecosystems. We analyzed the relative contributions of food crop, feed crop, and livestock product trade to P flows through agricultural soils for 12 countries from 1961 to 2007. Due to the intensification of agricultural production, average soil surface Ñ balances more than tripled from 6 to 21 kg P ha⁻¹ between 1961 and2007 for the 12study countries. Consequently, countries that are primarily agricultural exporters carried increased risks for water pollution or, for Argentina, reduced soil fertility due to soil P mining to support exports. In 2007, nations imported food and feed from regions with higher apparent P fertilizer use efficiencies than if those crops were produced domestically. However, this was largely because imports were sourced from regions depleting soil P resources to support export crop production. In addition, the pattern of regional specialization and intensification of production systems also reduced the potential to recycle P resources, with greater implications for livestock production than crop production. In a globalizing world, it will be increasingly important to integrate biophysical constraints of our natural resources and environmental impacts of agricultural systems into trade policy and agreements and to develop mechanisms that move us closer to more equitable management of nonrenewable resources such as phosphorus.
•We soil sampled 96 dryland no-till fields on working farms & long-term experiments.•Continuous rotations (no summer fallow) had 17% more SOC to 10 cm than wheat-fallow.•Continuous had greater ...aggregate stability and more soil fungi than wheat-fallow.•Rotational effects were robust amidst variability in management, climate, and soils.
Increasing soil organic carbon (SOC) is a critical but daunting challenge in semi-arid agroecosystems. For dryland farmers, low levels of SOC and aggregation exacerbate the risks of farming in a water-limited environment − risks that will compound with climate change. Many dryland farmers in semi-arid climates use year long periods called summer fallow, where no crops are grown and weeds are controlled, to store rainwater and increase the yield of the following crop. In semi-arid climates around the world, dryland farmers are increasingly replacing summer fallow with a crop, a form of cropping system intensification. Cropping system intensification has the potential to increase SOC, but the drivers of this effect are unclear, and may change based on environmental conditions and management strategy. We quantified SOC, water-stable aggregates, and fungal and microbial biomass on 96 dryland, no-till fields in the semi-arid Great Plains, USA, representing three levels of cropping system intensity from wheat-fallow to continuous (no summer fallow) rotations along a potential evapotranspiration gradient. Cropping system intensity was positively associated with SOC, aggregation, and fungal biomass, and these effects were robust amidst variability in environmental and management factors. Continuous rotations averaged 1.28% SOC at 0–10 cm and had 17% and 12% higher SOC concentrations than wheat-fallow in 0–10 cm and 0–20 cm depths, respectively. Aggregate stability in continuous rotations was about twice that in wheat-fallow rotations. Fungal biomass was three times greater in continuous rotations than wheat-fallow, but was not significantly different from mid-intensity rotations. Using structural equation modeling, we observed that continuous cropping, potential evapotranspiration, % clay content, and fungal biomass together explained 50% of the variability in SOC, and that SOC appears to enhance aggregation directly and as mediated through increases in fungal biomass. Overall, the model suggests that cropping system intensity increases SOC both directly, through greater C inputs to soil, and indirectly, by increasing fungal biomass and aggregation. Our findings suggest that continuous cropping has the potential to provide gains in SOC and soil structure that will help offset C emissions and enhance the resilience of dryland agroecosystems.
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.
Background and aims The selection of legume species and species mixtures influences agroecosystem nitrogen (N) and carbon cycling. We utilized a fertility gradient to investigate the effects of plant ...species interactions on biological N fixation of an annual and perennial legume in response to shifting soil resource availability. Methods Legume N fixation of annual field pea (Pisum sativum) and perennial red clover (Trifolium pratense) grown in monoculture and mixtures with oats (Avena sativa) or orchardgrass (Dactylis glomerata) was estimated using the 15N natural abundance method across 15 farm fields and we measured six soil N pools ranging from labile to more recalcitrant. Results Evidence of complementary and facilitative species interactions was stronger for the perennial red clover-orchardgrass mixture than for the annual field pea-oat mixture (N Land Equivalency Ratios were 1.6 and 1.2, respectively). We estimated that the transfer of fixed N from red clover to orchardgrass increased aboveground N fixation estimates by 15% from 33 to 38 kg N ha−1. Despite a more than 2-fold range in soil organic matter levels and more than 3-fold range in labile soil N pools across field sites, the N fertility gradient was not a strong predictor of N fixation. While grass N assimilation was positively correlated with soil N pools, we found only weak, inverse correlations between legume N fixation and soil N availability. In grass-legume mixtures, soil N availability indirectly influenced N fixation through plant competition. Conclusions These results suggest that increasing diversity of cropping systems, particularly through the incorporation of perennial mixtures into rotations, could improve overall agroecosystem N cycling efficiency.
•Cropping intensification impacts were evaluated across dryland agroecosystems.•Reducing summer fallow increased total and mineralizable nitrogen.•Continuous rotations had 300% more mycorrhizal root ...colonization and more P uptake.•Continuous rotations used 60% less herbicide than wheat-fallow rotations.•Reducing summer fallow increased productivity and profitability of dryland systems.
Rising use and costs of agri-chemical inputs to support agricultural production have placed an economic burden on farmers while contributing to environmental and human health issues. Ecologically based nutrient and weed management – the use of ecological processes to replace external chemical inputs – may represent a strategy to support crop growth while achieving positive environmental and economic outcomes. In dryland agroecosystems around the world, farmers are increasingly transitioning toward no-till and intensified cropping systems, in which unvegetated fallow periods are replaced with crops. This study seeks to determine if cropping system intensification represents an ecologically based strategy for managing nutrients and weeds relative to traditional crop-fallow systems, and to understand the implications for crop production and profitability. We quantified total and potentially mineralizable nitrogen (N), arbuscular mycorrhizal fungal (AMF) colonization of wheat roots and implications for plant phosphorus (P) uptake, 6 years of crop yields, fertilizer and herbicide use, and net operating income across dryland, no-till cropping systems in the semi-arid High Plains, USA. Three levels of cropping system intensity were represented ranging from wheat-fallow (unvegetated fallow every other year) to continuous cropping (no fallow years). After accounting for variability due to environment and site characteristics, total and potentially mineralizable N were 12% and 30% greater in continuous rotations relative to wheat-fallow, respectively. Mid-intensity (fallow every 2 or 3 years) and continuous rotations had roughly 2 and 3 times more AMF colonization than wheat-fallow, respectively, and AMF colonization was positively correlated with wheat plant P concentration. Farmers practicing continuous cropping applied 22 and 34 kg ha−1 less N fertilizer per crop compared to wheat-fallow and mid-intensity, respectively, despite similar and 60% greater annualized crop production than mid-intensity and wheat-fallow rotations, respectively. Additionally, farmers who practiced continuous cropping used less than half the total herbicide used by wheat-fallow farmers. Net operating incomes of continuous and mid-intensity rotations were an estimated 47 USD ha−1 yr−1 (80%) and 42 USD ha−1 yr−1 (70%) more than wheat-fallow, respectively. These results suggest that cropping system intensification, and especially continuous cropping, represents an opportunity to achieve more grain production while managing weeds and nutrients with fewer agri-chemical inputs, leading to greater profitability and improved environmental outcomes in no-till agroecosystems.
•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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