In addition to soil health and conservation benefits, cover crops (CCs) may offer weed control in the midwestern United States, but individual studies report varying effects. We conducted a meta-analysis of studies measuring weed biomass (WBIO) or density (WDEN) in paired CC and no-cover treatments in corn (Zea mays L.)-soybean [Glycine max (L.) Merr] rotations in the U.S. Midwest. Fifteen studies provided 123 paired comparisons of WBIO and 119 of WDEN. Only grass CCs significantly reduced WBIO, while no CC reduced WDEN. We found no evidence CC management factors (e.g., termination method) directly affected outcomes. Our dataset showed that a 75% reduction in WBIO requires at least 5 Mg ha −1 of CC. Simulations from a process-based model (SALUS) indicated achieving 5 Mg ha −1 requires substantially earlier fall planting and later spring termination in most years, conflicting with typical cash-crop planting and harvesting. We conclude CCs significantly reduce WBIO, but current CC management constraints render these reductions variable and uncertain.

Despite being generally accepted as a promising conservation practice to reduce nitrate pollution and promote soil sustainability, cover crop adoption in Midwestern US agriculture is low. Based on focus groups, surveys and partial budgets, we calculated the annual net returns to cover crop use for farmers in Illinois, Iowa and Minnesota; and elicited farmers’ perceptions about the pros and cons of incorporating cover crops to their row cropping systems. The novelty of our methodology resides in comparing each farmer's practices in the portion of their cropping system with cover crops (typically small), against their practices in the other portion of their cropping system without cover crops. The resulting comparisons, accounting for farmer heterogeneity, are more robust than the typical effects calculated by comparing indicators across cover crop users and unrelated non-adopters. Our results highlight the complicated nature of integrating cover crops into the crop production system and show that cover crops affect whole farm profitability through several channels besides establishment and termination costs. Despite farmers’ positive perceptions about cover crops and the availability of cost-share programs, calculated annual net returns to cover crops use were negative for most participants.

Global poverty and food insecurity continue to remain critical issues, especially in rural areas. Developing and fostering agricultural systems that not only require low to moderate amounts of economic capital and few external inputs but also maintain and enhance the resource base of production are key features of sustainable agricultural development. Sustainable agricultural development, including diversifying smallholder production to include livestock, is a pragmatic approach to address both rural poverty and food insecurity. Livestock play important roles in the lives of humans as converters, recyclers and banks of nutrients. Smallholders raise a diversity of livestock species and often raise multiple species simultaneously. High fecundity, diet flexibility and adaptability to a wide range of housing and management approaches are critical traits of livestock species well suited for producing meat for home consumption and marketing in the context of rural smallholders. Swine (Sus scrofa) and chicken (Gallus domesticus) meet many of these criteria and are well known livestock species. This paper examines the potential for a less common species of livestock, guinea pig (Cavia porcellus) to enhance food security and increase household income of rural smallholders. Although cultural acceptance of guinea pig as a source of nutrition and income is less ubiquitous than that of swine, chicken and other species, the biological, ecological and economic advantages of guinea pig deserve further examination by those working to alleviate global poverty and food insecurity.

Despite the active promotion of cover crops as a key conservation practice, their adoption is very limited. We developed a series of partial budgets based on a statewide survey of Iowa farmers to evaluate the changes in net returns resulting from the incorporation of cover crops into a corn or soybean production system. The average net returns to cover crop use for farmers who did not use cover crops for grazing livestock or forage were consistently negative across different planting and termination methods, tillage practices, and experience levels. Only farmers who used cover crops for grazing livestock or forage and received cost-share payments tended to derive net positive returns from cover crop use. Our results can be used as benchmarks for current or potential cover croppers and for ground-truthing agricultural and conservation policy design.

Maize system impacts of cover crop management decisions: A simulation analysis of rye biomass response to planting populations in Iowa, U.S.A.

Given certain ecologic and agronomic characteristics of conventional corn and soybean monocultures, cropping systems reliant solely on these two commodities inevitably lose soil and nutrients. Leaky cropping systems not only hamper society with negative externalities, but also erode the very natural resources needed to produce food and sustain civilization. The United States Department of Agriculture (USDA), state agriculture department staff, farmer organizations, agribusiness leaders, and conservation and environmental organizations now see cover crops as a solution to reduce the negative externalities of conventional row-crop agriculture. Farmers are asking for increased agronomic and economic research to help them understand the benefits of and implement the use of cover crops. Researchers for the most part are not keeping up with farmers' innovations on cover crops nor on providing the information sought by farmers. This article outlines the questions farmers are asking about cover crops and provides suggestions to agronomists, soil scientists, and researchers on research topics to best answer those questions. Additionally, social scientists must initiate a new round of research to understand the underlying concerns farmers have with cover crops and help to define the information (both content and source) that best informs and influences farmers. This article outlines specific issues and questions social scientists can research to contribute to the advancement of more sustainable farming practices and, in particular, cover crops.

Cool-season cover crops have been shown to reduce soil erosion and nutrient discharge from maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] production systems. However, their effects on long-term weed dynamics are not well-understood. We utilized five long-term research trials in Iowa to quantify germinable weed seedbank densities and compositions after 10+ years of cover cropping treatments. All five trials consisted of zero-tillage maize-soybean rotations managed with and without the inclusion of a yearly winter rye (Secale cereal L.) cover crop. Seedbank sampling was conducted in the early spring before crop planting at all locations, with three of the five trials having grown a soybean crop the preceding year, and two a maize crop. Two of the trials (both previously soybean) showed significant and biologically relevant decreases (4,070 and 927 seeds m−2, respectively) in seedbank densities in cover crop treatments compared to controls. In another two trials, one previously maize and one previously soybean, no difference was detected in seedbank densities. In the fifth trial (previously maize), there was a significant, but biologically unimportant increase of 349 seeds m−2. All five trials' weed communities were dominated by common waterhemp [Amaranthus tuberculatus (Moq.)], and changes in seedbank composition from cover-cropping were driven by changes in this species. Although previous studies have shown that increases in cover crop biomass are strongly correlated with weed suppression, in our study we did not find a relationship between seedbank changes and the mean amount of cover crop biomass produced over a 10-years period (experiment means ranging from 0.5 to 2.0 Mg ha−1 yr−1), the stability of the cover crop biomass production, nor the amount produced going into the previous crop's growing season. We conclude that long-term use of a winter rye cover crop in a maize-soybean system has the potential to meaningfully reduce the size of weed seedbanks compared to winter fallows. However, identifying the mechanisms by which this occurs requires further research into processes such as seed predation and seed decay in cover cropped systems.

No abstract