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The increasing attention around cover crops in US agriculture to address many sustainability challenges necessitates targeted educational approaches to support future agriculture professionals. This article describes the process by which a team of educators, with different areas of expertise and from different regions, collaborated to design and implement a multi-university, semester-long, hybrid course titled “Cover Crops in Agroecosystems.” Course development occurred over 2 years during which the format, learning outcomes, as well as synchronized topics and activities were discussed, negotiated, and finalized. The course consisted of weekly pre-recorded lecture videos, in-person labs, and remote synchronous multi-site meetings. An end-of-semester survey administered at six universities in fall 2022 found that students valued the multi-regional dimension of the course, including learning from different instructors and interacting with students from other institutions. The survey also found broad student agreement that learning objectives were achieved, particularly around topics of cover crop agronomy and management. The team’s experience with course development highlights how designing and implementing a multi-university course where students report a quality learning experience is achievable. However, course execution ultimately required considerable effort, more than 2 years of planning, as well as ongoing team discussions and modifications that did not significantly reduce the time needed to prepare a more traditional individual instructor-led course. Course execution also required considerable flexibility in decision-making that aligned with different university constraints, instructor styles, and student needs. This effort and flexibility resulted in a quality student experience on a topic area of importance for advancing sustainable agriculture. [ABSTRACT FROM AUTHOR]

Fertilization may impact ecosystem processes that sustain agriculture, such as nutrient cycling, by altering the composition of soil microbial communities that regulate such processes. These processes are crucial to low‐input, smallholder tropical agriculture, which supports 900 million of the world's poorest people. Yet little is known about how efforts to increase crop yield on such farms will affect the capacity of soil microbial communities to carry out ecosystem processes. We studied the diversity and functional capacity of microbial communities on smallholder farms in western Kenya. We measured functional capacity as the abundance of functional genes involved in several components of nutrient cycling as well as catabolism of multiple carbon substrates; taxonomic diversity was measured using metagenomic sequencing. Diversity and functional capacity were measured on short‐term, experimental mineral fertilizer addition plots and on actively managed farms that have maintained for at least seven years a management strategy of low mineral fertilization, high mineral fertilization, or high fertilization combined with legume rotations. Soil bacterial diversity decreased with mineral fertilizer addition, with a community shift towards taxa that thrive in high‐resource conditions. This taxonomic response did not correspond with decreased microbial functional capacity. Instead, functional capacity was increased, along with yields, when fertilizers were combined with legume rotations that add organic matter to soil. Policy implications. Mineral fertilizer use is associated with lower soil microbial diversity on smallholder farms, but not associated with changes in microbial functional capacity. Functional capacity is highest, along with yields, when mineral fertilizers are paired with legume rotations. Our findings suggest that this type of agroforestry can be an important strategy for maintaining the long‐term functional capacity of soil microbes as well as increasing crop yields on smallholder farms. These observations support proposals to achieve long‐term food production targets in sub‐Saharan Africa by combining mineral fertilizers with organic inputs.

Cover crops are well recognized as a tool to reduce NO3- leaching from agroecosystems. However, their effectiveness varies from site to site and year to year depending on soil, cash and cover crop management, and climate. We conducted a meta-analysis using 238 observations from 28 studies (i) to assess the overall effect of cover crops on NO3- leaching and subsequent crop yields, and (ii) to examine how soil, cash and cover crop management, and climate impact the effect of non-leguminous cover crops on NO3- leaching. There is a clear indication that nonleguminous cover crops can substantially reduce NO3- leaching into freshwater systems, on average by 56%. Nonlegume-legume cover crop mixtures reduced NO3- leaching as effectively as nonlegumes, but significantly more than legumes. The lack of variance information in most published literature prevents greater insight into the degree to which cover crops can improve water quality. Among the factors investigated, we identified cover crop planting dates, shoot biomass, and precipitation relative to long-term mean precipitation as potential drivers for the observed variability in nonleguminous cover crop effectiveness in reducing NO3- leaching. We found evidence indicating greater reduction in NO3- leaching with nonleguminous cover crops on coarse-textured soils and during years of low precipitation (<90% of the long-term normal). Earlier fall planting and greater nonleguminous shoot biomass further reduced NO3- leaching. Overall, this meta-analysis confirms many prior studies showing that nonleguminous cover crops are an effective way to reduce NO3- leaching and should be integrated into cropping systems to improve water quality. [ABSTRACT FROM AUTHOR]

Tropical smallholder agriculture is undergoing rapid transformation in nutrient cycling pathways as international development efforts strongly promote greater use of mineral fertilizers to increase crop yields. These changes in nutrient availability may alter the composition of microbial communities with consequences for rates of biogeochemical processes that control nutrient losses to the environment. Ecological theory suggests that altered microbial diversity will strongly influence processes performed by relatively few microbial taxa, such as denitrification and hence nitrogen losses as nitrous oxide, a powerful greenhouse gas. Whether this theory helps predict nutrient losses from agriculture depends on the relative effects of microbial community change and increased nutrient availability on ecosystem processes.We find that mineral and organic nutrient addition to smallholder farms in Kenya alters the taxonomic and functional diversity of soil microbes. However, we find that the direct effects of farm management on both denitrification and carbon mineralization are greater than indirect effects through changes in the taxonomic and functional diversity of microbial communities. Changes in functional diversity are strongly coupled to changes in specific functional genes involved in denitrification, suggesting that it is the expression, rather than abundance, of key functional genes that can serve as an indicator of ecosystem process rates. Our results thus suggest that widely used broad summary statistics of microbial diversity based on DNA may be inappropriate for linking microbial communities to ecosystem processes in certain applied settings. Our results also raise doubts about the relative control of microbial composition compared to direct effects of management on nutrient losses in applied settings such as tropical agriculture. [ABSTRACT FROM AUTHOR]