About

Gregg Johnson is an Associate Professor in the Department of Agronomy and Plant Genetics at the University of Minnesota Twin Cities. He specializes in annual and perennial cropping systems with a focus on maximizing productivity, efficiency, and ecosystem services. His work emphasizes applied production strategies that are designed around multi-value outcomes, including integrated weed management and cropping systems at the Southern Research and Outreach Center in Waseca. Johnson's research involves long-term cropping systems, cover crops, and the study of annual and perennial crops, contributing to sustainable agricultural practices and the development of cropping strategies that enhance ecosystem health and productivity.

Research topics

• Agronomy
• Biology
• Environmental science
• Soil science
• Environmental health
• Geotechnical engineering
• Botany
• Ecology
• Agroforestry
• Geology

Selected publications

• Water use of interseeded cover crops in rainfed maize–soybean rotations in the Northern U.S.

  Frontiers in Agronomy · 2026-03-23

  articleOpen access

  Introduction Cover crop adoption in U.S. crop rotations is steadily increasing. In the upper Midwest, where the conventional maize ( Zea mays L.)–soybean [ Glycine max (L.) Merr.] rotation is mostly rainfed, there is legitimate concern that cover crops may affect available soil water and the establishment of the subsequent main crop. Methods A study was conducted to evaluate 1) the effect of interseeded cover crops on soil moisture at seeding and termination, and subsequent maize and soybean yields, and 2) seasonal evapotranspiration ( ET ) or water use of the main crops and cover crops. Field trials were conducted from 2016 to 2019 at three locations in the upper Midwest using four treatments: monoculture cereal rye ( Secale cereale L.), two-species rye + crimson clover ( Trifolium incarnatum L.), three-species rye + clover + forage radish ( Raphanus sativus L.), and a fallow (no-cover planted) as the control. Results The ET of cover crops varied between 52 and 110 mm, 70% of which was attributed to its evaporation component. Meanwhile the ET for maize and soybean ranged from 364–516 mm and 378–503 mm, respectively, 20% of which was attributed to evaporation. Regardless of the interseeding strategy, the biomass of cover crops was low in two out of the three experimental years due to weather conditions, resulting in little to no effect on soil water content or crop yield. Discussion Our findings suggest that late interseeded cover crops for conditions in the northern U.S. may have limited impact on soil available water or the productivity of the subsequent crop when cover crop growth is low.

  PublisherOA PDFDOI

• Agronomic and economic trade‐offs of integrating camelina into the corn–soybean rotation

  Agronomy Journal · 2025-03-01 · 4 citations

  article

  Abstract Corn ( Zea mays L.) and soybean [ Glycine max (L.) Merr.] account for much of the arable land in the Upper US Midwest during the summer. Land is left fallow in late autumn after harvest through early spring leaving valuable growing degree days unused. Temporal intensification is a concept that considers planting crops such as winter camelina ( Camelina sativa L.) during these fallow periods. Winter camelina is a freeze‐hardy winter annual oilseed that can provide an economic benefit to farmers the following spring. However, there are significant agronomic and economic trade‐offs associated with integrating camelina into the corn–soybean rotation. The objectives were to assess the yield potential and seed quality of a corn–camelina–soybean rotation using (1) a range of corn hybrid maturities, (2) corn stover presence or absence, and (3) calculate the economic trade‐offs compared with a typical corn–soybean rotation. This study was conducted over the 2019 and 2020 growing seasons at two locations in Minnesota. Corn and soybean seed yield was maximized in treatments where camelina performed poorly and vice versa. Late corn harvest and stover presence had a negative effect on camelina establishment and yield but were favorable to soybean production. Based on both the agronomic and economic analyses for the aggregated cropping system, treatments that began with 90‐ and 95‐day relatively mature corn hybrids performed equally well, regardless of stover presence. This indicates there are multiple options to move forward with a corn–camelina–soybean cropping rotation.

  PublisherDOI

• Soil health management system impacts on dynamic soil hydraulic functions before and after rainfall

  Agriculture Ecosystems & Environment · 2025-07-23 · 3 citations

  articleOpen access

  Soil health management systems use agricultural practices incorporating living roots, persistent surface cover, diverse crop rotations, and minimal soil disturbance such as tillage. These systems are widely thought to improve soil hydraulic functions. However, intense rainfall can cause physical slaking of aggregates, loss of surface pores, and reduced hydraulic functions. Soil health management systems correlate with stable aggregates and large soil pores, but it is not clear how these properties change with rainfall in fine-textured soil profiles. Therefore, quantifying hydraulic function in soil health systems is important as climate change intensifies growing season rainfall. We investigated the effects of soil health systems on volumetric soil water content (VWC), soil aggregates, soil pore size distributions, and a suite of soil health indicators in response to rainfall. During 2021 and 2022, we collected data from five tillage and cover crop treatments in replicated plots at the Southern Research and Outreach Center (SROC) in Waseca, MN (tillage treatments included rip/chisel plow, strip till, no till, and cover crop treatments included no cover crops and cereal rye), and three paired systems (conventional and soil health management, which differ in tillage and cover crop use) at long-term (≥ 5 years), on-farm sites with fine-textured soils. We monitored volumetric soil water content and soil aggregates within 24 h before and after select rainfall events. Across all locations, few differences in water capture, evidenced by an increase in VWC after rain, were evident. Aggregate responses to rainfall were observed between the paired on-farm treatments. Generally, conventional sites had 5–20 % more < 0.053 mm and 0.053–0.25 mm aggregates following rainfall than soil health sites, but this effect was inconsistent across locations. Soil health systems on-farm generally retained 10–30 % more > 2 mm water-stable aggregates than conventional systems in response to rainfall. Based on soil water retention curves, on-farm soil health sites had 2.5–12.5 % more macroporosity (pore diameter > 75 µm) than conventional systems, despite having similar water capture. At the on-farm sites, greater microporosity and pore connectivity are attributed to an observed 0.25–2 cm/hr greater unsaturated hydraulic conductivity relative to soil health sites, validating the greater macroporosity observed in the soil health sites. Despite long-term treatment history at SROC plots, there were no differences in unsaturated hydraulic conductivity. At one on-farm site, the soil health system had higher soil health indicators than the conventional system, where the soil health system included 30 years of no-till and 12 years of cover crops compared to moldboard plowing in the conventional system. This research indicates the importance of holistically incorporating soil health practices into field systems for achieving enhanced soil functions. Figure (above): Sampling timeline. Data was collected from plots 24 h before, 24–48 h after, and 3–5 days after a rain event. • On-farm soil health systems had more aggregates after rain than conventional systems. • Soil health systems had positive effects on pore networks and hydraulic properties. • Combining soil health practices increased C pools relative to only select practices. • Small plots with single practices did not reflect field scale with multiple practices.

  PublisherDOI

• Rotational complexity increases cropping system output under poorer growing conditions

  One Earth · 2024-08-06 · 27 citations

  articleOpen access

  Growing multiple crops in rotation can increase the sustainability of agricultural systems and reduce risks from increasingly adverse weather. However, widespread adoption of diverse rotations is limited by economic uncertainty, lack of incentives, and limited information about long-term outcomes. Here, we combined 36,000 yield observations from 20 North American long-term cropping experiments (434 site-years) to assess how greater crop diversity impacts productivity of complete rotations and their component crops under varying growing conditions. Maize and soybean output increased as the number of species and rotation length increased, while results for complete rotations varied by site depending on which crops were present. Diverse rotations reduced rotation-level output at eight sites due to the addition of lower-output crops such as small grains, illustrating trade-offs. Diverse rotations positively impacted rotation-level output under poor growing conditions, which illustrates how diverse cropping systems can reduce the risk of crop loss in a changing climate.

  PublisherOA PDFDOI

• Stover removal has minimal impact on pennycress seeded into standing corn

  Crop Science · 2024-04-08

  articleOpen access

  Abstract In the Upper Midwest, corn ( Zea mays L.) and soybean [ Glycine max (L.) Merr.] are the most prominent agricultural crops, occupying land for only half the year. Their fallow periods are associated with nutrient leaching and soil erosion, but they also represent an opportunity to establish winter‐hardy crops, like pennycress ( Thlaspi arvense L.), that can reduce negative environmental impacts while contributing to farm profitability. A lack of agronomic best management practices remains a barrier to pennycress adoption. The objectives of this study were to evaluate the impact of stover presence on pennycress stand establishment and seed yield after seeding pennycress into R4 corn. This study was conducted over the 2014–2015 and 2015–2016 growing seasons with MN106 pennycress at three locations in Minnesota. At maturity, corn plants were removed from plots in 25% increments between 0% and 100% to simulate stover removal scenarios. Pennycress seedlings were unable to compete with corn for available light resources and did not have enough time following corn harvest to establish a dense stand in the autumn with only 5% and 10% green cover in 2014 and 2015, respectively. Despite poor early season emergence, the average seed yield, 1223 kg ha −1 , was high relative to other studies using MN106, indicating that challenges of growing pennycress under adverse conditions may not be a barrier to competitive seed yields. Experimentation on the corn–pennycress system should continue in the future to further explore and establish best management practices for this double crop.

  PublisherOA PDFDOI

• Effects of landscape position on perennial biomass and food crop performance in buffer areas

  Ecosphere · 2024-07-01 · 2 citations

  articleOpen accessCorresponding

  Abstract Due to the environmental consequences of annual‐dominated cropping systems, there is an increasing need to identify agronomic strategies that incorporate perennial crops. One strategy for increasing perennial cover is through the targeted use of annually harvested perennial food and bioproduct crops in buffer strips, which has the potential to create new revenue streams for farmers and substantially mitigate agricultural nutrient pollution from conventional cropping systems. As buffers are typically installed on marginal land, it is critical to understand how landscape position influences the success of perennial crops. The objectives of this study were to determine the relatively early influence of landscape position on the productivity of a variety of perennial crops and their subsequent soil nutrients and soil water storing capabilities. In this experiment, nine perennial (alfalfa, alsike clover, indiangrass, switchgrass, big bluestem, prairie cordgrass, intermediate wheatgrass, high‐diversity polyculture, low‐diversity polyculture) and two annual (corn, soybean) crops were planted across two landscape positions (hillslope and deposition). Plant biomass, plant tissue nitrogen, soil moisture, and soil NO 3 ‐N and NH 4 ‐N were measured and compared at two different locations in Minnesota. Overall, the polyculture mixes, and to some extent intermediate wheatgrass, performed the best with respect to biomass production while also providing ecosystem services across most soil by landscape position combinations tested in this study. However, there were some important findings specific to each soil and landscape position combination, mainly oriented toward biomass production. We also observed temporal patterns in soil moisture and depth‐related patterns in soil N reductions. This study presents an opportunity to optimize the use of perennial crops on marginal agricultural lands for improved environmental and economic benefit.

  PublisherOA PDFDOI

• Soil Health Management System Impacts on Dynamic Soil Hydraulic Functions Before and after Rainfall

  SSRN Electronic Journal · 2024-01-01

  preprintOpen access
  PublisherDOI

• Yield and Forage Characteristics of Winter Rye Cultivars for Use within the Upper Midwest

  Preprints.org · 2024-01-23 · 2 citations

  preprintOpen access

  Summer annual species are the most widely grown crops in the Upper Midwest, but reliance on a summer annual system has led to excessive soil and nutrient loss when crops are not present. Integrating winter rye (Secale cereale L.), known for its hardiness and environmental benefits, into the rotation can address these issues. However, there&amp;#039;s limited understanding of the phenotypic diversity in winter rye during key growth stages that overlap with the typical planting dates for corn (Zea mays L.), soybean [Glycine max (L.) Merr], and late-planted crops like dry bean (Phaseolus vulgaris L.). Thus, the objectives of this study were to evaluate changes in biomass accumulation and quality of winter rye and triticale (x Triticosecale Wittmack) cultivars at three growth stages. Twenty cultivars were assessed over the 2014-2015 and 2015-2016 growing seasons across three environments in Minnesota. Winter rye and triticale were harvested for biomass at the tillering, booting, and soft dough growth stages and rye biomass yield and quality [i.e., crude protein, neutral detergent fiber (NDF), and 48-hour digestibility (NDFD)] were determined following harvest. Overall, there was little variation in each parameter among the cultivars within a location and growth stage. NDFD had some variation at the soft dough stage where digestibility ranged from 273 to 324 g kg-1 at the Crookston site and 332 to 406 g kg-1 at the St. Paul site. The lack of difference between cultivars indicates a wide range of choice when selecting a winter rye cultivar.

  PublisherOA PDFDOI

• Maximizing soil organic carbon stocks under cover cropping: insights from long-term agricultural experiments in North America

  Agriculture Ecosystems & Environment · 2023-06-02 · 54 citations

  articleOpen access

  Cover crops are widely advocated for increasing soil organic carbon (SOC) levels, thereby benefiting soil health improvement and climate change mitigation. Few regional-scale studies have robustly explored SOC stocks under cover cropping, due to limited long-term experiments. We used the unique experimental data from the North American Project to Evaluate Soil Health Measurements conducted in 2019 to address this issue. This study included 19 agricultural research sites with 36 pairs of cover cropping established between 1896 and 2014. Explanatory variables related to site-specific environmental conditions and management practices were collected to identify and prioritize contributing factors that affect SOC stocks with cover crops, by coupling the Boruta algorithm and structural equation modeling. Overall, cover crops significantly (P < 0.05) improved several indicators of soil health, including greater SOC (concentration: +8%; stock: +7%), total nitrogen (+8%), water-stable aggregates (+15%), and potential carbon mineralization (+34%), on average, compared to no cover crop control. Likewise, on average, cover crops sequestered SOC 3.55 Mg C ha-1 (0–15 cm depth), with a sequestration rate of 0.24 Mg C ha-1 yr-1. In addition, we found climate (Hargreaves climatic moisture deficit) was important in explaining the variation of SOC stocks with cover crops, followed by soil properties (e.g., soil clay content). In terms of management practices, cover crop type had a significant positive (0.36) effect on SOC stocks, with non-legumes showing a greater impact, compared to legumes and mixtures. Crop rotational diversity also had a positive (0.28) effect on SOC accumulation. Our findings suggested that integrating non-legume cover crops into diverse crop rotation is likely to be a promising strategy to maximize SOC stocks with cover crops across North America.

  PublisherDOI

• Tillage and cover crop mixtures interseeded in maize–soybean in the upper Midwest

  Agronomy Journal · 2023-02-15 · 6 citations

  articleOpen access

  Abstract Ecosystem benefits of winter‐killed annual cover crops are less studied than winter hardy annuals. The objectives of this study were to determine (1) the effects of tillage practices and cover crop mixtures on biomass and soil cover of cover crops seeded into nearly mature maize ( Zea mays L.) and soybean [ Glycine max (L.) Merr.] and (2) if cover crop biomass can be estimated from soil surface coverage measurements. The study was conducted within two long‐term tillage trials from 2016 to 2018. Tillage included conventional—(CT), strip—(ST), and no‐till—(NT). Cover crops included annual ryegrass (AR; Lolium multiflorum L.); AR and crimson clover (CC; Trifolium incarnatum L.) mixture (ARCC); AR, CC, and forage radish (FR; Raphanus sativus L.) mixture (ARCCFR); and no‐cover (NC). Seeding rates for AR, ARCC, and ARCCFR were 28, 36, and 40.5 kg ha −1 , respectively. The ARCCFR mix produced the most biomass (256 kg ha −1 ), followed by AR (174 kg ha −1 ) and ARCC (165 kg ha −1 ). Cover crop biomass was 260 and 136 kg ha −1 in maize and soybean; and 218, 201, and 177 kg ha −1 in CT, ST, and NT, respectively. Cover crop soil coverage between rows was 25% in maize and 14% in soybean. Cover crop biomass was associated with soil surface coverage ( R 2 = 0.841). Given that cover crop biomass drives ecosystem services associated with cover crops, limited biomass and ground coverage of winter killed cover crops seeded into nearly mature maize and soybean may not add ecosystem services in the upper Midwest.

  PublisherOA PDFDOI

Frequent coauthors

• Xiying Hao

  Chinese Academy of Forestry

  155 shared

• Bijesh Maharjan

  University of Nebraska–Lincoln

  144 shared

• Mitchel P. McClaran

  University of Arizona

  142 shared

• Benjamin H. Ellert

  Agriculture and Agri-Food Canada

  142 shared

• Francis J. Larney

  Agriculture and Agri-Food Canada

  141 shared

• N. Millar

  Michigan State University

  139 shared

• Laura L. Van Eerd

  University of Guelph

  133 shared

• Marshall D. McDaniel

  Iowa State University

  132 shared

Education

• Ph.D., Agronomy

  University of Nebraska