About

Joshua Gamble is an Adjunct Assistant Professor in the Department of Soil, Water, and Climate at the University of Minnesota Twin Cities. His educational background includes a Bachelor of Arts from the University of Minnesota Duluth, obtained in 2005, and both a Master’s and a PhD from the University of Minnesota Twin Cities, completed in 2012 and 2016 respectively. His areas of interest encompass agroecology, cropping systems, and agronomy. His research contributions focus on sustainable agricultural practices, including the utilization of dairy manure as an agricultural amendment to benefit soil health, and the biophysical interactions in perennial biomass alley cropping systems. Gamble has also investigated the effects of harvest timing on biomass yield and nutrient content in bioenergy crops, as well as the establishment and early productivity of perennial biomass alley cropping systems. His work emphasizes sustainable land management practices, nutrient management, and the ecological interactions within cropping systems, contributing valuable insights to the fields of agroecology and sustainable agriculture.

Research topics

• Environmental science
• Agronomy
• Biology
• Political Science
• Chemistry
• Physics
• Ecology
• Geology
• Environmental engineering
• Metallurgy
• Geography
• Materials science
• Soil science

Selected publications

• Productivity dynamics of agroecosystems under prevailing and alternative management practices across the United States

  Agricultural and Forest Meteorology · 2026-05-17

  articleOpen access

  • Alternative practices enhance productivity and extend carbon uptake. • Carbon uptake period drives productivity consistently across sites. • Precipitation extends carbon uptake mainly under alternative management. Industrialized agriculture has dramatically increased crop yields over the last century, but this has led to soil erosion and reductions in soil organic matter, raising concerns about the long-term sustainability of agroecosystems under weather variability. The first step towards restoring soil organic matter in agroecosystems is achieving sustained net ecosystem carbon uptake, as reflected in positive net ecosystem productivity (NEP). Thus, we evaluated how prevailing and potentially more sustainable, alternative management practices influenced NEP across a range of agroecosystems in the United States. Specifically, we analyzed eddy covariance data from eleven Long-Term Agroecosystem Research cropland locations to compare gross primary productivity (GPP) and NEP dynamics in the two systems. At seven locations spanning diverse environments, mean annual NEP was higher under the alternative management. Five of these sites with cover crops exhibited longer carbon uptake period (CUP) than their prevailing management counterparts. Importantly, a longer CUP was associated with increases in both annual sum of GPP and NEP and their peak values. Increased precipitation at the alternative sites enhanced CUP length, which contributed to higher overall productivity while prevailing systems showed no sensitivity to precipitation. The relationship between annual NEP and CUP showed steeper slopes at drier sites, indicating potential benefits for NEP gains associated with extended CUP. Our findings demonstrate that sustainable management practices can strengthen carbon uptake capacity, highlighting their importance for maintaining agroecosystem productivity.

  PublisherDOI

• Temporal variability of soil health indicators under annual and perennial continuous living cover: Effects of annual weather and management

  Soil Science Society of America Journal · 2026-03-01

  articleOpen access

  Abstract Soil health indicators (SHIs) are used to detect changes in soil conditions in response to management. However, management effects must be disentangled from other factors influencing SHI variability. Specifically, how annual weather affects SHI remains poorly understood. To address this gap, we analyzed soil annually for 5 years at 64 sampling points in two silt loam fields, in Minnesota. One field had annual crops (maize, Zea mays L.; winter camelina, Camelina sativa L. Crantz.; soybean, Glycine max L. Merr.; wheat, Triticum aestivum L.; and winter barley, Hordeum vulgare L.) while the other had perennial crops (alfalfa, Medicago sativa L. and Kernza, Thinopyrum intermedium (Host) Barkworth & D.R. Dewey). We measured mineralizable carbon (MinC), extracellular enzymes, microbial biomass, soil organic carbon, mineral‐associated organic matter, and particulate organic matter (POM) at 0‐ to 15‐cm and 15‐ to 30‐cm depth. We present two key findings. First, growing season weather was correlated with annual changes in several indicators. The most striking relationships were between growing season mean air temperature (MAT) and 1‐, 4‐, and 12‐day MinC ( p < 0.001). MAT was not correlated with 21‐day MinC. MAT–MinC correlations were depth‐dependent: positive at 0–15 cm ( r = 0.65–0.68) and negative at 15–30 cm ( r = −0.39 to −0.60). Second, soil health improved in the perennial field. Most illustrative of this finding were gains in arbuscular mycorrhizal fungi ( p = 0.013), subsurface MinC, and POM ( p < 0.001). In summary, we recommend that soil health assessment account for annual weather, and suggest that perennial crops lead to improved soil health.

  PublisherDOI

• Perspective: Impacts of dairy forage management on soil carbon change and net zero accounting

  Journal of Dairy Science · 2025-03-04

  reviewOpen access1st authorCorresponding

  ) reported in the literature. However, biogenic emissions from soil C loss are not typically represented within C footprints or life cycle inventories. Using an example dairy farm, we demonstrate that including emissions associated with soil C losses under dairy forage production can increase the C footprint of milk nearly 2-fold. We suggest that this approach represents a more accurate estimate of the emissions impact of milk production, and that gains in the GHG efficiency of milk have come, in part, at the expense of soil C, where forage rotations are predominated by silage corn. The C balance of forage production systems can likely be improved with advanced manure management technologies and application strategies that return more manurial C to the soil while minimizing N and P loading. However, we argue that more extensive changes to forage cropping systems will also be required. Expanding the role of perennials and winter annual crops in forage rotations; breeding forages with greater yield, persistence, and deeper more extensive root systems; and additional creative solutions to retain more plant-derived C in soils are necessary to balance soil C budgets and achieve net zero emissions targets.

  PublisherOA PDFDOI

• Stock change accounting overestimates the potential climate benefit of soil carbon storage

  Soil Science Society of America Journal · 2024-03-04 · 4 citations

  article

  Abstract Agriculture is being called upon to increase carbon (C) storage in soils to reduce greenhouse gas (GHG) accumulation in the atmosphere. Cropping systems research can be used to support GHG mitigation efforts, but we must quantify land management impacts using appropriate assumptions and unambiguous methods. Soil C sequestration is considered temporary because it can be re‐emitted as carbon dioxide (CO 2 ) if the effecting practice is not maintained and/or the soil–plant system is disturbed, for example, as the result of changing climate. Because of this, the climate benefit of soil C sequestration depends on the time that C is held out of the atmosphere. When assessing the net GHG impact of management practices, soil C storage is often aggregated with non‐CO 2 (N 2 O and CH 4 ) emissions after converting all components to CO 2 equivalents (CO 2 e) and assuming a given time horizon (TH), in what is known as stock change accounting . However, such analyses do not consider potential re‐emission of soil C or apply consistent assumptions about time horizons. Here, we demonstrate that tonne‐year accounting provides a more conservative estimate of the emissions offsetting potential of soil C storage compared to stock change accounting. Tonne‐year accounting can be used to reconcile differences in the context and timeframes of soil C sequestration and non‐CO 2 GHG emissions. The approach can be applied post hoc to commonly observed cropping systems data to estimate GHG emissions offsets associated with agricultural land management over given THs and with more clearly defined assumptions.

  PublisherDOI

• Uncertainty in phosphorus fluxes and budgets across the US long‐term agroecosystem research network

  Journal of Environmental Quality · 2023-05-05 · 15 citations

  article

  Abstract Phosphorus (P) budgets can be useful tools for understanding nutrient cycling and quantifying the effectiveness of nutrient management planning and policies; however, uncertainties in agricultural nutrient budgets are not often quantitatively assessed. The objective of this study was to evaluate uncertainty in P fluxes (fertilizer/manure application, atmospheric deposition, irrigation, crop removal, surface runoff, and leachate) and the propagation of these uncertainties to annual P budgets. Data from 56 cropping systems in the P‐FLUX database, which spans diverse rotations and landscapes across the United States and Canada, were evaluated. Results showed that across cropping systems, average annual P budget was 22.4 kg P ha −1 (range = −32.7 to 340.6 kg P ha −1 ), with an average uncertainty of 13.1 kg P ha −1 (range = 1.0–87.1 kg P ha −1 ). Fertilizer/manure application and crop removal were the largest P fluxes across cropping systems and, as a result, accounted for the largest fraction of uncertainty in annual budgets (61% and 37%, respectively). Remaining fluxes individually accounted for <2% of the budget uncertainty. Uncertainties were large enough that determining whether P was increasing, decreasing, or not changing was inconclusive in 39% of the budgets evaluated. Findings indicate that more careful and/or direct measurements of inputs, outputs, and stocks are needed. Recommendations for minimizing uncertainty in P budgets based on the results of the study were developed. Quantifying, communicating, and constraining uncertainty in budgets among production systems and multiple geographies is critical for engaging stakeholders, developing local and national strategies for P reduction, and informing policy.

  PublisherDOI

• Abiotic and Biotic Drivers of Soil Fungal Communities in Response to Dairy Manure Amendment

  Applied and Environmental Microbiology · 2023-05-22 · 6 citations

  articleOpen access

  Manure amendments in agricultural systems can impact soil microbial communities via supplying growth substrates for indigenous microbes or by introducing manure-borne taxa. This study explores the consistency of these impacts on soil fungal communities and the relative importance of abiotic and biotic drivers across distinct soils. Different fungal taxa responded to manure among distinct soils, and shifts in soil fungal communities were driven largely by abiotic factors, rather than introduced microbes. This work demonstrates that manure may have inconsistent impacts on indigenous soil fungi, and that abiotic properties of soils render them largely resistant to invasion by manure-borne fungi.

  PublisherOA PDFDOI

• Influence of potassium fertilization on alfalfa leaf and stem yield, forage quality, nutrient removal, and plant health

  Agrosystems Geosciences & Environment · 2023-02-01 · 15 citations

  articleOpen access

  Abstract Potassium (K) is an essential nutrient for plant growth. In K‐deficient soils, fertilization has been shown to increase herbage yield of alfalfa. The purpose of this study was to determine the effects of K fertilization on alfalfa leaf and stem yield, forage quality, nutrient removal, and plant health of a nonlodging experimental germplasm. Five alfalfa rotations had K fertilizer applied at three rates (0, 186, and 372 kg K ha −1 ) to soils already containing sufficient soil test K (223 mg kg −1 ). No overall yield differences were found related to K application rates, though K removal in total herbage increased by 30–58% with K fertilization, depending on alfalfa stand age. Leaf:stem ratios were not impacted by K fertilization. The concentrations of B, Ca, and Na decreased with K fertilization, while K concentrations increased, which may have resulted in B deficiencies. Leaf in vitro digestibility decreased significantly with the application of K. There was no benefit to crown rot disease resistance with increased K fertilization. This study supports that the addition of K to already sufficient soils does not lead to any additional economic benefits and may reduce productivity due to the reduction of B uptake and in vitro digestibility.

  PublisherOA PDFDOI

• P‐FLUX: A phosphorus budget dataset spanning diverse agricultural production systems in the United States and Canada

  Journal of Environmental Quality · 2022-04-04 · 10 citations

  articleOpen access

  Quantifying spatial and temporal fluxes of phosphorus (P) within and among agricultural production systems is critical for sustaining agricultural production while minimizing environmental impacts. To better understand P fluxes in agricultural landscapes, P-FLUX, a detailed and harmonized dataset of P inputs, outputs, and budgets, as well as estimated uncertainties for each P flux and budget, was developed. Data were collected from 24 research sites and 61 production systems through the Long-term Agroecosystem Research (LTAR) network and partner organizations spanning 22 U.S. states and 2 Canadian provinces. The objectives of this paper are to (a) present and provide a description of the P-FLUX dataset, (b) provide summary analyses of the agricultural production systems included in the dataset and the variability in P inputs and outputs across systems, and (c) provide details for accessing the dataset, dataset limitations, and an example of future use. P-FLUX includes information on select site characteristics (area, soil series), crop rotation, P inputs (P application rate, source, timing, placement, P in irrigation water, atmospheric deposition), P outputs (crop removal, hydrologic losses), P budgets (agronomic budget, overall budget), uncertainties associated with each flux and budget, and data sources. Phosphorus fluxes and budgets vary across agricultural production systems and are useful resources to improve P use efficiency and develop management strategies to mitigate environmental impacts of agricultural systems. P-FLUX is available for download through the USDA Ag Data Commons (https://doi.org/10.15482/USDA.ADC/1523365).

  PublisherOA PDFDOI

• Ecohydrology of irrigated silage maize and alfalfa production systems in the upper midwest US

  Agricultural Water Management · 2022-03-29 · 10 citations

  article1st authorCorresponding
  PublisherDOI

• Abiotic and biotic filters determine the response of soil bacterial communities to manure amendment

  Applied Soil Ecology · 2022-07-30 · 17 citations

  article
  PublisherDOI

Frequent coauthors

• John M. Baker

  United States Department of Agriculture

  19 shared

• Gary W. Feyereisen

  13 shared

• Dean Current

  11 shared

• Rodney T. Venterea

  11 shared

• Jonathan Alexander

  University of Minnesota

  10 shared

• Chris Wente

  United States Department of Agriculture

  10 shared

• Kurt A. Spokas

  Agricultural Research Service

  9 shared

• Craig C. Sheaffer

  University of Minnesota

  7 shared

Labs

• Plant Science ResearchPI