About

Matt Ruark is a Professor and Extension Soil Scientist at the University of Wisconsin-Madison. He holds a Bachelor of Science degree in Environmental Science from the University of Minnesota, obtained in 1999, a Master of Science in Soil Science from the same university in 2002, and a PhD in Agronomy from Purdue University in 2006. Following his doctoral studies, he completed a postdoctoral appointment at the University of California-Davis from 2006 to 2008. His research focuses on nutrient cycling and agroecosystems, with particular emphasis on sustainable agricultural practices. He is involved in various projects including nutrient cycling, soil carbon, biology, and health, as well as potato and vegetable production in the Central Sands. Dr. Ruark serves as the Director of the Sustainable Dairy Project and is a faculty advisor for the Discovery Farms project. Additionally, he co-directs the Wisconsin Agribusiness Classic and is a faculty member of the Dairy Innovation Hub. His work aims to improve understanding of soil health and nutrient management to promote sustainable and productive agricultural systems.

Research topics

• Biology
• Agronomy
• Environmental science
• Soil science
• Ecology
• Agroforestry
• Computer Science
• Chemistry
• Mathematics
• Economics
• Econometrics

Selected publications

• Soybean response to cover crop and nitrogen fertilizer timing on sandy soil

  DRYAD · 2026-04-08

  datasetOpen accessSenior author

  The potential for nitrogen (N) fertilization to increase soybean yield is known to vary with environmental conditions, but the effects of N timing and rate remain unclear in sandy soils. We conducted a two-year irrigated field study on a Plainfield sandy soil (mixed, mesic Typic Udipsamments) in central Wisconsin to evaluate soybean growth and yield under varying N fertilizer treatments. Treatments included an unfertilized control; a starter application (34 kg N ha⁻¹); single applications of 101 kg N ha⁻¹ at 10, 30, 60, or 80 days after emergence (DAE); and split applications totaling 202 or 404 kg N ha⁻¹ applied at 30, 60, and 80 DAE. All fertilizer treatments were nested within a rye cover crop system, planted in the fall and chemically terminated in May prior to soybean planting. Soybean dry matter and N content were measured in June, July, and August, and yield was recorded at harvest. Fertilizer effects on yield varied by year. In 2019, the split404 treatment increased yield by 8% relative to the control, while in 2020, no fertilizer treatments significantly affected yield. Starter and 10DAE treatments increased August dry matter and N uptake, but only 10DAE avoided early-season reductions seen with starter. Cover cropping had no significant effect on soybean yield, dry matter, or N content. Split404 improved yield in 2019, but the yield gain was insufficient to justify the added fertilizer cost. Overall, we find no evidence that N fertilization improves yield in irrigated soybean grown on sandy soils in Wisconsin.

  PublisherDOI

• Both Inherent Soil Properties and Management Practices Shape Soil Microbial Communities Under Prolonged Organic Management

  Applied Soil Ecology · 2025-01-01

  preprintOpen access

  The soil microbiome is recognized as a key component of soil health; however, microbial community responses to agricultural management can be inconsistent and context dependent. Here, we investigated the connections between soil microbial communities, soil properties, and agricultural practices in the Driftless Region of southwestern Wisconsin, spanning 128 fields that have been under organic management for varying lengths of time (from 3 up to 51 years). We employed principal component analysis (PCA) and structural equation modeling (SEM) to uncover the effects of tillage, time under organic management, alfalfa use, and cover crop (CC) use on total carbon (C), nitrogen (N), and pH while examining their direct and indirect effects on bacterial biomass, bacterial diversity, relative abundance of arbuscular mycorrhizal fungi (AMF), and fungal diversity. Our multivariate analysis found that both bacterial and fungal community compositions were highly varied between fields that were recently transitioned to organic management but converged to a consistent state under prolonged organic management (> 20 years). SEM suggested that bacterial biomass increased with continuous alfalfa use, likely via improved nitrogen availability. Frequent tillage significantly reduced the proportion of AMF, limiting proliferation due to disturbance. Additionally, fungal diversity increased in acidic soils, while bacterial diversity was greater in neutral or basic soils. This study demonstrates how organic management in dairy forage systems likely shapes microbial community composition, especially through tillage and alfalfa use. These findings confirm the previous understanding of soil disturbance and soil chemical effects on soil microbial communities and caution that time under organic management per se should not be expected to lead to predictable changes in soil conditions. Rather, the direct and indirect consequences of specific management practices must be understood to develop cropping systems that build soil health over time.

  PublisherDOI

• Soil microbial community composition matters for crop growth, but only when mobilizing recalcitrant nutrient sources

  Plant and Soil · 2025-10-07 · 1 citations

  articleOpen accessSenior author

  Abstract Background and aims Soil microbes perform essential functions for agroecosystems, but it is unclear whether and when variation in the composition of the microbial community matters for agronomic outcomes since high functional redundancy may render compositional variation irrelevant for function. We hypothesized that the complexity of organic soil amendments would determine whether microbial community composition and richness matters for efficient decomposition and ultimately crop growth. Methods To test this hypothesis, we conducted a greenhouse experiment in which we grew maize and rye plants in pots inoculated with soil from 11 different farm fields, each grown with one of four nutrient sources which ranged in recalcitrance to microbial decomposition. Results As predicted, we found that crop growth responded more positively to live vs. sterilized soil, and the microbial inocula source explained more of the variation in crop biomass when nutrients were supplied as plant litter rather than a simple mineral form. We found that the initial richness of the bacterial community correlated positively with crop growth in the presence of complex organic, but not simple mineral, nutrient sources. Differences in management practices at the source farms, however, did not explain the microbial effects on plant growth. Conclusion These results suggest the make-up of soil microbial communities matters for maize and rye growth but only when these crops depend on nutrients from complex organic matter.

  PublisherOA PDFDOI

• Management Practices and Soil Health: Insights from Dairy Farms in the United States

  SSRN Electronic Journal · 2025-01-01

  preprintOpen access
  PublisherDOI

• Adapting an Agroecosystem Model to Account for Cover Crop Management in the Midwest USA

  SSRN Electronic Journal · 2025-01-01

  preprintOpen access
  PublisherDOI

• Data from: Soybean yield response to management practices (4–40 years) and soil health parameters

  Open MIND · 2025-01-01

  dataset

  Context or problem: The associations among soil health, management practices, and environmental conditions are complex, and research often focuses on specific practices or regional contexts. This have led to varying results regarding which soil health parameters are most influential for soybean yield. Objective: In this study, we investigated the effects of soil health measurements, agricultural management practices (4 - 40 years), inherent soil properties, location-specific factors, and soil fertility analytical results on soybean (Glycine max L. Merr.) seed yield. Methods: Soil samples (0–15 cm) were collected in 2023 from 17 agricultural research trials across the US. Soil health measurements, inherent soil properties, and soil fertility analytical results were assessed. Field management history and yield data were reported by the collaborators, and publicly available weather data (precipitation and temperature) were retrieved. Conditional inference trees were used to identify soybean yield influential factors. Results: Soybean seed yield was mainly driven by planting date. Trials planted before 26 May averaged 4,809 kg ha⁻¹, 55% greater yields than planting after 26 May (2,649 kg ha⁻¹). Longitude, along with soil organic carbon (SOC), autoclaved citrate extractable N (ACE-N), and soil test potassium (STK) were also important factors explaining yield variability. Conclusions: Our results demonstrated that planting date was the most critical factor driving soybean seed yield, yet yield responses are modulated to a lesser extent by longitude, SOC, ACE-N, and STK. Implications: To optimize soybean yield, conservation practices should prioritize early planting and soil health improvement. These findings can help identify soil health parameters associated with soybean seed yield for future long-term research.

• Potato (Solanum tuberosum L.) Responses to Nitrogen Fertilisation in Different Groundwater Nitrate Environments

  Potato Research · 2025-08-11 · 2 citations

  articleOpen access

  Abstract Reducing the over-use of nitrogen (N) fertiliser and mitigating leaching in highly cultivated agricultural areas have become the top priorities for potato researchers and the industry in the USA. In response, field trials were conducted in 2022 and 2023 at the University of Wisconsin Hancock Agricultural Research Station to explore the effects of different N fertilisation treatments on the in-season N status and at-harvest yield and size distribution of three potato ( Solanum tuberosum L.) cultivars (Colomba, Snowden, Goldrush) grown in irrigated sandy soil. The study was performed in two field sites with varied background irrigation groundwater nitrate–N concentrations. The findings revealed that (1) N treatment effects were season- and cultivar-dependent; (2) the high N rate at 350 kg N ha −1 significantly increased petiole nitrate–N during the latter part of tuber bulking, yet this increase was not always associated with higher total and marketable tuber yields at harvest; (3) in a year when high N inputs came from the background nitrate in irrigation water, high yields were observed even in the control treatment with no supplemental N added; (4) nitrate–N concentrations in irrigation could be confounding variables when assessing potato responses to N fertilisation. This study provides new insights into sustainable N management for potato production in irrigated sandy soil, emphasising that different nitrogen sources—including fertiliser N and nitrate in irrigation groundwater—should be accounted for when making N application recommendations.

  PublisherOA PDFDOI

• Nitrogen fertilizer equivalence of red clover when inter‐seeded into corn

  Agronomy Journal · 2025-07-01

  articleOpen accessSenior author

  Abstract Inter‐seeding red clover ( Trifolium pratense L.) provides an alternative method to incorporate cover crops into continuous corn ( Zea mays L.) in the Upper US Midwest. Red clover is a leguminous cover crop that can grow in low‐radiation environments and is winter hardy. Systems with red clover have demonstrated improved corn yield and a fertilizer N equivalence but understanding these effects with inter‐seeding warrants further investigation. The objectives of this study were to determine the effect of inter‐seeding red clover on (i) plant‐available N during and after red clover decomposition, (ii) optimum N rates for corn, and (iii) corn yields. The experimental design was a randomized, complete block‐split plot design, with cover crop as the main plot factor (treatments with and without inter‐seeded red clover) and N‐rate as a split‐plot factor (N‐rates between 0 and 315 kg‐N ha −1 in 45 kg‐N ha −1 intervals). Quadratic plateau response curves with a bootstrapping technique were used to determine differences in optimum N rate among treatments. Corn yields were evaluated with or without red clover inter‐seeded following the first inter‐seeding year. Red clover accumulated biomass values of 50 kg ha −1 up to 300 kg ha −1 pre‐termination when inter‐seeded with corn at the V4–V5 growth stage without detriment to yield. Corn yield was improved with clover treatments in one of four site years tested, resulting in a (15–17 kg ha −1 ) lower N requirement that year. Overall, our results indicate that inter‐seeding red clover into continuous corn did not provide an agronomically meaningful nitrogen fertilizer equivalence to the cropping system.

  PublisherOA PDFDOI

• High-resolution surface and rootzone soil moisture over US cropland: A novel framework assimilating multi-source remote sensing data, machine learning, and the Layered Green and Ampt Infiltration with Redistribution model

  Remote Sensing of Environment · 2025-12-06 · 3 citations

  articleOpen access

  Accurate and high spatiotemporal resolution soil moisture (SM) monitoring in cropland is important for water resource management, drought forecasting, and nutrient transport estimation at the field scale for sustainable crop production. Although recent research has applied machine learning (ML) to downscale coarse-resolution satellite SM products, most of this past work has focused only on surface SM estimation, and the performance of rootzone SM products has not been intensively evaluated in cropland. This study introduces a novel framework that integrates multi-source satellite-based ML models with the Layered Green and Ampt Infiltration with Redistribution (LGAR) model to produce high-resolution (100 m, hourly) SM products for both the surface layer (0–5 cm) and rootzone (0–100 cm) across cropland in the contiguous United States (CONUS). First, six ML models were trained using multiple high-resolution remote sensing datasets (Sentinel-1, Sentinel-2, and Landsat) to predict surface and rootzone SM. These ML predictions were then assimilated into the LGAR model using the ensemble Kalman filter (EnKF). The framework was developed and validated using an eight-fold cross-validation scheme with in-situ data from 431 cropland sites across CONUS, sourced from three networks (SCAN, USCRN, and PSA). The 100-m hourly SM data from this framework surpasses existing products (9-km SMAP L4, SMAP-based 1-km thermal hydraulic disaggregation of SM product) in spatial and temporal resolution and captures rootzone SM that is not available in the SMAP-HydroBlocks SM product. It achieves good performance, with median bias-corrected root mean squared error (ubRMSE) of 0.053 m3/m3 and median Kling-Gupta efficiency (KGE) of 0.379 in the surface layer, and median ubRMSE of 0.027 m3/m3 and median KGE of 0.302 in the rootzone. While the framework demonstrates strong performance, its accuracy varies across climatic regimes, with surface SM performing better in non-humid areas (median KGE = 0.375 versus median KGE = 0.416) and rootzone SM in humid regions (median KGE = 0.313 versus median KGE = 0.127). This high-resolution cropland SM product can potentially benefit multiple agricultural applications, such as irrigation management and nutrient leaching estimation, and provide valuable insights to support farmers and land managers in decision-making processes.

  PublisherDOI

• Nitrogen Fertilizer Equivalence of Red Clover When Inter-Seeded Into Corn

  Scholar Commons (University of South Carolina) · 2025-08-15

  articleOpen accessSenior author

  Inter-seeding red clover (Trifolium pratense L.) provides an alternative method toincorporate cover crops into continuous corn (Zea mays L.) in the Upper US Midwest. Red clover is a leguminous cover crop that can grow in low-radiation environments and is winter hardy. Systems with red clover have demonstrated improved corn yield and a fertilizer N equivalence but understanding these effects with inter-seeding war-rants further investigation. The objectives of this study were to determine the effect of inter-seeding red clover on (i) plant-available N during and after red clover decomposition, (ii) optimum N rates for corn, and (iii) corn yields. The experimental design was a randomized, complete block-split plot design, with cover crop as the main plot factor (treatments with and without inter-seeded red clover) and N-rate as asplit-plot factor (N-rates between 0 and 315 kg-N ha−1 in 45 kg-N ha−1 intervals).Quadratic plateau response curves with a bootstrapping technique were used to deter-mine differences in optimum N rate among treatments. Corn yields were evaluated with or without red clover inter-seeded following the first inter-seeding year. Red clover accumulated biomass values of 50 kg ha−1 up to 300 kg ha−1 pre-termination when inter-seeded with corn at the V4–V5 growth stage without detriment to yield. Corn yield was improved with clover treatments in one of four site years tested, resulting in a (15–17 kg ha−1 ) lower N requirement that year. Overall, our results indicate that inter-seeding red clover into continuous corn did not provide an agronomically meaningful nitrogen fertilizer equivalence to the cropping system.

  PublisherDOI

Frequent coauthors

• Birl Lowery

  University of Wisconsin–Madison

  30 shared

• Todd D. Stuntebeck

  29 shared

• F. W. Madison

  University of Wisconsin–Madison

  26 shared

• Kyle R Minks

  26 shared

• M. J. Komiskey

  Upper Midwest Water Science Center

  25 shared

• Donald Frame

  25 shared

• Randall D. Jackson

  University of Wisconsin–Madison

  12 shared

• Shawn P. Conley

  University of Wisconsin–Madison

  12 shared

Labs

• Nutrient Cycling and Agroecosystems LabPI

  Former Postdocs Tracy Campbell Ashley Waggoner Justin Gay Qiang (Ted) Li Yicaho Rui Sarah Collier   Former Graduate Students Claire Benning Ashmita Rawal Afona Irabor Monica Schauer Abigail Au…

Education

• B.S., Environmental Science

  University of Minnesota

  1999

• M.S., Soil Science

  University of Minnesota