Skip to main content

Josh Heitman

Professor and University Faculty Scholar

Williams Hall 3410


View all publications 


Date: 07/01/21 - 6/30/25
Amount: $495,359.00
Funding Agencies: National Science Foundation (NSF)

Terrestrial wetting and drying cycles keep soil water in a state of continuous transition. Soil water status, in turn, controls myriad processes including biogeochemical cycling within soil, plant- to system-level evapotranspiration, and feedback loops between land and atmosphere, among others. Capability to quantify soil water status at a point in time and space has drastically improved over the past several decades, and continues to be an area of emphasis in sensor development. On the other hand, there remain very few ways to determine soil water characteristics and hydraulic conductivity in situ. Yet, these too are dynamic, not only because they vary with soil water content, but also because they vary with the arrangement of the soil solid phase (i.e., density and structure) and its composition. Capability to predict and or interpret how soil water status at a point in time may transition to a new state (or how it arrived there from a previous state) depends on understanding how soil water characteristics and hydraulic conductivity will dictate change in soil water status under external forcing. Our objectives are to: 1) Determine co-variation in hydraulic, electrical, and thermal properties for structured and unstructured soils; 2) Develop models for prediction of soil water characteristics and hydraulic conductivity from electrical and thermal properties; 3) Evaluate hydraulic property models for prediction under transient field conditions.

Date: 02/19/21 - 2/15/25
Amount: $69,583.00
Funding Agencies: USDA - Natural Resources Conservation Service (NRCS)

PROJECT SUMMARY (Abstract) Overarching goals of this ????????????????On-Farm Trials??????????????? project are to (1) assistfarmers in the Southeastern Coastal Plain region to adopt field-validated and or oven soil-health management systems with cover crops and conservation tillage; and (2) evaluate the impact of these changes in management on soil health and farm profits. Recent research has shown there is a strong improvement in soil-test biological activity and net nitrogen (N) mineralization with adoption of no tillage and use of multi-species cover crops. These prime indicators of soil health can also predict the need for additional N to enhance corn yield. Although not tested in cotton systems, we have confidence that similar soil health changes will occur. Improvements in soil health condition will have high relevance to fine-tune soil fertility recommendations and increase farm profits in the Southeast U.S., as farmers in the region do not use soil testing to account for residual inorganic soil N or offer N credit from previous legume or cover crops while making soil N fertilizer recommendations. We propose to work directly with at least eight cotton growers each year in the Coastal Plain of South and North Carolina to demonstrate the value of cover crops and conservation tillage on promotion of soil health. Broader impacts of the project include demonstrating the importance of field-validated and proven soil-test biological activity on farms in the region, promoting the use of multi-species cover crops, engaging the participation of leading farmers and those curious in the concepts, and delivering social benefits to society (e.g. sustaining yield with optimized fertilizer inputs to improve environmental health).

Date: 02/08/22 - 1/20/25
Amount: $1,061,790.00
Funding Agencies: USDA - Natural Resources Conservation Service (NRCS)

On-farm trials will be used to measure mitigation of nitrous oxide and ammonia emissions from nitrogen fertilization of corn with and without the use of a urease and nitrification inhibitor. Control plots receiving zero N will be used to examine inherent soil health in the system and supply power relative to corn yields.

Date: 09/01/20 - 8/31/24
Amount: $473,871.00
Funding Agencies: USDA - National Institute of Food and Agriculture (NIFA)

The proposed project will use a chronosequence technique to evaluate changes in soil carbon storage and soil health indicators that occur over a 20 yr period from transition from conventional to organic management. Soil samples will be taken from on-farm sites that have been in organic management for a range of time and ensure and event distribution from year 0 to year 20. Soils from nearby abandoned or re-forested sites will be used as the regions maximum potential carbon accrual, while sites in year 0 or 1 of transition will be the theoretical starting point for carbon stock buildup. In addition to the on-farm trials, two intensive field experiments will be established at research stations on the coastal plains. These experiments will focus on carbon stock accrual within the first 3 years of transition from conventional to organic. Treatments will fall along a spectrum on management intensity, ranging from high intensity carbon building with organic amendments to business as usual production systems. This complementary study will allow inferences to be made around if active soil carbon building during transition can push the system further in the chronoseqenece and derive the potential benefits of increased soil health.

Date: 08/01/22 - 7/30/24
Amount: $311,357.00
Funding Agencies: NC Department of Transportation

One of the most common issues with highway construction is mud sticking to vehicle tires and being tracked onto public roads (herein referred to as ???trackout???). This can result in dangerous, slippery conditions on roads travelled by the public, and in addition drivers are not happy about the prospect of mud being flung onto their vehicles. By many accounts, trackout accounts for the majority of complaints and violations for construction companies. To prevent trackout, the conventional approach is to install a rock driveway at the site exit. This is intended to provide sufficient roughness to dislodge attached mud prior to the vehicle exiting onto a public road. There are a number of manufacturers of devices which work on the same principle ??? to vibrate the tire sufficiently to dislodge the mud. However, there has been virtually no testing of any system for preventing mud trackout, nor any information on where trackout is most likely. This project is intended to determine the force necessary to dislodge mud from tires, with an evaluation of the effects of soil particle size distribution and moisture conditions. In addition, testing of the rock driveway and at least two additional commercial systems will be conducted at full scale. The results should provide guidance on the best mud removal approaches and systems and conditions where these are most likely needed. Diamond grinding slurry (DGS) is a byproduct created by concrete pavement maintenance operations. Disposal of DGS is currently regulated based on minimal information. Currently, the NCDOT can land apply the material as a soil amendment, dispose of the material at a commercial facility, or use a mechanical press plate system to separate the water from the solids in order to reuse the water. Land application is possible, but the land required to safely apply the material is not always available. The other two methods are expensive as several million gallons for DGS are produced each year in North Carolina. Sediment basins used in sediment and erosion control have been effective at removing sediment from runoff. The proposed project is designed to determine if the same settling technology can be applied to DGS material to separate concrete residues from water in a cost effective basin. The water can then be reused in diamond grinding operations. Flocculating agents, such as polyacrylamide (PAM), will also be tested to see if they enhance separation of concrete particles. The results should provide improved guidance on DGS processing as well as the feasibility of a sediment basin compared to current disposal methods.

Date: 05/15/18 - 4/30/24
Amount: $402,674.00
Funding Agencies: National Science Foundation (NSF)

Soils play a fundamental role in myriad global processes. The need to understand the flow of elements, energy, and water through soils is immense and widely accepted across the geosciences community. Yet, the number of scientists trained with specific soils expertise is rapidly declining. The BESST REU Site utilizes a diverse, multi-disciplinary team of scientists to deliver individualized student research experiences in state-of-the art soil science topics, synergized through unifying themes and team training opportunities. Specific objectives are to: i) recruit outstanding students without extensive previous experience in soil science, with an emphasis on those from under-represented groups; ii) train these students by providing a substantive research experience and exposure to broad opportunities in basic and environmental soil science; and iii) develop a pool of future professionals empowered to advance understanding of soils in the geoscience community. Activities are supported by a university with well-developed infrastructure for undergraduate student research, and hosted by a department with a long-standing tradition of international excellence. Student recruitment is pursued through departmental and university collaboration with undergraduate-serving institutions, HBCUs, and national undergraduate research organizations. The program is assessed by external experts to ensure that it is rigorously evaluated and didactic impact maximized. The intellectual merit of the REU Site lies in constructing a critically needed pipeline for the next generation of geoscience researchers, equipped to address wide-ranging basic and environmental research problems in soils. Broader impacts are derived from training a diverse group of students to engage in addressing important societal and ecological issues throughout their careers. The REU site seeks to develop a new paradigm for soil science, extending student recruitment and training beyond traditional foundations in agriculture, and transforming soil science into an integral part of the geoscience research community. Student research opportunities highlight relationships between human activities and terrestrial environments, which are central topics in modern soil science that are broadly applicable to many other sub-disciplines of the Earth and environmental sciences.

Date: 04/01/22 - 3/31/24
Amount: $99,423.00
Funding Agencies: North Carolina Department of Agriculture & Consumer Services

Research supported by NCBRI has shown American sycamore to be especially well-suited to short-rotation woody coppice culture (SRWC) for bioenergy; it is productive with low inputs, resilient to biotic and abiotic stress, establishes well, and can be coppiced indefinitely. The goals of this new phase are to integrate knowledge of sycamore ecophysiology into conventional agricultural systems with the help of local farmers, forge relationships between major bioenergy constituencies in eastern NC, and create extension platforms that reach across the state. To do this, we will: 1) establish new sycamore bioenergy field trials on operational farms in proximity to existing Enviva wood pellet mills; 2) conduct mail surveys of constituencies across the state to gather data on perceived barriers and incentives to adoption of bioenergy cropping; 3) conduct outreach activities, including small group meetings, field tours, mill tours and annual field days to forge relationships and transfer technology, based on field trials and survey results; 4) perform an economic analysis comparing integrated agriculture-sycamore bioenergy SRWC to conventional agriculture (corn/soybeans) to assess market competitiveness; and 5) work with NCDA&CS/Commissioner Troxler/NCBRI to see if the legislature can be persuaded to consider support for (sycamore) bioenergy SRWC in the next NC Farm Bill.

Date: 02/01/23 - 1/31/24
Amount: $17,532.00
Funding Agencies: Corn Growers Association of NC, Inc.

Soil compaction is a common issue for corn growers in NC. Heavy equipment usage, field traffic, and continuous tillage at the same depth, and wet soil conditions cause subsurface compaction and limits available pore space, especially in soils with low organic matter. Soil pore structure controls root growth, carbon sequestration, and hence corn yield. Tillage and cover cropping can make a significant contribution to alter soil carbon stocks, reduce compaction, increase water infiltration, provide a softer seedbed, and balance soil water and air relations. This work provides an evaluation of different levels of soil disturbance (i) in conventional versus organic systems, and (ii) from minimal disturbance to severe disturbance within cover crop versus no cover crop integration. This study will provide information about soil strengths, soil compaction, carbon accumulation, and corn yield for two regions of NC with different soil types and climates. In two long term trials, a 28-year-old trial in Mills River (Mountains) and a 38-year experiment in Reidsville (Piedmont), we will study the intensity of tillage within cover crop vs no cover crop and conventional vs organic systems. At both locations, we will measure soil strength characteristics, changes in soil carbon and corn yield.

Date: 02/01/23 - 1/31/24
Amount: $20,620.00
Funding Agencies: Corn Growers Association of NC, Inc.

A flux gradient tower is currently being installed at the Tidewater Research Station in Plymouth NC. This systems allows for full field scale measurements of a variety of parameters. The field will be divided into four large quadrants each about ~8 acres in size. A trailer will be located at the center of the plots. Air intake towers will be placed in the center of each quadrant and air will be pulled into a trailers containing analyzers. Carbon dioxide (CO2), nitrous oxide (N2O), water vapor, evapotranspiration, net radiometry, soil moisture and soil temperature will be measured continuously throughout the year. In addition, background soil carbon stocks will be measured and at harvest crop yield, nitrogen uptake and residual soil nitrogen will be determined. This is planned as a 4-year study examining crop rotation management decisions. The following treatments are planned: 1. Business as Usual: Corn - Soybean - Corn - Soybean 2. Sustainable intensification: (Crimson Clover)- Corn-Wheat-Soybean-(Crimson Clover)-Corn-Wheat-Soybean 3. Cover Crop in Rotation: (Crimson Clover)-Corn-(Cereal Rye)-Soybean-(Crimson Clover)-Corn-(Cereal Rye)-Soybean 4. Continuous Corn: Corn-Corn-Corn-Corn This design allows for in-depth assessment of several corn growers identified priority areas. Including the use of cover crops as an N source in corn, the soil carbon sequestration potential of either double-cropping in rotation or using cover crops compared to business as usual corn-soy rotation. The continuous corn allows for an upper baseline of soil carbon sequestration due to the biomass being returned to the soil and also likely an upper baseline for nitrogen dynamics including nitrous oxide emissions and N leaching when compared to more complex rotations. Water budgets can be generated with technology in place, allowing for an assessment of water use dynamics over the 4 year period. Deep soil cores in at end of season will provide insights on N leaching as impacted by cover cropping. Corn will be harvested with yield monitor and grain N uptake will be measured. The 2023 season will be the corn phase of rotation and support is requested for an assessment of baseline soil carbon stocks, in-season nitrogen release dynamics of crimson clover in treatments 2 and 3, in-season N movement assessment after large rainfall comparing fertilizer only N application vs N fertilizer + cover crop N, corn tissue N for nutrient use efficiency assessments and end of season residual soil nitrogen. This is a one-of-a-kind experiment in the southeast and provides a true measure of GHG emissions and crop water use dynamics at a field scale. With the continued push for growers to consider climate-smart practices there is a great need for regional field scale assessments to ensure that these practices maintain or improve productivity in these systems.

Date: 01/01/20 - 5/31/23
Amount: $122,594.00
Funding Agencies: North Carolina Department of Agriculture & Consumer Services

To be widely adopted in North Carolina, a bioenergy cropping system must be compatible with existing farm practices, be productive enough to sustain an industry, and enhance environmental quality. We propose here that integrating short-rotation coppice (SRC) American sycamore for bioenergy into conventional agriculture will achieve all three goals. Our data from Butner, NC, suggests that sycamore can sustain high productivity with low inputs (no fertilizer/herbicides), may improve ag soil properties, and has shown no decrease in stool survival or productivity over two coppicing cycles (9 years). We propose here to test the generality of these results by: 1) continuing the original Butner study through a third rotation (up to12 years old), 2) expanding the study to include new ag fields near Butner and Wallace, NC, to contrast with lower coastal plain sites, 3) to work with ENVIVA to test sycamore biomass wood quality for pellet production and energy yield, 4) get input from local farmers on the potential to integrate sycamore biomass farming to produce purpose-grown feedstock for ENVIVA, and 5) quantify benefits to ag soil properties from sycamore SRC. Data will be available for use in new proposals, economic modeling, and life cycle analysis in cooperation with collaborators.

View all grants