About

Alan Franzluebbers is a Professor in the Department of Crop and Soil Sciences at NC State University, located in Williams Hall. His research focuses on soil ecology and management, with particular attention to soil health indicators, soil carbon and nitrogen dynamics, and the biological activity of soils under various land uses and management practices. His work includes exploring the diversity of soils in North Carolina, the effects of grassland management, and the responses of cotton lint yield to nitrogen fertilization. He has contributed to understanding how land use and management influence soil properties, including soil organic carbon, nitrogen, and biological activity, across different ecosystems such as grasslands, woodlands, and humid grazing lands. His research aims to define soil health targets and improve predictions of crop yields and soil carbon sequestration, with a focus on sustainable agricultural practices and ecosystem health.

Research topics

• Biology
• Environmental science
• Agronomy
• Agroforestry
• Ecology
• Soil science
• Mathematics
• Forestry
• Geography
• Statistics
• Chemistry

Selected publications

• Cotton lint yield responses to nitrogen fertilization are diverse in South Carolina

  Agronomy Journal · 2026-01-01

  articleOpen access

  Abstract Optimizing nitrogen (N) management in cotton ( Gossypium hirsutum L.) production across diverse environments in the southeastern United States remains a challenge. We examined cotton yield responses to N fertilization on multiple commercial farms with different management histories in four physiographic regions of South Carolina. Field experiments were conducted using a randomized complete block design with four N rates (0, 45, 90, and 135 kg ha −1 ) replicated three times at 50 trials from 2021 to 2023. Field management varied by previous crop, type of tillage, water regime, and history of conservation practices. Cotton lint yield was responsive to N fertilization in 52% of the trials. Economic optimum N rate (EONR) had an interquartile range of 0–135 kg ha −1 , with 68% of trials having values <78 kg ha −1 (below the recommended rate). The physiographic region influenced EONR ( p < 0.05), with higher EONR values at Coastal Plains and Sandhills compared to the Piedmont region, reflecting differences in soil types and the history of management. Sites with long‐term conservation practices had greater yield without N input, higher relative yields, and lower N factor (fertilizer N required per unit of lint) than conventionally managed sites. These sites exhibited greater residual soil N content, thereby reducing N fertilizer requirements. Current‐season management had varying impacts, and tillage primarily influenced how efficiently cotton used N (affecting EONR and N factor), while water regime affected yield potential indices (control, maximum, and profit‐maximizing yield) as well as EONR. These findings emphasize the need for site‐specific N recommendations that should consider physiographic characteristics, current‐season management practices, and the long‐term history of conservation practices. This study provides a foundation for developing more sustainable and efficient N management practices for cotton production.

  PublisherOA PDFDOI

• Key soil health indicators under humid grazing lands

  Grassland Research · 2026-02-10

  articleOpen access1st authorCorresponding

  Abstract Background Soil health describes critical soil functions influenced by land management. Although some key soil characteristics are inherent (such as texture, mineralogy, and landscape position), there are other soil properties and processes that are altered by land management (such as soil organic matter, nutrient concentrations, and the capacity to infiltrate and store water) to form the basis of soil health evaluation. Methods This perspective overview of soil health in humid grazing lands focused on key soil health attributes that should be considered to evaluate the sustainability of forage and grazing lands. Soil compaction, nutrient concentrations, and organic matter, along with their biological fractions, were emphasized. Results Soil bulk density is commonly measured to assess soil compaction. Density often increases with stocking rate, but it can be moderated by the accumulation of surface‐soil organic C and N. Many soil nutrients are concentrated near the soil surface, but soil type and management can influence these distributions. Soil‐test biological activity increases with time in forage management systems and is often greater with grazing than haying due to livestock excretal return to soil. Root‐zone enrichment of soil organic C was enhanced under grasslands compared with croplands but lower than under woodlands. However, root‐zone enrichment of total soil N was greater under grasslands than under other land uses, suggesting that the quality of organic matter under grasslands was greater than under woodlands, an essential feature that supports agricultural production. Conclusions This perspective overview of soil health in humid grazing lands illustrates the positive soil health benefits achievable with balanced agroecological farming approaches using forages.

  PublisherOA PDFDOI

• Soil carbon, nitrogen, and biological activity as affected by land use and grassland management across North Carolina

  Soil Science Society of America Journal · 2026-03-01 · 1 citations

  articleOpen access1st authorCorresponding

  Abstract Undisturbed land uses have the potential to enhance soil organic matter, but how and to what extent this occurs on private farms remains relatively unexplored. A cross‐sectional study of perennial grasslands and farm woodlots was undertaken across North Carolina to investigate stocks of soil organic C, total soil N, and soil‐test biological activity at 0‐ to 30‐cm depth. Root‐zone enrichment calculations allowed separation of management from pedogenic influences. From a total of 338 fields, total stock and root‐zone enrichment of soil organic C were 6.6 and 3.3 Mg C ha −1 greater under woodland than under grassland, respectively. However, total stock and root‐zone enrichment of soil N were 1.48 and 1.13 Mg N ha −1 lower under woodland than under grassland, respectively. Sand concentration had a large negative association with soil organic C, total soil N, and soil‐test biological activity. Soil C and N properties accumulated with older pastures, however, with modifications based on historical land use prior to grassland establishment. Rotational stocking of beef cattle was associated with greater root‐zone enrichment of soil organic C, total soil N, and soil‐test biological activity. A greater quantity of farm‐level hay feeding was associated with lower levels of soil C and N properties. Results from this on‐farm study revealed clear management influences, but it also showed the complex and confounding nature of multiple management decisions made on private farms, suggesting that large sampling sizes of farms and fields are necessary to make robust interpretations of management impacts at the regional level.

  PublisherDOI

• Ensemble Agroecosystem Modeling Enhances Predictions of Crop Yields and Soil Carbon Across the United States

  2026-03-09

  articleOpen accessSenior author

  Abstract. Accurately estimating crop yields and soil organic carbon (SOC) dynamics is essential for agricultural planning, carbon accounting, and sustainable land management. However, process-based agroecosystem models often produce divergent estimates due to variations in model structure, parameterization, and underlying assumptions. In this study, we developed a multi-model ensemble framework that integrates three widely used process-based models-Daily Century (DAYCENT), DeNitrification DeComposition (DNDC), and Ecosystem model (ECOSYS)-to simulate crop yields and SOC stock changes (0–30 cm) across cultivated lands of the continental United States (CONUS) at 4 km2 spatial resolution. Each model was parameterized using harmonized environmental, soil, and management datasets and evaluated using observed crop yields from the National Agricultural Statistics Service and measured SOC data from the Rapid Carbon Assessment. For the baseline period (2014-2023) under conventional corn-soybean rotation, the ensemble mean showed strong agreement with observations (corn: 7.7 vs. 8.5 Mg ha-1, RMSE = 3.0; soybean: 2.5 vs. 3.0 Mg ha-1, RMSE = 1.0), while simulated SOC stocks (5.5 vs. 4.8 kg C m-2, RMSE = 2.5) closely matched measured data. Spatially, the ensemble model projected SOC gains in the Midwest and Southeastern regions and losses in the Great Plains and Western United States, underscoring the importance of region-specific management practices. Overall, the ensemble approach improved predictive accuracy and reduced uncertainty relative to individual models, providing a scalable pathway for robust, data driven assessments of soil carbon and crop productivity across U.S. agroecosystems.

  PublisherOA PDFDOI

• Surface‐soil carbon and nitrogen mineralization under cropland, grassland, and woodland in Virginia

  Soil Science Society of America Journal · 2025-03-01 · 3 citations

  articleOpen access1st authorCorresponding

  Abstract Long‐term management of farmland can be expected to change the functioning of soil. Minimizing soil disturbance with conservation management is critical to changing surface organic matter conditions, but less is known of how canopy cover (e.g., plant species, residue quality, growth habit) may be affecting C and N properties and processes over time. A diversity of soils under different conservation land uses from 31 farms in the piedmont and mountain regions of Virginia (a warm‐moist, temperate region) were sampled at 0‐ to 10‐cm depth to assess soil C and N mineralization and associated properties. Interquartile range of surface residue N content was 76–143 kg ha −1 under cropland, 102–181 kg ha −1 under grassland, and 156–279 kg ha −1 under woodland. Median soil‐test biological activity and basal soil respiration were 39 ± 7% greater under grassland and woodland than under cropland. Median potential N mineralization was 37 ± 6% greater under grassland than under cropland and woodland. Residual soil ammonium‐N, despite relatively low concentrations, was strongly associated with biologically active soil C and N properties. Apparent nitrification during laboratory incubation (g NO 3 ‐N g −1 mineralized N) was high (>0.80) in all croplands, inhibited (≤0.80) in some grasslands (20% of soils), and dramatically inhibited in woodlands (85% of soils). The combination of high potential C and N mineralization and reduced nitrification may provide mechanisms for maintaining productivity while minimizing N losses to the environment in long‐term conservation land uses.

  PublisherOA PDFDOI

• Cumulative frequency distributions of soil health properties under grasslands and woodlands across North Carolina

  Soil Science Society of America Journal · 2025-09-01 · 4 citations

  articleOpen access1st authorCorresponding

  Abstract Soil health conditions can vary by inherent (climate, soil texture) and management (land use, practices) factors. A robust database to reference soil health conditions is a priority, particularly for soil metrics that vary by method. A survey of soil properties under 309 grassland fields and 29 farm woodlots on private farms was conducted across North Carolina. Classifying soil texture simply by sand concentration (kg kg −1 ) into fine (<0.2), medium (0.2–0.5), and coarse (>0.5) categories effectively separated the magnitude of most soil health metrics, particularly between medium and coarse textures. Most populations of soil properties under grasslands did not differ from those of a previous land use survey on research stations in North Carolina and private farmland in Virginia. Some exceptions were greater Mehlich‐3‐extractable phosphorus (P), zinc (Zn), and copper (Cu) under private grasslands in North Carolina, suggesting greater prevalence of animal manure applications. Similarity in populations of soil properties between studies indicates that consistent interpretations could be made across the region. Most soil chemical, physical, biological, and biogeochemical properties were greater under grassland than under woodland, while basal soil respiration and total, particulate, and non‐particulate organic carbon (C) were lower under grassland than under woodland. Soil health scores (0–1) using median values for each soil texture group were greater ( p < 0.001) under grassland (0.54 ± 0.02) than under woodland (0.37 ± 0.02). This study confirms that populations of dynamic soil properties sorted by soil textural group were effective to assess soil health across a diversity of soil types within a similar environmental setting, such as the southeastern US.

  PublisherOA PDFDOI

• Sand is the unifying textural component influencing surface‐soil carbon and nitrogen fractions across undisturbed land uses in North Carolina

  Soil Science Society of America Journal · 2025-01-01 · 7 citations

  articleOpen access1st authorCorresponding

  Abstract Soil organic matter concentrations are associated with soil texture in some but not in all studies. Why there are variable responses to soil texture can have logical reasons, the most obvious of which are inconsistent historical land uses, interactions with climatic and landscape settings, and management variations within a land use. In an evaluation of surface soils (0‐ to 10‐cm depth) under consistently undisturbed land use from 648 sites across relatively narrow climatic variations in North Carolina, large soil texture variations were assembled into structured populations ( n = 27) of sand and clay categories ( n = 24). Sand concentration varied from 220 to 881 g kg −1 , silt concentration varied from 67 to 517 g kg −1 , and clay concentration varied from 47 to 360 g kg −1 (5%–95% limits). Overwhelmingly, total, particulate, and non‐particulate organic C and N fractions were more statistically associated with sand concentration than with clay concentration alone. Sand concentration is the inverse of clay + silt summation and is a necessary feature when determining particulate organic C and N. Soil bulk density and sieved soil density were also more closely associated with sand concentration than with clay concentration alone. This study confirmed there was no saturation limit for the accumulation of non‐particulate organic C and N (sometimes labeled mineral‐associated organic matter). Therefore, sand concentration should be considered the best indicator of soil textural influence on soil organic matter properties and a key contextual feature necessary for soil health assessments.

  PublisherOA PDFDOI

• 114 Botanical composition varies in solar array grazed with sheep

  Journal of Animal Science · 2025-06-01

  articleOpen accessSenior author

  Abstract Installation of utility-scale solar arrays for energy production has created long-term changes to landscapes that were once used for timber, pasture, or row-crop production. Vegetation under panels is necessary for runoff control and it is becoming increasingly common for sheep to be utilized in combination with mechanical mowing for vegetation management. Variation in vegetation type and biomass production may impact the effectiveness of grazing as an alternative to mechanical vegetation management. The aim of this study was to evaluate botanical composition under different grazing conditions in a fixed panel solar array that was established in 2014. The Roxboro Farm solar project (Roxboro, NC) was utilized for the study. The entire site was mowed in late April 2024 to an equal vegetation height and subdivided into three treatment areas. A control area (1.5 ha) was isolated and only mechanical vegetation management used to maintain contract specifications. The second area (Low Stock Density, LS) was 4.8 ha and managed with ewes at 368 kg/ha. Another 2.1 ha area (High Stock Density, HS) was designated and further subdivided into three paddocks (0.7 ha each) to increase stock density to 2569 kg/ha. Ewes were moved between treatment areas at the discretion of farm management to meet contract specifications, minimize overgrazing, and maintain animal health. Grazing began May 18 and concluded November 3. Botanical composition was measured April 18 before grazing and October 9 near the end of the grazing season using step-point methodology and presented as a percentage of the total plants counted. Statistical analyses were performed using the Mixed Model procedure of SAS. Vegetation yield was determined based on sheep kg*days per ha. The three HS paddocks averaged 41,899 kg*days/ha whereas the LS allocation yielded 37,089 kg*days/ha. Plant species were categorized as desirable or undesirable. In the spring, there was no difference in the proportion of undesirable plant species under panels vs. between panels (P = 0.14). However, in the fall, a greater proportion of undesirable species were present between the panels vs. under (92% vs. 85%, respectively; P < 0.05). Before grazing, HS had greater undesirables compared to LS areas (82% vs. 65%, respectively; P < 0.01). However, there was no difference between these treatments in the fall. The most common undesirable species was Broomsedge Bluestem (BS, Andropogon virginicus). Regardless of season, there was a greater proportion of BS between vs. under panels (Spring: 46% vs. 7%, Fall: 64% vs. 10%, respectively; P < 0.01). Grazing treatment had no effect on BS proportions. Low density grazing resulted in a shift to more undesirable species by the end of the grazing season. Opportunities to improve soil health through high density grazing may aid in mitigating undesirable species while increasing grazing days.

  PublisherOA PDFDOI

• Soil structural characteristics affected by grassland management and land use along a soil texture gradient in North Carolina

  Soil Science Society of America Journal · 2025-11-01

  articleOpen access1st authorCorresponding

  Abstract Soil structure is an important feature that facilitates water infiltration, storage, and transport into the profile, as well as affecting soil organic matter storage, habitat for soil organisms, and nutrient cycling. How land use and grassland management affect soil structural characteristics in the warm, humid region of the southeastern US remains poorly described. A cross‐sectional study from 308 grassland fields and 29 woodlots was sampled at 0‐ to 10‐cm depth in North Carolina. Soils were mostly Ultisols (90%) and included some Alfisols, Inceptisols, and Entisols. Soil texture classes included sand (6%), loamy sand (7%), sandy loam (21%), sandy clay loam (27%), loam (17%), clay loam (13%), silt loam (7%), and silty clay loam (1%). Overall, soil bulk density was greater under grassland than under woodland (1.26 vs. 1.06 Mg m −3 , respectively) but the difference narrowed with finer soil texture. Mean‐weight diameter of water‐stable aggregation was greater under grassland than under woodland in fine‐textured soils but not in other soils. Soil stability index was not different between grassland and woodland, possibly due to high levels (>90%) in both land uses. Several grassland management factors influenced soil structural characteristics, including prior land‐use history, pasture age, stocking density, and forage utilization. Soil structural characteristics were strongly negatively associated with sand concentration and positively associated with soil‐test biological activity. Older pastures with moderate grazing pressure exhibited the strongest soil structural characteristics on medium‐ and fine‐textured soils, thereby delivering vital ecosystem services from this widely prevalent land use in the eastern United States.

  PublisherOA PDFDOI

• Soil and pasture health underlie improved beef nutrient density determined by untargeted metabolomics in Southern US grass finished beef systems

  npj Science of Food · 2025-07-24 · 7 citations

  articleOpen access

  As concerns regarding beef production on human and environmental health increase, interest in sustainable practices has grown. This study compared soil, plant, and meat samples from three Southern US grass-fed beef systems to a paired grain-fed beef system to assess soil health, forage phytochemical richness, and meat nutritional composition. Soil samples from pasturelands had 1.4 times higher organic matter and 1.7- to 3.0-fold higher levels of minerals like potassium, phosphorus, and calcium compared to paired feed croplands. Grass-fed beef contained 3.1-fold higher phytochemical antioxidants than grain-fed beef, resulting from a 118.2-fold higher phytochemical content in forage. Vitamins A and E in grass-fed beef were also 2.9- and 4.2-fold higher, respectively. Urate levels were 2.0-fold higher in grass-fed samples, while homocysteine and 4-hydroxynonenal glutathione, associated with reduced metabolic health, were elevated in grain-fed samples. The study provides evidence of the beneficial effects of grass-fed beef systems along the soil-plant-animal-human nutrition continuum.

  PublisherOA PDFDOI

Frequent coauthors

• J. A. Stuedemann

  Tift County School District

  67 shared

• R. F. Follett

  Agricultural Research Service

  27 shared

• Harry H. Schomberg

  Beltsville Agricultural Research Center

  26 shared

• Frank M. Hons

  Texas A&M University

  25 shared

• Carlos Alexandre Costa Crusciol

  Universidade Estadual Paulista (Unesp)

  21 shared

• D. A. Zuberer

  19 shared

• S. Del Grosso

  19 shared

• L. H. Allen

  19 shared

Education

• Ph.D., Soil and Crop Sciences

  Texas A&M University

  1995

• M.S., Agronomy

  University of Nebraska-Lincoln

  1991

• B.S., Horticulture

  University of Nebraska-Lincoln

  1985