About

Aziz Amoozegar is a Professor in the Department of Crop and Soil Sciences at NC State University, located in Williams Hall. His research interests include the movement of water and pollutants from municipal and agricultural wastes through soils and their underlying strata, the fate and transport of phosphorus in soil, and the characterization of soil materials for agricultural, environmental, and engineering purposes. His research programs focus on evaluating soil water and pollutant movement through soil and saprolite, assessing the fate and transport of phosphorus from fertilizers with and without fertilizer enhancers, and developing techniques for determining soil physical properties related to waste management, engineering, and agricultural practices.

Research topics

• Soil science
• Environmental science
• Geology
• Geotechnical engineering
• Chemistry
• Agronomy
• Materials science
• Environmental chemistry
• Horticulture
• Environmental engineering
• Ecology
• Metallurgy
• Botany
• Biochemistry
• Biology

Selected publications

• Microscale imaging of phosphate mobility under unsaturated flow as affected by a fertilizer enhancing polymer

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

  article1st authorCorresponding

  Abstract Phosphorus (P) fixation in soil following fertilizer application is a major issue that may be mitigated through a number of methods. Our main objective was to utilize an innovative unsaturated flow system to directly image the mobility of P in soil material as affected by AVAIL, a commercial copolymer phosphate fertilizer enhancer. Air‐dried clayey soil material, passed through a 0.25‐mm sieve and adjusted to pH 6, was packed in three side‐by‐side 1.4‐cm wide, 20‐cm long, and 0.6‐cm deep tracks. Water was applied to the tracks under approximately 1 cm tension and moved downstream by sorptivity. Five microliters of aqueous solutions containing 400 mmol P/L and varying levels of AVAIL were applied at a point near the upstream end of each track. Once water passed approximately 6 cm from the point of P application, each track was sectioned into small blocks and air‐dried. Synchrotron micro X‐ray fluorescence (μ‐XRF) images of P, silicon (Si), and aluminum (Al) were collected on block samples to measure relative movement of phosphorus along the soil tracks. Our results show that, despite the high affinity of soil minerals for P, it was relatively mobile with no enhancer under unsaturated flow conditions. Images showed diminished rate of P movement and enhanced clay dispersion with increasing proportion of AVAIL. We postulate that clay dispersion, corroborated by X‐ray computed tomography imaging, affected P transport due to interactions with Si and Al minerals. Our results demonstrate the potential utility of our unsaturated flow system combined with μ‐XRF imaging to measure convective mobility of plant nutrients or contaminants through soils.

  PublisherDOI

• Transport of Phosphorus from Three Fertilizers Through High- and Low-Phosphorus Soils

  Agronomy · 2025-10-15 · 2 citations

  articleOpen accessSenior authorCorresponding

  Chemical fertilizers are commonly used to supply phosphorus and other nutrients to crops, but due to high affinity of soils for P fixation, over-application of P fertilizer is common, which may result in groundwater and surface water pollution. To increase P use efficiency, different strategies, including different fertilizer formulations and types, have been developed. Two struvite-based fertilizers, Crystal Green® (CG) and Crystal Green Pearl® (CGP), are touted as environmentally safe, because they are insoluble in water but soluble in organic acids exuded from crop roots. The objective of this study was to assess fate and transport of P from diammonium phosphate (DAP), CG, and CGP through two loam soils with a significant difference in their initial P content. Two loamy soils, one collected from an experimental field receiving fertilizer continuously since 1985 and one from an adjacent area receiving no fertilizer, and a pure sand control were packed in 5 cm diameter and 5 cm long columns. Several grains equivalent to approximately 80 mg P from each fertilizer were imbedded at the bottom of the column. Distilled water was passed through the soil columns from the bottom at a relatively constant rate, and the outflow was collected every two hours using a fraction collector. Outflow samples from each treatment combination were analyzed for P by the colorimetric method, and the amount of P retained by the soils along the column at the end of the water application was determined by the nitric acid digestion method. Approximately 91% of P in DAP, 34% in CG, and only 3.8% in CGP was transported through the sand column. In contrast, the amounts of P transported were approximately 42.2% for DAP, 6.4% for CG, and 0.4% for CGP through the high-P soil and 22.4% for DAP, 0.6% for CG, and almost zero for CGP through the low-P soil. Overall, the results show a high solubility and transport for DAP, very low transport for CGP, and somewhat low to medium transport for CG fertilizers. In addition, the results show that even the high-P soil that has received fertilizer for about 40 years has the capacity to fix significant amounts of P.

  PublisherOA PDFDOI

• Analysis of Water Volume Required to Reach Steady Flow in the Constant Head Well Permeameter Method

  Hydrology · 2023-11-18

  articleOpen access1st authorCorresponding

  The most common method for in situ measurement of saturated hydraulic conductivity (Ksat) of the vadose zone is the constant head well permeameter method. Our general objective is to provide an empirical method for determining volume of water required for measuring Ksat using this procedure. For one-dimensional infiltration, steady state reaches as time (t) → ∞. For three-dimensional water flow from a cylindrical hole under a constant depth of water, however, steady state reaches rather quickly when a saturated bulb forms around the hole. To reach a quasi-steady state for measuring Ksat, we assume an adequate volume of water is needed to form the saturated bulb around the hole and increase the water content outside of the saturated bulb within a bulb-shaped volume of soil, hereafter, referred to as wetted soil volume. We determined the dimensions of the saturated bulb using the Glover model that is used for calculating Ksat. We then used the values to determine the volume of the saturated and wetted bulbs around the hole. The volume of water needed to reach a quasi-steady state depends on the difference between the soil saturated and antecedent water content (Δθ). Based on our analysis, between 2 and 5 L of water is needed to measure Ksat when Δθ varies between 0.1 and 0.4 m3 m−3, respectively.

  PublisherOA PDFDOI

• Influence of compost amendment rate and level of compaction on the hydraulic functioning of soils

  JAWRA Journal of the American Water Resources Association · 2023-03-16 · 15 citations

  articleOpen access

  Abstract There has been widespread interest in using compost to improve the hydrologic functions of degraded soils at construction sites for reducing runoff and increasing infiltration. The objective of this study was to determine the effects of compost amendment rate on saturated hydraulic conductivity ( K s ) and water retention in order to identify target compost rates for enhancing soil hydrologic functions. Samples were prepared with three soil textures (sandy loam, silt loam, and sandy clay loam), amended with compost at 0%, 10%, 20%, 30%, 40%, and 50%. All soils were tested at a porosity of 0.5 m 3 /m 3 , and the sandy loam was further tested at high (0.55 m 3 /m 3 ) and low (0.4 m 3 /m 3 ) porosities. The K s and water retention data were then used to model infiltration with HYDRUS‐1D. With increasing compost amendment rate, K s and water retention of the mixtures generally increased at the medium porosity level, with more compost needed in heavier soils. As porosity decreased in the sandy loam soil, the amount of compost needed to improve K s rose from 20% to 50%. Water distribution in pore fractions (gravitational, plant‐available, and unavailable water) depended on texture, with only the highest compost rates increasing plant‐available water in one soil. Results suggest soil texture should be taken into consideration when choosing a compost rate in order to achieve soil improvement goals. Hydrologic benefits may be limited even at a high rate of compost amendment if soil is compacted.

  PublisherOA PDFDOI

• How Does the Use of Biochar, Phosphate, Calcite, and Biosolids Affect the Kinetics of Cadmium Release in Contaminated Soil?

  Water Air & Soil Pollution · 2023-06-30 · 2 citations

  article
  PublisherDOI

• Water vapor transport through bioenergy grass residues and its effects on soil water evaporation

  Vadose Zone Journal · 2023-10-12 · 3 citations

  articleOpen access

  Abstract Miscanthus is a productive perennial grass that is suitable as a bioenergy crop in “marginal” lands (e.g., eroded soils) with low water holding capacity. However, little is known about the impact of miscanthus residues on vapor transport and soil water budgets. Laboratory experiments were conducted to measure the vapor conductance through miscanthus residues and its effect on soil water evaporation. The ranges for the length, width, and thickness of residue elements were 0.5–9.0, 0.1–0.5, and 0.1–0.5 cm, respectively. Average residue areal, bulk, and skeletal densities were 0.88 kg m −2 , 24 kg m −3 , and 1006 kg m −3 , respectively, giving a porosity of 0.98 m 3 m −3 . A power function described the decrease in conductance with increasing residue load. The corresponding conductance for a residue load of 0.88 kg m −2 was 1.6 mm s −1 . During the first days of a 60‐day drying experiment, cumulative evaporation showed logarithmic decay with increasing residue load. Conversely, cumulative evaporation during the last days of the study showed little difference between treatments. Measurements indicated that there is a “critical” residue load (∼1.0 kg m −2 ) beyond which evaporation no longer decreases appreciably when the soil is under the stage 1 evaporation regime. Results suggest that soil water conservation in marginal lands may be accomplished by maintaining moderate amounts of bioenergy grass residue covering the soil. Determining “critical” loads for different residue types is a knowledge gap that merits further research.

  PublisherOA PDFDOI

• Subsurface Lateral Solute Transport in Turfgrass

  Agronomy · 2023-03-18 · 1 citations

  articleOpen access

  Turfgrass managers have suspected that runoff-independent movement of herbicides and fertilizers is partially responsible for uneven turfgrass quality in sloped areas. We hypothesized that subsurface lateral solute transport might explain this phenomenon especially in areas with abrupt textural changes between surface and subsurface horizons. A study was conducted to track solute transport using bromide (Br−), a conservative tracer, as a proxy of turfgrass soil inputs. Field data confirmed the subsurface lateral movement of Br− following the soil slope direction, which advanced along the boundary between soil horizons over time. A model based on field data indicated that subsurface lateral movement is a mechanism that can transport fertilizers and herbicides away from the application area after they have been incorporated within the soil, and those solutes could accumulate and resurface downslope. Our results demonstrate that subsurface lateral transport of solutes, commonly ignored in risk assessment, can be an important process for off-target movement of fertilizers and pesticides within soils and turfgrass systems in sloped urban and recreational landscapes.

  PublisherOA PDFDOI

• Comparison of soil particle density determined by a gas pycnometer using helium, nitrogen, and air

  Soil Science Society of America Journal · 2022-08-27 · 19 citations

  article1st authorCorresponding

  Abstract Soil particle density (ρ s ) is often assumed as 2.65 g cm −3 (density of quartz). The objectives of this study were to compare the use of different gases for determining ρ s in a gas pycnometer and relate measured ρ s to soil particle size distributions. The ρ s of 36 natural soil samples representing 12 USDA textural classes, fine glass beads, crushed granite rock, kaolinite, and bentonite were measured by a commercial gas pycnometer using He, N 2 , and dry air. The ρ s of 30 of the soil samples, glass beads, and crushed rock were also determined with a water pycnometer. The ρ s of 36 soil samples determined by He and 30 samples determined by water had narrow ranges with averages of 2.65 and 2.59 g cm −3 , respectively. The ρ s determined by air and N 2 had much wider ranges with averages of 2.93 and 2.97 g cm −3 , respectively. There was a near 1:1 relationship between ρ s of all samples determined by air and N 2 with a highly significant ( p < .001) correlation coefficient ( r = .99). The average ratio of ρ s determined by He and water was 1.03, but the correlation coefficient for their relationship was only .416. Although the relationship between ρ s determined by He and either air or N 2 was relatively strong ( r < .61), the regression coefficient was <.17. There was a strong relationship between soil clay content and ρ s determined by N 2 or air but a weaker, yet statistically significant ( p < .05) relationship when using He.

  PublisherDOI

• Particle Densities of Horticultural Substrates

  HortScience · 2022-01-28 · 9 citations

  articleOpen access

  The heterogeneity of horticultural substrates makes basic physical characteristics, such as total porosity and particle density, difficult to estimate. Due to the material source, inclusion of occluded pores, and hydrophobicity, particle density values reported from using liquid pyknometry, vary widely. Gas pycnometry was used to determine the particle density of coir, peat, perlite, pine bark, and wood substrates. Further precision was examined by gas species and separation by particle size. The calculated particle densities for each material determined by He, N 2 , and air were relatively constant and varied little despite the species of gas used. Particle size affected the measured particle density of perlite and pine bark but was minimal with coir, peat, and wood. Reducing the particle size removed more occluded pores and the measured particle density increased. Given the small variability, the use of particle density values obtained by gas pycnometry provides repeatable, precise measurements of substrate material total porosity.

  PublisherOA PDFDOI

• Evaluation of imazapic and flumioxazin carryover risk for Carinata (<i>Brassica carinata</i>) establishment

  Weed Science · 2022-05-11 · 6 citations

  articleOpen access

  Abstract Carinata ( Brassica carinata A. Braun) is a potential crop for biofuel production, but the risk of injury resulting from carryover of soil herbicides used in rotational crops is of concern. The present study evaluated the carryover risk of imazapic and flumioxazin for carinata. Label rates of imazapic (70 g ai ha −1 ) and flumioxazin (107 g ai ha −1 ) were applied 24, 18, 12, 6, and 3 mo before carinata planting (MBP). The same herbicides were applied preemergence right after carinata planting at 1X, 0.5X, 0.25X, 0.125X, 0.063X, and 0X the label rate. When either herbicide was applied earlier than 3 MBP, there was no difference in plant density compared with the nontreated control. Carinata damage was &lt;25% when flumioxazin or imazapic was applied at least 6 MBP in Clayton, NC (sandy loam soil), while in Jackson Springs, NC (coarser-textured soil and higher precipitation), at least 12 MPB were needed to lower plant damage to &lt;25%. Preemergence application of 0.063X each herbicide decreased plant density by 40%, with damage reaching &gt;25%. Quantification of herbicide residues in both soils showed that imazapic moved deeper in the soil profile than flumioxazin. This was more evident in Jackson Springs, where 0.68, 3.52, and 7.77 ng of imazapic g −1 soil were detected (15- to 20-cm depth) when the herbicide was applied at 12, 6 and 3 MBP, respectively, while no flumioxazin residues were detected at the same soil depths and times. When residues were 7.78 and 6.90 ng herbicide g −1 soil in the top 10 cm of soil for imazapic and flumioxazin, respectively, carinata exhibited at least 25% damage. Rotational intervals to avoid imazapic and flumioxazin damage to carinata should be between 6 and 12 MBP depending on soil type and environmental conditions, with longer intervals for the former than the latter.

  PublisherOA PDFDOI

Frequent coauthors

• Joshua L. Heitman

  North Carolina State University

  18 shared

• M. J. Vepraskas

  North Carolina State University

  15 shared

• Owen W. Duckworth

  North Carolina State University

  10 shared

• Dean Hesterberg

  Brazilian Synchrotron Light Laboratory

  10 shared

• David Lindbo

  Natural Resources Conservation Service

  7 shared

• Christopher P. Niewoehner

  North Carolina State University

  7 shared

• Wayne P. Robarge

  North Carolina State University

  6 shared

• Richard A. McLaughlin

  North Carolina State University

  6 shared