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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOGEOCHEMICAL PROCESSES INFLUENCING FORMATION AND STABILIZATION OF SOIL ORGANIC MATTER AND SOIL STRUCTURE
2007 Annual Report


1a.Objectives (from AD-416)
1)Develop a mechanistic understanding of processes controlling the formation and stabilization of organic matter in soils that enhance stabilization of soil structure. a) Determine the relative contributions of biochemical compounds to aggregation and C sequestration. b) Determine the role of clay minerals and charcoal in the formation and stabilization of soil organic matter and soil structure. c) Determine the nature of reactions between smectites and pesticides. d) Determine the effects of anaerobic soil conditions on biochemical processes that influence soil nutrient cycling. e) Develop integrative methods for fractionating SOM into meaningful pools..
2)Develop tools for in situ assessment of soil organic carbon and soil structure. a) Develop a multi-function probe (electrical and thermal properties) to evaluate soil structure. b) Develop and evaluate a field mobile NIRS tool for sensing soil carbon and various soil properties.


1b.Approach (from AD-416)
Field plot and column leaching studies will be used to quantify the impact of adding charcoal to soils on nutrient cycling, soil productivity, C sequestration, pesticide leaching, and on the formation and stabilization of clay-humic complexes. Interactions between selected pesticides and reference clays will be investigated to elucidate bonding mechanisms between organic molecules and clay surfaces. Seasonal patterns for cycling of phenolic and organic nitrogen compounds will be compared for routinely flooded and non-flooded soils. Anticipated products will include more accurate predictions of how crop and soil management effect nutrient cycling and soil organic matter stabilization. We will develop and test electrical and thermal soil probes to characterize soil structure. A regional non-linear multivariate calibration model for a recently developed on-the-go in situ near infrared diffuse reflectance soil probe will be evaluated to determine if the system can accurately map the spatial distribution of numerous soil properties (organic C, total N, CEC, moisture, buffer pH, and extractable nutrients) at the field scale.


3.Progress Report
Both laboratory and field studies were initiated to determine the effects of bio-char (charcoal derived from biomass) on soil properties, agricultural productivity, and the potential use of biochar in sequestering carbon as a means of mitigating global climate change. A practical method for spreading biochar in agricultural fields was developed. Test plots were established at three locations in agricultural fields. A soil column study was established and is underway. The soil column study is designed to quantify the impact of biochar additions to soil on soil physical and chemical properties and on the leaching of nitrate and phosphorous. Development of a method to physically separate biochar from soil is underway and samples of biochar isolated from soil have been characterized by various techniques.

Development of near-infrared tools for analyzing the spatial distribution of soil properties at a field scale is continuing. Laboratory analyses of samples collected from 11 fields in central Iowa are complete. Preliminary statistical analysis of spectral data and the soil laboratory data has been completed.

Studies were designed and conducted to quantify the interaction between cation exchange selectivity and adsorption of an organic compound (dinitrobenzene) by clay minerals. Preliminary results suggest that organic molecules on clay surfaces influence the affinity of the clay for various cations and conversely the type of cation on the clay surfaces influences the affinity of the clay for organic molecules through a complex feed-back system. This research was conducted under subordinate project 3625-11120-003-06R.

Analytical tools for the analysis of amino acids, amino sugars, phenolic acids, and carbohydrates in soils are essential for meeting Objectives 1A and 1D. To strengthen their laboratory development, an exhaustive literature review was conducted to identify strengths and weaknesses of various proposed methods for analyses of these compounds. The literature review is being developed into a peer-reviewed publication. Potential improvements to the analytical methods for aminos and phenols were identified and are being evaluated in ongoing laboratory work. Collaborations were established with scientists who perform alternative analyses for amino acids and phenols, and soil samples will be jointly analyzed. One comparison of phenols analyses has been completed for a set of humic samples. The phenols analysis was installed at a Vietnamese university, where collaborating researchers are conducting field and greenhouse studies that conform to Subobjective 1D.

Work is continuing on development of electrical and thermal probes that can be used to analyze soil structure. Undisturbed soil samples were collected from a prairie and nearby soybean field. Soil electrical properties were analyzed using a refined twelve-wire insertion probe, and thermal properties were analyzed with a dual heat pulse probe. Soil structural properties related more to thermal properties than to electrical properties. Further soil sampling from other states is in progress, to expand to a broader range of soils.


4.Accomplishments
Title: Electrical spectra of undisturbed soil samples. Problem addressed: Determining soil electrical properties (electrical conductivity and permittivity) across a range of frequencies (the spectra) assist in understanding soil response to soil moisture sensors and electrical conductvitiy determination. Electrical spectra determined from disturbed, repacked soil may not easily relate to the undisturbed soil in the field. Accomplishment: We successfully measured the electrical spectra of undisturbed soil samples using a home-made, twelve-wire, quasi-coaxial probe that could be inserted into the soil. Impact: The research will lead to the development of improved soil moisture sensors. National Program 202: The research contributes to NP202 Problem Area 2, "Soil Management to Improve Soil Structure and Hydraulic Properties."

Title: Interactions between nitroaromatic compounds and soil clay minerals. Problem addressed: Recent research has shown that nitroaromatic compounds are adsorbed on soil clays at much higher levels than anticipated, which suggests a lack of understanding of the mechanisms by which these compounds interact with clays. Accomplishment: Through a series of studies we have shown that 4, 6- dinitro-o-cresol (DNOC) is adsorbed on smectite clays as a complex with potassium ions and that this adsorption can occur at acidities (pHs) well above the dissociation constant (pKa) of DNOC, and primarily occurs on the outside surfaces of clay particles in aqueous suspensions. Due to the dynamic nature of clay particles, DNOC may become trapped inside of clay particles as a clay suspension dries. Impact: This research will help scientists to better understand how nirtoaromatic compounds are adsorbed on soil clays and thus to better predict fate of these compounds in soil environments. National Program 202: The research contributes to NP202 Problem Area 7, "Managing Pesticides in Soils."


5.Significant Activities that Support Special Target Populations
ARS scientists participated in the southern regional soil physics information group (5/10-11/2007) that included participation by scientists from 1890 schools. ARS scientist is editing a book entitled "Soil Science: Step-by-Step Field Analyses" that includes authors or co-authors on book chapters from 1890 schools.

ARS scientists coordinates the U.S. Chapter of the International Humic Substances Society. Members include university and government researchers, students, and private sector employees, mostly vendors of humic products.


6.Technology Transfer

Number of active CRADAs and MTAs2
Number of non-peer reviewed presentations and proceedings12

Review Publications
Charles, S., Teppen, B.J., Hui, L., Laird, D.A., Boyd, S.A. 2006. Exchangeable Cation Hydration Properties Strongly Influence Soil Sorption of Nitroaromatic Compounds. Soil Science Society of America Journal. 70(5):1470-1479.

Li, H., Pereira, T., Teppen, B., Laird, D.A., Johnston, C.T., Boyd, S. 2007. Ionic Strength-Induced Formation of Smectite Quasicrystals Enhances Nitroaromatic Compound Sorption. Journal of Environmental Science and Technology. 41(4):1251-1256.

Laird, D.A. 2006. Influence of layer charge on swelling of smectites. Journal of Applied Clay Science. 34:74-87.

Pils, J., Laird, D.A., Evangelou, V.P. 2006. Role of cation demixing and quasicrystal formation and breakup on the stability of smectitic colloids. Journal of Applied Clay Science. 35:201-211.

Pils, J., Laird, D.A. 2007. Sorption of tetracycline and chlortetracycliine on K- and CA- saturated soil clays, humic substances, and clay-humic complexes. Environmental Science and Technology. 41(6):1928-1933.

Li, H., Teppen, B., Laird, D.A., Johnston, C., Boyd, S. 2006. Effects of Increasing Potassium Chloride and Calcium Chloride Ionic Strength on Pesticide Sorption by Potassium- and Calcium-smectite. Soil Science Society of America Journal. 70(6):1889-1895.

Logsdon, S.D. 2006. Uncertainty effects on electrical conductivity and permittivity spectra. Soil Science. 171:737-746.

Last Modified: 9/22/2014
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