Progress 10/01/07 to 09/30/13
Outputs
Target Audience: The target audience includes researchers, graduate students, and extension personnel. The knowledge obtained from the project has been delivered to researchers, graduate students, and extension personnel through national, regional and local professional meetings. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? A Ph.D. student and a visiting scientist have worked closely with the PD of the project. They have acquired a number of biochemistry and process-level techniques. They have been given a number of opportunities to present their work at national, regional and local professional meetings and to participate in professional development workshops. How have the results been disseminated to communities of interest? The results of the project have been disseminated to researchers, graduate students and extension personnel via formal and informal communications, professional meetings, and seminars. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Issue: Dissolved soil organic matter play significant roles in nutrient availability, carbon sequestration, and detoxification of contaminants. However, there is a wide gap in knowledge of the production and consumption of dissolved organic matter and their control factors. This project examines microbial controls on the abundance and composition of dissolved soil organic matter and assesses the relationship between dissolved organic matter and nutrient availability. What have been done and broader impacts: Researchers at North Carolina State University have examined the relationships between soil enzyme activity and dissolved soil organic matter, elucidated enzyme controls on the bioavailability of simple sugars and amino acids, and quantify the biodegradability of dissolved organic matter and its association with soil nitrogen availability. We have collected substantial evidence to support that the chemical composition of dissolved organic matter is correlated with soil peroxidase activity and soil C and N mineralization. Peroxidase enhances soil C and N mineralization via improving the bioavailability of reducing sugars and amino acids. Accomplishments under the objective one: Interrelationships among dissolved organic matter, soil enzyme activity, and soil C and N mineralization were examined in diverse agroecosystems. These systems included a conventional cropping, organic cropping, integrated crop-livestock, plantation forestry, and succession from an abandoned agricultural field. We collected surface soil samples and examined the concentrations of soil-derived dissolved organic carbon and nitrogen, soluble phenolics, reducing sugars, and amino acids, the activities of beta-glucosidase, exoglucanase, phenol oxidase, peroxidase, and beta-glucosaminidase, and the rates of soil carbon and nitrogen mineralization. The integrated crop-livestock system showed the highest concentrations of dissolved soil organic carbon as well as phenolic compounds, reducing sugars, and amino acids, and these components were up to three-fold greater than soils under the other systems. However, soil beta-glucosidase activity in the integrated crop-livestock system was significantly lower than the other systems and appeared to reflect the inhibitory role of soluble phenolics on this enzyme. Among the five enzyme activities examined, only peroxidase activity was correlated significantly with the chemical composition of dissolved organic matter as well as soil carbon and nitrogen mineralization. By examining interactions among soil enzymes, dissolved organic matter, and soil carbon and nitrogen mineralization, our study helps to gain new insights into enzymatic controls on soil carbon and nitrogen dynamics in agroecosystems. Accomplishments under the objective two: Biodegradability of dissolved organic matter was examined under a wide range of soil moisture content. Soils with contrasting acidity and alkalinity were collected from golf courses in Las Vegas, NV and in Pinehurst, NC, respectively. Following soil preparation, an incubation experiment of a 2 x 7 factorial design was set up, with two soil types and seven moisture conditions (0, 20%, 40%, 60%, 80%, 100%, and 120% of soil water holding capacity). During the incubation, the activities of soil enzymes including beta-glucosidase, exoglucanase, xylanase, phenol oxidase, peroxidase, and glucosaminidase were determined by using colorimetric methods. Total dissolved organic carbon and nitrogen were measured with a TOC analyzer. Soluble reducing sugars, amino acids, and phenolic compounds were analyzed with phenol-sulfuric acid, ninhydrin, and Folin-Denis methods, respectively. Soil carbon and nitrogen mineralization were qualified by carbon oxide evolution and net change in inorganic nitrogen over the incubation. Regardless of soil acidity and alkalinity, dissolved organic carbon and phenolic compounds were generally lower at 40-80% soil water holding capacity than at the other water holding capacities. By contrast, soil carbon mineralization was generally higher at 40-80% water holding capacity than at the other values. Therefore, soil C mineralization was strongly and negatively correlated with dissolved organic carbon as well as with soluble phenolic compounds. Accomplishments under the objective three: Microbial controls on the quantity and quality of dissolved organic matter were examined via a modification of soil enzyme activities. First, an arable soil was amended with horseradish peroxidase at 0, 0.1, and 0.2 activity units per gram of soil, and then examined for peroxidase and hydrolase activities, water-extractable phenolic content, and soil carbon and nitrogen mineralization over a three-week incubation. Soil carbon mineralization was enhanced by peroxidase addition, but it was not correlated with the concentration of water extractable phenolics or hydrolase activity. Exoglucanase and beta-glucosidase activities were significantly lower in soil amended with peroxidase at 0.2 units than at 0.1 units. Second, peroxidase, cellulase, protease or their combinations were added into sterile soils to examine enzyme-catalyzed productions of soluble reducing sugars and amino acids. Reducing sugar concentration was increased after peroxidase addition and this effect was more pronounced when both peroxidase and hydrolases were added. Thus-produced reducing sugars and amino acids were significantly correlated with soil carbon and nitrogen mineralization. Through well-controlled enzyme-addition laboratory incubation experiments, this study improves our understanding on peroxidase-mediated soil organic matter degradation. When peroxidase oxidizes phenolic moieties of humus, simple phenolic compounds can be produced for microbial assimilation. Simultaneously, peroxidase oxidation can improve the accessibility and thus bioavailability of compounds, such as sugars and proteins that are otherwise bound to soil humus.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Tian L, Shi W. Soil peroxidase regulates organic matter decomposition through improving the accessibility of reducing sugars and amino acids. Biology and Fertility of Soils. 10.1007/s00374-014-0903-1
- Type:
Journal Articles
Status:
Submitted
Year Published:
2014
Citation:
Tian L, Shi W. Dynamic, level and stoichiometry of soil enzyme activity: litter type effects. Applied Soil Ecology, in review.
- Type:
Book Chapters
Status:
Published
Year Published:
2012
Citation:
Shi W, Bowman D, Rufty T. Microbial control of soil carbon accumulation in turfgrass systems. In Lal R, Augustin B (Eds.), Caron Sequestration in Urban Ecosystems, Springer. pp 215-232.
- Type:
Book Chapters
Status:
Published
Year Published:
2011
Citation:
Shi W. Agricultural and ecological significance of soil enzymes: soil carbon sequestration and nutrient cycling. In Girish Shukla and Ajit Varma (Eds.), Soil Enzymology. Soil Biology Series, Springer. pp 43-60.
- Type:
Theses/Dissertations
Status:
Published
Year Published:
2011
Citation:
Tian L. Understanding soil organic matter mineralization in agroecosystems: soil enzyme perspectives. NCSU Dissertation, Raleigh, NC.
- Type:
Journal Articles
Status:
Published
Year Published:
2010
Citation:
Tian L, Dell E, Shi W. Chemical composition of dissolved organic matter in agroecosystems: correlations with soil enzyme activity and carbon and nitrogen mineralization. Applied Soil Ecology 46, 426-435.
- Type:
Other
Status:
Other
Year Published:
2011
Citation:
Tian L. Understanding soil organic matter mineralization in agroecosystems: soil enzyme perspectives. Soil Science Seminar Series, North Carolina State Univ.
- Type:
Other
Status:
Other
Year Published:
2010
Citation:
Tian L, Shi W. Towards a mechanistic understanding of peroxidase controls on soil carbon and nitrogen mineralization. Annual Meeting Abstracts, ASA/CSSA/SSSA Annual Meetings, Long Beach, California.
- Type:
Other
Status:
Other
Year Published:
2010
Citation:
Tian L. Chemical composition of dissolved organic matter in agroecosystems: correlations with soil enzyme activity and carbon and nitrogen mineralization. Soil Science Seminar Series, North Carolina State Univ.
- Type:
Other
Status:
Other
Year Published:
2009
Citation:
Shi W. Soil enzymes: from Microbial Physiology to Ecosystem Function. Invited speaker, ASA/CSSA/SSSA Annual Meetings, Pittsburgh, Pennsylvania.
- Type:
Other
Status:
Other
Year Published:
2009
Citation:
Tian L, Dell E, Shi W. Chemistry and biology of dissolved organic matter in agro-ecosystems: implications on soil processes. Annual Meeting Abstracts,
- Type:
Other
Status:
Other
Year Published:
2007
Citation:
Shi W. Soil microbial community in managed ecosystems: advancing basics and hoping for applications. Soil Science Seminar Series, North Carolina State Univ.
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Progress 10/01/11 to 09/30/12
Outputs
OUTPUTS: Organic matter decomposition often initiates with soil enzyme-catalyzed biochemical reactions. It is generally believed that enzymatic depolymerization is a rate limiting step of decomposition. Yet, this notion has not adequately been examined. This study investigated the relationships among soil enzyme activity, dissolved organic matter, and soil carbon and nitrogen mineralization under a wide range of soil moisture conditions. Soils with contrasting acidity and alkalinity were collected from golf courses in Las Vegas, NV and in Pinehurst, NC, respectively. Following soil preparation, an incubation experiment of a 2 x 7 factorial design was set up, with two soil types and seven moisture conditions, i.e., 0, 20%, 40%, 60%, 80%, 100%, and 120% of soil water holding capacity (WHC). During the incubation, the activities of soil enzymes including beta-glucosidase, exoglucanase, xylanase, phenol oxidase, peroxidase, and glucosaminidase were determined by using colorimetric methods. Total dissolved organic carbon and nitrogen were measured with a TOC analyzer. Soluble reducing sugars, amino acids, and phenolic compounds were analyzed with phenol-sulfuric acid, ninhydrin, and Folin-Denis methods, respectively. Soil carbon and nitrogen mineralization were qualified by carbon oxide evolution and net change in inorganic nitrogen over the incubation. Two-way ANOVA with repeated measures were performed to examine the effects of soil moisture, pH and their interactions on soil enzyme activities, dissolved organic carbon and nitrogen, reducing sugars, amino acids, phenolic compounds, and soil carbon and nitrogen mineralization. Pearson's correlation was used to assess the relations among soil enzyme activities, dissolved organic matter and chemical compositions, and soil carbon and nitrogen mineralization. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Regardless of soil acidity and alkalinity, dissolved organic carbon and phenolic compounds were generally lower at 40-80% WHC than at the other WHC values. By contrast, soil carbon mineralization was generally higher at 40-80% WHC than at the other WHC values. Therefore, soil C mineralization was strongly and negatively correlated with dissolved organic carbon as well as with soluble phenolic compounds. However, potential activities of soil enzymes were found to be little affected by soil moisture regimes. There were no correlations of soil enzyme activities with dissolved organic carbon and nitrogen, reducing sugars, amino acids, phenolic compounds, and carbon and nitrogen mineralization. Hence, this incubation study did not support that soil enzyme activities limited organic carbon and nitrogen decomposition under low and high soil moisture conditions.
Publications
- Shi W, 2011. Agricultural and ecological significance of soil enzymes: soil carbon sequestration and nutrient cycling. In Girish Shukla and Ajit Varma (Eds.), Soil Enzymology. Soil Biology Series, Springer. pp 43-60.
- Shi W, Bowman D, Rufty T, 2012. Microbial control of soil carbon accumulation in turfgrass systems. In Lal R, Augustin B (Eds.), Caron Sequestration in Urban Ecosystems, Springer. pp 215-232.
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Progress 10/01/10 to 09/30/11
Outputs
OUTPUTS: Crop residue management and soil liming are common soil management practices in agricultural production systems. However, their effects on soil enzyme activities have received inadequate attention. This study examined how plant litter quality regulated microbial production of extracellular enzymes involved in C and N transformations and how soil pH affected the stabilization of soil enzymes. Two soils were collected by coring technique from organic and conventional farms, respectively. The farms were located in Goldsboro, NC where crops were rotated annually, including corn, peanut, cotton, soybean, wheat, sweet potato, and sorghum. The conventional farm was applied annually with synthetic N, P, and K fertilizers and with herbicides, insecticides, and fungicides as needed. The organic farm was applied with turkey litters and the application rate was dependent on specific crops. Gypsum was used to lime soils at both farms. Twenty soil cores were collected randomly from each of the three plots at each farm and pooled, leading to three composite soil samples. Plant litters of different C:N ratios were collected from senescent vegetation ground covers after exposure to sunlight for a while, including long-leaf pine needles; a mixture of grass materials of switchgrass, eastern gamagrass, indiangrass, and big bluestem; and soybean residues. The C:N ratios were 139, 50 and 9 for pine needles, grass materials, and soybean residues, respectively. Effects of plant litter on microbial production of extracellular enzymes were examined in a 90-day incubation experiment with three replications. Six treatments were made based upon a 2 x 3 factorial design (2 soils and 3 plant litter types). Respective plant litter was amended into ~ 50 g of soil at 2 mg C/g soil and then the treated soil was incubated at the room temperature in dark for three months. The activities of soil phenol oxidase, exoglucanase, glucosidase, and glucosaminidase were analyzed 6 hours and 14, 21, 28, 52, 73, and 90 days after the start of incubation. Effects of soil pH on the stabilization of soil enzymes were examined in a 42-day incubation experiment with three replications. To minimize soil enzyme production, microbial activity was inhibited by using cycloheximide, a fungicide at 15 mg/g soil and streptomycin sulfate, a bactericide at 3 mg/g soil. Six treatments were made based upon a 2 x 3 factorial design (2 soils and 3 soil pH levels). Besides the initial slightly-acidic pH, two additional pH values were made by increasing ~0.9 units and ~1.8 units from the initial value, respectively, with 5 M KOH solution. Enzymes were then added into soils as a mixture of horseradish peroxidase, cellulase, laccase, and tyrosinase. Treated soils were incubated at the room temperature in dark for 42 days and analyzed for the activities of peroxidase, exoglucanase, glucosidase, and phenol oxidase 6 hours and 7, 25 and 42 days after the start of incubation. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Soil glucosidase and glucosaminidase activities increased quickly and peaked a few weeks after plant litter addition; this dynamic pattern was independent of plant litter quality. However, microbial production of polymer-degrading enzymes, i.e., cellulase and phenol oxidase showed different patterns after litter addition. Addition of soybean residues or grass materials stimulated microbial cellulase production, but addition of pine needles had little impact. Instead, addition of pine needles stimulated microbial production of phenol oxidase, specifically at the late period of incubation. Among three plant litters, grass materials generally had great impact on microbial production of cellulase and glucosidase, whereas soybean residues exerted more influence on glucosaminidase and pine needles on phenol oxidase. However, soil enzymes could lose activities due to physical and chemical interactions with soil minerals as well as organic matter. The enzymes examined in this study appeared to be more stable and active at higher soil pH.
Publications
- Tian L, Shi W, 2010. Towards a mechanistic understanding of peroxidase controls on soil carbon and nitrogen mineralization. Annual Meeting Abstracts, ASA/CSSA/SSSA Annual Meetings,Long Beach, California.
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Progress 10/01/09 to 09/30/10
Outputs
OUTPUTS: Soil peroxidase activity has been found to be capable of interpreting the variation in soil organic matter content; however, the fundamental mechanisms of peroxidase controls on organic matter degradation are unclear. The objectives of this study were to assess fundamental relationships between soil peroxidase activity and soil C and N mineralization as well as the underlying mechanisms in controlled experiments. Via soil amendments of horseradish peroxidase and/or hydrolytic enzymes, the hypothesis that peroxidase could enhance soil C and N mineralization through improving the bioavailability of carbohydrates and proteins was tested. An arable soil of top 10 cm was collected from an organic farm in Goldsboro, NC. First, the soil was amended with different amounts of horseradish peroxidase and then examined for the activities of peroxidase and hydrolytic enzymes, water-extractable phenolic contents, and potential rates of soil C and N mineralization over a 21-d incubation. Second, peroxidase, cellulase, protease or their combinations were amended into autoclaved soils to examine the enzyme-mediated production of reducing sugars and amino acids. After days of enzyme additions, sterile soils were then inoculated with a small amount of unautoclaved soil for additional 7-day incubation to examine the associations between enzyme-mediated products and the rates of soil C and N mineralization. Furthermore, the effects of phenolic compounds of different complexity on soil hydrolytic enzyme activities were examined by phenolic addition experiments. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
This study improves our understanding on peroxiase-mediated soil organic matter degradation. When peroxidase oxidizes the phenolic moieties of humus and lignin, thereby producing simple phenolic compounds for microbial assimilation, it may simultaneously produce bioavailable compounds such as sugars and peptides that are otherwise bound to soil humus. We observed that soil addition of peroxidase produced phenolic compounds that were able to inhibit the activities of soil hydrolytic enzymes and thus exerted negative effects on soil organic matter degradation. By contrast, we found that reducing sugars or amino acids as a fraction of dissolved organic C or N were increased in soil addition of peroxidase alone and combination of peroxidase and hydrolytic enzymes. Soil C mineralization in the treatment of both cellulase and peroxidase addition was about 15% more than the treatment of cellulase alone and 30% more than the treatment of peroxidase alone and control soil. Similarly, soil N mineralization in the treatment of protease and peroxidase addition was about 40% greater than protease alone and 60% greater than the treatment of peroxidase alone and control soil. Our results appeared to support that peroxidase mediated soil organic matter mineralization through controls on the availability of carbohydrates and peptides more than simple phenolic compounds.
Publications
- Tian L, Dell E, Shi W, 2010. Chemical composition of dissolved organic matter in agroecosystems: Correlations with soil enzyme activity and carbon and nitrogen mineralization. Applied Soil Ecology 46, 426-435.
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Progress 10/01/08 to 09/30/09
Outputs
OUTPUTS: This project aims to address whether the chemistry and biology of dissolved organic matter can be used to predict soil C and N mineralization in arable soils. The study was conducted in a farming systems-unit, located in the Center for Environmental Farming Systems, Goldsboro, NC. This unit was established in 1999 and included five farming systems: conventional farming, organic farming, integrated crop and livestock, plantation forestry, and old agricultural field succession. Dissolved organic matter was analyzed for C and N content, aromaticity determined by UV absorbance at 280 nm, phenolic compounds, amino acid-N, reducing sugar-C, and C and N mineralization potential. Soil was analyzed for total soil C and N, microbial biomass C and N, soil pH, and the activity of soil enzymes including peroxidase, phenol oxidase, cellulase, beta-glucosidase, and betaglucosaminidase. Not only did the concentration of dissolved organic C (18.4 - 60.2 mg/kg soil) and dissolved organic N (6.7-7.9 mg/kg soil) differ in the five ecosystems, but also the chemical composition of dissolved organic matter varied. Integrated crop and livestock system held the highest concentration of dissolved organic C as well as phenolic compounds, reducing sugars, and amino acids, whereas conventional farming system contained relatively lower amounts of respective chemicals. We observed that more than 80% of dissolved soil organic C and N was mineralized at varying rates among the five ecosystems. Coefficient of variation in the concentration of dissolved organic carbon or nitrogen was greater than that of total soil organic carbon or nitrogen, respectively, indicating that dissolved organic matter could be a sensitive soil parameter to manifest soil processes and management practices. Indeed, the chemistry and biology of dissolved organic matter, together with soil enzyme activities appeared to characterize fundamental differences in soil processes associated with specific agro-ecosystems. In the integrated crop and livestock system, low activities of phenol oxidase and peroxidase led to the high concentration of phenolics in dissolved soil organic matter, which in turn inhibited the activity of glucosidase and resulted in the slow degradation of reducing sugars. Due to possibly slow turnover of dissolved organic matter, soil organic C or N mineralization was low. As compared to cropping systems, forest plantation and natural succession of old agricultural fields were lower in inorganic nitrogen. Low nitrogen availability appeared to stimulate the activity of nitrogen-acquiring soil enzymes, e.g., glucosaminidase, thereby causing rapid turnover of nitrogen-containing compounds, amino acids. Soil C and N mineralization were significantly correlated with relative abundances of reducing sugars and amino acids (i.e., the ratio of reducing sugars-C to dissolved organic C and the ratio of amino acids-N to dissolved organic N). Our results indicated that the chemistry and biology of dissolved organic matter were coupled with soil C and N mineralization and thus dissolved organic matter could be an important soil property for making informed management decisions. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
This project has addressed a fundamental and applied question, whether or not dissolved soil organic matter can be used to assess management-associated soil and ecological processes. The research findings have provided new information on the dynamic and sensitivity of dissolved organic matter with soil and agricultural management practices and therefore may help the development of more sensitive indicators for learning about management impacts in a timely manner.
Publications
- No publications reported this period
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Progress 10/01/07 to 09/30/08
Outputs
OUTPUTS: This project aims to provide baseline information on dissolved soil organic matter (DOM) in various farming systems and quantify the relationships of DOM with basic soil chemical and biological properties. DOM, defined as organic substances of less than 0.45 micrometer in aqueous solution, is produced largely from the depolymerization of soil organic matter and the decay of plant litters via microbial enzymatic reactions. It comprises a range of organic compounds, including those with hydrophilic versus hydrophobic characteristics and aromatic versus aliphatic structure. The properties and structures of these compounds partially control their fate in agricultural soils. Studies on DOM in a range of ecosystems have led to a conclusion that DOM can be an important controller of many soil and ecosystem processes, including soil C sequestration, nutrient cycling, and pollutant detoxification, and the ecological roles of DOM are dictated by its chemical composition and biodegradability. Despite the critical roles played by DOM in soils, its chemistry and biodegradability are poorly understood in agricultural systems. This project seeks to fill this crucial knowledge gap by characterizing the chemistry and biodegradability of DOM in agricultural soil environments. In order to reliably examine relationships between DOM and other soil chemical and biological properties, we need to collect DOM that differs greatly in quantity and quality. The Center for Environmental Farming Systems (CEFS), Goldsboro, NC is the suitable study site because the CEFS comprises five different management systems: conventional farming, organic farming, integrated crop and livestock, plantation forestry, and old agricultural field succession. These systems were thoughtfully designed and initiated in 1998. Since then, the systems have been well managed and operated for about 10 years by faculty and staff from North Carolina State University. We collected surface soils using coring techniques from the five management systems in the spring 2008 before annual-crop seedling or perennial-vegetation growth. By excluding plant root exudates, which are often environmentally short-lived, our sampling schedules allow us to examine DOM mainly from soil organic matter. At least 15 soil cores were collected from each field plot via random patterns and then pooled to form representative soil samples. DOM was analyzed for C and N content, aromaticity determined by UV absorbance at 280 nm, phenolic compounds, amino acid-N, reducing sugar-C, and C and N mineralization potential. Soil was analyzed for total soil C and N, microbial biomass C and N, soil pH, and the activity of soil enzymes including peroxidase, phenol oxidase, cellulase, beta-glucosidase, and betaglucosaminidase. We observed that DOM parameters, i.e. dissolved organic C, UV absorbance at 280 nm, phenolic compounds, and amino acids varied among the five farming systems more greatly than the soil parameters, i.e., soil C and N, microbial biomass C and N and soil pH. Our results suggested that DOM was dynamic and sensitive to farming practices and thus can be potentially used to assess management impacts on soil processes. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
This project has addressed a fundamental and applied question, whether or not dissolved soil organic matter can be used to assess management-associated soil and ecological processes. The research findings have provided new information on the dynamic and sensitivity of dissolved organic matter to soil and agricultural management practices and therefore may help the development of more sensitive indicators for learning about management impacts in a timely manner.
Publications
- No publications reported this period
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