Progress 10/01/06 to 09/30/09
Outputs
OUTPUTS: We used laboratory column and batch studies, and soil carbon fractionation to demonstrate that in general, sodium sulfate rich waters leach more organic carbon from semi-arid soils than water dominated by calcium and chloride ions. Rainwater was also found to leach large amounts of soil organic carbon, in quantities equal to or exceeding sodium sulfate dominated waters. Therefore, irrigation water TDS may not always be a predictor of soil organic carbon losses during irrigation. The dissolution of soil carbonates was correlated to increases in soluble organic carbon. This suggests that soluble organic carbon is trapped in soil carbonates and that the dissolution of these minerals leads to soil organic and inorganic carbon losses in semi-arid, calcareous soils. In practice, the selective removal of sodium and sulfate ions from irrigation waters is not cost-effective due to the large quantities of water used in agriculture. However, hard, alkaline, calcium dominated irrigation water sources should be favored over sodium dominated waters when possible, as these may limit the dissolution of SOC-rich soil carbonates. On the positive side, SOC lost from the root zone enhances denitrification below the root zone and controls nitrate groundwater pollution. In addition, irrigated, semi-arid calcareous soils may increase carbon sequestration below the root zone via the dissolution and leaching of carbonates and bicarbonates, and soluble organic carbon forms. This (published) information will be of interest to irrigation specialists, and carbon-cycling scientists interested in C sources and sinks in terrestrial environments. PARTICIPANTS: Collaborator in manuscript review and preparation. James L. Walworth, Professor, Department of Soil, Water & Environmental Sciences, Shantz Bld. Room 429. The University of Arizona. Tucson, AZ 85721 TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Irrigation water quality and soil organic matter content influence crop yields and soil properties such as salinity and soil particle aggregation. We used laboratory column and batch studies, and soil carbon fractionation to study potential organic carbon (OC) losses from a Typic Torrifluvent with 0.79% total organic carbon (TOC) and 4.7% inorganic carbon (as carbonates). About 4% of the TOC fraction was determined to be water-soluble organic carbon (SOC). Under saturated flow, a significant amount of SOC (20 to 35%) was lost from this soil (Pima clay loam) with just two pore volumes of irrigation water. Sodium and sulfate-rich waters and rainwater were up to twice as effective at releasing SOC as waters dominated by calcium and chloride ions. Not all OC losses can be attributed to well-known soil particle dispersive effects of sodium and rainwater. Soluble OC losses were also highly correlated to the progressive dissolution of the soil inorganic carbon (IC) fraction. During this research, we applied the use of UV-254nm light absorption as an analog for the quantification of soluble organic carbon to soil extracts. We found this technique, once calibrated, faster to implement and more precise than the tradition high temperature combustion methods to measure soluble organic carbon within the concentration range of this research. We also applied (with modifications) a novel soil carbon fractionation method to quantify the various organic carbon fractions of a calcareous, semi-arid soil with 1.27% total soil carbon. Our findings suggest that most of the soil carbon fraction is in the form of relatively soluble carbonates (0.56%), humic and fulvic acids constituted 0.35% of the soil carbon, including 0.03% soluble organic carbon. The more refractory soil organic carbon forms (lipids, kerogen, and black carbon) constituted the majority (0.44%) of the soil organic carbon. Water quality has a measurable impact on OC and IC losses from OC-poor, carbonate-rich soils. Changes in irrigation water quality may increase or decrease OC leaching from semi-arid soils, depending on the amounts and types of soluble constituents. Additional soil organic carbon losses, while potentially deleterious to the structure and fertility of soils, may have two positive outcomes; they may increase vadose zone denitrification, thereby protecting ground water from common nitrate pollution and they may increase carbon sequestration in and below the root zone of irrigated semi-arid soils.
Publications
- Artiola, J.F. and J.L. Walworth. 2009. Irrigation water quality effects on dissolution and leaching of organic carbon from a semi-arid, calcareous soil. Soil Science. 174(7):356-371, July 2009.
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: We used laboratory column and batch studies, and soil carbon fractionation to demonstrate that in general, sodium sulfate rich waters leach more organic carbon from semi-arid soils than water dominated by calcium and chloride ions. Rainwater was also found to leach large amounts of soil organic carbon, in quantities equal to or exceeding sodium sulfate dominated waters. Therefore, irrigation water TDS may not always be a predictor of soil organic carbon losses during irrigation. The dissolution of soil carbonates was correlated to increases in soluble organic carbon. This suggests that soluble organic carbon is trapped in soil carbonates and that the dissolution of these minerals leads to soil organic and inorganic carbon losses in semi-arid, calcareous soils. In practice, the selective removal of sodium and sulfate ions from irrigation waters is not cost-effective due to the large quantities of water used in agriculture. However, hard, alkaline, calcium dominated irrigation water sources should be favored over sodium dominated waters when possible, as these may limit the dissolution of SOC-rich soil carbonates. On the positive side, SOC lost from the root zone enhances denitrification below the root zone and controls nitrate groundwater pollution. In addition, irrigated, semi-arid calcareous soils may increase carbon sequestration below the root zone via the dissolution and leaching of carbonates and bicarbonates, and soluble organic carbon forms. This (published) information will be of interest to irrigation specialists, and carbon-cycling scientists interested in C sources and sinks in terrestrial environments. PARTICIPANTS: Collaborator in manuscript review and preparation: James L. Walworth, Professor, Department of Soil, Water & Environmental Sciences, Shantz Bld. Room 429. The University of Arizona, Tucson, AZ 85721 TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Irrigation water quality and soil organic matter content influence crop yields and soil properties such as salinity and soil particle aggregation. We used laboratory column and batch studies, and soil carbon fractionation to study potential organic carbon (OC) losses from a Typic Torrifluvent with 0.79% total organic carbon (TOC) and 4.7% inorganic carbon (as carbonates). About 4% of the TOC fraction was determined to be water-soluble organic carbon (SOC). Under saturated flow, a significant amount of SOC (20 to 35%) was lost from this soil (Pima clay loam) with just two pore volumes of irrigation water. Sodium and sulfate-rich waters and rainwater were up to twice as effective at releasing SOC as waters dominated by calcium and chloride ions. Not all OC losses can be attributed to well-known soil particle dispersive effects of sodium and rainwater. Soluble OC losses were also highly correlated to the progressive dissolution of the soil inorganic carbon (IC) fraction. During this research, we applied the use of UV-254nm light absorption as an analog for the quantification of soluble organic carbon to soil extracts. We found this technique, once calibrated, faster to implement and more precise than the tradition high temperature combustion methods to measure soluble organic carbon within the concentration range of this research. We also applied (with modifications) a novel soil carbon fractionation method to quantify the various organic carbon fractions of a calcareous, semi-arid soil with 1.27% total soil carbon. Our findings suggest that the most of the soil carbon fraction is in the form relatively soluble carbonates (0.56%), humic and fulvic acids constituted 0.35% of the soil carbon, including 0.03% soluble organic carbon. The more refractory soil organic carbon forms (lipids, kerogen, and black carbon) constituted the majority (0.44%) of the soil organic carbon. Water quality has a measurable impact on OC and IC losses from OC-poor, carbonate-rich soils. Changes in irrigation water quality may increase or decrease OC leaching from semi-arid soils, depending on the amounts and types of soluble constituents. Additional soil organic carbon losses, while potentially deleterious to the structure and fertility of soils, may be have two positive outcomes; they may increase vadose zone denitrification, thereby protecting ground water from common nitrate pollution and they may increase carbon sequestration in and below the root zone of irrigated semi-arid soils.
Publications
- Artiola, J. F. and J. L. Walworth. 2009. Irrigation water Quality Effects on Dissolution and Leaching of Organic Carbon from a Semi-arid, Calcareous Soil. Soil Science. Acceptance pending Revisions.
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Progress 01/01/07 to 12/31/07
Outputs
Irrigation water quality had significant influence on organic carbon (OC) losses from a cultivated semi-arid climate soil. Soil carbon (C) fractionation and laboratory studies were used to study potential OC carbon losses from this soil, a Typic Torrifluvent, contained 0.79% organic carbon (TOC), 4.7% inorganic carbon (as CaCO3). About 4% of the TOC fraction was determined to be water soluble organic carbon (SOC) and trapped in the soil carbonate fraction.This suggests that the precipitation and dissolution of carbonates is directly correlated to the release of soluble forms of OM trapped in this soil phase.
Impacts
Fresh water sources will have to be managed with increasing attention to their increasing salinity. Present trends suggest that total dissolved solids will continue to increase in irrigation water, due to climate change and increase use of reclaimed water. The cumulative effects of these water quality changes will not only affect salinity-related plant-water relationships such as yields, but also soil-carbon content changes. This research thus far has shown that water quality that favors the dissolution of soil inorganic carbon (carbonates, bicarbonates) also increases the leaching organic carbon forms from soils.
Publications
- Submitted for publication October 2007, and in Review in: Communications in Soil Science and Plant Analysis.
- Soil Organic Carbon influenced by irrigation water quality in a semi-arid climate. J.F. Artiola 2008
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Progress 01/01/06 to 12/31/06
Outputs
Irrigation and aeration of soils leads to significant increase in soil microbial activity in the soil environment with concurrent carbon losses as carbon dioxide. Thus, large changes in soil organic matter (OM) content have been documented as a result of continued agricultural activities. Water can also leach soluble soil constituents below the plow layer and the root zone. Therefore, water quality may also have a significant influence on OM losses from irrigated, cultivated soils. The results of this research show that under optimum conditions significant amounts (up to 3%) of OM can be lost from the top 15 cm of a soil (Pima Clay Loam) with just two pore volumes of water. And, the cumulative OM losses could be up to 15% each season, depending on the irrigation practices. The data also suggest that sodium (high ESP) and sulfate rich waters dissolve significantly higher amounts of OM from this soil. Whereas, water rich in Ca and Cl ions has significantly less impact
on the solubility of soil OM. Rain water (simulated using deionized water) also increased the solubility of soil OM to levels similar to those observed in Na and SO4 rich water. This suggests that water quality could in the future be managed to minimize OM losses from irrigated which are low in OM, particularly in the semi-arid Southwest U.S.
Impacts
Fresh water resources will have to be managed with increasing attention to water quality in the not too distant future. The impact of irrigation water quality on agricultural land will become increasingly important if increased salinity has cumulative negative effect on soils that extends beyond salinity-related plant-water relationships. Significant increases in organic matter removal from soils, if related to water quality, will also become part future management considerations for the sustainability of irrigated lands.
Publications
- Soil Organic Matter influenced by irrigation water quality. 1997. In preparation
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Progress 01/01/05 to 12/31/05
Outputs
To determine with more certainty the influence of specific water quality (ion species) on the removal of OC from soils, batch studies were carried out, initially with mixed results. Batch studies using spiked Ca or Na ion concentrations of up to 5,000 mg/L failed to provide a clear cut separation in the influence of OC from soils by monovalent versus divalent ions. However, again, Na dominated water removed more OC from soil than Ca dominated waters with the exception of the control de-ionized water (DI) which surpassed all other treatments. It appears that, just as with Na dominated waters, the dispersive effect of de-ionized water (similar to rainwater) plays a very important role in the removal or OC from soils. During these experiments it was observed that perhaps OC removal from soils by irrigation water could also be influenced by the dominant counter ions present (Cl-, SO4=). The influence of carbonate and bicarbonate ions was not measured since the Pima clay
loam soil contains >5% CaCO3. Batch studies using an indirect method of OC measurement (UV-254nm) proved to be much more precise than direct methods of OC analysis using combustion methods. Using this spectrometric technique the following trends (statistically different) were observed using tap and CAP and simulated (1000mg/L Ca or Na) waters: NaSO4 > DI > tap > CAP > NaCl > CaSO4 > CaCl. Thus, in general NaSO4 dominated water appears to remove 30% more OC from the Pima Clay Loam soil than the CaCl dominated water. Future studies plan to strengthen and further quantify these trends and validate them using column studies (saturated and unsaturated flow) to better quantify OC losses under more realistically simulated field conditions.
Impacts
Improved soil and water management. Provide more information about carbon cycling (sources and sinks) in the soil environment.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
Batch studies data suggest that significant amounts soil organic matter can be lost from an Arizona agricultural soil (pima clay loam) also suggest that soil organic matter loses are influenced not only by the presence of divalent versus monovalent cations, but also the type of counter ions present, for example chloride versus sulfate ions. Batch studies, although simpler to perform, also remove up to 7 times more OM from the Pima clay loan with comparable one pore volume extractions. However, first flush OM values from columns may exceed 400 mg/L TOC during the first 1/10th of a pore volume. This suggest that column studies may not reflect the true potential OM losses that may occur under field irrigation situations. However, batch studies show greater variability in the data. More batch and column studies will be performed to quantify the differences in OM removal, focusing on the presence of dominant chloride versus sulfate ions in the irrigation water and verify
the observed trends.
Impacts
Improved soil and water management. Provide more information about carbon cycling (sources and sinks) in the soil environment.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
Initial column and batch studies data suggest that significant amounts soil organic matter are leached during irrigation events. One to two % or the total soil organic matter may be leached with two pore volumes of irrigation water. Data using an Arizona agricultural soil (pima clay loam) also suggest that soil organic matter loses by may be influenced by soil particle dispersion. This is in turn influenced by the dominant presence of monovalent ions like sodium or divalent ions like calcium, or the absence of ions (rain water). The observed trends suggest that soluble organic matter loses from this soil increase as follows: Ca dominated < Ca+Na dominated < Na dominated demineralized (rain) water. More studies are needed to verify and quantify these observed trends and evaluate their significance.
Impacts
Improved soil and water management. Provide more information about carbon cycling (sources and sinks) in the soil environment.
Publications
- No publications reported this period
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Progress 07/01/02 to 12/31/02
Outputs
Preliminary laboratory columns (saturated flow) studies have started using fully characterized surface soil (sandy Clay loam) from the Agricultural Research Center of Marana. Initially, groundwater from the Tucson basin is being used to flush organic matter from the soil-packed columns. Pore volume fractions are being analyzed for organic matter, salinity and inorganic carbon. This initial work is being done with very limited funds and only with part-time student assistants. With an MS student, more extensive and detailed laboratory (column) work on the effect of water quality in soil organic matter removal will be conducted this year.
Impacts
(N/A)
Publications
- No publications reported this period
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