Progress 10/01/00 to 09/30/05
Outputs
Additions of carbon-rich agricultural amendments can have positive impacts on soil by increasing soil organic matter (SOM) levels and phosphorus (P) availability by increasing the concentration of water-soluble P (WSP). The degree of P saturation (DPS) has been shown to be a suitable initial indicator of P loss potential from agricultural soils to surface waters. The objectives of this study were to determine the relationship between SOM levels and WSP and to investigate how SOM affects the DPS values of agricultural soils of the northeastern U.S. The soils were divided into 3 SOM classifications depending on their loss-on-ignition contents and analyzed for WSP, modified-Morgan soil test P (STP) and oxalate-extractable P, Al, and Fe. The slopes of the regression lines of WSP as a function of STP were 0.050, 0.036, and 0.021 (mg WSP kg-1 soil / mg STP kg-1) for the low, medium, and high SOM classification groups, respectively. This suggests that SOM decreases the level
of WSP found in soil solution. The mechanism for the decrease in WSP at higher SOM levels is believed to be due to two factors that contribute to lower DSP with increasing SOM levels: 1) higher metal oxide content of soils with higher native SOM levels and 2) competitive sorption of the dissolved organic matter fraction of SOM onto metal oxide sorption sites. A change point at 15% DPS, which corresponds to a modified-Morgan STP value of 14 mg P kg-1, was derived as the point where WSP release becomes greater with increasing levels of STP.
Impacts
This study shows that organic matte level of soils can affect the chemical characteristics of the soil which in turn results in changes in phosphorus bioavailability.
Publications
- No publications reported this period
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Progress 10/01/03 to 09/30/04
Outputs
The use of fluorescence spectrometry has been suggested as a method to determine the extent of natural organic matter humification. Humification indices are calculated by dividing fluorescence intensity at longer wavelengths by intensity at shorter wavelengths. The results show that humification index values are sensitive to DOM concentration in solution an exact correction using explicit correction factors for both primary and secondary inner filtration effects was shown to give humification index values which are concentration invariant. A study was conducted to investigate the effects of animal- and legume-based cropping systems in place for six to eleven years on soil organic matter and P soil sorption/desorption chemistry. Two cropping systems received animal manure and two other systems were primarily legume-based rotations. The amount of dissolved organic matter (DOM) desorbed was higher in the treatment plots that received manure than in the unamended plots,
but not for plots that only received legume residue. Similar to the DOM effect, the two cropping systems that received animal manure had higher concentrations of water soluble P than unamended plots. There was a linear relationship between DOM concentration and water-soluble P concentration in soil:water extracts of the four cropping systems soils indicating the importance of DOM in controlling the concentration of water-soluble P. This study shows that cropping systems that include animal manure can increase soil P availability. Four types of biosolids resulting from different stabilization processes used at municipal treatment plants and three animal manure sources were evaluated for potential use as alternative nutrient sources for phosphorus. Soil test P levels measured by the Morgan and anion exchange strip methods were highly correlated. The P uptake by ryegrass agreed well with predicted P availability. Worm casts have been proposed as a source of plant nutrients which also
contributes organic matter to the system. Soil NO3- increased rapidly in the cast and compost treatments by 30 days of incubation, attaining 290 and 400 mg N kg-1 soil, respectively. Nitrate in the cast treatment, however, declined to 120 mg N kg-1 soil by day 70. All organic amendments significantly (p<0.05) improved wheat P uptake compared to either the nonamended control or the mineral fertilizer treatment. Microbial respiration (CO2 production) was significantly (p<0.05) greater (2X) in compost-treated compared to cast-treated soil for 35 days of incubation. Afterwards, similar rates were observed. Both, however, generated significantly (p<0.05) greater CO2 than either the mineral fertilizer or control treatments. Microbial biomass was significantly (p<0.05) lower in cast treated soil compared to compost-treated soil for 35 days. Cast materials were shown to differ significantly from compost and mineral fertilizer treatments in the effects on microbial respiration, microbial
biomass, and plant nutrient uptake.
Impacts
This study shows that animal manure application can affect the chemical characteristics of the soil which in turn results in changes in phosphorus bioavailability.
Publications
- Ohno, T., T.S. Griffin, M. Liebman, and G.A. Porter. 2004. Green- and animal-manure based cropping systems effects on soil phosphorus and organic matter. Agric. Ecosystem Environ. (in press).
- Montgomery, M., T. Ohno, T.S. Griffin, C.W. Honeycutt and I.J. Fernandez. 2004. Phosphorus mineralization and bioavailability in soils amended with biosolids and manures. Bio. Agric. Hort 22:321-334.
- Ohno, T., P. Chen, E. Mallory, E. K. McCormick, S. Shah. 2004. Sorption of crop residue-derived dissolved organic matter by soils and its relevance to allelopathic expression. Alleopathy J. 14:13-22.
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Progress 10/01/02 to 09/30/03
Outputs
To minimize purchased inputs, sustainable agricultural systems often use green- or animal-manure as a alternative nutrient source for nonleguminous crops. It was clearly demonstrated in the a field study that organic matter isolated from animal manure and plant biomass have differential effects on both the soil organic matter chemistry and soil phosphorus chemistry. It was hypothesized that an important factor in the mid- to long-term effect of organic matter addition is the chemical characteristics of the material being amended. The laboratory based study was conducted to determine the molecular weight and E2/E3 ratios of dissolved organic matter isolated form crop residues, crop root biomass, and animal manures. High performance size exclusion chromatography was used to determine the molecular weight of these dissolved ligands. The results showed that the dissolved organic matter from these diverse range of materials are poly-disperse with two to five distinct size
fractions present in solution. The weight-averaged molecular weight for the crop residue, root biomass, and manures were 5490, 3010, and 3880, respectively. Sorption experiments with soil minerals demonstrated that sorption of the organic matter ligands was significantly related (P = 0.026) to increasing molecular weight of the ligand and that there was preferential sorption for more humified fractions of the dissolved organic matter. This suggests that the sorption of dissolved organic matter is sensitive to the chemical nature of the ligand. The differential ability of crop biomass to affect the sequestration of carbon and phosphorus bioavailability may be partially dependent on the initial sorption of the organic matter to soil surfaces.
Impacts
This study shows that animal manure application can affect the chemical characteristics of the soil which in turn results in changes in phosphorus bioavailability.
Publications
- Chaoui, H.I., L.M. Zibilske, and T. Ohno. 2003. Effects of earthworm cast and compost on soil microbial activity and plant nutrient availability. Soil Bio. Biochem. 35:295-302.
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Progress 10/01/01 to 09/30/02
Outputs
The specific objectives of the study conducted were to investigate how the different cropping systems affect (1) the quantity-intensity relationship of soil P and (2) the quantity and chemical characteristics of DOM isolated from the soils. The addition of organic amendment significantly increased total soil C content for the ECO study at the P < 0.05 level and for GF study at the P < 0.10 level. The ECO and GF studies incorporated beef manure as a component of amendment materials, while the LER and PR studies which did not increase the total and DOM C content in the soils were green manure based rotations. Similar to the total C data, the organic amendment treatment had significantly greater DOM content for the ECO study at the P < 0.05 level and for GF study at the P < 0.10 level, but no significant differences for the green manure based rotations. The contrasting ability of beef manure and green manure amendments to increase the total C content and DOM levels of
the soil may be related to chemical nature of organic matter ligands released from these materials. Studies have shown that higher molecular weight fraction of organic matter are preferentially sorbed to soil components. Sorption may be important step in the stabilization of C to more recalcitrant forms. The fluorescence-based HIX and UV absorbance-based E2/E3 ratio were used to investigate the spectroscopic properties of the DOM extracted from the cropping system treatments. The HIX values were not significantly affected by the addition of organic amendment, however there was a strong influence on the cropping system on HIX values. The E2/E3 ratio did show a organic amendment treatment effect at the P < 0.1 level with the E2/E3 value for the +OM treatment being lower than in the -OM treatment for the ECO cropping system. The total P content of the soils varied widely amongst the different cropping systems due to differing management practices. There was no organic amendment effect on
total P which is due to both the balanced P inputs into both during the study period and the reserve P present in soils. The water-soluble P concentration was the P parameter which had an organic amendment effect significant at the P < 0.05 level. Similar to the DOM results, only the ECO cropping study had a statistically significant result with the organic amended plots having higher soluble P levels than in the unamended plots. The relationship between soluble P and DOM content across all four cropping studies was highly significant. This strong correlation suggests the important role of DOM in controlling the concentration of soluble P in soils. Furthermore, the ability of one regression to fit the data for all four cropping systems suggests the quantity of DOM is the most important factor in controlling soluble P and that any differences in the chemical properties of DOM are secondary. Quantity/Intensity isotherms trends also followed the organic matter data with the manured soils
showing differences and the green-manure soils showing no effect of organic matter treatment on soil P chemistry.
Impacts
This work shows that the addition of manure inputs will alter both the quantity and chemical properties of organic matter in soils. However, the use of a legume based green manure system may not alter the levels of soil organic matter. Thus, the use of animal manure in agricultural systems may be much more advantageous than green-manure systems.
Publications
- Ohno, T. 2002. Response to comment on "Fluorescence inner filtering correction for determining the humification index of dissolved organic matter". Environ Sci. Technol. 36:4196.
- Ohno, T. 2002. Fluorescence inner filtering correction for determining the humification index of dissolved organic matter. Environ. Sci. Technol. 36:742-746.
- Ohno, T., M.Y. Horesh, K.A. Merritt, and R. Wagai. 2002. Calcium and pH effects on salicylic acid phytotoxicity. Allelopathy J. 9:19-25.
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Progress 10/01/00 to 09/30/01
Outputs
The chemical nature of natural organic matter has been investigated intensively due to its involvement in environmental processes such as the complexation of trace metals and C cycling in the ecosystem. Natural organic matter is formed through a humification process which converts specific, lower molecular weight organic compounds derived from plant and animal products to more condensed, higher molecular weight polymers primarily by microbial synthesis. Soil organic matter has become recognized for its critical role in environmental issues related to long-term sustainability of agroecosystems and the terrestrial sequestration of C. The use of fluorescence spectrometry has been suggested as a simple method to determine the extent of natural organic matter humification by quantifying the red-shifting of fluorescence emission which occurs with increasing humification. Humification indices are calculated by dividing fluorescence intensity at longer wavelengths by
intensity at shorter wavelengths. These indices calculated without any specific efforts to standardize dissolved organic matter (DOM) concentration will result in index values that vary with DOM concentration due to fluorescence inner filtering effects. This study critically evaluated the effect of DOM concentration on humification index determination using organic matter isolated from field corn extract, soil:water extract, and soil fulvic acid. The results show that humification index values are sensitive to DOM concentration of the solution and are linear with respect to transmittance of the solution at the 254 nm used as the excitation wavelength. An approximate correction for DOM is to exploit the linear nature of the regression fit and determine index values at the extrapolated 100% transmittance value. An exact correction using explicit correction factors for both primary and secondary inner filtration effects was shown to give humification index values which are concentration
invariant when absorbance of the solution at 254 nm was less than approximately 0.3 units. Defining the humification index as the fluorescence intensity in the 300 to 345 nm region divided by the sum of intensity in the 300 to 345 nm and 435 to 480 nm regions was statistically advantageous. This study suggests that for quantitative results which can be used to compare humification of natural organic matter across different studies, correction of the fluorescence emission spectra for inner filtration effects is needed. With due consideration of these DOM concentration effects, the fluorescence-based HIX provides a robust tool for determining the extent of humification, and thus the stability of the organic matter being investigated.
Impacts
Although organic matter is present as a continuum, it may be conceptualized as being composed of at least three pools at different stages of humification: active, labile pool with turnover time <1 year; intermediate pool with turnover times from years to centuries; and a passive, stable pool persisting in soils for thousands of years. With increased awareness of the role of natural organic matter in the global carbon cycle, tools such as the one investigated in this work are needed to evaluate the effects of environmental and soil management perturbations on the distribution of organic matter pools in terrestrial and aquatic ecosystem.
Publications
- Ohno, T. 2001. Oxidation of allelopathic cinnamic acid derivatives by soil and its relevance to phytotoxicity. J. Environ. Qual. 30:1631-1635.
- Ohno, T. and Doolan, K. 2001. Effects of red clover decomposition on phytotoxicity to wild mustard seedling growth. J. Appl. Soil Ecol. 16:187-192.
- Ohno, T., Doolan,K., Zibilske, L.M., Liebman, M., Gallandt, E.R., and Berube, B. 2000. Phytotoxic effects of red clover amended soils on wild mustard seedling growth. Agric. Ecosystems Environ. 78:187-192.
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