Progress 01/01/00 to 09/30/04
Outputs
The initial focus studied changes in soil nitrate-N above fragipan soils. These studies used suction lysimeters implanted into soils at various depths down to the fragipan. Residual nitrate-N after cropping was reduced by 80% during the period of late fall through early spring. Rainfall is concentrated during this period with little evapo-transpiration from a vegetative canopy. Another study used buried lysimeter pans in a non-fragipan soil profile to study movement of nitrate-N and pesticides in an upland soil profile. This study had manure, N-containing fertilizer, and pesticides (atrazine and alachlor) applied to surface plots. Profile leachate results indicated that soon after application, leachate contained high levels of the pesticides which steadily declined over the next two months. Pesticide leaching was not affected by manure application rates. Nitrate-N exceeded 10 mg/L 38% of the time under spring applications of N fertilizer compared to 15% of the time
under spring manure treatments. However, after three years of manure application, nitrate-N concentration in leachate under these plots was significantly higher than fertilizer treated plots. The project then focused more on soil water quality related to P adsorption in surface soils using both fragipan and non-fragipan containing soils. The first study added rates of inorganic P, the soils were incubated and then extracted with soil test extractant (Mehlich III). The amount of change in soil test P depended on the initial P soil test value. At low values, more P was required to change soil test and at higher initial values, less P was required to change soil test. When initial soil test P exceeded 200 mg/kg, the change was nearly linear. A second study determined sorption fractions and characteristics using 18 chemically diverse soils. Total sorbed P was highly related (R2 = 0.90) to oxalate extractable iron and aluminum. Total amounts sorbed until solution reached 1 mg P/L ranged
between 82 and 403 mg P/kg soil.
Impacts
Fragipan soils have the ability to reduce significant quantities of residual nitrate-N in perched water tables. However, upland soils have some ability to leach significant amounts of nitrate-N and pesticides. Soils have the ability to sorb and hold considerable amounts of P that otherwise have the potential to contaminate either groundwater or surface water. The amount of P that a soil can sorb is highly related to oxalate extractable Fe and Al. Soils testing low in P initially require more P to change soil test levels. The amount of P required to change P soil test values decreases with increase in P soil test.
Publications
- Thom, W. O. and J. Dollarhide. 2002. Phosphorus soil test change following the addition of phosphorus fertilizer to 16 Kentucky soils. Cooperative Extension Service, University of Kentucky, Agronomy Notes Vol. 34 Two
- DAngelo, E., M. Vandiviere, W. Thom and F. Sikora. 2003. Estimating soil phosphorus requirements and limits from oxalate extract data. J. Environ. Qual. 32:1082-1088.
- Stoddard, C. S., J. H. Grove, M. S. Coyne, and W. O. Thom. 2005. Fertilizer, tillage and dairy manure contributions to nitrate and herbicide leaching. J. Environ. Qual. 34:
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Progress 01/01/03 to 12/31/03
Outputs
Studies on soil water quality related to phosphorus adsorption in surface soils was expanded during this past year. The purpose of these expanded studies was to determine whether easily measurable soil characteristics were related to soil phosphorus requirements and movement into soils. The soil phosphorus requirement is the phosphorus necessary to maintain a predetermined phosphorus concentration in soil solution. The phosphorus requirement was determined for 18 chemically diverse soils from sorption isotherm data (corrected for native sorbed phosphorus). Results indicated that oxalate-extractable iron and aluminum were highly correlated (R2 = 0.90) with total sorbed phosphorus. One benefit of determining the phosphorus requirement is to determine the maximum amount of phosphorus that can be added to a soil to reach an acceptable level in soil solution. The maximum amount was calculated as the difference between the phosphorus requirement and the native level already
in the soil. For the 18 soils studied, the maximum amount of phosphorus that could be added for reaching 1 mg per L in solution ranged between 82 and 403 mg phosphorus per kg of soil indicating that significant amounts could be added to the 18 soils before they would pose a significant threat to either groundwater or surface water quality based on this criterion. These research results need to be verified across a wider range of soils, and they need to be linked to more common soil extractants such as Mehlich III. Also, in fragipan soils, will a phosphorus laden layer develop due to significant downward movement.
Impacts
Predicting a soils' ability to contribute to higher phosphorus concentrations in either groundwater or surface water can be advanced with the use of sorption parameters. The maximum amount of phosphorus a soil can hold minus the existing amount predicts an amount that can be added without exceeding either groundwater or surface water quality limits.
Publications
- D'Angelo, E., M. Vandiviere, W. Thom and F. Sikora. 2003. Estimating soil phosphorus requirements and limits from oxalate extract data. J. Environ. Qual. 32:1082-1088.
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Progress 01/01/02 to 12/31/02
Outputs
Soil water quality related to phosphorus adsorption in surface soils was studied during this past year. In this study, 3 soils exhibiting fragipan characteristics were studied along with 13 other soil series not exhibiting fragipan characteristics in the subsoil. This project studied the rate of phosphorus soil test change with the addition of an inorganic source of phosphorus. Results indicated that the rate of soil test P change depended on the initial soil test P with larger amounts of P required to change soil test P one unit at lower initial test and that smaller amounts of added P were required to change soil test P one unit at higher initial soil test levels. When initial soil test P was >200 lbs/acre, only about 1.0 lb P was required to change soil test P 1 lb/acre. At initial soil test P values <30 lbs/acre, from 3.5 to 11 lbs P was required to change soil test P one unit. When P is added to a surface soil at low soil test P levels, it is expected that little
movement downward within the profile will occur due to the high capacity to adsorb P in the surface soil. However, if the soil test P is already above 200 lbs/acre, it is expected that P as the soluble inorganic compound can move more rapidly below the surface soil and therefore be a potential pollutant in water discharging on side slopes from above the fragipan.
Impacts
High P laden water could originate from above fragipans when surface soil test P is >200 lbs P/acre as the surface soil has little capacity to adsorb additional added P. This study can help more accurately predict soil P carrying capacity in order to minimize P pollution of waters.
Publications
- Thom, W. O. and J. Dollarhide. 2002. Phosphorus soil test change following the addition of phosphorus fertilizer to 16 Kentucky soils. Cooperative Extension Service, University of Kentucky, Agronomy Notes Vol. 34 (2).
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Progress 01/01/01 to 12/31/01
Outputs
The objective was to prepare a detailed examination of the water transport and quality above a well-defined fragipan in western KY. Depth was determined on a 1 ha site at Princeton, soil cores were collected and replaced with peizometers. Ten data logging wells were also installed. From 1/2000 to present, water samples were collected monthly. Depth to water, temp., pH, redox, nitrate-N, ammonium-N, ortho P, chloride, iron (III), iron (II), and DOC data were collected. The soil cores were characterized by 10 cm increments and data collected for microbial analysis, pH, % OM, and total N. The fragipan does not follow the surface topography, nor does it occur at a uniform depth below the surface. Depth below the surface ranged from 50 to 105 cm (mean 81 cm +/- 10 cm). Table 1. Characterization of soil above a western KY fragipan. Depth(cm) Total N(Lb/A) %OM pH 0 - 10 3743a 3.52a 6.62a 10 - 20 1465b 1.33b 6.60a 20 - 30 949c 0.76cd 6.13b 30 - 40 744d 0.52cde 5.61c 40 - 50
566de 0.34de 5.10d 50 - 60 484e 0.33de 4.98de 60 - 70 605de 0.33de 5.03de 70 - 80 407e 1.02bc 5.03de 80 - 90 354e 0.19e 4.77e Fragipan 381e 0.21e 4.84e Values in the same column followed by the same letter(s) are not significantly different at p<0.05. Although there is an increase in total N, % OM and pH above the fragipan, the only significance is with % OM. Analyzing the 20 cm of soil immediately above the fragipan regardless of depth below the surface resulted in the data in Table 2. Table 2. Analysis of 20 cm of soil immediately above fragipan. Depth(cm) Total N(Lb/A) %OM pH 20 - 10 above 504a 0.29a 5.03a 10 - 0 above 416b 0.68a 5.02a Fragipan 381b 0.21a 4.84b Values in the same column followed by same letter are not significantly different at p<0.05. It appeared that changes in soil properties became significant only at 10 - 20 cm above the level of the fragipan, not immediately at the interface with the overlying soil. Biological assessments of nitrate reducers (using log MPN)
was higher near the fragipan compared to a depth increment located 40 to 50% between the soil surface and the fragipan. Nitrate reducers made up an increasing proportion of the facultative anaerobe population at the fragipan. Nitrogen immobilization rather than N mineralization was more characteristic of soils below the surface until close to the fragipan. In July, when the soil samples were taken, denitrification was not evident at 10 cm or more below the surface. However, the nitrate reducers were stratified at the fragipan surface. Considerable data has been collected on water quality but the data analysis has not been completed. Subsequent study at this site will focus on mapping solute flow in saturated and unsaturated conditions, examining the influence of surface amendments on N transformations in the water, and removing additional cores to further examine N reduction dynamics at the fragipan-soil interface.
Impacts
Chemical and biological conditions at the soil-fragipan interface appear to be significantly different than the overlying soil and have the potential to greatly influence nitrogen dynamics that can lead to significant nitrogen removal. There is a potential for soils with underlying fragipans to be effective removers or reducers of decomposable materials containing significant amounts of soluble N.
Publications
- Coyne, M.S. and J.A. Thompson. 2000. Stratification of N transformations above a fragipan in western Kentucky. Southern Branch of ASA, Lexington, KY, January 30-31, 2000
- Coyne, M.S., J.A. Thompson and L. Murdock. 2000. Stratification of denitrifiers above a fragipan in western Kentucky. KWRRI Annual Symposium, Lexington, KY, Feb. 24-25, 2000.
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Progress 01/01/00 to 12/31/00
Outputs
Due to Dr. Thompson's departure for a position at North Carolina State University, no report was submitted.
Impacts
(N/A)
Publications
- No publications reported this period
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