January - February 2004: Volume 59, Number 1
Table of Contents
Features
As the planet heats up, will the topsoil melt away?
By Paul D. Thatcher
Research
- Impact of the return to cultivation on carbon (C) sequestration
H.A. Torbert, S.A. Prior, and G.B. Runion
- A statewide assessment of the impacts of phosphorus index implementation in Pennsylvania
W.J. Kogelmann, H.S. Lin, R.B. Bryant, D.B. Beegle, A.M. Wolf, and G.W. Petersen
- Stream bank erosion adjacent to riparian forest buffers, row-crop fields, and continuously-grazed pastures along Bear Creek in central Iowa
G.N. Zaimes, R.C. Schultz, and T.M. Isenhart
- Storm runoff and soil erosion in south Florida as affected bt water table fluctuations
M.R. Savabi, D. Shinde, D.A. Bulgakov, and L.D. Norton
- Applying RUSLE 2.0 on burned-forest lands: An appraisal
G. González-Bonorino and W.R. Osterkamp
- Special Section---Conservation implications of climate change
Departments
- Home Front
- Viewpoint—Jan Vis Kees
- Raise Your Voice
- Notebook
- Conservogram
Impact of the return to cultivation on carbon (C) sequestration
(Full text appears in the Journal of Soil and Water Conservation, Vol.59, No. 1)
H.A. Torbert, S.A. Prior, and G.B. Runion
ABSTRACT: A growing body of science indicates that carbon (C) can be sequestered in soil as a result of changes in land management. Generally, this requires land be taken out of cultivated agriculture; however, it has been postulated that gains in soil C can be quickly eliminated with return to cultivation. The objective of this study was to examine the impact of converting land back into cultivated agricultural management on C sequestration within two different soil types. Soil samples from nine depth increments (0-5, 5-10, 10-15, 15-30, 30-45, 45-60, 60-75, 75-90, 90-105 cm) (0-2, 2-4, 4-6, 6-12, 12-18, 18-24, 24-30, 30-36, 36-42 in) were collected from a Blanton loamy sand (loamy, siliceous, semiactive, thermic Grossarenic Paleudults) and an Urbo clay loam (fine, mixed, active, acid, thermic Vertic Epiaquepts) in central Alabama, USA, that were under different land management systems. Management systems included forest, permanent pasture, and pasture converted to continuous cultivation for 1 and 2 years. Within the loamy sand soil, land management also included continuously cultivated (>40 yr), weedy-fallow for 5 years, and returned to cultivation after weedy-fallowed for 4 years. Soil samples were analyzed for total nitrogen (N), organic C, and soil C:N ratio. The clay loam soil had higher capacity to sequester C [147 Mg ha-1 (66 tons ac-1) for pasture], than the loamy sand soil [74 Mg ha-1 (33 tons ac-1) for pasture]. Little difference was observed between the forested soil and the permanent pasture in the clay loam soil, with 139 Mg ha-1 (62 tons ac-1) and 147 Mg ha-1 (66 tons ac-1), respectively. In the loamy sand soil, large differences were observed for C between the forested and the permanent pasture sites, with 127 Mg ha-1 (57 tons ac-1) and 74 Mg ha-1 (33 tons ac-1), respectively. Results indicate that the vulnerability of soil to lose sequestered C will likely depend on soil type. The clay loam soils, although having higher levels of C, lost 55% of its C with 2 years of cultivation, while the loamy sand soil showed little significant loss of C content [below 0-5 cm (0-2 in)] within the same time frame.
Keywords: C sequestration, land management, organic C, soil type, tillage, total N
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A statewide assessment of the impacts of phosphorus index implementation in Pennsylvania
(Full text appears in the Journal of Soil and Water Conservation, Vol.59, No. 1)
W.J. Kogelmann, H.S. Lin, R.B. Bryant, D.B. Beegle, A.M. Wolf, and G.W. Petersen
ABSTRACT: Phosphorus (P) based nutrient management regulations may affect the viability of agricultural enterprises in Pennsylvania. Identification of areas likely to be affected by impending P-based regulations will allow regulators and conservation officials to better target technical and financial assistance. A statewide GIS analysis based on an extensive soil testing database and available geospatial data (including land cover, streams, and livestock density) found that various regions of Pennsylvania would be affected by the P-index restrictions for different reasons. In the southeast and parts of the northeast, high soil test P levels associated with intensive animal agriculture required a full assessment of P source and transport factors under the P-Index. In north- and south-central and southwest Pennsylvania, the P-index assessment was required because of the proximity of much of the region’s farmland to surface waters. Additionally, nearly half of agronomic soil samples exceeded the optimum P level for crops suggesting widespread over fertilization and an ongoing build up of soil P stocks. Soil P was found to increase with increasing animal density and the highest animal density areas had a large number of nutrient impaired streams. When samples were separated based on cover type, croplands exhibited the highest P levels, followed by grasslands and then pastures. Finally, a weighted combination of the percentage of soil samples exceeding 200 ppm P and the proportion of agricultural lands within 150 ft (45.7 m) of streams indicated that southeastern Pennsylvania, especially Lancaster County, would be most affected. How farm operators adapt to P-based nutrient management, via on- and off-farm strategies, will determine the severity of the impact and the necessity of government assistance.
Keywords: Animal density, GIS, nonpoint source pollution, nutrient management, phosphorus index, soil phosphorus, water quality
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Stream bank erosion adjacent to riparian forest buffers, row-crop fields, and continuously-grazed pastures along Bear Creek in central Iowa
(Full text appears in the Journal of Soil and Water Conservation, Vol.59, No. 1)
G.N. Zaimes, R.C. Schultz, and T.M. Isenhart
ABSTRACT: Row-crop agriculture, continuous-grazing, and stream channelization, have accelerated stream bank erosion and increased sediment load. Stream bank erosion rates and total soil loss were compared among riparian forest buffers, row-crop fields and continuously grazed pastures along a continuous 11 km (6.8 mi) stream reach in central Iowa. Exposed erosion pins were measured to estimate stream bank erosion rates, approximately every month from June 1998 to June 1999, except during the winter months. Total stream bank soil losses for each treatment were estimated from the mean bank erosion rate, mean bulk density, and the total stream bank eroding area. Row-crop fields had the greatest stream bank erosion rate and total soil losses followed by continuously grazed pastures while riparian forest buffers had the lowest. If riparian forest buffers had been established along all of the non-buffered segments of the 11 km (6.8 mi) stream reach, total stream bank soil loss would have been reduced by approximately 72%.
Keywords: Bank soil loss, bulk density, channelization, eroding bank length, fluid entrainment, freeze/thaw
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Storm runoff and soil erosion in south Florida as affected by water table fluctuations
(Full text appears in the Journal of Soil and Water Conservation, Vol.59, No. 1)
M.R. Savabi, D. Shinde, D.A. Bulgakov, and L.D. Norton
ABSTRACT: One goal of the Everglades Restoration Plan in south Florida is to increase water flow to the Everglades National Park, which may result in an elevated water table in parts of Miami-Dade County. Useful hydrologic data concerning rainfall-runoff relations, soil erosion, and water holding capacity are limited for this county. The objective of this study was to measure storm runoff, soil water retention curve, and soil erosion for the dominant soils in south Miami-Dade County under different water table regimes. Our results indicated that the rainfall-runoff relations were similar for the three dominant soil types (Perrine, Krome, and Chekika) when tested under a rainfall simulator. However, soil loss from Perrine soil was significantly greater than from Chekika and Krome soils as a result of fewer rock fragments and higher erodibility. In addition, Perrine soil had higher soil water content than did Chekika and Krome soils at any given tension. The results of this study should help water management planning that may result after alteration of the south Florida hydrology by restoration effects in the Everglades National Park.
Keywords: Erosion, Everglades, soil moisture, water table
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Applying RUSLE 2.0 on burned-forest lands: An appraisal
(Full text appears in the Journal of Soil and Water Conservation, Vol.59, No. 1)
G. González-Bonorino and W.R. Osterkamp
ABSTRACT: Forestlands disturbed by wildfire commonly constitute major and long-lasting sources of sediment that degrade water quality and cause siltation. Postfire restoration of the resistance to erosion of the forest soil is largely controlled by the rate of regrowth of vegetation and may take several years to return to prefire levels, particularly in areas of high-severity burns in semiarid climate. Time-instantaneous prediction techniques such as the Universal Soil Loss Equation (USLE) fail to describe the long-term effect. The latest version of the Revised the Universal Soil Loss Equation (RUSLE version 2.0) includes a time-varying option that can model seasonal or pluri-year variations in biomass and other factors; also it has revised governing equations and an updated database. RUSLE 2.0 claims to be land-use independent and, thus, it should apply to burned-forest lands with proper input for forest vegetation. This paper discusses this matter and concludes there still exist in RUSLE 2.0 built-in routines and parameters inherited from its agricultural application that hinder its use on burned-forest soils. Moreover, many forest lands are characterized by soil textures and slope gradients that fall near, or outside, the limit of the database used for validating USLE/RUSLE, a condition that may counter RUSLE’s overall improvement in precision and accuracy.
Keywords: Erosion, forest fire, RUSLE
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Expected climate change impacts on soil erosion rates: A review
(Full text appears in the Journal of Soil and Water Conservation, Vol.59, No. 1)
M.A. Nearing, F.F. Pruski, and M.R. O’Neal
ABSTRACT: Global warming is expected to lead to a more vigorous hydrological cycle, including more total rainfall and more frequent high intensity rainfall events. Rainfall amounts and intensities increased on average in the United States during the 20th century, and according to climate change models they are expected to continue to increase during the 21st century. These rainfall changes, along with expected changes in temperature, solar radiation, and atmospheric CO2 concentrations, will have significant impacts on soil erosion rates. The processes involved in the impact of climate change on soil erosion by water are complex, involving changes in rainfall amounts and intensities, number of days of precipitation, ratio of rain to snow, plant biomass production, plant residue decomposition rates, soil microbial activity, evapo-transpiration rates, and shifts in land use necessary to accommodate a new climatic regime. This paper reviews several recent studies conducted by the authors that address the potential effects of climate change on soil erosion rates. The results show cause for concern. Rainfall erosivity levels may be on the rise across much of the United States. Where rainfall amounts increase, erosion and runoff will increase at an even greater rate: the ratio of erosion increase to annual rainfall increase is on the order of 1.7. Even in cases where annual rainfall would decrease, system feedbacks related to decreased biomass production could lead to greater susceptibility of the soil to erode. Results also show how farmers’ response to climate change can potentially exacerbate, or ameliorate, the changes in erosion rates expected.
Keywords: Climate change, runoff, sediment, soil erosion, soil loss
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Impacts of changing precipitation patterns on water quality
(Full text appears in the Journal of Soil and Water Conservation, Vol.59, No. 1)
J.L. Hatfield and J.H. Prueger
ABSTRACT: Changing climate across the United States has been observed in the increasing intensity and amount of precipitation. One of the predicted areas for this impact is in the upper Midwest or the Corn Belt, and one concern is that current soil management practices in this region may not adequately protect the soil under these changes resulting in water quality impacts. To address this concern, this study was conducted to survey the current literature on the water quality impacts from current soil management practices and evaluate potential impacts on runoff and drainage from soil management practices under a number of precipitation scenarios. Soil management practices, e.g., crop residue, no-till, incorporation of manure, provide protection under today’s climate. However, increasing precipitation amounts, or frequencies, rapidly decrease the effectiveness of these practices with the deleterious effect being even greater on soils with low water holding capacity and limited depth. The water quality impacts may be even more dramatic with the likelihood of increased surface runoff events. Soil management practices need to be developed and evaluated under precipitation patterns that may represent future scenarios so that producers can begin to adopt these practices into their management programs.
Keywords: Conservation practices, drainage, soil management, soil water balance, surface runoff, water quality
