March-April 2002: Volume 57, Number 2  
Table of Contents

• Improving Water and Soil Quality with Conservation Buffers--
  By Richard Lowrance, Seth Dabney, and Richard Schultz
• The Landscape in 2025: Alternative future Landscape Scenarios, a means to consider agricultural policy--
  By Joan Nassauer, Rob Corry, and Richard Cruse

Research

• Targeting soil-conservation policies for sustainability: new empirical evidence
  J. Popp, D. Hoag, and J. Ascough II
• Total organic carbon losses in subsurface flow under two management practices
  L.B. Owens, G.C. Starr, and D.L. Lightell
• Water infiltration rates following reintroduction of Lumbricus terrestris into no-till fields
  G.L. Willoughby and E.J. Kladivko
• Spatial and statistical differences between 1:250,000- and 1:24,000-scale digital soil databases
  K. E. Juracek and D. M. Wolock
• Image rectification for recompiling and digitizing soil survey maps
  J.M. Beck, J.N. Shaw, P.L. Chaney, and J.E. Hairston
• Soil conservation practices on leased land: a two-state study
  J.D. Cole and B. Johnson
• Impact of agricultural land use on nitrate levels in Lake Manatee, Florida
  R. A. Clarke, C. D. Stanley, B. L. McNeal, and B. W. Macleod
• Utilizing swine effluent for sprinkler-irrigated corn production
  M.M. Al-Kaisi and R.M. Waskom
• Conservation Reserve Program: Effects on soil organic carbon and preservation when converting back to cropland in northeastern Colorado
  R. A. Bowman, and R. L. Anderson
  

Departments

• Home Front
• Viewpoint
• Raise Your Voice
• Notebook
• Conservogram

Targeting soil-conservation policies for sustainability: new empirical evidence
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No.2)

J. Popp, D. Hoag, and J. Ascough II

ABSTRACT: Sustainable resource management is one of the most complex concerns today. Society has spent billions of dollars conserving soils in production, yet it is unclear whether these efforts buy sustainability, or even what sustainability is. Further study about which soils need conservation merits consideration. We use a simulation model, regression, and optimization analysis to examine the sustainability of resource management in objective, measurable ways. Soil quality, represented by a new index, and other nonirrigated corn production data are placed into a dynamic model to identify: 1) the conditions where soil conservation is efficient, and 2) under what definitions conservation is sustainable. Results show that decisions to use or conserve soil and the impacts of these decisions are highly dependent upon soil type and how sustainability is defined. In general, while soil conservation slowed degradation on erodible soils, it seemed to be more effective and economically efficient the better the initial quality of the soil. This calls into question whether U.S. conservation policy that focuses on marginal soils supports sustainability. Economic research was undertaken to study which soils might best be targeted for conservation, using economic and sustainability criteria. An economic model of nonirrigated corn production was created to determine—under requirements of maintaining a certain level of production or maintaining soil quality—if, when, and where it was best to apply conservation practices. Results show that decisions to use or conserve soil and the impacts of these decisions are highly dependent upon the characteristics of the soil and how sustainability is defined. In general, while soil conservation slowed degradation on erodible soils, it seemed to be more effective and economically efficient the better the initial soil quality.

Keywords: Resource management, soil conservation, soil quality, sustainability

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Total organic carbon losses in subsurface flow under two management practices
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No.2)

L.B. Owens, G.C. Starr, and D.L. Lightell
ABSTRACT: Greenhouse gases and global warming have become major topics. Much of the greenhouse gas discussion has dealt with carbon dioxide (CO2) and methods to sequester or store atmospheric carbon in soils and forests. The entire carbon cycle needs to be studied to better understand the overall process. The major carbon transformations are loss of CO2 to the atmosphere or the storage of carbon in sinks such as soil. Although it is a minor pathway, carbon leached through the soil and into groundwater needs to be quantified. Numerous carbon studies have been performed, but concentrations and losses of total organic carbon (TOC) moving through a soil profile have received little attention. Therefore, this study was to assess TOC levels in subsurface flow under two management practices. TOC was determined monthly in the percolate from large soil blocks, called lysimeters, (2.4 m [8 ft] deep) with undisturbed soils under row crops. Most of the TOC concentrations in the percolate ranged from 0.5 to 6.0 mg/L with the corn/soybean-rye rotation. Developed springs in two rotational grazing systems were sampled for 10 years. TOC concentrations in the groundwater from the springflow developments had less variability than in the lysimeter percolate. Most TOC values from these pasture systems were in a concentration range of 1 to 3 mg/L. Annual averages of TOC transport were similar for the lysimeter percolate and groundwater springs, ranging from 3.7 to 6.0 kg/ha (3.3 to 5.4 lb/ac).

Keywords: Carbon concentrations, carbon transport, groundwater, subsurface flow

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Water infiltration rates following reintroduction of Lumbricus terrestris into no-till fields
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No.2)

G.L. Willoughby and E.J. Kladivko

ABSTRACT: The deep-burrowing earthworm species Lumbricus terrestris (nightcrawler) can have significant impacts on water infiltration rates in soils. Many farmers using no-till practices want to encourage higher nightcrawler populations in their fields, and a few have questioned whether it would be useful to distribute collected or purchased nightcrawlers throughout their fields. In this study, adult L. terrestris were reintroduced into some no-till fields to determine their survival, population growth, and subsequent impact on infiltration rates. Three no-till fields devoid of L. terrestris, as evidenced by the absence of surface middens, established 12 quadrats, 2 m x 2 m each, in spring 1994. Six quadrats were seeded at a rate of 20 L. terrestris /m2, and six were left as controls. Over two years, the number of middens varied from 0 to 6.5 L. terrestris /m2 in each seeded quadrat, with none in the control plots. We determined infiltration using a sprinkling infiltrometer that applied 7.5 cm of water per hour. In seeded plots, final infiltration rates ranged from 1.20 to 0.33 mm/min (average 0.80) across both years, and in control plots they ranged from 1.17 to 0.38 mm/min (average 0.71). Presence of L. terrestris significantly increased infiltration rates in 1995; however, in 1996 there were no significant increases in infiltration rates, probably because of a large decrease in population numbers from 1995 to 1996. Six larger (4 m x 4 m) quadrats were also seeded with 20 L. terrestris /m2, and another six were left as controls. Within these quadrats, a comparison of sprinkler vs. ponded infiltration methods was performed. There were no significant differences in infiltration detected between seeded and control quadrats at the end of 55 or 90 minutes, but there was a trend for greater infiltration in the seeded quadrats. There were no significant differences between infiltration methods when data were analyzed at the end of 55 minutes (the duration of the sprinkling infiltrometer procedure). Higher populations of L. terrestris may be needed before significant differences in infiltration rates or methods are detected. Results of the first two years indicate that nightcrawlers may survive and become reestablished in many no-till fields, but the rate of population growth and soil property improvements may be slow enough to discourage large-scale seeding efforts by farmers.

Keywords: Earthworms, infiltration, Lumbricus terrestris, nightcrawlers, no-till

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Spatial and statistical differences between 1:250,000- and 1:24,000-scale digital soil databases
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No.2)

K. E. Juracek and D. M. Wolock

ABSTRACT: In this study, 1:250,000- and 1:24,000-scale digital soil databases for Kansas were compared statistically and spatially. The soil attributes used in this comparison were soil perme­ability, percent clay, and hydrologic group. Results indicate that, although the two databases were correlated, the potential exists for substantial site-specific variability between them. The largest differences between the two databases typically are in and along the stream networks. With distance away from the stream networks, the mean differences generally stabilize. The results also indicate the possibility of systematic bias between the two databases that varies with landscape position. For applications using mean soil attribute values, the two soil databases usually yield similar values for the three soil attributes analyzed, especially for areas of 25 km2 (9.7 mi2) or larger. However, for applications where more detailed information on soil variability and the spatial pattern of soil properties within the landscape is required, such as for studies focused on small areas or areas in and along stream networks, the two soil databases are sufficiently dif­ferent such that using one or the other may result in substantially different results.

Keywords: Hydrologic group, Kansas, landscape position, percent clay, soil permeability, SSURGO, STATSGO.

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Image rectification for recompiling and digitizing soil survey maps
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No.2)

J.M. Beck, J.N. Shaw, P.L. Chaney, and J.E. Hairston

ABSTRACT: The U.S. Department of Agriculture Natural Resources Conservation Service (USDA NRCS) is placing soil survey data in digital format. To accomplish this mission, existing soil survey information must be digitized. Map scale differences and publication of older surveys on non-ortho aerial photography complicates this task. For effective use, soil survey maps need to be recompiled and digitized to an ortho-photo base at 1:24,000. This paper describes an image matching technique to facilitate the recompilation and digitization of published soil survey reports. In addition, the accuracy of using a polynomial equation versus a triangle-based finite element approach for rectifying non-ortho aerial photographs to digital ortho-photo quadrangles (DOQs) was evaluated. It was hypothesized that the triangle-based method would be more accurate if a large number of ground control points (GCPs) were used. However, results showed that accuracy differences were minimal and that the critical factor was the quality, not quantity, of GCPs. Our image matching technique is a cost effective digitizing approach for regions of low to moderate relief.

Keywords: Digitizing, rectification, soil survey maps.

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Soil conservation practices on leased land: a two-state study
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No.2)

J.D. Cole and B. Johnson

ABSTRACT: The leasing market for cropland in the United States is significant. More than 40% of U.S. farmland is leased. This study was conducted to evaluate the relationship lease arrangements have upon land use management and conservation practices. The Revised Universal Soil Loss Equation (RUSLE) was used to predict soil loss on share and cash leased tracts in Nebraska and South Dakota. Several longstanding hypotheses concerning the soil loss from leased land were tested. Evidence suggests physical location and features of the tract are primary determinants for soil loss on a particular tract. Factors such as lease type, length of lease, size of operation, business structure, and tenants’ perception of retaining a leased tract did not seem to affect stewardship adversely. These results suggest that agricultural producers steward the land they operate in an environmentally conscientious manner regardless of ownership status. Tenants surveyed perceived community norms and social pressure to farm leased land as they would their own. Reputations and perceptions of individual tenants do matter. This finding coupled with their own beliefs and values concerning production agriculture and long term resource management, is reflected in their production practices, which tend to conform closely to conservation interests of owners as well as those of society in general.

Keywords: Beliefs, conservation, cropland leasing, erosion, RUSLE, soil loss, stewardship, values

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R. A. Clarke, C. D. Stanley, B. L. McNeal, and B. W. Macleod

ABSTRACT: Algal blooms in the Lake Manatee reservoir necessitate treatment of the drinking water for taste degradation, creating an economic burden. This study was conducted to assess the extent to which agricultural activities in the Lake Manatee watershed may contribute to nutrient loading of the reservoir.Water quality data for Lake Manatee were collected from eight strategically selected sites within the lake from 1983 to 1993, and were correlated with historical agricultural activity (vegetable and citrus production) in the watershed to determine if evidence for agricultural NO3-N loading was apparent. The watershed was divided into sub basins related to sampling locations in an attempt to evaluate the effects of specific agricultural activities on NO3-N levels in the lake. This allowed the separation of sampling points representing sub-basin watershed areas where 1) no agricultural activities occurred, 2) exclusively vegetable or citrus production occurred, or 3) mixed production occurred. Data were analyzed using trend analysis along with a technique to deseasonalize the data for more valid overall interpretation. Results showed that the average lake NO3-N concentration during the period was only 0.18 mg L-1 (0.18 ppm) and that seven of the eight sampling sites showed average annual NO3-N increases of 5-10% throughout the study period, depending on sampling location (p< 0.10). However, no strong correlation with agricultural activity in the watershed was demonstrated. This conclusion was supported by data collected in a watershed sub-basin with no agricultural activity, which showed a comparable NO3-N concentration increase during the study period.

Keywords: Citrus, vegetables, water management, water quality, watershed

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Utilizing swine effluent for sprinkler-irrigated corn production
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No.2)

M.M. Al-Kaisi and R.M. Waskom

ABSTRACT: The rapid expansion of large swine production facilities in northeast Colorado prompted a need to evaluate the impact of swine effluent applied on irrigated corn grown on sandy soil. The objectives of this study were 1) to evaluate the use of swine effluent as a nutrient source for irrigated corn production, 2) to evaluate the response of irrigated corn grown on sandy soils to different application rates, and 3) to evaluate N movement through the soil profile under swine effluent and commercial-N fertilizer for irrigated conditions. The three year study started in 1995 on a 14.5 ha (36 ac) sprinkler-irrigated (center pivot) Valent sand field, (Mixed, mesic Ustic Torripsamments) planted to grain corn (Zea mays L.). Both swine effluent and commercial-N fertilizer treatments were applied at four N rates labeled control, low, agronomic, and high. All treatments were replicated three times in a randomized complete block (RCB) design. Approximately 90% of the total nitrogen from the two-stage lagoon effluent was in ammoniacal form, and the total dry matter content of the effluent was only 0.1 - 0.2% by volume. Corn yields increased with the increase of both swine effluent and commercial-N fertilizer rates. In contrast to the swine effluent treatments, significant soil-N buildup was observed at the 1.5 - 3.0 m (5 - 10 ft) depths for the commercial-N fertilizer treatments. Higher total N and P plant removal for the swine effluent treatments resulted in little N accumulation below the root zone. As the swine effluent application rate increased, the plant N and P removal and recovery rate increased, even at rates of 50 kg ha-1 (45 lb ac) above the recommended agronomic rate. An increase in extractable P in the top 15 cm (6 in) of the soil was observed in the effluent-treated soils. The results indicate that managing swine effluent-N becomes very similar to managing commercial-N fertilizer under irrigated conditions.

Keywords: Corn yield, irrigation, N and P recovery, N and P removal, and swine effluent, water management, water quality, watershed

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Conservation Reserve Program: Effects on soil organic carbon and preservation when converting back to cropland in northeastern Colorado
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No.2)

R. A. Bowman, and R. L. Anderson

ABSTRACT: Information on the potential for carbon sequestration from the Conservation Reserve Program (CRP) and knowledge concerning the fate of accrued carbon on sod takeout and recropping to a wheat-based rotation are essential. We conducted two separate field studies in northeastern Colorado to quantify the soil organic carbon (SOC) changes after various amounts of time in the CRP program, and to assess problems associated with converting CRP grass to cropland and the potential for loss of accrued SOC with different tillage systems. For our first objective, we assessed six CRP sites, with three sites showing increased SOC content over the adjacent winter wheat/summer fallow sites, and three sites showing no differences. In the conversion study, systems with little or no tillage yielded more winter wheat (Triticum aestivum L.) grain than systems with tillage because of more available soil water at planting time. Furthermore, SOC loss was less with no-till and reduced-till (herbicides plus one tillage) systems than by conventional tillage with numerous sweep plow operations. Thus, NT and reduced-till systems designed to control perennial CRP grasses will enable producers to maintain some of the gains in SOC when CRP land is converted to cropland.

Keywords: Carbon sequestration, crop biomass, native sod, soil organic matter, wheat/fallow.