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Home » Journal of Soil and Water Conservation » Abstracts and Archives » Nov-Dec 2002
Nov-Dec 2002

   
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November - December 2002: Volume 57, Number 6  

Table of Contents

Features

  • Technical Service Providers: What's the potential?

  • Using GIS to locate suitable sites for growing agroforestry specialty products
    By Gary Bentrup and Tim Leininger
     

Research

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Essentials of a national nitrate leaching index assessment tool
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6 or click here for PDF of full text.)

J.A. Delgado and M.J. Shaffer

ABSTRACT: Nitrogen (N) inputs are essential for increasing yields and maintaining the economic viability of farming systems worldwide. Although best irrigation and N management practices have been used, increases in worldwide use of N fertilizers combined with average N use efficiencies of 50 percent have contributed to increased leakage from the N cycle (e.g., higher nitrate-nitrogen (NO3-N) leaching losses). Specific land use patterns have been correlated with higher NO3-N concentrations in underground water resources. There is a critical need to continue improving best management practices to reduce NO3-N leaching losses, increase the economic viability of farming operations, and conserve water quality.

To help meet these objectives, this paper recommends the essentials for the development of a national NO3-N leaching assessment tool. The resulting NO3-N leaching index (NLI) should be based on hydrological soil properties and climate, must consider management practices and associated crop rotations, and incorporate off-site effects. Development of the NLI should include the use of simulation models and expert systems; databases for soils, climate, and management; and use of the Internet. The index also needs to allow input of local site-specific information from producers and field personnel. The index needs to be national in scope and yet flexible enough for use in specialized or difficult cases. Routine use of the index needs to be kept simple and quick with minimal input from the user so that field office personnel can apply the tool on a regular basis. Application of the NLI should be linked to the phosphorus (P) index so that management of key nutrients—N and P—can be accomplished simultaneously.

We recommend a 3-tier approach to developing the NLI that would provide a uniform index yet allow for refinement of accuracy in the index values as necessary to meet study needs. Tier 1 would involve the initial use of an expert system to separate medium, high, and very high NO3-N leaching potentials from low and very low potential levels by qualitatively screening non-numeric inputs obtained from users. This initial screening technique is similar to that used to develop the P index, but would be designed specifically for NO3-N leaching. Tier 2 would involve computation of the NO3-N leached (NL) index using application models or databases based on models, followed by introduction of off-site effects and local interpretation and normalization to produce the final NLI. In difficult cases, a tier 3 study involving detailed research models and field data would be needed along with the off-site effects, interpretation, and normalization. The NLI could be used routinely in conjunction with the P index to allow alternative management scenarios that optimize both N and P for maximal economic return while protecting the environment.

Keywords: Nitrate, nitrate leaching index, nitrogen, underground water, water quality

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Assessment of concentrated flow through riparian buffers
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

M.G. Dosskey, M.J. Helmers, D.E. Eisenhauer, T.G. Franti, and K.D. Hoagland
ABSTRACT: Concentrated flow of surface runoff from agricultural fields may limit the capability of riparian buffers to remove pollutants. This study was conducted on four farms in southeastern Nebraska to develop a method for assessing the extent of concentrated flow in riparian buffers and for evaluating the impact that it has on sediment-trapping efficiency. Field methods consisted of mapping field runoff areas and their pathways to and through riparian buffers to streams. Mathematical relationships were developed from a model (VFSMOD) that estimates sediment-trapping efficiency from the ratio of buffer area to field runoff area. Among the farms surveyed, riparian buffers averaged 9 to 35 m wide, and gross buffer area ranged from 1.5 to 7.2 ha, but the effective buffer area that actually contacts runoff water was only 0.2 to 1.3 ha. Patterns of topography and microrelief in fields and riparian zones prevented uniform distribution of field runoff across entire buffer areas. Using the mathematical relationships, it is estimated that riparian buffers at each of the four farms could potentially remove 99%, 67%, 59%, and 41% of sediment from field runoff if the runoff is uniformly distributed over the entire gross buffer area. However, because of non-uniform distribution, it is estimated that only 43%, 15%, 23%, and 34%, respectively, would actually be removed. The results indicate that concentrated flow through riparian buffers can be substantial and may greatly limit filtering effectiveness in this region.

Keywords: Concentrated flow, nonpoint source pollution, riparian buffers, sediment, surface runoff, vegetative filter strips

 

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Soil quality of two Kansas soils as influenced by the Conservation Reserve Program (CRP)
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

X. Huang, E.L. Skidmore, and G.L. Tibke
ABSTRACT: Achieving and maintaining a good soil quality is essential for sustaining agricultural production in an economically viable and environmentally safe manner. The transition of land management provides an opportunity to measure soil-quality indicators to quantify the effects of those management practices. This study compared soil chemical and physical properties after 10 years of grass on Conservation Reserve Program (CRP) land with those in continuously cropped land (CCL). The sample sites, located in central Kansas, have two mapping units, Harney silt loam (fine, montmorillonitic, mesic Typic Arigiustolls) and Naron fine sandy loam (fine-loamy, mixed, thermic Udic Argiustolls). Soil samples were collected at two depth increments, 0 to 5 cm and 5 to 10 cm. Soil-quality indicators measured were soil acidity (pH), exchangeable cations, nutrients, total carbon, structure, and aggregation. Soil pH was significantly lower in CCL than in CRP. Soil total C and N in the surface layer (0 to 5 cm) was much greater than in the deeper layer (5 to 10 cm) in the CRP site. The mass of total carbon of Naron soil was significantly higher for 0 to 5 cm and lower for 5 to 10 cm depth in CRP land than in CCL. However, the mass of total carbon of Harney soil was significantly higher in no-tilled CCL than in CRP. Bulk density significantly increased in CCL. Based on dry and wet aggregate stability analysis, the results indicated that CRP land had a greater resistance to erosion by both water and wind than CCL. The improvements in soil quality resulting from CRP included reducing soil acidification, alleviating compaction, and reducing topsoil susceptibility to erosion. However, when CRP was taken out for crop production with conventional tillage, total carbon in the surface layer (0 to 5cm) and aggregate stability gradually decreased. This suggested that appropriate land management practices are needed to extend residual benefit from CRP on soil quality.

Keywords: Aggregate stability, CRP, soil quality, soil total carbon, wind erosion

 

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Assessment of runoff and sediment yield using remote sensing, GIS, and AGNPS
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

S.J. Bhuyan, L.J. Marzen, J.K. Koelliker, J.A. Harrington Jr., and P.L. Barnes
ABSTRACT: A model that can predict runoff and soil loss from a watershed is an important tool that can be used for planning and for watershed assessment and management. An application that combined the capabilities of remote sensing, Geographic Information Systems (GIS), and the Agricultural NonPoint Source Pollution (AGNPS) model was used to assess runoff and sediment yield from various sub-watersheds above Cheney Reservoir in Kansas. Remotely sensed Landsat thematic mapper (TM) images were used to obtain land cover and associated AGNPS model input parameters, including the Universal Soil Loss Equation’s (USLE) cropping factors (C-factor), based on estimates of vegetative cover for rangeland and crop residue. Several input parameters of the AGNPS model were extracted from GIS layers using the AGNPS-ARC/INFO interface. C-factors and curve numbers (CNs) of agricultural crops were adjusted on the basis of management practices and hydrologic conditions of the watershed during various runoff events. Surface-water quantity and quality data, including total suspended solids (TSS) for major runoff events, were obtained from United States Geological Survey (USGS) gaging stations in the watershed and were used for evaluation of this AGNPS modeling process. Base-flow separation was done so that measured runoff and TSS levels could be compared directly with the AGNPS model output. Use of remote sensing along with GIS reduced the time to obtain input for the modeling process and added to the confidence in the representation of watershed conditions. The modeling process was effective for small watersheds (up to 145 sq km [56 sq mi]) with adequate available rainfall data. However, for larger watersheds with substantial variations of rainfall, this process was less satisfactory.

Keywords: AGNPS-ARC/INFO, antecedent moisture condition, curve number, model estimation

 

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Modification and performance of the Coshocton wheel with the modified drop-box weir
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

J.V. Bonta
ABSTRACT: Water-chemistry, sediment, and runoff data from erosion plots and small watersheds are often needed for erosion and water-quality studies where sediment concentrations can be large. Data may also be needed under conditions where approach channels are not appropriate for conventional measuring devices, such as in steep and skewed channels. The performance (sampler fraction) of the modified drop-box weir as the approach to the Coshocton wheel proportional water sampler was evaluated to meet these needs. Three splash-shield configurations on the sampling slot of the Coshocton wheel were investigated to control splashing of water and duplicate water sampling. Of the three shields, a dual-splash shield was required to control water splashing below the sampling slot and to insure proportional sampling of large flows. The Coshocton wheel worked well with the drop-box weir as the sampler approach under steady and unsteady flow conditions. The average proportional sampler fraction for the dual-shield configuration under steady flows was 0.0127 and for unsteady flows was 0.0120. This difference was not statistically significant. Coshocton wheel rotational speed was regular and increased with flow rate to about 35 rpm. After that, rotation became irregular, and the wheel stalled. No difference was found in a maximum-depth-of-flow parameter needed for sizing a drop-box weir based on sampler performance, compared with the parameter determined by performance of the drop-box weir alone (i.e., the wheel sampled proportionally at 100% of the design flow for the weir). This study extends the utility of the combined drop-box weir and Coshocton wheel system to steep and skewed channels.

Keywords: Composite sampler, drop box weir, erosion plot, flow measurement, flow proportional sampler, sediment, water sampler

 

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GIS-based spatial indices for identification of potential phosphorus export at watershed scale
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

E. Giasson, R.B. Bryant, and S.D. DeGloria
ABSTRACT: Spatial indices for identifying potential pollution resulting from manure spread on agricultural lands were developed for evaluating lands in support of decision- and policy-making. An existing nutrient-delivery ratio was modified by calculating actual distance that water would have to travel to reach a stream and was further tailored to better represent runoff source areas in New York state by incorporating soil drainage class. The Animal Manure Potential Pollution Index (AMPPI) was derived from this modified delivery ratio and animal population census data. The AMPPI and other derived indices use geographical information and nutrient application data to identify and rank geographical areas with respect to potential nutrient export to streams. These indices were applied in the Cannonsville Reservoir Basin in Delaware County, New York. Results demonstrate the potential for using the AMPPI and its derivative indices for selecting priority areas for implementing conservation practices or enrolling lands in programs such as the Conservation Reserve Program. For example, conservation practices would result in large reductions of potential pollution per unit of area when implemented in identified areas of croplands with high AMPPI. Additionally, an efficient way to reduce total nutrient concentration in those streams that have high nutrient loading would be to enroll in conservation programs those farms located in subbasins with high nutrient export per unit area, which correspond to areas with high animal density. Farms located in subbasins that have high ratios of nutrient loss per animal unit would benefit from improved manure-management practices, such as improved manure allocation.

Keywords: Soil, water quality, watershed, New York, Cannonsville, pollution, dairy, manure, model, GIS

 

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Soil phosphorus status under restored plant covers established to control land degradation in Red Soil Region of South China
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

Y.X. Chen, Y.F. He, S. Kumar, Q.L. Fu, G.M. Tian, and Q. Lin
ABSTRACT: Irrational exploitation has brought about serious consequences causing severe soil erosion and loss of soil productivity in the red soil region of China. Different vegetation systems were thus established for soil conservation. Five systems—composed of eroded area (Er), bamboo (Bmb), Chinese fir (CF), citrus orchard (Ctr), and rice field (Rf)—were studied to monitor the status of phosphorus in their ecosystems. Generally, soil P was concentrated in the surface soil layer. The rank order for soil total phosphorus and microbial biomass phosphorus in the surface layer was: Rf > Ctr > Bmb > CF > Er and Bmb > CF > Ctr > Rf > Er, respectively. Among the established vegetation covers, external nutrient input had intensely contributed to the buildup of soil P status as systems receiving manure or fertilizer (Bmb, Ctr and Rf) and showed considerably higher P level in their profiles as compared with their forest counterpart (CF). The amount of total P lost from the soil by erosion depended mainly on the mass of soil eroded, mainly via particulate forms. The level of soil erosion was the highest in Er, followed by CF > Ctr > Bmb, and the amount of total P loss by soil erosion in descending order was the same: Er > CF > Ctr > Bmb. All these indicated that vegetation covers reduced soil erosion and nutrient loss significantly.

Keywords: Available phosphorus, microbial biomass phosphorus, soil erosion, total phosphorus, vegetation systems

 

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Quantifying the loss mechanisms of nitrogen
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

J.A. Delgado
ABSTRACT: Nitrogen (N) is a key factor in maintaining higher yield production and worldwide economic viability of agricultural systems. Since N is one of the most dynamic and mobile elements, its management is difficult, especially in irrigated systems where significant losses can be produced by leaching or denitrification. The major pathways for N loss are ammonia (NH3) volatilization; emissions of nitrous oxide (N2O), oxides of N (NO and NO2), and dinitrogen (N2) gases; leaching of nitrates (NO3); and off-site transport due to wind and water erosion of N tied in the organic matter and in the inorganic NO3 and ammonium (NH4) compartments. Nitrogen is dynamic and mobile. Its fate and transport in agricultural systems is affected by management and unpredictable events. Its average worldwide N use efficiencies (NUEs) have been reported to be about 50% and even as low as 33% for cereals.

Farmers usually apply a uniform rate of N to agricultural fields assuming that N sources, sinks, and mechanisms for loss are constant across fields. It is well documented that variability of soil properties that affect N sources makes managing N to maximize NUE difficult. Such variable soil properties include soil organic matter content, residual soil NO3-N, amount of crop residue returned to the surface soil, yield variability (N sink), and changes in soil chemical and physical properties. Fields vary from coarse gravelly areas where N losses are primarily attributed to NO3- leaching, to clayey areas where water is ponded and N losses may be primarily dominated by denitrification (N2/ N2O). Management is being established as the predominant factor that can reduce N losses in the environment. If we are to improve N management to increase NUE we will need to do it within the context of the N cycle accounting for N loss mechanisms and how to manage them. This paper will review how we can quantify these N losses.

Keywords: Denitrification 15N, nitrogen, nitrate leaching, NOx, nutrient management

 

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Quantifying phosphorus losses from the agricultural system
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

J.L. Lemunyon and T.C. Daniel
ABSTRACT: Phosphorus is transferred from agricultural lands to water bodies dissolved in surface runoff, attached to eroded sediment, and leached through the soil profile. It is also removed from the agricultural system as a component of the harvested crop. While communicating with landowners and producers during the nutrient management planning process, it is important to emphasize the relative quantity of phosphorus losses via these mechanisms. This manuscript covers methods of assessing these losses. Field specific parameters such as runoff volume, erosion rate, soil test phosphorus, and crop phosphorus concentration need to be considered in relation to estimates of total P enrichment ratios, sediment delivery ratios, and soil sediment enrichment ratios. These estimates can be used to assess how best soil and water conservation practices and other techniques minimize off-site transport of phosphorus. These estimates of phosphorus field loss will contribute to a better understanding of nutrient application risks, wise land use decisions, and increased implementation of management practices.

Keywords: Erosion, phosphorous, runoff, sediment delivery ratio, sediment enrichment ratio

 

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Nitrogen fate and transport in agricultural systems
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

R.F. Follett and J.A. Delgado
ABSTRACT: To sustain and maximize agricultural production in order to supply the nutritional needs of a continually growing world population, agricultural systems will need nitrogen (N) inputs. In its inert form as elemental dinitrogen (N2) gas in the atmosphere (78%), nitrogen does not impact environmental quality. But the extensive use of N in agricultural systems and the associated transformations of N into various ions or gaseous forms contribute to leaks from the N cycle. These N losses may contribute to the degradation of water, air, and soil in many regions of the world. When N is in its nitrate (NO3-) form, it is one of the most mobile ions in agricultural systems, and NO3- leaching is a primary source of the contamination in drinking water. Soil erosion that transports soil particles and N also contributes to surface water contamination. The gaseous transport of ammonia (NH3) from manures and the denitrification of NO3- and nitrite (NO2-) ions and their transformation into gaseous forms of N such as nitrous oxide (N2O) and nitric oxide (NO) can contribute to air quality and greenhouse warming impacts. Since N inputs are necessary for maintaining the viability of intensive agricultural systems, we must understand how management impacts the transformations, transport, and fate of N. The discussion of the transport and fate of N through agricultural systems must take into account the N cycle. Mitigation strategies that reduce the primary and secondary flows of N through the environment and that benefit farming and livestock operations must be developed.

Keywords: Agricultural systems, air quality, gaseous N losses, nitrate leaching, nitrogen fate, nitrogen transport, water quality

 

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The fate and transport of phosphorus in agricultural systems
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

N.C. Hansen, T.C. Daniel, A.N. Sharpley, and J.L. Lemunyon
ABSTRACT: Phosphorus (P) is an important input for economic crop and livestock production systems. Excessive losses of P from agricultural systems to surface waters can accelerate eutrophication and degrade water quality. This paper reviews the behavior of P in agricultural soils and discusses the transport of P from land to water. The forms, measurement, and sorption processes of P in both soil and water are discussed. Soil test P, the most common soil P analysis, is described relative to other forms of soil P and its use for agricultural and environmental purposes is explained. Loss of soil P to water can occur in particulate forms with eroded surface soil and in soluble forms in runoff, soil interflow, and deep leaching. This paper discusses the relative importance of each transport pathway as affected by soil type and management. Soil P dynamics and water quality risks associated with fertilizer and manure application are illustrated with several examples. Finally, the paper reviews management practices that can effectively reduce the loss of agricultural P to surface waters.

Keywords: Best management practices, reactive P, P sorption, particulate P, soil test P, soluble P, stable P, water quality

 

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Nitrogen modeling for soil management
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

M.J. Shaffer
ABSTRACT: Simulation models of the nitrogen (N) cycle have been used for well over 20 years to help estimate nitrate (NO3-N) leaching, soil residual NO3-N, fertilizer N requirements, soil organic N status, and gaseous N emissions associated with agriculture. These models have been coupled with simulations of other related processes such as water and solute transport, crop growth, soil chemistry, temperature regimes, and management to make more complete models of cropping systems. At the core of these tools have been databases for soils, climate, model coefficients, and field/farm/watershed management scenarios. This paper reviews the basic types of N models, modeling techniques, and required databases. The accuracy of N models along with their strengths and limitations are discussed in a management context. Tips are provided on initializing N constituent pools, on using N models in Geographic Information Systems (GIS) applications, on developing confidence bands for N model output, and on using web-based N models. Finally, methods are described to analyze simulated NO3-N leached, nitrous oxide (N2O) emissions, and N use efficiencies.

Keywords: C/N cycling, fertilizers, manure, N2O emissions, nitrate leaching, nutrient management, water quality

 

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Modeling phosphorus transport in agricultural watersheds: Processes and possibilities
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

A.N. Sharpley, P.J.A. Kleinman, R.W. McDowell, M. Gitau, and R.B. Bryant
ABSTRACT: Modeling phosphorus (P) loss from agricultural watersheds is key to quantifying the long term water quality benefits of alternative best management practices. Scientists engaged in this endeavor struggle to represent processes controlling P transport at scales and time frames that are meaningful to farmers, resource managers, and policy makers. To help overcome these challenges, we reviewed salient issues facing scientists that model P transport, providing a conceptual framework from which process-based P transport models might be evaluated. Recent advances in quantifying the release of soil P to overland and subsurface flow show that extraction coefficients relating soil and flow P are variable but can be represented as a function of land cover or erosion. Existing information on best management effects on P export should be linked to watershed models to better represent changes in P transport. The main needs of P transport models are inclusion of flexible coefficients relating soil and overland flow P, fertilizer and manure management and P loss, stream channel effects on edge-of-field P losses prior to water body input, and linkage of watershed and water-body response models. However, it is essential that the most appropriate model be carefully selected, according to a user’s needs in terms of available input data, level of predictive accuracy, and scale of simulation being considered.

Keywords: Agricultural runoff prediction, erosion, eutrophication, manure management, nonpoint source models, overland flow, ubsurface flow, Total Maximum Daily Loads, water quality modeling, watersheds

 

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Phosphorus indexing for cropland: Overview and basic concepts of the Iowa phosphorus index
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

A.P. Mallarino, B.M. Stewart, J.L. Baker, J.D. Downing, and J.E. Sawyer
ABSTRACT: Excessive phosphorus (P) loss from soils impairs surface water resources. An assessment tool or index has been proposed to identify fields with high potential risk of P delivery. The P index integrates P source and transport factors into a decision making process that may lead to changes in current P management and soil conservation practices. The index recognizes that a single soil P threshold alone is not an appropriate evaluation factor because of the varying conditions across fields. Although most indices being developed in the United States include similar factors, source and transport characteristics are considered in various ways to best address the variable conditions across regions. The Iowa P index reflects conditions that predominate under grain-crop production systems, considers source factors in a multiplicative manner within three main transport mechanisms, and approximates loads of P likely to enter and become available to aquatic ecosystems. An erosional component considers sheet and rill erosion, P enrichment, total soil P, buffers, sediment delivery, distance to a stream, and the long term biotic availability of particulate P in lake ecosystems. A runoff component considers water runoff based on a modification of the runoff curve number (RCN), soil-test P (STP), rate, time, and method of P application. An internal drainage component considers the presence of tiles, water flow to tile lines, subsurface recharge from subsurface flow, and soil-test P. When the erosion risk is high, the index weighs particulate P loss heavily compared with dissolved P loss, and emphasizes long-term processes comparatively more than short-term processes. This P assessment tool helps identify alternative P and soil conservation management options for reducing total P delivery from fields to surface water resources.

Keywords: Phosphorus, phosphorus assessment tool, phosphorus index, phosphorus management, phosphorus risk index

For a PDF version of the complete article, click here

 

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Evaluation of phosphorus-based nutrient management strategies in Pennsylvania
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

J.L. Weld, R.L. Parsons, D.B. Beegle, A.N. Sharpley, W.J. Gburek, and W.R. Clouser
ABSTRACT: Farm management and financial impacts of three phosphorus (P) nutrient management strategies outlined in the U.S. Department of Agriculture (USDA) and U.S. Environmental Protection Agency (USEPA) (1999) Unified Strategy for Animal Feeding Operations—soil test crop response (STCR), environmental soil P threshold (ESPT), and P Index (PI)—were evaluated on ten Pennsylvania farms. For each farm, a nutrient management plan (NMP) writer and project economist developed one nitrogen-based and three P-based NMPs and associated partial budgets. Greater management and financial restrictions occurred on high animal density (> 2 animal equivalent units ac-1) and multiple production enterprise farms. Although NMPs for the PI were more expensive to develop, writers and farmers found it the most flexible and practical strategy. Variable P-based NMP impacts indicated the need for a strategy such as the PI that accounted for multiple farm management factors. First-year total NMP implementation costs (across all ten farms) were $61,690 for the STCR, $47,862 for the ESPT, and $45,380 for the PI.

Keywords: Eutrophication, farm economic analysis, nonpoint source pollution, nutrient management planning, phosphorus, phosphorus index, soil phosphorus

 

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Carbon and nutrient cycles
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

J.A. Delgado and R.F. Follett
ABSTRACT: Soil erosion and off-site transport of nutrients are reducing soil productivity and impacting water bodies across the world. Additionally, anthropogenic activities are increasing the atmospheric concentrations of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and nitric oxide (NO) that contribute to global warming. We want to present the concept that nutrient management plans should incorporate soil organic carbon (SOC) management to reduce soil erosion, cycle macro- and micronutrients, increase nutrient use efficiency, and conserve air, soil, and water quality. Plant-derived materials are the primary source of carbon (C) in soil organic matter (SOM), with C being the most abundant constituent and common partner of nitrogen (N), phosphorous (P), and sulfur (S). Manures, compost, and other organic sources can help cycle organic C and other nutrients. Organic C can contribute to forming chelate compounds that increase the availability of essential micronutrients that interchange with the root surface. Management practices that increase C inputs, help reduce erosion, and increase SOC improve soil quality factors such as cation exchange capacity, water holding capacity, aggregate formation, porosity, and drainage. Carbon management and nutrient cycling should be an integral part of nutrient management plans for maintaining the sustainability of our biosphere.

Keywords: Biosphere, carbon, macronutrients, micronutrients, nitrogen, nutrient cycling, nutrient management

 

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Accounting for seasonal nitrogen mineralization: An overview
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

M.F. Vigil, B. Eghball, M.L. Cabrera, B.R. Jakubowski, and J.G. Davis
ABSTRACT: Accurately predicting the amount of nitrogen (N) made available for crop use by N mineralization (Nmin) of native soil organic matter (SOM) is complicated by different soils, climate, and management, all highly variable from one location to the next. In this paper, we have compiled seasonal estimates of Nmin from eleven field studies. We only include data for native SOM and do not include organically-amended soils. Initially, the data sets were graphed and regression was performed on the data as is. To further analyze the data, and because different incubation times were used for the different studies, we normalized reported Nmin to

a twenty-week incubation period. Values of Nmin for a season range between 0.4 and 152 kg

N ha-1 (0.3 and 136 lb N ac-1). The average amount of Nmin for all of these studies was 49.3 kg N

ha-1 (44 lb N ac-1). A graph of Nmin for all of the data against SOM shows a negative relationship.

A simple linear fit on that data results in a non significant R2 of 0.0008. A similar fit of all of the data against total N was also of little value. Eliminating the data collected from short incubations (less than fifteen weeks long) improved the fit; 42% of the variability in normalized twenty-week Nmin could be explained by total N. Regression analyses of the total soil N and of SOM content on the seasonal Nmin indicated that neither SOM nor total N is a good predictor for the seasonal Nmin amount. Soil type, management, and climate at the various locations obviously influence the magnitude of the estimates. More importantly, this review supports the push for an accurate predictive simulation model for seasonal Nmin that is non site-specific.

Keywords: Nitrogen mineralization, soil organic matter

 

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Mineralization of manure nutrients
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

B. Eghball, B.J. Wienhold, J.E. Gilley, and R.A. Eigenberg
ABSTRACT: In order to apply manure or compost to fulfill the nutrient requirements of a crop, knowledge of the amount of nutrients mineralized following application is needed. Nutrient mineralization from applied manure depends on temperature, soil moisture, soil properties, manure characteristics, and microbial activity. Since these factors cannot be accurately predicted, nutrient mineralization from applied manure can only be approximated. Nitrogen (N) availability from applied manure includes the inorganic N (NO3-N and NH4-N) in manure plus the amount of organic N mineralized following application. Nitrogen mineralization differs for different manure types since the inorganic/organic fraction and quality of organic N varies among manure types. Mineralization of organic N is expected to be low for composted manure (~ 18%) and high for swine or poultry (hens) manure (~ 55%). Phosphorus (P) availability from all animal production sources of manure is high (> 70%), as most of the manure P is inorganic and becomes plant-available after application. Potassium (K) availability from manure is nearly 100%; therefore, manure can be used similar to K fertilizer. When manure was analyzed for plant-available nutrients, greater than 55% of calcium (Ca) and magnesium (Mg) and less than 40% of zinc (Zn), iron (Fe), manganese (Mn), copper (Cu), sulfur (S), and boron (B) were plant-available. To effectively utilize the nutrients in manure, their mineralization potential should be considered when determining application rates.

Keywords: Animal waste, compost, micronutrients, nutrient availability

 

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Nutrient variability in manures: Implications for sampling and regional database creation
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

J.G. Davis, K.V. Iversen, and M.F. Vigil
ABSTRACT: The variability of manure nutrient levels within and across farms makes manure sampling and development of reliable tabular values challenging. The chemical characteristics of beef, dairy, horse, sheep, and chicken solid manures in Colorado were evaluated by sampling six to ten different livestock operations for each manure type and comparing the results to values found in the literature. Due to the semi-arid climate of Colorado, manure tends to be drier and have lower ammonium (NH4-N) levels and higher phosphate (P2O5) and potash (K2O) levels than those reported in the Midwest. Within-farm variability was assessed by analyzing ten sub-samples from each of nine manure sources. Coefficients of variation were calculated and the sample numbers necessary to achieve 10% probable error were determined. On average, about 25 sub-samples are necessary for nitrogen (N), phosphorus (P), and potassium (K) characterization of solid manures, but determining NH4-N and nitrate (NO3-N) concentrations requires over 100 sub-samples to form a representative sample, due to their relatively low concentrations. Data from Colorado, Utah, and New Mexico were combined to form a Mountain West Manure Database. The manure types, with a minimum of 72 farms represented in the database, have narrow confidence intervals. Until we have adequate sample numbers (>72 farms) to establish reliable table values based on local data for all manure types, manure sampling will be recommended.

Keywords: Manure sampling, manure variability, regional manure database

 

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Soil testing for different phosphorus pools in cropland soils of the Great Plains
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

R.A. Bowman and M.F. Vigil
ABSTRACT: Knowledge of soil phosphorus (P) pools and their measurements is important in nutrient cycling studies. An overview of the P cycle, with emphasis on calcareous cropland soils of the Great Plains, was prepared to meet this objective. Phosphorus pools can broadly be placed into four main groups: primary P minerals, secondary P minerals, occluded P minerals, and organic P. The dominant groups and their amounts in the soil are highly dependent upon soil pH, weathering intensity, P fertilization, cropping history, and crop-residue management. Chemical procedures for the first three groups are usually based upon the ability of the extractant to separate P from the dominant cations, such as calcium, iron, and aluminum, or from reactive clay surfaces. Generally, the first three groups exist in inorganic forms, and the fourth as part of the soil organic matter. These pools require combustion or oxidation to orthophosphate before analysis. The primary and secondary P minerals, through equilibrium with the soil solution P, contribute to the plant available P, and consequently to the extractable P in a soil test. The organic P requires mineralization to orthophosphate first before it becomes a part of the available P, and the occluded P requires dissolution of an outer protective coating. Areas of similar soil mineralogy and pH (acid soils, calcareous soils, etc.) usually use the same soil test or P-availability index. Thus, in arid western states, the sodium bicarbonate (Olsen) procedure is used, and in areas of greater rainfall where acid soils exist, the Bray-1 procedure is used. More universal methods include the Mehlich 3 procedure, which is acceptable for both acid and basic soils. Other P procedures exist, but regardless of the procedure used, all have to show good correlation with soil P levels and P uptake and crop yields. Thus, categories (low, medium, high) are established for soil-test values based upon the probability of response of a crop to added fertilizer P. Knowledge of the cycling and fate of this nutrient, the second-most-important soil element for plant growth, is essential for good soil management and productivity.

Keywords: Available P, Bray-1, calcareous soils, organic P, phosphorous, phosphorus pools, threshold soil P

 

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Principles for managing nitrogen leaching
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

J.J. Meisinger and J.A. Delgado
ABSTRACT: Managing leaching presents a challenge to nutrient managers who must develop nitrogen (N) management plans that consider rate and application strategies that account for soil properties, hydrology, and crop-tillage systems of specific sites. Nitrogen-leaching losses from common grain-production systems typically range from 10% to 30% of the total N input. Major leaching events occur when soil N concentrations are high and water is moving through the soil profile. The universal tools for managing N leaching include understanding the soil-crop-hydrologic cycle, avoiding excess N applications, and applying N in phase with crop demand. Specific cropping system tools for managing leaching include use of grass cover crops, adding a legume to a rotation, and adding crops that more fully utilize the soil-water resources. The primary water-management tool to reduce N leaching is irrigation scheduling. Other watershed approaches to reduce leaching losses include use of riparian zones and conservation reserve program areas. Site monitoring tools such as the pre-sidedress soil-nitrate test, the leaf chlorophyll meter, and tissue-nitrate tests are useful in identifying N-sufficient sites and avoiding excess N rates. Real-time monitoring techniques, such as the N Reflectance Index, can be combined with global positioning systems and geographic information systems to produce maps of the crop N status. Crop simulation models can also be used to integrate N and water dynamics during a growing season, and they can provide guidance in designing practices for reducing N leaching. The application of the above N management tools to fields, or to specific management areas within fields, will improve crop N recoveries with subsequent reductions in N leaching.

Keywords: Irrigation, nitrate, nitrogen leaching, nutrient leaching, nutrient management plan

 

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Management effects on nitrogen leaching and guidelines for a nitrogen leaching index in New York
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

H.M. van Es, K.J. Czymmek, and Q.M. Ketterings
ABSTRACT: Management practices may affect the potential for nitrate leaching from agricultural systems. Two studies are discussed that used plot-size lysimeters on loamy sand and clay loam soil in Northern New York. One was conducted from 1991 to 1994 and involved sod plowing and the use of three rates of fertilizer on maize (Zea mays L.). The other study was conducted from 1997 to 2000 and quantified N-leaching losses under maize and orchardgrass (Dactylis glomerata L.) as affected by the timing of manure application. These studies showed that timing and rate of N fertilizer and manure additions, timing of green-manure incorporation, and soil type strongly influenced N-leaching losses. Losses from fall-applied N sources were high, especially on coarse-textured soils. Lower N losses in fine-textured soils were primarily the result of higher denitrification losses, rather than reduced percolation rates. It was concluded that the current N Leaching Index ignores important processes and requires a more dynamic approach that includes management factors. In the interim, we established a set of best management practices for N to reduce the potential for N leaching losses.

Keywords: Manure, N fertilizer, nitrate leaching, N Leaching Index, soil type, timing of application

 

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Managing soil denitrification
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

A.R. Mosier, J.W. Doran, and J.R. Freney
ABSTRACT: Denitrification of nitrate in the soil can be a mechanism of significant loss of fertilizer and soil nitrogen, but it can also serve to remove excess NO3- that is leached below the root zone. Inappropriate management of irrigation water and fertilizer N in irrigated corn has resulted in leaching of excess N from the rooting zone and contamination of groundwater and also has contributed to the increasing concentration of N2O in the atmosphere. Denitrification can be both microbial and chemical, but the microbial process dominates in most soils through a stepwise reduction of NO3- to N2 . Soil atmosphere O2 concentration, which is regulated by soil water content interactively with soil texture and microbial respiration, is the main controller of the process. The oxygen consumption rate depends on the amount of easily degradable organic C compounds and the interplay of water and carbon in developing in the soil reduced oxic conditions, which regulate not only the amount of total denitrification but also the ratio of N2O to N2 produced. Appropriate management of nutrient input, relative to crop demand and soil water status, can limit nitrogen loss from denitrification. This paper describes the role of denitrification in the nitrogen economy of crop production and the environment, describes the process involved, and presents suggestions for limiting N loss caused by denitrification.

Keywords: Gaseous N loss, N2, N2O, nitrification

 

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Use of site-specific management zones to improve nitrogen management for precision agriculture
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

R. Khosla, K. Fleming, J. A. Delgado, T. M. Shaver, and D.G. Westfall
ABSTRACT: Nitrogen (N) input is one of the most important factors in maximizing yields and economic returns to farmers. Of the essentials nutrients, N is required in large quantities, and it is the most mobile and dynamic nutrient in soil systems. It is well-documented that soil physical and chemical properties are spatially variable and affect N dynamics and the mechanisms for its losses. For example, N dynamics could vary from high denitrification N2 losses from ponded areas with low drainage to high NO3- leaching losses from coarse-gravelly areas of the field. Recent developments in new technologies are allowing us to identify, measure, and map these changes across the field. We found that N management using site-specific management zones (SSMZ) that account for soil variability and productivity provides the amounts of N needed to increase yields and maximize the agronomic use efficiency of the applied N. The SSMZ-based N application outperformed treatments that used yield-goal-based and uniform N application rates. Grid-based N application treatments performed as well as the SSMZ for yields but were more inefficient as far as the unit of yields produced by unit of N fertilizer applied. The SSMZ can be used to improve N management and use efficiency of the applied N to increase yields and reduce N losses to the environment.

Keywords: Nitrogen, nitrogen management, precision agriculture, site-specific management zones

 

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Remote sensing for nitrogen management
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)
P.C. Scharf, J.P. Schmidt, N.R. Kitchen, K.A. Sudduth, S.Y. Hong, J.A. Lory, and J.G. Davis

ABSTRACT: Nitrogen application often dramatically increases crop yields, but N needs vary spatially across fields and landscapes. Remote sensing collects spatially dense information that may contribute to, or provide feedback about, N management decisions. There is potential to accurately predict N fertilizer need at each point in the field. This would reduce surplus N in the crop production system without reducing crop yield, which would in turn reduce N losses to surface and ground waters. Soil spectral properties (color) are related to soil organic matter and soil moisture levels, factors that influence the N-supplying ability of the soil. Plant spectral properties reflect crop N status and soil N availability, and they can be useful for directing in-season variable-rate N applications. Plant color may also be useful for assessing the adequacy of crop nitrogen supply achieved with a given nitrogen management practice. We outline the current status of these approaches, offer examples, discuss several N management contexts in which these approaches might be used, and consider possible future directions for this technology.

Keywords: Aerial, imagery, nitrogen, satellite, soil organic matter, spectral, variable-rate

 

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Nutrient losses in surface irrigation runoff
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

D.L. Bjorneberg, D.T. Westermann, and J.K. Aase
ABSTRACT: Runoff from surface-irrigated fields is typically managed to improve infiltration uniformity by reducing differences in infiltration opportunity times between the upper and lower ends of fields. Runoff water not used on other fields within an irrigation tract is discharged to streams or rivers, along with sediment and nutrients. Return flow nutrient and sediment concentrations may be greater than in the diverted water, but the total sediment and nutrient mass returned may be less if most of the diverted water infiltrates within the irrigation tract. Controlling erosion reduces total phosphorus loss, because total phosphorus concentration relates directly to sediment concentration. On-farm management practices, such as polyacrylamide (PAM) application and conservation tillage, reduce erosion from fields, while sediment ponds in the field or on return-flow streams trap suspended sediment that is not controlled by on-farm practices. Surface irrigation return-flow water quality can be improved with an organized effort using a combination of practices.

Keywords: Erosion, irrigation runoff, nutrient enrichment, phosphorus, sediment

 

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Managing runoff following manure application
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

ABSTRACT: Rainfall patterns, soil factors, topography, climate, and land use may all influence runoff. To minimize environmental concerns, excessive runoff should be avoided on areas where manure has been applied. Management practices used to control runoff include contouring, strip cropping, conservation tillage, terraces, and buffer strips. In some cases, secondary containment systems, sedimentation basins, or ponds may be necessary to collect runoff. More than one runoff-control practice may be necessary for protection in areas with high runoff potential. Soil properties, including infiltration, may be improved by manure application. The method, rate and timing of manure application should be considered to reduce environmental impacts. The transport of nutrients and pathogens by overland flow is influenced by manure characteristics, loading rates, incorporation, and the time between manure addition and the first rainfall. Through proper management, manure can serve as a valuable nutrient source and soil amendment without causing environmental concerns.

Keywords: Animal waste, conservation planning, land application, manure application, manure management, manure runoff, pollution control, runoff, runoff volume

 

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Variable-source-area controls on phosphorus transport: Bridging the gap between research and design
(Full text appears in the Journal of Soil and Water Conservation, Vol.57, No. 6)

W.J. Gburek, C.C. Drungil, M.S. Srinivasan, B.A. Needelman, and D.E. Woodward
ABSTRACT: Transport factors incorporated within most versions of the phosphorus index (PI) are expected to represent the potential for phosphorus (P) to be mobilized on the field and subsequently move from the field source to a stream or other surface-water body. Consequently, these factors must be designed to capture the nature of the hydrologic properties of both the field and the watershed. The field-related transport factors typically included in PIs, e.g., the NRCS soil runoff class and erosion loss via RUSLE are generally accepted as sufficient to represent edge-of-field P loss. However, there has not been a unified approach to represent connectivity of field to stream within the PI. Here, we develop a generalized connectivity factor for inclusion in PIs based on design rainfall, the variable-source-area (VSA) hydrologic concept, and readily available watershed geomorphic data. The NRCS curve number method is used to determine runoff volume from the watershed for design rainfalls representing a range of return periods. A simplification of VSA hydrology is used to derive the contributing area from which this runoff is expected to occur. Finally, the width of land adjacent to the stream contributing surface runoff is estimated using drainage density. For illustration, the methodology is applied to a small upland watershed in east-central Pennsylvania, and the results are examined in light of hydrologic investigations being conducted on the watershed.

Keywords: Nutrient management, phosphorus index, runoff, transport, watersheds
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