NC_old1178: Impacts of Crop Residue Removal for Biofuel on Soils
(Multistate Research Project)
NC_old1178: Impacts of Crop Residue Removal for Biofuel on Soils
Duration: 10/01/2014 to 09/30/2019
Statement of Issues and Justification
The growing importance of renewable energy, specifically as biofuels, is indicative of the insatiable energy demands of the globalizing and growing world economy but hidden in this is the high economic and environmental costs of fossil fuels. In his State-of-the-Union address on 23 Jan. 2007, President Bush enthusiastically proposed to cut U.S. gasoline consumption by up to 20% by 2017 through an increase in ethanol production to 35 billion gallons a year, or a fivefold increase over current ethanol production requirements. There are now 217 North American ethanol plants, with 87 % primarily sited in the Corn Belt of the Midwest. Most of the existing ethanol plants are corn grain-to-ethanol refineries. The long-term goal is to produce 60 billion gallons of ethanol per year to replace 30% of the ground transportation fuel demand of the U.S.
To meet these demands, the use of crop residues is being considered as a source of lignocellulosic feedstock for producing ethanol (Wilhelm et al., 2004), although it is not yet a routine practice (Johnson et al., 2004). However, in 2013, about 14 million gallons will be produced by up to four production plants across the USA (Schnefp and Yacobucci, 2013; EPA, 2013). The National Renewable Fuel Standards (RFS) estimates that 16 billion gallons of cellulosic fuel or 44 % of renewable fuels will necessarily be required from cellulosic sources (Schnefp and Yacobucci, 2013). The production of these fuels will require more intensive use (intensification) of agroecosystems and agricultural lands.
One ton of corn stover or any other cellulosic biomass could theoretically produce 100 gallons of ethanol. An annual production of 60 billion gallons of ethanol from cellulosic biomass would require 600 million tons of biomass per year. The overall goal for ethanol production is to procure 1 billion tons of biomass for the U.S. (Somerville, 2006) and about 4 billion tons for the world. The current rate of residue production from all crops is about 500 million tons in the U.S. and about 4 billion tons in the world. Some analysts argue that 300 million tons of corn residue could be harvested for meeting the U.S. ethanol demands. Similar to the U.S., 34 straw-burning power plants were being built at the end of 2006 in rural areas in China with a capacity of producing 1.2 million kW of power. The straw-burning power industry is likely to grow in China and associated geographic regions. Of the 600 million tons of straw produced annually, China plans to use 300 million tons to produce energy. India, which produces about 440 million tons of crop residues annually, also has plans to build straw-burning power plants. When crop residue is removed from soil, there is increased potential for erosion, reduction in soil organic C (SOC) pools, and deterioration of soil properties, resulting in a subsequent decline in soil quality, reduction in crop yield, and decrease in local and regional water quality (Simpson et al., 2008).
Crosson (1984) estimated a monetary loss in the U.S. from soil erosion due to reduced cropland productivity to be 40 million dollars in a given year. In 2001, den Biggelaar et al. (2001) estimated the loss at $55.6 million. Others, Crosson (1986) and Pimentel et al. (1995), have estimated the loss to be over $100 million. The results vary depending on the erosion rates, climate, and crop prices for the years covered in the study. For many soils, continued erosion results in degraded and reduced topsoil thickness. Reduced crop yields occur as root restrictive layers, such as fragipans, subsoil horizons with a large amount of clay, or coarse sand become closer to the soil surface (Langdale et al., 1985).
Offsite damages to the environment caused by soil erosion and subsequent deposition of sediments in the U.S. are considerable (Pimentel, 1992). Deposition of eroded soil materials in surface water bodies such as reservoirs, lakes, rivers, and streams cause a decline in water quality, reduce environmental quality, and decrease the functional life expectancy of reservoirs. Eroded sediments often contain not only soil materials from the organic surface soil which are enriched in nutrients and C, but often include commercial and/or organic (animal waste) fertilizers, pesticides, and agricultural pharmaceuticals (from animal waste).
Management practices such as residue removal affect soil physical, chemical, and biological properties. Soil organic C is one of the critical indicators of development of soil physical, chemical, and biological properties (Blanco-Canqui et al., 2013). If management practices increase SOC, the physical, chemical, and biological properties are positively affected, and vice versa. Excessive removal of crop residues, particularly corn stover, can adversely affect SOC pools, soil quality and exacerbate the problem of soil erosion. Residue removal increases the susceptibility of the soil surface to crusting/increased surface sealing because of rainfall-induced consolidation and abrupt wetting and drying (Or and Ghezzehai, 2002). Residue mulch increases aggregation (Mochizuki et al., 2008), improves soil hydraulic properties (Strudley et al.2008) and intercepts raindrops responsible for crust-forming processes such as detachment of soil particles and dispersion of surface aggregates. Crusts are thin soil surface layers about 5 cm thick (USDA-NRCS, 1996), but they are denser and less permeable than the underlying soil layers. Because of their greater strength and low permeability, crusts can modify soil surface processes, restricting seedling emergence (Baumhardt et al., 2004), reducing water infiltration and aeration (Wells et al., 2003), and increasing surface runoff (Bajracharya and Lal, 1998) thus inducing a greater level of soil erosion with long-term detrimental effects on plant growth (Maiorana et al., 2001).
Some researchers have estimated that ranges of about 30% (Nelson, 2002), 40% (Kim and Dale, 2004), and 58% (Lindstrom et al., 1979) of the total corn stover production in the U.S. Corn Belt region may be available for biofuel production. These removals are, however, based mainly on the residue requirements to reduce soil erosion risks and not on the needs to maintain soil quality, crop productivity, or SOC pools. Allowable removal rates of corn stover based on the need to reduce soil erosion in the U.S. Corn Belt region are site-specific (Lindstrom et al., 1979; Nelson, 2002; Kim and Dale, 2004). Thus, the quantity of stover that must be retained on the soil to maintain soil quality and SOC storage or retention is also likely to depend on site-specific conditions such as tillage and cropping system (Kladivko, 1994), duration and intensity of management (Karlen et al., 1994), soil properties (Gupta et al., 1987), as well as agro-ecosystem and climate (Salinas-Garcia et al., 2001). Knowledge of the threshold levels of stover removal in relation to the numerous soil ecosystem services is urgently needed to design residue management options for biofuel production while maintaining soil and water quality as well as enhancing SOC pools and sustaining agricultural productivity.
While studies on the interacting effects of traditional tillage systems vs. residue management on soil properties are many (Larson et al., 1978; Lindstrom et al., 1979; Kladivko, 1994), changes in SOC dynamics resulting from differential corn stover removal are not well documented. The magnitude of the impacts of crop residue removal on SOC dynamics and related properties can be variable depending on soil textural characteristics, management, and climate (Karlen et al., 1994). Many of the soils of the North Central region possess silty surface textures which are naturally more susceptible to physical degradation and reduction in SOC pools. Decline in soil organic C concentration and deterioration of soil structural properties as a result of stover removal can be significant. Several studies in the Midwestern U.S. Corn Belt region including those from Iowa (Larson et al., 1972), Indiana (Barber, 1979), Minnesota (Allmaras et al., 2004; Wilts et al., 2004), Wisconsin (Karlen et al., 1994); and Ohio (Blanco-Canqui and Lal, 2007) have shown that stover removal may reduce the SOC concentration. In other regions, reductions in soil organic C concentration due to stover removal may, however, be small or not significant (Hooker et al., 2005). The SOC concentration is also positively correlated with aggregate stability (McVay et al., 2006). Stover removal may then degrade soil physical properties and reduce SOC pool. In South Dakota, Hammerbeck et al. (2012) reported that stover removal reduced mean weight of diameter of both 0.84-2.0 mm water-stable aggregates and >19.2 mm dry aggregates from no-till corn-soybean rotation after 8 yr of management. The same study found that stover removal reduced concentration of soil organic matter and particulate organic matter in all aggregate size fractions.
An increase in stover removal rate may also increase soil temperature fluctuations (Sharratt, 2002), increase evaporation (Flerchinger et al., 2003), and decrease plant available water (Moebius-Clune et al., 2008), all of which are variables that can impact soil productivity from year to year. Stover removal impacts on crop yields, and therefore, soil productivity, can be inconsistent. Stover removal may (Wilhelm et al., 1986; Varvel et al., 2008) or may not (Karlen et al., 1994) reduce crop yields, depending on the management and site-specific conditions. Excessively wet and cold soils during the germination period under stover mulch may delay emergence and reduce crop yields in some soils (Swan et al., 1994). Furthermore, stover removal may not affect corn yield in fertile and flat soils (Karlen et al., 1994), particularly in the short term, but it may rapidly reduce corn yield in sloping and erosion-prone soils. In Ohio, removal rates of 50 and 75% resulted in a 1.95 Mg ha-1 decrease in grain yield, and 100% removal decreased yield by 3.32 Mg ha-1 on a silt loam with 10% slope, but differences in grain yield due to stover removal were not significant in flat clayey and silt loam soils (Blanco-Canqui and Lal, 2007). In eastern Nebraska, averaged across four years, each Mg ha-1 of stover removed reduced grain yield by 0.1 Mg ha-1 and stover yield by 0.30 Mg ha-1 (Wilhelm et al., 1986). Another study in eastern Nebraska found that, averaged across five years, 51% stover removal consistently reduced grain and stover yield (Varvel et al., 2008). The above studies were conducted under rainfed conditions. Published data on stover removal impacts on grain and stover yield for irrigated conditions are practically unavailable. Furthermore, the cited studies illustrate the range in effects of residue removal that can occur in the North Central Region of the U.S.
Blanco (2013) published a recent review article, examining options for replenishment of SOC that will be lost from soils following crop residue harvest. The possibilities reviewed in this paper were the addition of cover crops to no-tillage (single or multiple species), addition of animal manures or compost, the return of bioenergy byproducts such as biochar to the soil, and finally, the addition of perennial bioenergy crops to the landscape. Note that there are very few studies that currently examine the removal of residue plus the intensification of the cropping system through these additional inputs, but rather, these are practices with a long and known history of increasing SOC pools. The predicted rapid expansion of the demand for crop residues for bioenergy will create a market, and thus more incentive to study such intensified systems.
Previous work by members of NC-1017 and NC-1178 has demonstrated the importance of storing SOC (through increasing organic matter) for improving soil quality, including soil physical properties such as improved water holding capacity (Lal, 1999). However, a strong connection between soil erosion and the global C balance has not been well established. There is also a need for developing sound methodology for obtaining a quantitative estimate of the actual distribution of soil C on various eroded and non-eroded landscapes in the Midwest. Also, there is a need to examine the alternative of intensified agroecosystems as a source for feedstock. It was recognized during the Kyoto Protocol that net emissions of greenhouse gases, such as CO2 and CH4 could be decreased by either reducing emissions or by increasing the rate of C sequestration or retention in soils. Agricultural soils are one of the largest reservoirs of C, and thus have a great potential to mitigate the increasing concentration of CO2 in the atmosphere (FAO, 2001). Evaluation of the C pool in soils is difficult because of its heterogeneity in time and space (FAO, 2001). The global loss of C because of erosion is estimated to be in the range of 150 to 1500 million tons per year (Lal, 1995; Gregorich et al., 1998; Lal, 2003) but the processes are not well understood. Erosion is a selective process involving detachment and transport of the light soil fraction consisting of SOC and clay (Sharpley, 1985). The fate of eroded soil particles is complex depending on many parameters including soil properties, landscape elements and properties, drainage net and soil management. Many of the soil particles eroded are moved down slope and may remain in the same field or watershed for a considerable length of time. However, this movement results in increased spatial variability of soil properties across the landscape, especially soil organic matter and those elements of environmental concern that are associated with it - carbon and nitrogen (Schumacher et al., 1999).
This proposal outlines a project designed to help better understand changes in soil quality including soil degradation resulting from crop residue removal and the impact of intensified agroecosystems on soil health and soil carbon dynamics for biofuel production and animal production systems. It will also provide needed data on the changes in the soil C reservoir related to intensive land use and residue removal for some of the major soils in the North Central region. This study will contribute to our understanding of soil-landscape processes with the potential to provide data that will contribute to improved management of our soil and water resources. We view this approach as a natural progression related to the past research efforts of NC-174, NC-1017, and NC-1178.
Knowledge gained from the proposed research will contribute to a more quantitative understanding of the effects of intensified agroecosystem management (crop residue removal) on global C balance; erosional processes; the amounts and landscape distribution of C and organic matter; and changes in soil quality. The proposed regional research project will provide information that can be used to enable sustainable management of natural resources in different ecosystems, over the varying climates and soil landscapes that occur in the participating states. The findings from this project can provide baseline information on soil sustainability impacted by possible climate change such as increased intense rainfall events, decreased total precipitation, and increased temperatures.
Related, Current and Previous Work
Society demands that current agricultural systems to be environmentally sound. This vision may be realized through system diversification and intensification to mitigate negative impacts on environmental quality and enhance agroecological services. Modern agriculture promotes specialization in the form of a monoculture row cropping system for simplification of planting, management and harvesting. However, this traditional agriculture system is increasingly facing environmental challenges giving the climate change and the extreme cycles of dry and wet conditions. Therefore, a new shift in current agriculture systems is imperative to reduce stress on soil and ecological functions. Studies of agroecosystems over the past several decades documented the negative ecological and environmental impacts of high intensity monoculture agriculture (Dore et al, 2011). One of the approaches to mitigate ecological negative impact is ecological intensification and diversification of agroecosystem. Ecological intensification has generally considered to be based on the use of biological regulation to manage agroecosystem (Dore et al., 2011). Diverse multispecies agroecosystems have been proposed as viable alternatives to low diversity monoculture systems to sustain agricultural productivity into the future (Kirschenmann, 2007). Like other natural and semi artificial ecosystems, agroecosystems can provide services, such as soil C sequestration or retention and other physical and biological benefits. The intensification of agroecosystem provides these services, which are not always guaranteed through traditional agricultural systems. The intensification and diversification of agroecosystem by introducing perennial crops and or cover crops for example relative to annual crops that offer a low-input, less polluting, and more efficient alternative to annual monocultures for enhancing ecological services and sustaining system productivity for multiple added value products such feedstock for bioenergy production (Tilman et al., 2006). Perennial polycultures also produce more ground cover to reduce soil erosion (Pimentel et al., 1987); minimize nutrient leaching (Dinnes et al., 2002) and sequester more carbon in soils (Follett et al., 2012; Freibauer et al., 2004). It has been argued that the mission of multi-objective agriculture could be best achieved by using biological regulators mechanisms at different levels, such as, crop management, cropping system design, landscape layout, and management inputs (Matson et al., 1997; Mediene et al., 2011).
The current trend in providing feedstock for bioenergy is focusing on the use of crop residue (i.e., corn residue) for cellulosic ethanol production. This approach can have significant short and long-term environmental impacts and degradation of soil health and water quality. Offsite damages to the environment caused by soil erosion and subsequent deposition of sediments in the U.S. are considerable (Pimentel, 1992). Deposition of eroded soil materials in surface water bodies such as reservoirs, lakes, rivers, and streams caused a decline in water quality, reduced environmental quality, and decreased the functional life expectancy of reservoirs. Eroded sediments often contain not only soil materials from the organic surface soil which are enriched in nutrients and C, but often include commercial and/or organic (animal waste) fertilizers, pesticides, and agricultural pharmaceuticals (from animal waste). To mitigate such potential damages new agroecosystem that include perennials and cover crops need to be considered to provide multiple ecoservices that include protection of soil, water quality, providing feedstock sources, and protection of wild life habitat. In intensified agroecosystem, one of the main benefits is nutrient use efficiency and cycling by reducing for example nitrogen loss due to access water leaching or greenhouse gas emissions by reducing the carbon footprints from fossil fuel input (Galloway et al., 2008; Spiertz, 2010). The oversimplification of current agriculture cropping systems and the emphasis on mono-annual cropping system coupled by intensive tillage and other synthetic fossil fuel based input led to ignoring of the biological nature of plant-soil relationship and the potential negative impacts on soil and environmental quality. To restore the role of biological regulator, the agroecology has emerged in reaction to such specialization by placing biological component back in the system (Altieri, 1989). The natural ecosystem can provide an excellent model for the development and implementation of agroecosystem to enhance and maximize soil and environmental services to sustain soil health, increases soil C sequestration or retention, and reduce greenhouse gases emissions (Altieri, 202; Vandemeer, 2003). The concept is based on the assumption that natural system is more adaptable to the changes and constraints of regional conditions. The incorporation of certain aspects of natural system into agroecosystem would eventually improve and enhance services of agroecosystems that include productivity stability and other ecological functions such as biodiversity, SOC pools, soil physical properties, etc. (Fukai, 1993).
Past and future NC-1178/NC-1017/NC-TEMP-1017/NC-174/NCT-199 research efforts are summarized in Table 1 (see attached). The sequence represents a natural progression from studying soil productivity-erosion relationships to determining C distributions, dynamics and sequestration, and changing management in eroded landscapes.
During the first 5-year phase of the NC-174 project (1983-1988) we identified and documented the effects of erosion on soil properties and corn or small grain yield for research sites located in 11 states (Table 1). Five years of data were collected to better document the effects of weather on the interaction between soil properties and corn yield in the north central United States. First phase achievements included 13 refereed journal articles and chapters in books. Once the database was enlarged, emphasis was placed on selection of management and restoration alternatives at either the initial or a new research site (Table 1, phase 2). The NTRM (Nitrogen, Tillage, Residue and Management) and EPIC (Erosion-Productivity Impact Calculator) models were used in conjunction with the existing data base collected during the initial phase of the NC-174 project to identify factors limiting crop productivity of each soil series investigated. The models were used to evaluate long-term effect of management and restoration alternatives prior to field testing.
The second phase (Table 1) of the project (1988-1993) was to field test the practices selected to maintain or enhance current productivity and to determine the extent to which productivity of eroded soils can be restored. Phase 2 outputs included 25 journal articles and chapters in books.
The third phase (Table 1) of the project (1993-1998) determined threshold soil property values for the restoration of productivity and quality of eroded soils to initial levels. Third phase accomplishments included 74 refereed journal articles and chapters in books.
During the fourth phase (Table 1) of the project, from 1998 to 2003, we examined the erosional and landscape impacts on soil processes and properties as well as assessed the management effects on eroded soil productivity and the quality of soil, air, and water resources. Achievements during phase 4 of the project included 70 refereed journal articles and chapters in books.
In the fifth phase (2004-2009) (Table 1) the main focus was on C distribution and sequestration within the landscape. This focus was integrated with the previous phase by examining the impact of management and erosion on C distribution within the landscape and related to soil quality and productivity. Fifth phase achievements included 84 refereed journal articles and chapters in books. The fifth phase included representation external to the North Central region including participants from Guam and Manitoba.
The sixth phase (2009-2014) (Table 1) builds on previous achievements by examining the role of crop residue removal on factors affecting crop productivity and C sequestration or retention. The findings from these studies are being linked to existing studies that relate management and erosion on C distribution within the landscape to soil properties associated with soil quality and productivity. At this time, sixth phase achievements include 26 refereed journal articles and book chapters.
The seventh phase (this phase, 2014-2019) will build on work and achievements from the sixth phase but will also include the impacts of utilizing cover crops and perennial crops in intensifying land use in agronomic systems that are being included in biofuels production. This work will evaluate the impacts of continuous biomass removal on soil C distribution and soil properties that impact land management and soil erosion on landscapes common to the region.
There is currently only one multistate project that is related to our proposed project. This project is NCERA-059 (Soil Organic Matter: Formation, Function and Management).
NCERA-059 is an unfunded committee that does not coordinate joint research across participants. The objectives of NCERA-059 are broad and diverse. These include: 1) Coordinating research collaborations and information exchange on the biochemistry, biological transformations, and physical/chemical fractions of soil organic matter; 2) Identifying and evaluating indicators that can be used to assess soils as a resource for ecosystems services; 3) Conducting outreach activities to scientists in relate disciplines and practitioners to promote the ecological management of soils, including practices that repair or sustain functionally important SOM fractions in both managed and undisturbed systems; 4) Co-sponsoring symposia at national and international meetings; and 5) Interacting with other regional committees. NC-1178 currently has one individual who is also a member of NCERA-059. The two multistate committees have been in communication with each other and have jointly participated in combined meetings in the past.
Nationally, there are two projects that have some relationship to our proposed project. These are S-1048 (Assessment of the Carbon Sequestration Potential of Common Agricultural Systems on Benchmark Soils Across the Southern Region Climate Gradient) and SCC-083 (Quantifying Linkages Among Soil Health Organic Farming and Food). Both are located in the Southern Region.
S-1048 coordinates joint research across participants. Its main objective is to directly assess the soil C sequestration potential of common agricultural and natural ecosystems of varying ages on Benchmark soils across the southern climate gradient. Its sub-objectives include: 1) Evaluate the effects of land use, crop rotation, tillage practice, soil texture and ecosystem age/rotation duration on soil C concentration, content and sequestration and related soil physical and chemical properties; 2) Quantify and understand the physical and chemical processes that relate to and control soil C sequestration; and, 3) Investigate spatial variability issues associated with soil C content and sequestration.
SCC-083 is similar to NCERA-059 in that it is an unfunded committer that does not coordinate joint research across participants. Its objectives include: 1) Coordinate activities and information exchange among researchers involved in active projects designed to quantify the impact of conservation tillage, cover crop, crop rotation, and soil amendment practices on soil health and food quality in organic farming systems; 2) provide opportunities for experienced and new organic farming researchers to establish collaborative projects designed to identify linkages between organic farming practices, soil health and food quality; 3) Conduct outreach activities that provide unbiased scientific information on the impact organic farming can have on soil health and food quality at local, regional, national and international scales; and, 4) Interact with the multi-state research coordinating and information exchange committee NCERA-059 and other regional committees dedicated to enhancing the soil resource base in organic farming systems.
Based on a current CRIS search, there are no other current research projects noted that are not related to one of the above regional efforts or to the current NC-1178 project. Results from past research in this area has been covered in the Related, Current and Previous Work section above.
Evaluate the impact of intensifying agroecosystems inputs (e.g., cover crops, perennial crops) on maintaining/enhancing soil organic C, soil quality, productivity and the environment.
Assess management effects (e.g., crop residue removal, tillage) on soil organic C, GHG emissions, soil erosion, and productivity.
MethodsObjective 1. Evaluate the impact of intensifying agroecosystems inputs (e.g., cover crops, perennials) on maintaining/enhancing soil organic C, soil quality, productivity and the environment. Most states will participate in Objective 1. It is recommended that each participating state, a minimum of two sites with contrasting agroecosystems, but similar soil-landscape relationships will be sampled. For most states the least disturbed ecosystem will be native grass or timber, depending on the location in the NC and other Multi-State regions. The other site will be an intensively managed agroecosystem used for continuous row crop or wheat production, and the integration of cover crops or perennial grasses within the study design. All treatments will be established, if possible, in a randomized completed block design, with a minimum of three plots (replications) per treatment. Initial (baseline) soil C data will be collected prior to treatment establishment (Olson, 2013). Three soil cores should be collected from center of each plot/treatment with a 120-cm long, 6-cm diameter solid steel sampling tube containing a 5.7-cm acetate contamination liner to a recommended minimum depth of 1 meter (sampling depth may depend on thickness of soil root zone and presence or absence of carbonates). In the laboratory, the cores will be cut into 5-cm, 15-cm, or 30-cm sections and core bulk density will be determined on each section. Each core section will constitute one soil sample. The soils will be air-dried and crushed to pass a 2-mm screen. The soil profiles will be described using standard procedures and sampled as described above. Particle-size analysis, pH, bulk density, total C, particulate organic matter (POM), and SIC (if carbonates are present) or SOC (if carbonates are not present), and moisture at time of sampling will be completed for each sample. A minimum of three cores will be collected per treatment to compensate for soil variability within the local study area. No less than two cores will be collected per treatment to account for variability. Preference will be given to section the cores by defined depth increments rather than by horizon because it is simpler to later compile the data to calculate C mass in the soil. Horizons are not the same thickness from plot to plot or treatment-to-treatment. The depth increments will not be less than 5-cm and will be selected based on the soils and treatments being studied. Ideally, the first one or two increments from the surface should be 5-cm because of the expected rapidly changing differences due to management practices. Deeper in the profile, the increments will be at least 15-cm. Addition of cover crops and perennials to intensified agroecosystems may have more rapidly change concentration of labile C fractions or POM than on total C, a detailed characterization of SOC components will be done. Analysis of coarse and fine POM will be performed on the whole soil and aggregates following the procedures outlined by Cambardella and Elliot (1992). All the cores collected from a given study will have the same depth increments for ease of comparing treatment effects. Approximately 10-15 g subsamples will be further ground to pass a 100 mesh screen for C analysis. The C content of soils will be adjusted for soil bulk density and reported as kg C /m3 or Mg C/ha/m if sampled to 1 meter and as kg C /m2/ root zone depth or Mg C/ha/root zone depth if carbonates are present. A procedure manual will be developed to accommodate regional soil (such as presence or absence of carbonates) and weather differences to insure as much uniformity in sampling procedure and laboratory analyses as possible. The impact of different agroecosystem treatments on several soil parameters and soil quality indicators such as, soil surface physical properties The impact of crop residue removal on soil surface physical properties including cone index, infiltration, air permeability, saturated hydraulic conductivity, and wet aggregate stability will be evaluated for the control. The surface air permeability will be measured with an air permeameter (Ball and Schjonning, 2002; Grover, 1955). Surface soil saturated hydraulic conductivity will be measured with a tension infiltrometer (Clothier and Scotter, 2002; Wooding, 1968; Lowery and Morrison, 2002). A minimum of three of each of these measurements of soil physical properties will be made in each plot. Data from physical property measurements will be analyzed with appropriate statistical method(s). In addition, other soil quality indicators such soil aggregate stability (Guzman and Al-Kaisi, 2011) and microbial biomass C (Horwath and Paul 1994) will be determined. It is recommended that soil samples for aggregate stability be collected for the top 15 cm using golf course cutter of 15 cm long and 15 cm in diameter (Guzman and Al-Kaisi, 2011). The soil will sieved through 8-mm sieve at filed moisture condition and left to air dry on brown paper. Aggregate fractions can be separated by wet sieving or dry sieving with set of sieves range between 4 to 0.053 mm in diameter. Soil C can be evaluated for each fraction size. Aggregate associated C must be based on sand-free fraction by determining sand content for each aggregate faction size. The soil samples for microbial biomass will be collected for the top 15 cm. Soil samples can be collected using hand probe. The soil samples should be kept in 4o C if they are not processed immediately in the same day. Soil samples must be processed the next day by removing the soil samples from the cold storage to the laboratory and sieve soil samples through 2 mm sieve. Microbial biomass C will be determined by using the procedure by Horwath and Paul (1994). Objective 2. Assess management effects (e.g., crop residue removal, tillage) on soil organic C pools, GHG emissions, soil erosion, and productivity. All states will participate in Objective 2. In each participating state, a minimum of two sites with contrasting ecosystems but similar soil-landscape relationships will be sampled. For most states the least disturbed ecosystem will be native grass or timber, depending on the location in the NC and other Multi-State regions. The other site will be an intensively managed agroecosystem used for continuous row crop or wheat production. Different rates of crop residue management, to be implemented on replicated plots, will include selected rates of removal and addition of crop residue from the previous year. The percentage of stover mulch cover in each plot will be estimated using the line transect or photograph method or equivalent methods (Sloneker and Moldenhauer, 1977; Lowery et al, 1984). Soil sampling and soil analytical procedures used for Objective 1 will also be used for this objective. Greenhouse gas (GHG-CO2, N2O and CH4) emissions rates will be measured following sampling protocol of GRACEnet Chamber-based Trace Gas Flux Measurement (Parkin and Venterea, 2010). Two PVC rings (30 cm diameter and 10 cm tall) will be installed in each plot to a depth of approximately 6 cm. In each plot one ring will be placed directly in the plant row. The other ring will be placed between plant rows. Flux measurements will be performed by placing vented chambers (30 cm diameter and 10 cm tall) on the PVC rings and collecting gas samples 0, 30, and 60 min following chamber deployment. At each time point chamber headspace gas samples (10 mL) will be collected with polypropylene syringes and immediately injected into evacuated glass vials (6 mL) fit with butyl rubber stoppers. GHG concentrations in samples will be determined with a gas chromatography (GC) instrument.
Measurement of Progress and Results
- Enhanced understanding of soil-landscape processes thus contributing to improved management of soil and water resources.
- Documentation of changes in the soil C pool and surface soil physical properties related to biomass/feedstocks management for selected major soils in the NC and other participating regions.
- Identification of most sensitive SOC pool fractions that influenced by soil and biomass management practices.
- Contributions of information for use in decision aides designed for evaluation of biofuel production systems applied to marginal lands.
- Analysis of the effects of landscape positions on soil erosion, SOC distribution, and soil physical properties.
- Scientific publications, guidebooks, and fact sheets that address the specific benefits of crop residue management practices on soil and crop productivity as well as environmental quality.
- Organization of workshops and meetings designed to extend information to land managers and policy makers.
Outcomes or Projected Impacts
- Reduced soil degradation in previously eroded landscapes. Information generated in this project will provide an analysis of the interaction of crop residue management impacts on soil organic C and soil surface properties critical to sustained biofuel and crop production applicable to a wide geographic region. We will have a better understanding of changes in surface soil properties resulting from intensive cropping and residue removal for biofuel production on soil quality among selected agroecosystems.
- An increase in scientific knowledge concerning soil-landscape processes. Knowledge generated in this project will be useful for documenting economic and environmental benefits for adoption of conservation based biofuel production systems that enhance soil organic C and soil surface properties that sustain crop productivity in eroded landscapes. This information will foster improved management of our resources and enhanced environmental quality.
- Biofuel and conservation policies and management practices based on science based information. Information generated from this project will provide information based on regional coordinated experiments that can be used by policy makers and land managers to make informed decisions about policies and production practices that apply to erodible landscapes.
Milestones(2014): Site selection/treatment modifications at existing sites
(2016): Mid-term Review
(2018): Completion of sample and laboratory analyses
(2018): Workshops and meetings; Begin posting of findings on project website and state agricultural experiment station and extension service web sites.
(2019): Project Completion
Projected ParticipationView Appendix E: Participation
Results will be presented in refereed publications and in posters and symposia at National Meetings of the American Society of Agronomy, Soil Science Society of America, and the Soil and Water Conservation Society. We will also provide the information to collaborating agencies such as the NRCS and various federal, state, and local agencies. Findings will be posted on websites devoted to the transfer of information to the general public including University websites and our project website. Additionally, committee members will extend this information at workshops, local field days, field tours, and through preparation of fact sheets. The Committee will also organize a symposium on residue removal impacts on soil quality at either the SSSA or SWCS annual meetings in 2016 and 2017, respectively.
The Regional Technical Committee will follow the operational procedures listed in the State Agricultural Experiment Directors, CSREES and ESCOP document entitled "Guidelines for Multistate Research Activities" revised and dated April 2002. The voting membership of the Regional Technical Committee includes one representative from each cooperating agricultural experiment station or institution appointed by the director and a representative of each cooperating USDA-ARS research unit or location. The administrative advisor and the CSRS representative are non-voting members. All voting members of the Technical Committee are eligible for office. The offices of the Regional Technical Committee include the Chair, the Vice-Chair and the Secretary. The chair, secretary, and secretary-elect will be elected by committee membership and serve for one year. The secretary will assume the chair position upon the completion of the term of the chair. The secretary-elect will assume the secretarys position when the vice chair assumes the chairs position and then the chairs position. The annual meetings will be hosted by the chair at his/her location or at a location determined by the committee membership.
The duties of the Technical Committee are to coordinate work activities related to the project. The Chair, in accord with the Administrative Advisor, will notify the Technical Committee of the time and place of the meeting will prepare the agenda and preside at meetings of the Technical Committee and Executive Committee. He or she is responsible for preparing the annual progress report and coordinating the preparation of regional reports. The Vice-Chair assists the Chair in all functions and the Secretary records the minutes and performs other duties assigned by the Technical Committee or Administrative Advisor. The Chair appoints subcommittees as needed. Annual meetings will be held by the Technical Committee, as authorized by the Administrative Advisor, for the purpose of conducting business related to the project.
One of the tasks of the Committee is to seek external funding for strengthening research and teaching components. The Committee members will prepare and submit grant proposals for seeking funding support from several sources including USDA(NRI), USEPA, and industry. The focus of the grant proposal(s) will be conducting research on the impact of harvesting crop residues on: (1) mass balance of C,N and water, (2) structural properties including crusting and
surface sealing,(3) gaseous emissions including C dioxide, methane and nitrous oxide, (4) soil erodibility and erosion.
Allmaras, R.R., D.R. Linden and C.E. Clapp. 2004. Corn-residue transformations into root and
soil carbon as related to nitrogen, tillage, and stover management. Soil Sci. Soc. Am. J. 68: 366-¬375.
Altieri, M.A. 2002. Agroecology: the science of natural resource management for poor farmers
in marginal environments. Agric. Ecosyst. Environ. 93:1-24.
Altieri, M.A. 1989. Agroecology-a new research and development paradigm for world
agriculture. Agric. Ecosyst. Environ. 27:37-46.
Bajracharya, R.M. and R. Lal. 1998. Crusting effects on erosion processes under simulated
rainfall on a tropical Alfisol. Hydrol. Processes 12:1927-1938.
Ball, B.C., and P. Schjonning. 2002. Air permeability. p. 1141-1158. In J.H. Dane and G.C.
Topp (ed.) Methods of soil analysis Part 4: Physical methods. Soil Sci. Soc. of Am. Book Series 5. SSSA, Madison, WI.
Barber, S.A. 1979. Corn residue management and soil organic matter. Agron. J. 71:625-627.
Baumhardt, R.L., P.W. Unger and T.H. Dao. 2004. Seedbed surface geometry effects on
soil crusting and seedling emergence. Agron. J. 96:1112-1117.
Black, A.L. 1973. Soil property changes associated with crop residue management in a
wheat-fallow rotation. Soil Sci. Soc. Am. Proc. 37:943-946.
Blanco-Canqui, H., C.A. Shapiro, C.S. Wortmann, R.A. Drijber, M. Mamo, T.M. Shaver, and R.B. Ferguson. 2013. Soil organic carbon: The value to soil properties. J. Soil Water Conserv. 68:129A-134A.
Blanco-Canqui, H. 2013. Crop residue removal for bioenergy reduces soil Carbon pools: How
can we offset losses? Bioenerg. Res. 6:358-371.
Blanco-Canqui, H., and R. Lal. 2007. Soil and crop response to harvesting corn stover for
biofuel production. Geoderma 141:355-362.
Cambardella CA and Elliot ET. 1992. Particulate soil organic matter changes across a grassland cultivation sequence. Soil Sci. Soc. Am. J. 56:777-83.
Clothier, B., and D. Scotter. 2002. Unsaturated water transmission parameters obtained from
infiltration. p. 879-898. In J.H. Dane and G.C. Topp (ed.) Methods of soil analysis Part 4: Physical methods. Soil Sci. Soc. of Am. Book Series: 5. Madison, WI.
Crosson, P.R. 1984. New perspectives on soil conservation policy. J. Soil Water Conserv.
Crosson, P.R. 1986. Agriculture and the Environment In: T. Phipps, P. Crosson, and K. Price,
(eds.). Resources for the Future, Washington, DC. pp. 35-73.
den Biggelaar, C., R. Lal, K. Wiebe, and V. Breneman. 2001. Soil erosion impacts on crop
in North America. Advances in Agronomy 72(1). pp. 1-52.
Dinnes, D.L., D.L. Karlen, D. B. Jaynes, T. C. Kaspar, J. L. Hatfield, T. S. Colvin and C. A.
Cambardella. 2002. Nitrogen management strategies to reduce nitrate leaching in tile-drained Midwestern soils. Agron. J. 94:153-171
Dore, T., D. Makowski, E. Maleezieux, N. Munier-Jolain, M. Tchamitchian, and P.
Tittonell. 2011. Facing up to the paradigm of ecological intensification in agronomy: Revisiting methods, concepts, and knowledge. Europ. J. Agronomy. 34:197-210.
EPA. 2013. Regulation of Fuels and Fuel Additives: 2013 Renewable Fuels Standards. Docket
ID No. EPA-HQ-OAR-2012-0546. www.regulations.gov. (verified 12 August 2013).
Food and Agriculture Organization (FAO). 2001. Soil carbon sequestration for improving land
management. World Resource Rep. #96. p. 62. Published by Food and Agriculture Organization for the United Nations.
Follett, R. F., K. P. Vogel, G. E. Varvel. R. B. Mitchell, and J. Kimble. 2012. Soil carbon sequestration by switchgrass and no-till maize grown for bioenergy. Bioenerg. Res. DOI 10.1007/s12155-012-9198-y.
Flerchinger, G.N., T.J. Sauer, and R.A. Aiken. 2003. Effects of crop stover cover and
architecture on heat and water transfer at the soil surface. Geoderma 116:217-233.
Freibauer, A., M. D. A. Rounsevell, P. Smith, and J. Verhagen. 2004. Carbon sequestration in
the agricultural soils of Europe. Geoderma 122: 1-23.
Fukai, S. 1993. Intercropping-base of productivity-introduction. Field Crop Res. 34:239-245.
Galloway, J.N., A.R. Townsend, J.W. Erisman, M. Bekunda, Z. Cai, J.R. Freney, L.A.
Martinelli, S.P. Seitzinger, and M.A. Sutton. 2008. Transformation of the nitrogen cycle: recent questions, and potential solutions. Science 320:889-892.
Gregorich, E.G., K.J. Greer, D.W. Anderson, and B.C. Liang. 1998. Carbon distribution
and losses: erosion and deposition effects. Soil Tillage Res. 47:291-302.
Grover, B.L. 1955. Simplified air permeameters for soil in place. Soil Sci. Soc. Am. Proc.
Gupta, S.C., E.C. Schneider, W.E. Larson and A. Hadas. 1987. Influence of corn residue
on compression and compaction behavior of soils. Soil Sci. Soc. Am. J. 51:207-212.
Guzman, J.G., and M.M. Al-Kaisi. 2011. Landscape position effect on selected soil physical
properties of reconstructed prairies in south central Iowa. J. Soil Water Conserv. 66: 183-191.
Hammerbeck, A.L. , S.J. Stetson, S.L. Osborne, T.E. Schumacher, and J.L. Pikul. 2012. Corn
residue removal impact on soil aggregates in a no-till corn/soybean rotation. Soil Sci. Soc. Am. J. 76:1390-1398.
Hooker, B.A., T.F. Morris, R. Peters and Z.G. Cardon. 2005. Long-term effects of tillage and
corn stalk return on soil carbon dynamics. Soil Sci. Soc. Am. J. 69:188-196.
Johnson, J.M.F., D. Reicosky, B. Sharratt, M. Lindstrom, W. Voorhees and L. Carpenter-
Boggs. 2004. Characterization of soil amended and the by-product of corn stover fermentation. Soil Sci. Soc. Am. J. 68:139-147.
Horwath, W.R., and E.A. Paul, 1994. Microbial biomass. In Methods of Soil Analysis Part 2:
Microbiological and Biochemical Properties, ED. S.H. Mickelson, Madison, WI.
Soil Sci. Soc. Am. 753-774.
Karlen D.L., N.C. Wollenhaupt, D.C. Erbach, E.C. Berry, J.B. Swan, N.S. Eash, and J.L. 1994.
Crop residue effects on soil quality following 10-years of no-till corn. Soil Tillage Res. 31:149-167.
Kim, S. and B.E. Dale. 2004. Global potential bioethanol production from wasted crops and crop
residues. Biomass Bioenergy 26:361-375.
Kirschenmann, F. L. 2007. Potential for a new generation of biodiversity in agroecosystems of
the future. Agron. J. 99:373-376.
Kladivko, E.J. 1994. Residue effects on soil physical properties. p. 123-162. In P.W. Unger
(ed.) Managing agricultural residues. Lewis Publishers, Boca Raton, FL.
Lal, R. 1999. (ed). Soil Quality and Soil Erosion. CRC Press. Boca Raton, FL. 329p.
Lal, R. 2003. Soil erosion and the global carbon budget. Env. Intl. 29:437-450.
Langdale, G.W., H.P. Denton, A.W. White, Jr., J.W. Gilliam, and W.W. Frye. 1985. Effects of
soil erosion on crop productivity of Southern soils. p. 251-269. In R. J. Follett and B.A. Stewart (eds.) Soil Erosion and Crop Productivity. Am. Soc. Agron., 677 S. Segoe Road, Madison, WI.
Larson, W.E., C.E. Clapp, W.H. Pierre, and Y.B. Morachan. 1972. Effects of increasing
amounts of organic residues on continuous corn. II. Organic carbon, nitrogen, phosphorus and sulfur. Agron. J. 64:204-208.
Larson, W.E., R.F. Holt and C.W. Carlson. 1978. Residues for soil conservation. p. 1-15. In
W.R. Oschwald (ed.) Crop residue management systems. Spec. Pub. 21. ASA, Madison, WI.
Lindstrom, M.J. E.L. Skidmore, S.C. Gupta and C.A. Onstad. 1979. Soil conservation
limitations on removal of crop residues for energy production. J. Environ. Qual. 8:533-537.
Lowery, B., T.M. Lillesand, D.H. Mueller, P. Weiler, F.L. Scarpace, and T.C. Daniel. 1984.
Quantitative determination of crop residue using a microdensitometer. J. Soil Water Conserv. 39: 402-403.
Lowery, B., and J.E. Morrison, Jr. 2002. Soil penetrometers and penetrability. p. 363-388. In
J.H. Dane and G.C. Topp (ed.) Methods of soil analysis Part 4: Physical methods. Soil Sci. Soc. of Am. Book Series: 5. Madison, WI.
Maiorana, M., A. Castrignano and F. Fornaro. 2001. Crop residue management effects on
soil mechanical impedance. J. Agric. Eng. Res. 79:231-237.
Matson, P.A., W.J. Parton, A.G. Power, and M.J. Swift. 1997. Agriculture intensification and
ecosystem properties. Science 277: 504-509.
McVay, K.A., J.A. Budde, K. Fabrizzi, M.M. Mikha, C.W. Rice, A.J. Schlegel, D.E. Peterson,
D.W. Sweeney and C. Thompson. 2006. Management effects on soil physical properties in long-term tillage studies in Kansas. Soil Sci. Soc. Am. J. 70(2):434-438.
Mediene, S., M. Valantin-Morison, J.P. Sarthou, S. de Tourdonnet, M. Gosme, M. Bertrand,
J. Roger-Estrade, J.N. Auberttor, A. Rusch, N. Mortisi, C. Pelosi, and T. Dore. 2011. Agroecosystem management and biotic interactions. A review. Agron. Sustain. Dev. doi: 10.1007/s13593-011-0009-1.
Mochizuki, M.J., A. Rangarajan, R.R. Bellinder, H.M. van Es and T. Bjorkman. 2008. Rye
mulch management affects short-term indicators of soil quality in the transition to conservation tillage for cabbage. Hortsci. 43(3):862-867.
Moebius-Clune, B.M., H.M. van Es, O.J. Idowu, R.R. Schidelbeck, D.J. Moebius-Clune, D.W.
Wolfe, G.S. Abawi, J.E. Thies, B.K. Gugino, and R. Lucey. 2008. Long-term effects of harvesting maize stover and tillage on soil quality. Soil Sci. Soc. Am. J. 72:960-969.
Morachan, Y.B. W.C. Moldenhauer and W.E. Larson. 1972. Effects of increasing amounts of
organic residues on continuous corn: I. Yields and soil physical properties. Agron. J. 64:199-203.
Nelson, D.W. and L.E. Sommers. 1982. Total carbon, organic carbon, and organic matter.
p. 539-579. In A.L. Page (ed). Methods of Soil Analysis Part 2, Chemical and Microbiological Properties (2nd edition). Agronomy Monograph No. 9. American Society of Agronomy. Madison, WI.
Nelson, R.G. 2002. Resource assessment and removal analysis for corn stover and wheat straw in
the Eastern and Midwestern United States-Rainfall and wind-induced soil erosion methodology. Biomass Bioenergy 22:349-363.
Parkin, T.B. and Venterea, R.T., 2010. Sampling protocols. In R.F. Follett, (ED.). Chamber-
based trace gas flux measurements. Sampling Protocols. pp. 3-39.
Olson, K. R. 2013. Soil organic carbon sequestration, storage, retention and loss in U.S.
Croplands: Issues paper for protocol development. Geoderma 195-196:201-206.
Or, D. and T.A. Ghezzehei. 2002. Modeling post-tillage soil structural dynamics: A review.
Soil Till. Res. 64:41-59.
Pimentel, D. 1992. Energy inputs in production agriculture. Energy World Agric. 6:13-29.
Pimentel, D., J. Allen, A. Beers, L. Guinand, R. Linder, P. McLaughlin, B. Meer, D. Musonda,
D. Perdue, S. Poisson, K. Siebert, R. Stoner, R. Salazar, and A. Hawkins. 1987. World agriculture and soil erosion. Bioscience 37:277-283.
Pimentel, D., C. Harvey, P. Resosudarmo, K. Sinclair, D. Kurz, M. McNair, S. Crist, L.
Shpritz, L. Fitton, R. Saffouri, and R. Blair. 1995. Environmental and economic costs of soil erosion and conservation benefits. Science 267:1117-1123.
Salinas-Garcia, J.R., A.D. Báez-González, M. Tiscareno-López and E. Rosales-Robles. 2001.
Residue removal and tillage interaction effects on soil properties under rain-fed corn production in Central Mexico. Soil Till. Res. 59:67-79.
Schnepf, R and B. D. Yacobucci. 2013. Renewable Fuel Standards (RFS): Overview and
Issues. Congressional Research Service R40155. http://nationalaglawcenter.org/assets/crs/R40155.pdf. (verified 12 August 2013).
Schumacher, T.E., M.J. Lindstrom, J.A. Schumacher, and G.D. Lemme. 1999. Modeling spatial
variation in productivity due to tillage and water erosion. Soil Tillage Res. 51: 331-339.
Sharpley, A.N. 1985. The selective erosion of plant nutrients in runoff. Soil Sci. Soc. Am. J.
Sharratt, B.S. 2002. Corn stubble height and stover placement in the northern US Corn Belt. Part I. Soil physical environment during winter. Soil Till. Res. 64:243-252.
Shaver, T.M., G.A. Peterson, L.R. Ahuja, D.G. Westfall, L.A. Sherrod and G. Dunn. 2002.
Surface soil physical properties after twelve years of dryland no-till management. Soil Sci. Soc. Am. J. 66:1296-1303.
Simpson, T.W., A.N. Sharpley, R.W. Howarth, H.W. Paerl, and K.R. Mankin. 2008. The new
gold rush: Fueling ethanol production while protecting water quality. J. Environ. Qual. 37:318¬324.
Sloneker, J.L., and W.C. Moldenhauer, 1977. Measuring the amounts of crop residue remaining
after tillage. J. Soil Water Conserv. 32:231-236.
Spiertz, J.H.J. 2010. Nitrogen, sustainable agriculture and food security. A review. Agron.
Sustain. Dev. 30, 43-55.
Somerville, C. 2006. The billion-ton biofuel vision. Science 312:1277.
Strudley, M.W., T.R. Green and J.C. As cough. 2008. Tillage effects on soil hydraulic
properties in space and time: State of the science. Soil & Tillage Res. 99(1):4-48.
Swan, J.B., R.L. Higgs, T.B. Bailey, N.C. Wollenhaupt, W.H. Paulson, and A.E. Peterson. 1994.
Surface residue and in-row treatment on term no-tillage continuous corn. Agron. J. 86:711-718.
Thierfelder, C., E. Amezquita, and K. Stahr. 2005. Effects of intensifying organic manuring and
tillage practices on penetration resistance and infiltration rate. Soil & Tillage Res. 82:211-226.
Tilman, D., J. Hill, and C. Lehman. 2006. Carbon-negative biofuels from low-input high-
diversity grassland biomass. Science 314:1598-1600.
U.S. Department of Agriculture-Natural Resources Conservation Service. 1996. Soil quality
indicators: Soil crusts. http://soils.usda.gov/sqi/files/sq_sev_1.pdf (verified 29 Sept. 2005).
Vandemeer, J.H. 2003. Tropical Agroecosystems. CRC Press, Boca Raton, FL. (USA).
Varvel, G.E., K.P. Vogel, R.B. Mitchell, R.F. Follett, and J.M. Kimble. 2008. Comparison of
corn and switchgrass on marginal soils for bioenergy. Biomass Bioenergy 32:18-21.
Wells, R.R., D.A. DiCarlo, T.S. Steenhuis, J.-Y. Parlange, M.J.M. Römkens and S.N. Prasad.
2003. Infiltration and surface geometry features of a swelling and following successive simulated rainstorms. Soil Sci. Soc. Am. J. 67:1344-1351.
Wilhelm, W.W., J.W. Doran, and J.F. Power. 1986. Corn and soybean yield response to crop
residue management under no-tillage production systems. Agron. J. 78:184-189.
Wilhelm, W.W., J.M.F. Johnson, J.L. Hatfield, W.B. Voorhees, and D.R. Linden. 2004. Crop
and soil productivity response to corn stover removal: A literature review. Agron. J. 96:1-17.
Wilts, A.R., D.C. Reicosky, R.R. Allmaras and C.E. Clapp. 2004. Long-term corn residue
effects: harvest alternatives, soil carbon turnover, and root-derived carbon. Soil Sci. Soc. Am. J. 68:1342-1351.
Wooding, R.A. 1968. Steady infiltration from a shallow circular pond. Water Resour.