Duration: 10/01/2006 to 09/30/2011

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Statement of Issues and Justification

The global challenge of meeting ever-increasing demand for food, fiber and energy from maize-based (Zea mays L.) agro-ecosystems requires the efficient use of fertilizer nitrogen (N) resources. Adequate N supply is required for achieving high maize yields. However, improper N fertilizer use threatens environmental quality and human health at both local and global scales through leaching losses to groundwater, hypoxia, surface water degradation, and greenhouse gas emissions. Fertilizer N also accounts for approximately 50% of the fossil energy input to maize production. With rising energy costs, this has become a major impediment to both the profitability and sustainability of maize-based cropping systems.

Since the relationship between crop yield and N uptake is tightly conserved, achieving higher yields to meet demand will require greater crop N uptake. This is most efficiently achieved not by simply increasing fertilizer N inputs, rather by also improving N use efficiency and reducing the amount of reactive N that is released to the environment (Cassman et al., 2002.).

The principal determinants of plant-available N supply are the net N release or mineralization of N from soil organic matter and crop residues, contributions from applied inorganic and organic N sources, and losses from the plant-available N pool. Therefore the supply of N from indigenous soil N resources and the synchrony of mineralization in relation to crop demand are key considerations in determining the optimal timing and rate of fertilizer N application and achieving more efficient use of fertilizer N. Since soil contents of C and N are closely related and the soil C:N ratio is relatively stable, cropping practices that enhance primary crop productivity and C input to soil will also increase indigenous soil N and over the long-term result in a reduction in fertilizer N requirement. The magnitude and annual variability of indigenous soil N supply are largely unknown, even though this N pool is of primary importance to designing efficient systems for fertilizer N management.

Indigenous soil N can be affected by diverse factors. For example, the quantity, quality and timing of carbon inputs to soil influence the formation of new soil organic matter and the storage and release of soil C and N. Empirical evidence has long suggested that both fertilizer N use efficiency and maize productivity can be improved through crop rotation. However, new evidence suggests that maize-soybean (Glycine max (L.) Merr.) rotations, the dominant crop rotation practiced in the north-central region, results in declining stocks of both soil C and soil N. (Baker and Griffis, 2005; Verma et al., 2005). Maize is also a rotation crop in many cropping systems for both grain and forage and therefore this research has broader implications as evidenced by the diverse NC-218 membership from different regions.

Improvements recorded in fertilizer N use efficiency in maize- based rotation result from exploitation of indigenous soil N, placing in question the long-term sustainability of maize-soybean rotations. Net mineralization of the indigenous N supply is influenced by cropping sequence, and it also varies greatly over time. These diverse sources of variation complicate the prediction of the indigenous N supply and the development of efficient N fertilizer applications that incorporate measures of indigenous soil N supply. To illustrate this point, no single soil test to predict N availability has been adopted by commercial soil test labs.

The majority of C and N in soil cycles slowly, over time-spans ranging from years to centuries. Only a small fraction of soil associated with decomposer activity and recent organic matter inputs cycles a rate fast enough to affect seasonal N availability. This small fraction of actively cycling N may contain significant quantities of recently deposited organic material including fine roots and fungal hyphae and is often referred to as particulate organic mater or light fraction (Tisdall and Oades 1982). Hence only a portion of indigenous soil C and N is significantly involved in seasonal N cycling, creating the need to study the active fractions of soil C and N in order to predict N mineralization and availability. Specifically we need a more explicit understanding of the nature and dynamics of active soil C and N and how management and cropping system influence the storage and release of both C and N from these pools.

The efforts of the NC-218 committee over the past decade have concentrated on the measurement of indigenous soil N supply through rapid laboratory analyses that are designed to measure the amounts of inorganic N released through chemical treatment of soil C and N or through temporal analysis of soil nitrate. These tests were evaluated and found to be incapable of predicting either the spatial variation in crop uptake of indigenous soil N as influenced by inherent edaphic properties and site productivity or the temporal variation as influenced by cropping system and previous soil and crop management practices. This absence of a broad predictive capability most likely results from the fact that no single laboratory procedure that releases inorganic N from organic N pools can act on all active N pools without simultaneously acting on older, more stabilized N pools that do not contribute to short-term N cycling under field conditions. The committee believes that this statement also applies to other rapid analyses that the committee did not evaluate. Hence the proposed new activities will not further evaluate rapid analyses for soil N availability. Instead a new research direction is proposed for improving the management of indigenous soil N.

Recent work has demonstrated the short-term activity of discrete organic fractions of soil C and N that are extracted intact from soil. The light fraction, which is extracted from the soil based on density, and the mobile humic acid fraction, which is extracted with sodium hydroxide, were shown to be highly involved in seasonal N cycling both in maize-based rotations of Nebraska (Legorreta-Padilla, 2005) and continuous rice fields in California (Bird et al., 2002). The masses and carbon contents of these organic fractions were also shown to be responsive to recent crop management. These two fractions provided complementary insights into the dynamics of short-term N and C cycling, as their constituent materials are bound in the soil by different manners and are at slightly different stages of decomposition. The stability, size, and N contribution/turnover within these pools are influenced by the nature of residue quantity and quality, anthropogenic inputs of N, and the physical environment.


To elucidate the processes that control the availability and crop uptake of indigenous soil N in maize-based rotations, members of the NC-218 committee will conduct a series of measurements on N forms and dynamics in a range of long-term field experiments and farmers fields that encompass a variety of crop rotations and soil types. A core experimental approach will be utilized across this range of experimental environments to measure gross and net N mineralization and the change in soil N and C storage and release from crop residues. Inorganic N and crop N uptake will be measured periodically during the growing seasons, and soil samples will be collected for extraction of the light fraction and mobile humic acid fraction. These fractions will be analyzed for their masses and biochemical natures. One key measurement will be their contents of specific amino acids and amino sugars, using a newly developed method of anion chromatography that identifies nearly 90% of all organic N in soil, a far greater proportion than has been possible with previously available analyses. Experiments on research farms of participating universities will be sampled in order to identify longer-term interactions between crop rotation, tillage and fertilizer treatments that affect cycling of indigenous N. Shorter-term dynamics of indigenous N will be studied in plots of N fertilizer rates that will be installed in farmers fields that have tended to differ from each other in the responsiveness of crop growth to N fertilizer rates. External funding will be sought for application of stable N and C isotopes into some sites for quantifying the rates of specific N processes in the soil, including gross mineralization and gross immobilization. The regional and cross-regional perspectives and the range of environment and expertise provided by the participants will lead to broad applicability of the findings from this research. The use of a common core experimental approach plus the centralized, collaborative arrangements for analytical work and interpretation are advantages of the regional research approach.

Impacts from the successful completion of the proposed work include a quantitative survey of indigenous N supply under a wide range of edaphic and climatic regions as influenced by cropping system and N management. In addition, we will have obtained a more complete understanding of the consequence of cropping systems on soil C sequestration potential and its link to soil N sequestration, indigenous N supply and fertilizer N use efficiency.

Related, Current and Previous Work

The amount of organic N bound in soil organic matter is several times greater than the annual rates of fertilizer N that producers typically apply. Gradual mineralization of N from this large organic pool into inorganic molecules provides much of the N supply to crops. Our ability to predict and manage the rate of N mineralization has been limited by an incomplete understanding of gross N mineralization, chemical forms of soil organic N and the factors that control their gradual mineralization.


The classical extraction for identifying chemical forms of soil organic N--hydrolysis in hot hydrochloric acid--identifies only about half of all soil N, namely as amino acids and amino sugars (Stevenson, 1994). Yet newly developed spectroscopic technologies suggest that amino compounds collectively comprise 80% or more of soil organic N (Vairavamurthy and Wang, 2002; Mahieu et al., 2002; Abe and Watanabe, 2004). Using anion chromatographic separation and pulsed amperometric detection, Martens and Loeffelmann (2003) identified 86% of N in a range of Midwestern agricultural soils as specific amino acids and amino sugars, and Martens et al. (2006) correlated maize grain yields on different soil types in an Iowan field with springtime levels of these amino compounds, the strength of correlation varying with annual precipitation.


Because soil organic matter is a blend of materials that range in age from weeks to millennia, one useful approach for studying seasonal N mineralization has been to extract organic matter from soil as discrete fractions that vary in their age. Several procedures can be used to extract the fractions, and none provides complete separation of materials by age. One chemical extraction distinguishes the labile mobile humic acid (MHA) fraction from the recalcitrant calcium humate (CaHA) fraction based on binding to polyvalent soil cations (Olk et al., 1995; Mahieu et al., 2002). In tropical rice soils, the MHA fraction was found to be highly involved in seasonal N cycling, while the polyvalent cation-bound CaHA fraction was only slightly more involved than was total soil organic matter (Olk et al., 2006). The quantity and chemical nature of carbon in the MHA fraction were sensitive to recent crop management, and their trends in some long-term field experiments suggested chemical binding of soil N by phenolic compounds that accumulated under multiple annual cropping of rice. This binding would be consistent with a decrease in crop N uptake that was observed under such long-term intensive cropping.


The MHA fraction has been shown to have much younger residence times than the CaHA as determined by 14C-dating (Campbell et al., 1967). Radiocarbon dating of these two fractions in a calcareous vermiculitic soil revealed a MRT of 290" 60 yr for CaHA while the MHA was modern (Olk et al., 1995). In addition, the CaHA had 54% less hydrolysable amino acids than the MHA. In comparison to whole SOM, the chemical properties of these two fractions suggest that MHA represents an early stage and CaHA a later stage in the development of SOM. The MHA would have potentially greater activity in nutrient cycling and represent a more labile fraction where much of the active N of SOM resides. The CaHA represents a chemically stabilized fraction of humic acid with an older mean age and thus is not as closely tied to short-term N supply as is the MHA. Both of these humic acid fractions comprise between 10-40% of soil organic matter, and the MHA fraction represents a larger portion of soil organic matter than do many of the labile organic matter fractions that have been used in other studies.

Besides chemical extractions, organic matter fractions can also be separated through physical extractions. One popular physical extraction separates the light fraction, material that floats when soil is immersed in a liquid that is denser than water (Gregorich et al., 2006). The light fraction has been successfully used to study short-term C cycling in natural and agricultural soils, but its usefulness in depicting N fluxes has been less consistent. To evaluate N and C cycling in Nebraskan soils that were cropped to maize-based rotations, an initial separation of the light fraction from the soils was followed by chemical extraction of the soil for the MHA and CaHA fractions (Legorreta-Padilla, 2005). The light fraction was found to have highly dynamic seasonal fluxes of C and N, while the MHA fraction indicated slower patterns of N cycling that spanned the two growing seasons under evaluation. The CaHA fraction and unextractable soil organic matter provided complementary information by acting as recalcitrant pools. Few studies have combined chemical and physical fractionations in this manner. Integrated use of these fractionations promises improved insights into the dynamics of soil organic matter as affected by the chemical and physical controls that occur simultaneously under field conditions.


The two existing Regional Projects that are most related to our proposal are NCERA-59 (Soil Organic Matter: Formation, Function, and Management) and NC-1017 (Carbon Sequestration and Distribution in Soils of Eroded Landscapes). They have related yet distinct mandates. NCERA-59 promotes discussion and interaction on a range of issues related to soil organic matter, including N mineralization but also several other issues, including C sequestration, soil biodiversity, soil physical properties, water quality, and soil pathogen control. NCERA-59 is unfunded and does not develop plans for committee-wide research activities. Its current research objectives are:

1. Promote research cooperation among its members and NC-174 members.
2. Promote the use of standard techniques of characterizing soil organic matter and assessing soil quality.
3. Foster interest in understanding the basic principles of soil organic matter dynamics and in the application of those principles to soil quality problems of regional and national scope.
4. Work with national and international societies to co-sponsor soil organic matter / soil quality oriented symposia.


Currently two researchers are members of both NCERA-59 and NC-218. They will continue to share information between the two committees, and they will ensure that both committees discuss the possibility of joint meetings.


NC-1017 focuses on using C sequestration to mitigate soil erosion and does not study soil N cycling. Its current research objectives are:


1. Determine spatial C distribution and dynamics in soils of eroded landscapes including 3-dimensional model assessments for better quantification.
2. Assess management (cropping systems, amendments and tillage) effects on C sequestration, productivity and soil quality including the importance of no-tillage on increasing C sequestration in eroded soils.
3. Coordinate research efforts, work and interpretations with NCR-59.


Currently NC-218 is the only multistate regional project addressing the important issues of N mineralization, soil N availability and the impact of these parameters on sustainability of maize production and fertilizer use efficiency. A search of the entire CRIS database identified 77 projects with some activity related to soil nitrogen mineralization. Examination of these projects indicated that 11 of the Appendix E participants are in one or more of these projects, indicating that the participants in the proposed work represent a substantial proportion of the national effort on this subject.


The members of the NC-218 committee have a long history of successful cooperation and collaboration through a core experimental approach to accomplish project objectives. Our core experimental approach consists of a common protocol designed to address each specific project objective in which members from each state within the region conduct identical experiments and pool the data for a regional analysis. We have and will employ a centralized analytical and data interpretation approach to assure uniformity of data collection. The nature of the work proposed here has led to the realization that the expertise of scientists outside of the NC region are needed to complete this work as indicated in the participant list (Appendix E).

Objectives

1. Conduct fundamental work to enhance current understanding of the role of active N and C pools in cropping systems and to predict N mineralization toward more efficient use of N fertilizers.
   
2. Assess the response of crop N uptake to varying rates of N fertilizer in on-farm trials and explain the responses through the dynamics of the quantities and chemical properties of active fractions of soil C and N, including the light fraction and the mobile humic fraction.
   
3. Quantify the magnitude and annual variation in the indigenous soil N supply in on-farm trials as influenced by key edaphic properties, climate and cropping system.
   

Methods

Site Selection and Data Handling: Among the participating institutions listed in Appendix E of this proposal, a common field experimental design and a centralized analytical laboratory approach will be used to accomplish the stated objectives. Planning, including grant writing, for the next mission will begin during the last year of the current project mission of NC-218. Our goal is to complete field work for the proposed project by the end of the third year.  The field component of the project will involve the installation of N fertilizer response experiments in producer fields that are representative of soils and cropping/tillage systems that dominate maize production in regions from NC-218 representatives. Sites will be selected to include soils that have been under uniform management and at production levels that are representative of current on-farm practices. Selected sites will be limited to continuous maize or maize-based rotations.  Comparison of tillage approaches will be done a regional basis where appropriate.  Each producer site will receive at least five N rates (including a no N control) that will bracket the range of the anticipated optimum N rate for the experimental location. Each plot will have an area of approximately 9.0 x 10^-3 ha and will be replicated at least four times in each field. 

In addition to on-farm sites, each state has identified locations where replicated plots of long-term N fertilizer additions to maize (in both continuous maize and maize-based rotations along with long-term N exclusion plots have been maintained. These sites will be utilized in experiments described under objective 2 to assess the long-term impact of N fertilization and crop rotation on the status of the mass, C composition, N content, and biochemical nature of the light fraction and MHA. 

Soil samples that are collected from each of these sites will be shipped in a field-moist condition to selected laboratories for the various analyses outlined in Objectives 1 and 2 of the proposal.  Prepared soil samples will be provided to Dr. Dan Olk, the official NC-218 representative form the USDA Tilth Lab in Ames, Iowa, for extraction of MHA and determination of amino acid and amino sugar composition of the light fraction, MHA and whole soil.  Dr. Daniel Walters, the official representative from the University of Nebraska will perform LF extraction and the determination of total C and N on all soils and organic matter fractions. Dr. William Horwath, the official NC-218 representative form the University of California Davis will perform stable isotope analyses on all whole soil, LF, MHA and plant material collected at each site. This centralized laboratory approach to processing samples and generation of raw data will assure that a uniform QA/QC protocol will be conducted for all sites.

Data from these core experiments will be shared among all members via an established FTP site to provide access to information and data processing to all members as soon as data are generated. Pooled data will be subjected to a uniform statistical analysis, and interpretation of the data will be done by committee at annual meetings.  

We have no record of previous attempts by the committee to secure external funds for committee-wide research efforts. External funds were secured for projects that were conducted by subgroups of committee members and run in parallel with committee activities. To support the work outlined in this proposal, we will develop a grant proposal for submission in the 2006/07 federal fiscal year to the National Research Initiative (NRI) of the U.S. Department of Agriculture, Cooperative State Research, Education, and Extension Service.

Objective 1:  Conduct fundamental work to enhance current understanding of the role of active N and C pools in cropping systems and to predict N mineralization toward more efficient use of N fertilizers.

In combination with the above on-farm fertilizer rate studies, we will assess soil N availability through isotope (¹⁵N) pool dilution. The study design will address the temporal variability of soil N, influence of soil type, factors affecting immobilization and regional differences in maize production systems.  Fertilizer use efficiency will be determined through isotopic ¹⁵N uptake and by difference method as part of the fertilizer rate trail.  The uptake of ¹⁵N is used to assess available soil N through isotope pool dilution. The concept has been traditionally called the A-value though this term is rarely used in the literature.  The isotope dilution approach reflects the size of the available soil N pool as compared to the availability of an added labeled N source (Fried and Dean, 1955). All soil processes that have an effect on available soil N will be reflected in a change in the uptake of the labeled ¹⁵N fertilizer or the A value. An increase in the A-value of the soil strongly correlates with the rate of N uptake (Broadbent, 1970). The A-value, in essence, is a parameter that can be used as an indicator of the capability of soils to supply N brought about by changes in management practices or past fertilizer or manure use (Stevenson et al., 1997).  The approach will provide information on the magnitude of N mineralization.

Only fields that have been under five to seven years of similar management will be used for this study.  A minimum of 3 to 5 microplots, each measuring 1.5 to 2 m², will be established in each field. The experiment will be blocked and configured in a randomized design. The microplots will receive a rate of N equivalent to 5 kg N per ha at 10 atom% ¹⁵N excess. The N will be added prior to planting, ideally within 1 to 3 days of planting and will be in addition to the suggested N application rates of the region.  However, since soil management may differ among states and regions, application may be considered at the time of side dressing.

Soil ammonium and nitrate (5:1 2 M KCl:soil) will be extracted prior to planting and at the end of the growing season from composite soil cores 0 to 15 and 15 to 30  cm in depth. Total soil and plant N and ¹⁵N content will be determined. Inorganic ¹⁵N content within the same soil depths will also be determined at harvest.  Maize yield will be measured in the fertilizer rates trials described above. Finally, fertilizer use efficiency and the A-value will be determined.

The ¹⁵N fertilizer use efficiency is a direct measure of fertilizer N uptake.   The A-value provides for a unit-less parameter, and therefore, requires little or no standardization or normalization for cross-site comparison.  Edaphic parameters (soil texture, drainage class, organic matter content) and crop and soil management histories will be correlated to N use efficiency to more accurately assess intra-region soil N characteristics.  Deeper soil samples on larger ¹⁵N plots could be considered to assess leaching and denitrification potential.

In a separate smaller effort, we will use an isotope pool dilution study to assess gross N mineralization in in conjunction with the fertilizer use efficiency estimations. In this approach, isotopically labeled N (¹⁵N-labeled NH₄ ⁺) is added to soil cores and incubated for 24 hr. As N is mineralized, the pool of added ¹⁵N will be diluted with mineralized soil N. By recording changes in inorganic and organic speciation of labeled and non-labeled N, gross N mineralization and immobilization rates can be calculated using the model detailed by Kirkham and Bartholomew (1954, 1955). This approach will determine the amount of soil N mineralized (gross mineralization). The more frequent determination of gross N mineralization will provide insight on edaphic factors, soil management approaches and climate on the factors controlling soil N mineralization. Isotopic fertilizer use efficiency and gross N mineralization methods taken together will form a complete picture on the fate of soil and fertilizer N not possible by measuring plant uptake and soil N inorganic alone.  The information is required to develop regional solutions and management approaches to increase fertilizer N use efficiency while maintaining maximum yield potential and minimal loss of N to the environment.

Objective 2:  Assess the response of crop N uptake to varying rates of N fertilizer in on-farm trials and explain the responses through the dynamics of the quantities and chemical properties of active fractions of soil C and N, including the light fraction and the mobile humic fraction.

Two separate experimental protocols will be conducted for objective 2 depending upon whether the site is a long-term N addition/N exclusion trial (long-term sites) or an on-farm location under farmer management. 

For soils from all on-farm trials, the LF and MHA fraction will be extracted from all replicates of both N exclusion and high N rate plots.  Along with the unextractable organic matter and whole soil, they will be characterized for their contents of C and N and biochemical compounds as described below.  Seasonal changes in these parameters, especially for N content and organic N forms, will be compared to crop response to N fertilizer application and crop uptake of mineralized soil N to establish whether specific amino acids or amino sugars are contributing substantially to available soil N for any of the soil types or field treatments. 

For the on-farm plots that had been amended with ¹⁵N-labeled fertilizers, active pools of soil N and C will be studied by extracting the light fraction (LF) and mobile humic acid fraction (MHA).  These analyses will be made on composite soil cores taken at four times to a depth of 0-15 and 15-30 cm over an 18-month period. Sampling times will be preplant-year 1, post harvest-year 1, preplant-year 2 and post harvest-year 2.  The LF will first be extracted by immersing the soil in a dense (specific weight 1.6 g cm^-3) solution of sodium polytungstate. The light fraction (LF) will be recovered from the solution phase through centrifugation, filtering and oven-drying.  The heavy fraction that sinks in this solution will then be extracted by sodium hydroxide to recover the MHA fraction.  Both fractions will be cleansed of soil and salt contaminants and freeze-dried.

For all sampling times, both the LF and MHA fractions in addition to the unextracted organic matter plus whole soil samples will be analyzed by continuous flow isotope ratio mass spectrometry for their contents of ¹⁵N, total N, total C and *¹³C on a mass basis. Seasonal changes in these quantities will be compared to crop uptake of ¹⁵N and effects of field treatments will be established.  To evaluate changes in the chemical forms of organic N, the quantities of several amino acids and two amino sugars in all fractions and whole soil will be determined by anion chromatography/pulsed amperometry (Martens and Loeffelmann, 2003).  The levels of carbon forms will be determined for carbohydrates (Martens and Loeffelmann, 2002) and non lignin-drived phenols (Martens, 2002). The changes in isotopic analysis of *¹³C, LF and MHA mass and total C content will allow for the determination of the contribution of annual crop C input to these labile soil organic pools.  Seasonal shifts in contents of specific amino compounds will be calculated for the LF and mobile humic acid fraction and compared to corresponding changes in total soil N in order to determine whether (i) these fractions are serving as sensitive indices of subtler changes in total soil N, and (ii) whether the amino contents of the labile fractions constitute significant proportions of the crop N supply.  Seasonal shifts in total N contents of these fractions will be compared to corresponding shifts in their ¹⁵N contents to determine the respective contributions of fertilizer N and indigenous soil N to N cycling through these fractions.

On those sites with a long-term history of N exclusion and cropping practice, pre-plant and post-harvest samples from long-term N exclusion and long-term N addition plots will be sampled at the same depths described above for analysis of LF, MHA, total N, C and *¹³C, and biochemical nature. The relative proportions of the LF and MHA to total soil C and N will be assessed in relation to edaphic site properties and long-term C and N inputs to the cropping system.

Objective 3: Quantify the magnitude and annual variation in the indigenous soil N supply in on-farm trials as influenced by key edaphic properties, climate and cropping system.

The relationship of N and C dynamics established in objectives 1 and 2 to final maize yield will be assessed in relation to the crop response to fertilizer rate and total crop N uptake and internal N use efficiency.  Maize grain yield, total vegetative production, harvest index and total N uptake in grain and stover will be measured in each plot at the end of the growing season following a strict protocol. This will allow identification of the economic N rate and construction of an N response model at each site. Annual variation in site-specific N response and economic optimum N rate will be due, in part, to annual variation in the internal N use efficiency of the crop (yield/ kg N uptake) as well as variation in the genetic expression of yield potential due to climate and/or variation in indigenous N supply.  Total grain and vegetative biomass and N uptake will be used to determine apparent indigenous N supply, internal N use efficiency and apparent fertilizer use efficiency. Annual site-specific yield potential will be determined with the Hybrid-Maize model (Yang et al., 2004a, 2004b) using site-specific rainfall, solar radiation and rainfall data. The difference between climate limiting yield potential and actual non-N limiting yield provides an index of site specific limitations to yield other than N supply. The relationship of this index to crop N response and internal N use efficiency will be used to determine the contributions of climate and/or physiological limitations to crop N response in relation to N supply.

Measurement of Progress and Results

Outputs

• Quantitative survey of the size and annual variation in indigenous soil N supply across the major maize producing regions of the North Central region.
• Quantitative survey of the response of maize yield to external fertilizer N input for several major soil types across the major maize-producing regions of the North Central region.
• Enhanced understanding of the impact of continuous maize vs maize/soybean rotation on the flux of C and N within active soil C and N pools.
• Enhanced understanding of the role of cropping systems and external fertilizer N input on the short-term storage and release of soil C and N.
• Initial database on the contributions of specific amino compounds to either N availability and crop N uptake or to soil N sequestration.
• An analysis of the annual variation in maize N response to N fertilization in relation to site-specific climate-limited yield potential
• An analysis of the annual variation in the relative contribution of N supply and climate-induced physiological limitations to maize yield.
• A comparative analysis of the quantitative difference between apparent fertilizer N use efficiency based on uptake from N exclusion plots and fertilizer use efficiency determined through the isotope dilution technique.

Outcomes or Projected Impacts

• <b>Increased scientific information based on results from this project. </b>Information gathered through analysis and interpretation of the data gathered in this project will provide a quantitative analysis of the amount and variation of indigenous N supply and its relative importance to fertilizer N substitution, efficiency and survey across a broad geographic area.
• <b>Greater profitability and improved environmental protection. </b> Acquired information will enable more efficient use of indigenous soil N, allowing possible reduction in fertilizer N rates while maintaining or increasing yield levels. These outcomes will in turn reduce expenses incurred by producers and reduce environmental degradation caused by over-fertilizing.

Milestones

(0):er to attachment

Projected Participation

View Appendix E: Participation

Outreach Plan

The main client groups for information generated from this project are agricultural and environmental scientists and practicing agricultural professionals including consultants, county and regional Extension staff, industrial agronomists, and producers. Acquired information regarding field options for improving N use efficiency will reach practicing agricultural professionals through a regional publication, extension publications, web sites designed for interactive assessment of N application rates, state and regional workshops on site-specific crop management techniques, extension meetings, and field days conducted on local, state, and regional bases. Process-level information will reach scientific clientele through refereed journal publications, presentations at scientific meetings and conferences, and published articles in conference proceedings.

Organization/Governance

The Technical Committee will consist of the project leaders for each of the cooperating agencies, the Administrative Advisor and CSREES consultant. The technical Committee shall elect for two years a chair, a secretary, and an executive committee member-at-large. At the end of the 2-year term, a new member will become secretary, The chair will appoint working committees as needed in the conduct of the project and insofar as possible will reside at meetings of the Technical Committee. The secretary will keep the official minutes of all meetings of the Technical Committee and Executive Committee which the chair is unable to attend and will become chair of the Technical Committee in the event that the elected committee chair is for any reason unable to continue in this capacity.

The Technical Committee will have an Executive Committee consisting of the current chair, the secretary and the member-at-large and, at the discretion of the chair, the Administrative Advisor and such additional members as may be appointed by the chairs in consultation with the Administrative Advisor can be designated as ex-officio members of the Executive Committee. The Executive Committee will review and make recommendations concerning the conduct of business by the technical Committee. The Technical Committee will have a regularly scheduled annual meeting. In addition, the Chair may call other meetings of the Technical Committee and the Administrative Advisor.

Literature Cited

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Baker, J.M. and T.J. Griffis. 2005. Examining strategies to improve the carbon balance of corn/soybean agriculture using eddy covariance and mass balance techniques. Agricultural and Forest Meteorology 128:163-177.
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Campbell, C.A., E.A. Paul, D.A. Rennie and K.J. McCallum. 1967. Applicability of the carbon-dating method of analysis to soil humus studies. Soil Sci. 104:217-224.

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Kirkham D. and W.V. Bartholomew. 1954. Equations for Following Nutrient Transformations in Soil, Utilizing Tracer Data I. Soil Sci. Soc. Am. Proc. 18:33-34.

Kirkham D. and W.V. Bartholomew. 1955. Equations for Following Nutrient Transformations in Soil Utilizing Tracer Data: II. Soil Sci. Soc. Am. Proc. 19:189-192.
Legorreta-Padilla, F. 2005. The impact of maize and soybean cropping systems on carbon and nitrogen dynamics in soil organic matter. Ph.D. thesis, University of Nebraska, Lincoln.
Mahieu, N., D.C. Olk and E.W. Randall. 2002. Multinuclear magnetic resonance analysis of two humic acid fractions from lowland rice soils. J. Environ. Quality 31:421-430.

Martens, D.A. 2002. Identification of phenolic acid composition of alkali-extracted plants and soils. Soil Sci. Soc. Am. J. 66:1240-1248.

Martens, D.A. and K.L. Loeffelmann. 2002. Improved accounting of carbohydrate carbon from plants and soils. Soil Biol. Biochem. 34: 1393-1399.

Martens, D.A. and K.L. Loeffelmann. 2003. Soil amino acid composition quantified by acid hydrolysis and anion chromatography-pulsed amperometry. J. Agric. Food Chem. 51:6521-6529.

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Attachments

Land Grant Participating States/Institutions

CA, CO, IA, IN, KS, KY, MN, MO, NE, OH, SD, WI

Non Land Grant Participating States/Institutions

USDA-ARS/Iowa, USDA-ARS/Minnesota