Progress 10/01/00 to 09/30/06
Outputs
In this last installation on the hatch project addressing particulate organic matter and soil N management, I report that results continue to support the notion that POM is an effective integrator of soil condition. The influence of cropping systems and amendments applied in the Lakeland Wisconsin Integrated Cropping Systems Trial on total hydrolyzable organic N (THN) fractions and particulate organic matter (POM) was investigated after a decade in a conventional cash grain system (Conv) of continuous maize amended with inorganic fertilizer, an organic cash-grain system (Org-CG) that relied on legume N, and an organic animal-based system (Org-AN) that included alfalfa and manure additions. Maize yields had consistently ranked Org-CG < Conv < Org-AN. The THN and amino acid-N (AA-N) contents were ranked Org-AN > Org-CG > Conv. Amino sugar-N (AS-N) contents, which reflect microbially derived N, did not differ among systems and concentrations were quite high (346.5 mg
AS-N/kg soil in the 0-50 cm depth). This and soil variability were attributed to the sites' history of manure application. The amount (1.3 g POM-C/kg soil) and proportion (7.5% of total SOC) of POM-C were quite low and did not differ among systems. Failure to accumulate SOC or POM in these soils, even under organic management, is attributed to rapid C decay and/or limited root growth. An N rate study was added the fall before samples were taken and N addition did increase yield in the Conv and Org-CG systems despite evidence of soil N surplus. This suggests that either amino N is unavailable to plants or that root N acquisition is limited by other constraints. Low POM-C contents accompanied by high AS-N and AA-N levels reveal an imbalance in these soils which are likely to be C limited. Based on this, we conclude excess N has prevented use of organic practices from enhancing soil quality at this site.
Impacts
The characteristics of POM-C and organic N fractions integrate management history and can be used diagnostically to identify nutrient imbalance. Quality benefits associated with accumulation of labile C, here understood through measurement of POM, were not achieved as a result of organic management in a site with a history of manure application. Failure to accumulate POM-C under practices that typically result in organic matter accumulation was explained by very high levels of plant available N indicated by high AS-N and AA-N levels. Based on organic matter characteristics alone, one could predict biotic factors and not soil N-supplying capability is limiting yield.
Publications
- Wander, M.M., Yun, W., Goldstein, W.A., Aref, S. and Khan, S.A. 2007. Organic N and particulate organic matter fractions in organic and conventional farming systems with a history of manure application. Plant and Soil (In Press).
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Progress 01/01/05 to 12/31/05
Outputs
Soil organic matter (SOM) fraction characteristics need to be developed as indices that can be related to specific soil functions. The general effects of organic management on promising indices of SOM status (particulate organic matter, POM, and a rapid measure of base hydrolyzable N (the Illinois N test or IL-N))) were determined by comparing the characteristics of organic and conventionally managed soils obtained from nine long-term trials in North America. The free, light POM (FPOM; <1.6 g cm-3) not occluded within aggregates and occluded POM (OPOM; <2.0 g cm-3) were compared to an undifferentiated POM fraction (coarse fraction, CF; >53 micron) obtained by wet sieving. In the multi-site comparison, legume- and manure-based organic systems performed equally well in their ability to increase the quantity of SOM as well as enrich the proportion of POM assessed using a variety of methods. The quantity of C and N in the CF, FPOM, and OPOM were similar in soils from
legume and manure-based systems. The amount of POM-N recovered using these various methods was equal to the amount of N recovered by the IL-N and more than twice that required to support a full crop of maize. Organic farming systems had greater quantities of C and N in the OPOM and CF and greater IL-N contents in all POM fractions considered. The OPOM's C/N ratio (16-19) was least in the manure + legume-based organic, intermediate in the legume-based organic, and greatest in the conventional systems (P <0.10). Trends in OPOM C/N and IL-N abundance suggested occluded POM was most decomposed, and possibly a greater N reservoir, in the manured soils. The FPOM quality reflected the residues added to each system and its removal improved resolution of quality-based differences in POM associated with long-term management. Subdivision of POM revealed differences in its quality that were not evident using the undifferentiated CF. Quantification of hydrolysable N (IL-N) in POM did not enhance
our understanding of management's affect on SOM quality. This multi-site comparison showed organic management simultaneously increased the size of the labile N reservoir and the amount of POM protected within aggregates; and that occluded POM is more decomposed in manure + legume- than in legume-based organic systems. The characteristics of POM reveal how organic practices improve SOM and suggest the nutrient and substrate decay dynamics of organic systems may differ as a result of the N fertilization strategies they employ.
Impacts
Identifying fractions that are sensitive enough to track short-term changes in both SOM quantity and quality is an important first step in developing fertility management tools for organic and sustainable farmers seeking to maximize the nutrient and water use efficiency of their production systems by enhancing soil quality. Our work confirms that POM has potential as such an index and reveals how fractionation strategies affect POM's qualitative and quantitative attributes and thus, its functional relevance. Our work demonstrates how the quality and quantity of POM can serve as powerful integrators of system characteristics and shows how different approaches to SOM characterization can amplify or obscure important differences in the fertility status of soils under different management strategies. Findings suggest it is possible to make direct links between POM status (quantity and quality) and soil N supply and gain an understanding of soil's physical and biological
condition. Strategies for POM fractionation and interpretation should be developed to address specific problems and inform management. By refining methods used to recover the coarse fraction (>53 micron) to remove human contributions to variability, increase reproducibility, and minimizing processing time, our work will help us bring POM into use in a soil-testing context.
Publications
- Marriott, M.E. and Wander, M.M. 2006 Total and labile soil organic matter in organic farming systems. Soil Science Society of America (In Press).
- Marriott, M.E. and Wander, M.M. 2006 Using qualitative and quantitative differences in particulate organic matter to assess fertility in organic and conventional farming systems Soil Biology and Biochemistry (In Press).
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Progress 01/01/04 to 12/31/04
Outputs
Soil organic matter (SOM) fraction characteristics need to be developed as indicies of their multiple benefits. The general affects of organic management on prominsing indicies of SOM status were determined by comparing the characteristics of organic and conventionally managed soils obtained from nine long-term trials in North America. In addition, a more detailed study was conducted of POM and of hydrolyzable N at a site where use of organic practices failed to increase SOM. In the multi-site comparison, legume- and manure-based organic systems performed equally well in their ability to increase the quantity of SOM as well as enrich the proportion of particulate organic matter (POM). However, aggregate occluded POM was more humified and contained a greater amount of plant available N. The amount of POM-N was equal to that recovered by hydrolysis and more than twice that required to support a full crop of maize. Base hydrolyzable N was no more sensitive to management
than was total N. Results from an aberant organic site, where SOM levels remained low and yields lagged in the legume based system, were reflected in POM contents. SOM fraction characteristics suggest that disease, rather than N insufficiency, may be limiting yield and organic matter accumulation at that site. Use of multiple measure of labile SOM, including POM which reflects subtrate quantity and quality, and a separate measure of plant available N, one can start to discern the various contributions SOM makes to biologically based fertility.
Impacts
Results are site- and soil-condition specific. Research must determine whether specific soil attributes or characteristics of SOM can be used to optimize C and N cycling. It is particularly critical that N fertility be managed in an efficient and effective manner in order to minimize NO3 leaching and other adverse environmental effects. The purpose of this work is to improve the utility of organic matter measures and utlimately promote production practices that enhance soil organic matter quality thereby improving the productivity and efficiency of our cropping systems and soils' environmental function.
Publications
- Wander, M.M. 2004. Soil organic matter fractions and their relevance to soil function. In: Advances in Agroecology. Magdoff, F. and R. Weil (eds). CRC pp.67-102.
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Progress 01/01/03 to 12/31/03
Outputs
Many have suggested that cropping systems that rely on mixed-crop production and organic sources of fertility cycle N and C more efficiently. Cropping systems that use diverse crop rotations are thought to optimize C and N cycling primarily through improved management of soil organic matter. This type of speculation about efficiency is often related to soil C and N balance, which are difficult to assess. Long-term studies that suggest greater efficiency in soil C and N cycles may not adequately document inputs. Still, in many experimental cases where N additions have been abundant, unexpected N deficiencies have been noted while in systems where N additions have been scanty there have been unexpected gains. Denitrification and N fixation are possible explanations for these trends. Regardless of how soil organic matter (SOM) quality is enhanced, where SOM is aggraded, soil fertility and yields are enhanced, while negative environmental impacts including N leaching and
erosion can be reduced. Conservation tillage practices, which are also seen as a means to increase or improve SOM may also help producers sequester C and optimize their N use. Unfortunately, conclusions drawn from farming systems comparisons make it difficult to identify the specific factors contributing to enhanced N-use and environmental efficiency. The objective of this project is to determine how soil structure and soil organic matter (SOM) quality can be used to understand the C and N economy of soils. Current work focuses on two SOM fractions, particulate organic matter (POM) C and amino sugar N because these two fractions appear to have potential for development into fertility or stewardship indices. To determine whether fertility practices lead to consistent SOM traits, soil samples (approximately 0 to 25 cm depth) were obtained from corn or soybean entry points at eight different long-term farming system trials in the spring of 2002 and/or 2003. Treatments were categorized as
manure-based organic, legume-based organic, or conventional based on fertility management strategies and rotations that were used. POM was fractionated based on size (>53 mm). Total organic C (TOC), total N (TN), POM C, and POM N were determined by combustion analysis. Amino sugar and exchangeable NH4+-N was analyzed in whole soils using the Illinois N test (Khan et al., 2001). All SOM fractions examined were able to differentiate between organically and conventionally managed soils but POM fractions were most sensitive to management. Although manure has elsewhere been found to have a large and lasting impact on amino sugar N, manure-based systems were no more enriched in amino sugar N than were legume- based systems. The main difference in the SOM characteristics of the manure and legume based systems was in the relationships between POM C and amino sugar N. A strong positive relationship between POM C and amino sugar N was found in the legume-based organic system while no such
relationship existed in the manure-based system.
Impacts
Results are site- and soil-condition specific. Research must determine whether specific soil attributes or characteristics of SOM can be used to optimize C and N cycling. It is particularly critical that N fertility be managed in an efficient and effective manner in order to minimize NO3 leaching and other adverse environmental effects. The purpose of this work is to improve the utility of organic matter measures and utlimately promote production practices that enhance soil organic matter quality thereby improving the productivity and efficiency of our cropping systems and soils' environmental function.
Publications
- No publications reported this period
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Progress 01/01/02 to 12/31/02
Outputs
Objective: To determine how soil structure and soil organic matter quality can be used to understand the C and N economy of soils. As part of a recently completed project we tested the hypothesis that particulate organic matter (POM) and aggregate dry mean weight diameter (DMWD) are related to fertilizer-use efficiency (FUE) and leaching susceptibility. Soil cores (15 cm diam. x 50 cm depth) were collected from 12 farm fields representing three cropping systems: conventional (CT) and no-tillage (NT) management of corn (Zea mays L.)-soybean (Glycine max (L.) Merr.) rotations, and conventional tillage applied to more diversified corn-soybean-based rotations (R-CT). Three of the four R-CT farms were organically managed. In a 95-day greenhouse trial, cores were seeded with corn, amended with 15N-labeled urea applied at four rates (0, 75, 150, 225 kg N ha-1), and subjected to a stressful moisture regime. Aggregate DMWD, which serves as a rough index of pore-size
distribution, was greater in NT cores. Although total leached N was similar in all cropping systems, increased macropore flow in NT cores led to greater leaching of fertilizer-N and less leaching of soil-derived N, as well as greater moisture stress and decreased plant N uptake. The R-CT cores had more POM and soil organic carbon (SOC) in the top 30 cm of soil and higher crop biomass and biomass-N content. However, FUE in R-CT cores was relatively low since FUE does not account for contributions of indigenous N. For the same reason, FUE remained relatively high in CT systems despite less labile organic matter. Both FUE and SOM conservation declined with increasing N application rates. Increasing labile sources of N, reflected in POM pools, through crop diversification can substitute for incremental increases in fertilizer-N and improve long-term productivity in this region.
Impacts
By determining whether specific soil attributes or characteristics of SOM can be used to optimize C and N cycling we hope to be able to optimize farming systems to maximize profitability and environmental efficiency. It is particularly critical that N fertility be managed in an efficient and effective manner in order to minimize NO3 leaching and other adverse environmental effects.
Publications
- Nissen, T.N. and Wander, M.M. 2003. Fertilizer-use efficiency, leaching, and SOM conservation as influenced by crop rotation and tillage, and their relation to aggregation and particulate organic matter. SSSAJ (Under Review).
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Progress 01/01/01 to 12/31/01
Outputs
The objective of this work is to determine how soil structure and soil organic matter quality can be used to understand the C and N economy of soils. Studies are being conducted using samples from controlled studies, University Experiment Stations and farm fields where management practices have influenced the quantity and character of soil organic C and N fractions. A variety of physical and chemical fractionation methods are being explored. Soil C and N dynamics are being assessed using a variety of methods. Results will be used in combination with empirical models to refine our understanding of how organic matter quality influences C and N dynamics in soils.
Impacts
The development of organic matter dependent soil tests will allow us to manage mainstream production systems without polluting air and water resources or degrading soils.
Publications
- No publications reported this period
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