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Evaluation of commercial soil health tests using a medium-term cover crop experiment in a humid, temperate climate

DOI:10.1007/s11104-018-3653-2
Authors:
Inderjot Chahal at University of Guelph
Inderjot Chahal
Laura L. Van Eerd at University of Guelph Ridgetown Campus
Laura L. Van Eerd
  • University of Guelph Ridgetown Campus
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Abstract and Figures

Background and aims Various tests have been developed for quantifying soil health, such as Haney soil health test (HSHT), Solvita, and Solvita labile amino N (SLAN). Although commercially available, their applicability in temperate agroecosystems are largely unknown. Therefore, these tests were evaluated using a medium-term cover crop (CC) experiment established in 2007 (repeated 2008). Methods Treatments of four different summer-planted CCs and a no CC control (no-CC), with a split-plot of cereal straw removal were used to assess soil health treatment differences and correlations with crop yield, soil organic C (SOC), and 2 day cumulative C mineralization (Cmin2d). Results Average crop yield with CC was 7.9 to 22% greater than no-CC depending on the year. Similarly, compared to no-CC, plots with CC had 8.4 to 9.3% greater average SOC concentrations and 5.6 to 6.5% greater Cmin2d, suggesting the suitability of this trial to evaluate soil health tests. Inconsistencies between years with HSHT, Solvita and SLAN in (i) detecting CC treatment differences and (ii) correlations with crop yield or soil indicators (SOC, Cmin2d) suggests limited the applicability of these soil health tests. Conclusions This research furthers our understanding of CC systems on soil quality, C storage and by extension agroecosystem sustainability.
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REGULAR ARTICLE
Evaluation of commercial soil health tests
using a medium-term cover crop experiment in a humid,
temperate climate
I. Chahal &L. L. Van Eerd
Received: 9 December 2017 /Accepted: 13 April 2018 /Published online: 23 April 2018
#Springer International Publishing AG, part of Springer Nature 2018
Abstract
Background and aims Various tests have been devel-
oped for quantifying soil health, such as Haney soil
health test (HSHT), Solvita, and Solvita labile amino
N (SLAN). Although commercially available, their ap-
plicability in temperate agroecosystems are largely un-
known. Therefore, these tests were evaluated using a
medium-term cover crop (CC) experiment established
in 2007 (repeated 2008).
Methods Treatments of four different summer-planted
CCs and a no CC control (no-CC), with a split-plot of
cereal straw removal were used to assess soil health
treatment differences and correlations with crop yield,
soil organic C (SOC), and 2 day cumulative C mineral-
ization (Cmin
2d
).
Results Average crop yield with CC was 7.9 to 22%
greater than no-CC depending on the year. Similarly,
compared to no-CC, plots with CC had 8.4 to 9.3%
greater average SOC concentrations and 5.6 to 6.5%
greater Cmin
2d
, suggesting the suitability of this trial
to evaluate soil health tests. Inconsistencies between
years with HSHT, Solvita and SLAN in (i) detecting
CC treatment differences and (ii) correlations with crop
yield or soil indicators (SOC, Cmin
2d
)suggestslimited
the applicability of these soil health tests.
Conclusions This research furthers our understanding
of CC systems on soil quality, C storage and by exten-
sion agroecosystem sustainability.
Keywords Catch crop .Service crops .Haney soil health
test .Soil organic carbon .Soil respiration .Carbon
dioxide .Toma to Solanum lycopersicum .Biomass
removal .Soil quality .Solvita
Abbreviations
CC Cover crop
HSHT Haney soil health test
no-CC No cover crop control
OSR Oilseed radish
OSR&Rye Mixture of oilseed radish and winter ce-
real rye
Cmin
2d
Cumulative 2 day soil C mineralization
SOC Soil organic C
SLAN Solvita labile amino N
+S Straw retained
-S Straw removed
WEOC Water extractable organic C
WEON Water extractable organic N
Introduction
Tom at o (Solanum lycopersicum L.) is an important hor-
ticultural crop in Ontario with 451,000 t produced and a
farm value of CAD $91 million in 2016 (Mailvaganam
2017). Numerous studies have been conducted
Plant Soil (2018) 427:351–367
https://doi.org/10.1007/s11104-018-3653-2
Responsible Editor: Zucong Cai
I. Chahal :L. L. Van Eerd (*)
School of Environmental Sciences, University of Guelph,
Ridgetown Campus, Ridgetown, Ontario N0P2C0, Canada
e-mail: lvaneerd@uoguelph.ca
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Cover crops can shape the soil microbiome by providing different C and nutrient sources via rhizodeposits and litter, via signaling or allelopathic compounds in root exudates (directly or via other organisms), or by modifying the soil abiotic environment 13,30 . In this study, CCs affected some aspects of soil microbial structure, consistently with other soil biological, chemical and physical properties 27 . Still, short-and mid-term microbial responses were relatively minor considering CCs had been applied for 7 successive years and were also present at sampling. ...
... Besides constituting a source of C and nutrients, residues also modify soil temperature and moisture content 21 , therefore modifying the soil environment. Even so, consistently with previous results on other soil properties 27 , residue management effects in this study were smaller than CC effects, and negligible for most variables. Throughout the 8-year trial, crop residues were removed only twice while CCs were applied 6 times, but we expected clearer effects because it was carried out on the sampling year. ...
... We might have missed a transient response 53 or, alternatively, tillage accelerated residue mineralization and a large proportion of C was lost as CO 2 instead of being used for microbial growth 21 . The latter is supported by higher C mineralization levels one month before sampling 27 . In terms of composition and taxa, crop residue affected fungi more so than prokaryotes, possibly because fungi are more capable of breaking down plant cell wall polymers. ...
Cover crop-driven shifts in soil microbial communities could modulate early tomato biomass via plant-soil feedbacks
Article
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  • Jun 2022
Sustainable agricultural practices such as cover crops (CCs) and residue retention are increasingly applied to counteract detrimental consequences on natural resources. Since agriculture affects soil properties partly via microbial communities, it is critical to understand how these respond to different management practices. Our study analyzed five CC treatments (oat, rye, radish, rye-radish mixture and no-CC) and two crop residue managements (retention/R+ or removal/R−) in an 8-year diverse horticultural crop rotation trial from ON, Canada. CC effects were small but stronger than those of residue management. Radish-based CCs tended to be the most beneficial for both microbial abundance and richness, yet detrimental for fungal evenness. CC species, in particular radish, also shaped fungal and, to a lesser extent, prokaryotic community composition. Crop residues modulated CC effects on bacterial abundance and fungal evenness (i.e., more sensitive in R− than R+), as well as microbial taxa. Several microbial structure features (e.g., composition, taxa within Actinobacteria, Firmicutes and Ascomycota), some affected by CCs, were correlated with early biomass production of the following tomato crop. Our study suggests that, whereas mid-term CC effects were small, they need to be better understood as they could be influencing cash crop productivity via plant-soil feedbacks.
... The use of soil health indicators as outcome or response variables has led to a circular logic in the broader arc of implementation and interpretation. Much of the current soil health literature essentially asks "does management change the values of these soil health indicators?" (Congreves et al., 2015;Chahal and Van Eerd, 2018;Dhakal and Islam, 2018;Diederich et al., 2019;Wade et al., 2019;Agomoh et al., 2020;Williams et al., 2020), and a change in indicators is interpreted as a change in soil health. These studies are valuable for understanding management effects and the sensitivity of indicators across contexts. ...
... While many studies have linked total soil organic matter content to productivity data (Lal et al., 2004;Congreves et al., 2015;Oldfield et al., 2019), other soil health indicators-many of which are presumed to represent smaller and more biologically active pools of soil organic matter (Wander, 2004)-have had less success. Overall, individual soil health indicators are moderately correlated with productivity (Culman et al., 2013;Chahal and Van Eerd, 2018; van Es and Karlen, 2019), providing inconsistent, yet often better information about productivity than total organic matter measurements. For example, a direct comparison showed that soil health indicators related more strongly to productivity than SOC in 12 out of 14 comparisons, although the specific preferred indicator varied by context (Hurisso et al., 2016). ...
... Uniqueness (u 2 ) is the proportion of variance that is not represented by the factors, where u 2 = 1-h 2 . uncertainty of the indicator (Hurisso et al., 2016;Chahal and Van Eerd, 2018;Gannett et al., 2019;Agomoh et al., 2020Agomoh et al., , 2021Adhikari et al., 2021), whereas our approach allows for better attribution of uncertainty. Specifically, we show that the indicators associated with our soil tilth and fertility trait-POXC, mineralizable C, soil protein, and WAS-represent a similar trait across all three contexts, though that trait does not have a consistent effect on corn silage yield in the New York-2 dataset. ...
Rigorous, empirical, and quantitative: A proposed pipeline for soil health assessments
Article
Soil health is a promising lens through which to approach land management, having the potential to serve as a descriptor of biophysical processes and as an effective communication tool across stakeholders. However, this potential has been largely unrealized due to difficulty in quantitatively assessing soil health and linking those assessments to outcomes. Here we discuss many multiple persistent obstacles to quantitative soil health assessment and outline a suite of analyses to help address those obstacles. Specifically, we propose a quantitative approach to developing and selecting soil health indicators that help connect management-induced changes in soil health to specific outcomes (e.g., yield or water quality). To demonstrate the utility of this approach, we perform a small case study using published data from North Carolina and New York cropping systems. Additionally, we outline how this approach is scalable and flexible enough to integrate future soil health metric development. The proposed approach stands to provide a quantitative, empirical basis for future measurement, assessment, and interpretation of soil health.
... Morrow et al. (2016) evaluated soil health associated with five field experiments using Haney's SHT and found it was necessary to increase the number of tests at sites with significant spatial heterogeneity to detect any management effects. Three commercially available soil health tests [Solvita CO 2 -burst test, Solvita labile amino nitrogen (SLAN), and Haney's SHT] were compared in Canada by Chahal and Van Eerd (2018), but the results showed no consistent relationship with crop yield or significant correlation with Haney's SHT scores. The three tests were also evaluated by Chu et al. (2019) for a cover crop experiment in USA established in 2013 on a no-till corn-soybean rotation. ...
Soil health assessment methods: Progress, applications and comparison
Article
... Morrow et al. (2016) evaluated soil health associated with five field experiments using Haney's SHT and found it was necessary to increase the number of tests at sites with significant spatial heterogeneity to detect any management effects. Three commercially available soil health tests [Solvita CO 2 -burst test, Solvita labile amino nitrogen (SLAN), and Haney's SHT] were compared in Canada by Chahal and Van Eerd (2018), but the results showed no consistent relationship with crop yield or significant correlation with Haney's SHT scores. The three tests were also evaluated by Chu et al. (2019) for a cover crop experiment in USA established in 2013 on a no-till corn-soybean rotation. ...
Soil health assessment methods: Progress, applications and comparison
Chapter
Soil health assessment tools are needed to quantify effectiveness of various agricultural practices toward meeting sustainable development goals. Although several soil health tools have been developed and tested through global soil management research, ease of use and site-specific accuracy for farmers and agronomists needs to be optimized. This comprehensive review examines the theories, compares approaches, and examines applications of five soil health assessment methods, and then compares their advantages, disadvantages, application limitations, and feasibility before suggesting potential improvements at various scales. The two predominant soil health assessment tools [Soil Management Assessment Framework (SMAF) and Cornell's Comprehensive Assessment of Soil Health (CASH)] were coupled with six classical mathematical models [Principal Component Analysis, Analytic Hierarchy Process, Iterative Algorithm, Entropy weight method, Euclidean distance and Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS)] to create 11 approaches that were compared using field-based soil health indicator measurements. The data were collected from field experiments with cover crops and soil amendments in Mississippi, USA. The Standard Scoring Functions (SSF) associated with the SMAF and the CASH tools were evaluated. Our results, reflecting different data normalization and weighting, created 14 different soil health scores that showed significant differences based on method. Among the three data normalization methods (CASH, SSF, and entropy weighting), soil health scores using SSF were relatively high, while those using entropy weighting were much lower. The latter method, TOPSIS, had the advantage of being able to maximize differences among treatments and thus can help select an optimal management solution. Scores obtained through SSF, SSF + PCA and SSF + AHP had some of the best correlations) with corn (Zea mays L.) and soybean [Glycine max (Merr.) L.] yields, indicating the SSF parameters selected for our study were applicable. CASH provided similar results with a more simplistic approach. Other methods generated soil health scores with poorer fits when compared to the yield data. Overall, we conclude all 11 methods and 14 soil health scores can be useful for soil health evaluation in the study area. The results re-emphasized that soil health assessment is useful for soil researchers, farmers, and any other stakeholder group wanting to determine if specific agricultural practices contribute to sustainable development.
... To address our goal of evaluating soil health for the various cropping systems in Tennessee, we selected the CASH and ASHI methods because CASH is a comprehensive and popular soil health assessment approach, while ASHI originated in the southeast U.S. region. Numerous studies using CASH for soil health assessment revealed contrasting responses of management practices on soil health (Birri, 2020;Chahal & Van Eerd, 2018;Chahal & Van Eerd, 2019;Roper et al., 2017). For example, after an extensive evaluation, Chahal and Van Eerd (2019) recommended a weighted index of five soil health indicators over CASH for better soil health differentiation among management practices in Ontario, Canada. ...
Cropping system management responses to cornell and alabama soil health assessment methods in the Southeastern United States
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Soil texture influences on soil health scoring functions in Ontario agricultural soils: A possible framework towards a provincial soil health test
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Rigorous, empirical, and quantitative: a proposed pipeline for soil health assessments
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A three-year field experiment was conducted to evaluate the effects of straw combined with potassium fertilizer on maize yield, potassium utilization efficiency and soil potassium balance. The study consisted of two straw treatments (S1: straw returning; S0: no straw returning) and five K levels (0,30,60,90,120 kg K ha⁻¹). The results showed that compared to S0, the maize yield and available K content in S1 increased by 2.9%~6.2% and 19.3%~37.4%. The average of agronomy efficiency and surplus rate in S1 were 7.3%~35.4% and 24.8%~84.7% higher than S0 respectively, but the recovery efficiency, partial factor productivity under S0 and S1 were statistically identical. When the surplus rate is 0, the amount of potassium fertilizer required and the corresponding yield to maintain the soil K balance in S1 were 87.9 kg ha⁻¹ and 12,424.6 kg ha⁻¹. Compared to S0, S1 can decrease potassium fertilizer application rate by 10.2% while increasing maize yield by 3.5%. Overall, straw return combined with potassium fertilizer can improve maize yield and soil available potassium content, it can also reduce chemical fertilizer input while increasing fertilizer utilization efficiency, and play a positive role in keeping soil K balance simultaneously.
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Much of cover crop research to date focuses on key indicators of impact without considering the implications over multiple years, in the absence of a systems-based approach. To evaluate the effect of three years of autumn cover crops on subsequent processing tomato (Solanum lycopersicum L.) production in 2010 and 2011, a field split-split-plot factorial design trial with effects of cover crop type, urea ammonium nitrate fertilizer rate (0 or 140 kg N ha-1 preplant broadcast incorporated) and tomato cultivar (early vs. late) was conducted. The main plot factor, cover crop, included a no cover crop control, oat (Avena sativa L.), winter cereal rye (hereafter referred to as rye) (Secale cereale L.), oilseed radish (OSR) (Raphanus sativus L. var. oleiferus Metzg Stokes), and mix of OSR and rye (OSR + rye) treatments. Cover crop biomass of 0.5 to 2.8 and 1.7 to 3.1 Mg ha-1 was attained in early Oct. and the following early May, respectively. In general, OSR increased soil mineral N during cover crop growth and into the succeeding summer tomato growing season, while the remaining cover crops did not differ from the no cover crop control. The lack of a cover crop by N rate interaction in soil and plant N analyses at harvest suggests that growers may not need to modify N fertilizer rates to tomatoes based on cover crop type. Processing tomato fruit quality at harvest (rots, insect or disease damage, Agtron colour, pH, or natural tomato soluble solids (NTSS)) was not affected by cover crop type. In both years, marketable yield in the no cover crop treatment was lower or not statistically different than all planted cover crops. Partial profit margins over both years were 1320 $ ha-1 higher with OSR and $960 higher with oat compared to the no cover crop control. Thus, results from a systems-based approach suggest that the cover crops tested had no observed negative impact on processing tomato production and have the potential to increase marketable yield and profit margins.
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Soil health (SH) refers to the ability of a soil to function and provide ecosystem services. The Comprehensive Assessment of Soil Health (CASH) is an approach that measures 15 physical, biological, and chemical soil indicators, which are interpreted through scoring functions. This study reports on the SH status of 5767 samples from the Mid-Atlantic, Midwest, and Northeast regions of the USA as evaluated using CASH. Descriptive statistics and ANOVAs of subdatasets by region and soil textural group for SH indicators, in addition to correlation coefficients, principal component (PC) analysis, and best subsets regression (BSR) were performed. From these analyses, new CASH scoring functions were developed. Separate scoring functions by textural group (fine, medium, coarse) were necessary for Wet Aggregate Stability (WAS), Available Water Capacity (AWS), Organic Matter (OM), Active Carbon (AC), and Protein. Differences existed among regions, especially for WAS, OM, Protein, and Respiration (Resp), where the Midwest had relatively lower mean values compared to the Mid-Atlantic and Northeast. Biological properties and WAS showed moderately strong correlations (r = 0.58-0.78) and the highest loadings for the first two PCs. BSR results using the overall soil quality index as the response variable indicated that AC accounts for 45% of the variation, with additional predictability from Penetration Resistance, Resp, and WAS (68%). These four indicators are suggested for simplified SH tests. We conclude that the CASH approach can be successfully applied to evaluate the health status of soils with differing pedogenetic histories. © 2017 by the Soil Science Society of America, Inc. All Rights reserved.
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Changes in Water-Extractable Organic Carbon with Cover Crop Planting under Continuous Corn Silage Production
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Long-term row crop agricultural production has dramatically reduced the pool of soil organic carbon. The implementation of cover crops in Midwestern agroecosystems is primarily to reduce losses of nitrogenous fertilizers, but has also been shown to restore soil carbon stocks over time. If labile carbon within agricultural soils could be increased, it could improve soil health, and if mobilized into subsurface drainage, it may positively impact watershed biogeochemistry. We tested for potential differences in water-extractable organic carbon (WEOC) at two different soil profiles (0–5 cm and 5–20 cm) between plots planted with cereal rye/daikon radish (cover crop), corn, and zero control (no vegetation) within the Illinois State University Research and Teaching Farm. We also tested for potential differences in denitrification within the upper soil profile throughout the growing year. We modeled excitation–emission matrices from soil cores through parallel factor analysis. We found no difference in WEOC concentrations between each crop treatment (P = 0.2850), but concentrations of WEOC were significantly lower in the 5–20 cm profile than that in the upper (0–5 cm) profile (P = 0.0033). There was a significant increase in WEOC after each treatment in samples after cover crop termination. The parallel factor analysis model found humic and fulvic acids to be the dominant fractions of WEOC in all soils tested. Humic and fulvic acids accounted for ~70% and 30% of model variation. Denitrification rates did not differ across treatments (P = 0.3520), which is likely attributed to soil WEOC being in limiting quantities and in primarily recalcitrant fractions. After three years, cover crops do not appear to alter soil WEOC quantity and type. Restoring the availability of carbon within agricultural soils will not be a short-term fix, and fields will likely be a net carbon sink, contributing minimal labile carbon to receiving waterways.
Soil Health Indicators Do Not Differentiate among Agronomic Management Systems in North Carolina Soils
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  • Jul 2017
Recent soil tests evaluating “soil health” on a broad scale may not properly consider the intrinsic limitations of soil properties, and have not been assessed in regionally unique soil conditions. To evaluate three soil tests in North Carolina, we used long-term agronomic management trials from three distinct physiographic regions: mountain (22 yr), piedmont (32 yr), and coastal plain (17 yr). Mountain and coastal plain trials included combinations of organic or chemical management with or without tillage; the piedmont trial included nine different tillage treatments. Soil samples were collected and submitted for analysis as recommended by the North Carolina Department of Agriculture and Consumer Services, Haney soil health test (HSHT), and Cornell comprehensive assessment of soil health (CASH). Plant nutrient concentrations varied but were still sufficient for crops. The CASH physical soil indicators, such as surface hardness and aggregate stability, were not statistically different, regardless of tillage intensity or management. Biological soil indicators (e.g., CO2 respiration) responded differently to management, but this differentiation was inconsistent among locations and tests. Despite many years of conservation management, the CASH results described mountain soils as “low” or “very low” soil health for all but no-till organic management, which received a “medium” score. The HSHT results considered soil from all but moldboard plowing (piedmont) to be in good health. Finally, there was no correlation between soil health tests and crop yields from North Carolina soils. Soil health tests should be calibrated to better differentiate among soil management effects that vary depending on intrinsic soil limitations. © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA. All Rights reserved.
Cover Crops Could Offset Crop Residue Removal Effects on Soil Carbon and Other Properties: A Review
Article
  • Sep 2017
Crop residue removal for livestock or biofuel production is common. Excessive residue removal may reduce soil organic carbon (SOC) and other soil properties. Cover crop (CC) could be a strategy to ameliorate negative effects of residue removal, but this has not been widely discussed. We synthesized studies on the impacts of CC addition following crop residue removal on SOC and related properties, discussed opportunities and challenges of using CC after residue removal, and highlighted research needs. We first briefly reviewed the separate effects of residue removal and CC before reviewing their combined effects. Our review found that ≥50% residue removal reduced SOC stocks by 0.87 Mg ha–1 yr–1 and <50% removal by 0.31 Mg ha–1 yr–1. However, CC increased SOC by 0.49 Mg ha–1 yr–1, suggesting that CC could offset at least part of the SOC lost with removal. Studies evaluating CC effects on soil properties after residue removal are few and short term (<6 yr) but appeared to show limited potential of CC to offset residue removal effects. However, some studies indicated trends for increased SOC, suggesting CC may offset removal effects in the long term. While opportunities exist to integrate residue removal with CC use, challenges including low CC biomass and reduction in crop yield in water-limited regions must be addressed. Further research on interactive effects of CC and residue removal is needed across different cropping systems and climates.
Cover cropping and no-tillage improve soil health in an arid irrigated cropping system in California’s San Joaquin Valley, USA
Article
The concept of soil health has attracted considerable attention during the past two decades, but few studies have focused on the effects on soil health of long-term soil management in arid irrigated environments. We investigated the effects of cover cropping and no-till management on soil physical and chemical properties during a 15-year experiment in California?s San Joaquin Valley (SJV) USA. Our objective was to determine if soil health could be improved by these practices in an annual crop rotation. The impact of long-term no-tillage (NT) and cover cropping (CC) practices, alone and in combination, was measured and compared with standard tillage (ST) with and without cover crops (NO) in irrigated row crops after 15 years of management. Soil aggregation, rates of water infiltration, content of carbon, nitrogen, water extractable organic carbon (WEOC) and organic nitrogen (WEON), residue cover, and biological activity were all increased by NT and CC practices relative to STNO. However, effects varied by depth with NT increasing soil bulk density by 12% in the 0?15 cm depth and 10% in the 15?30 cm depth. Higher levels of WEOC were found in the CC surface (0?5 cm) depth in both spring and fall samplings in 2014. Surface layer (0?15 cm) WEON was higher in the CC systems for both samplings. Tillage did not affect WEON in the spring, but WEON was increased in the NT surface soil layer in the fall. Sampling depth, CC, and tillage affected 1-day soil respiration and a soil health index assessment, however the effects were seasonal, with higher levels found in the fall sampling than in the spring. Both respiration and the soil health index were increased by CC with higher levels found in the 0?5 cm depth than in the 5?15 and 15?30 cm depths. Results indicated that adoption of NT and CC in arid, irrigated cropping systems could benefit soil health by improving chemical, physical, and biological indicators of soil functions while maintaining similar crop yields as the ST system.
Microbial crop residue decomposition dynamics in organic and conventionally managed soils
Article
Agricultural practices can influence soil microbial communities, which are the primary regulators of soil carbon and nutrient cycling processes. Differences in microbial community composition have the potential to affect the fate of carbon and nutrients during decomposition and may therefore influence the retention of C and provisioning of crop nutrients in agroecosystems. Long term management-induced shifts in microbial communities and resource availability may interact to affect the microbial utilization of fresh inputs of crop residues in the short term, with lasting impacts on soil C accrual and fertility. The objective of this study was to investigate whether long-term organic and conventional management resulted in differences in microbial residue decomposition. Soils under conventional and organic management planted with annual crops or with a mix of annual crops and three years of perennial alfalfa were collected from a long-term (19 y) field study in Saskatchewan, Canada and were incubated in the laboratory with and without 13C-labelled barley residues for 98 d. We measured extracellular enzyme activities (EEAs) and the incorporation of crop residue-derived C within major microbial groups (fungi, actinobacteria, and Gram positive and negative bacteria) during decomposition. Total PLFA biomass and EEAs were highest in soils from the conventional-annual system, similar between the conventional and organic perennial systems, and similar or lowest in the organic-annual system. Crop residue additions alleviated these differences; that is, in residue-amended soils total PLFA biomass, EEAs, and the abundance of the fungal biomarker increased in the organic systems compared to the unamended soils to become similar to the conventional systems. In contrast, residue additions induced small or no changes in biomass and EEAs in the conventional-annual soils. Using 13C-PLFA-SIP we showed that the general pattern of microbial succession during decomposition was similar among soils, but that fungi and especially actinobacteria were relatively more dominant in organic compared to conventionally managed soils during early and later stages of decomposition, respectively. Thus, shifts in the decomposer community composition were greater in soils originating from organic management, possibly as a result of larger changes in resource availability during the incubation that advanced the rate of microbial succession. This may reinforce long term differences in SOC quality and nutrient availability between management regimes. Organically-managed cropping systems are particularly reliant on biological cycling of organic nutrients to support crop growth. This work reinforces the importance of adequate crop residue returns for maintaining soil function, particularly where external organic amendments are not applied to balance nutrients exported as crop products.
DRIFT Spectroscopy to Assess Cover Crop and Corn Stover Decomposition in Lab-Incubated Soil
Article
  • Mar 2016
Cover crops are recommended for improving soil quality; however, the assessment of their benefits to soil is difficult and has typically involved the use of tedious, destructive methods. This study evaluated the applicability of diffuse reflectance infrared fourier transform (DRIFT) spectroscopy, a rapid nondestructive method for its potential to characterize soil organic constituents and plant residue decomposition processes. Soil from a 4-yr autumn cover cropping trial with a no cover crop control was amended with crop residues and used in a 72-d incubation study where data from DRIFT spectroscopy were compared with evolved CO2 in measuring decomposition of cover crop biomass with (+S) and without (-S) corn stover residue. Treatment differences within model parameters of polysaccharide-C (1170-950 cm-1 spectral region) decomposition curves were similar to those generated from the C decay curves. All soil amendment treatments had lower C mineralization and polysaccharide decomposition rates compared with the control, which suggests that the cover crops tested have the potential in the shortterm to replenish labile organic C pools and to reduce C losses compared with the no cover crop control. In soil amended with crop residues DRIFT spectra revealed a disappearance of bands corresponding to labile polysaccharide-C during the incubation, which related to CO2 evolution and was consistent with labile aliphatic-C bands (2930 cm-1). This is the first study to demonstrate the use of DRIFT spectroscopy to assess crop residue decomposition in a soil matrix.
Evaluating Measures to Assess Soil Health in Long-Term Agroecosystem Trials
Article
  • Mar 2016
Monitoring soil health is an important component of any land management system that sustains soil resources. As metrics of soil health, we evaluated surface soil organic matter (SOM) properties from five field experiments ranging from 2 to 30 yr old and representing diverse agroecosystems across the inland Pacific Northwest (iPNW). The SOM properties measured included soil organic C (SOC), total N, acid nonhydrolyzable C (NHC), acid nonhydrolyzable N (NHN), acid-hydrolyzable C (HC), acid-hydrolyzable N (HN), microbial biomass C (MBC), microbial biomass N (MBN), carbon mineralization (Cmin), permanganate oxidizable C (POXC), ion exchange membrane N (IEM N), and potential N mineralization (PNM). We further evaluated these SOM metrics and the Haney soil health index (SHindex) relative to the following seven criteria as a framework to judge the effectiveness of soil health tools: (i) evidence based, (ii) sensitive to change, (iii) logistically sensitive, (iv) cost effective, (v) accurate and precise, (vi) performed in situ, and (vii) valued for management decisions. Measures of active SOM were highly variable, particularly 1-d Cmin (CV, 3-53%), IEM N (CV, 9-55%), and SHindex (CV, 4-37%) and subsequently not highly sensitive to management. Permanganate oxidizable C displayed sensitivity to more stabilized SOM, indicated by strong correlations to NHC (r = 0.84) and NHN (r = 0.80), and coupled with IEM N provided complimentary information important to soil health. Using these seven criteria to gauge soil health metrics, POXC scored the highest and should be considered as a component for soil health assessment within the iPNW. © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA. All Rights reserved.