W. E. Curnoe

University of Guelph, Guelph, Ontario, Canada

Are you W. E. Curnoe?

Claim your profile

Publications (17)29.46 Total impact

  • Source
    Science of The Total Environment - SCI TOTAL ENVIR. 01/2010; 408(9):2180-2180.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Polybrominated diphenyl ethers (PBDEs), perfluorinated alkylated substances (PFAS), and metals were monitored in tile drainage and groundwater following liquid (LMB) and dewatered municipal biosolid (DMB) applications to silty-clay loam agricultural field plots. LMB was applied (93,500 L ha(-1)) in late fall 2005 via surface spreading on un-tilled soil (SS(LMB)), and a one-pass aerator-based pre-tillage prior to surface spreading (AerWay SSD) (A). The DMB was applied (8 Mg d wha(-1)) in early summer 2006 on the same plots by injecting DMB beneath the soil surface (DI), and surface spreading on un-tilled soil (SS(DMB)). Key PBDE congeners (BDE-47, -99, -100, -153, -154, -183, -209) comprising 97% of total PBDE in LMB, had maximum tile effluent concentrations ranging from 6 to 320 ng L(-1) during application-induced tile flow. SS(LMB) application-induced tile mass loads for these PBDE congeners were significantly higher than those for control (C) plots (no LMB) (p<0.05), but not A plots (p>0.05). PBDE mass loss via tile (0-2h post-application) as a percent of mass applied was approximately 0.04-0.1% and approximately 0.8-1.7% for A and SS(LMB), respectively. Total PBDE loading to soil via LMB and DMB application was 0.0018 and 0.02 kg total PBDE ha(-1)yr(-1), respectively. Total PBDE concentration in soil (0-0.2m) after both applications was 115 ng g(-1)dw, (sampled 599 days and 340 days post LMB and DMB applications respectively). Of all the PFAS compounds, only PFOS (max concentration=17 ng L(-1)) and PFOA (12 ng L(-1)) were found above detectable limits in tile drainage from the application plots. Mass loads of metals in tile for the LMB application-induced tile hydrograph event, and post-application concentrations of metals in groundwater, showed significant (p<0.05) land application treatment effects (SS(LMB)>A>C for tile and SS(LMB) and A>C for groundwater for most results). Following DMB application, no significant differences in metal mass loads in tile were found between SS(DMB) and DI treatments (PBDE/PFAS were not measured). But for many metals (Cu, Se, Cd, Mo, Hg and Pb) both SS(DMB) and DI loads were significantly higher than those from C, but only during <100 days post DMB application. Clearly, pre-tilling the soil (e.g., A) prior to surface application of LMB will reduce application-based PBDE and metal contamination to tile drainage and shallow groundwater. Directly injecting DMB in soil does not significantly increase metal loading to tile drains relative to SS(DMB), thus, DI should be considered a DMB land application option.
    Science of The Total Environment 12/2009; 408(4):873-83. · 3.16 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Land application of municipal biosolids can be a source of environmental contamination by pharmaceutical and personal care products (PPCPs). This study examined PPCP concentrations/temporally discrete mass loads in agricultural tile drainage systems where two applications of biosolids had previously taken place. The field plots received liquid municipal biosolids (LMB) in the fall of 2005 at an application rate of approximately 93,500 L ha (-1), and a second land application was conducted using dewatered municipal biosolids (DMB) applied at a rate of approximately 8Mg dw ha (-1) in the summer of 2006 [corrected].The DMB land application treatments consisted of direct injection (DI) of the DMB beneath the soil surface at a nominal depth of approximately 0.11 m, and surface spreading (SS) plus subsequent tillage incorporation of DMB in the topsoil (approximately 0.10 m depth). The PPCPs examined included eight pharmaceuticals (acetaminophen, fluoxetine, ibuprofen, gemfibrozil, naproxen, carbamazepine, atenolol, sulfamethoxazole), the nicotine metabolite cotinine, and two antibacterial personal care products triclosan and triclocarban. Residues of naproxen, cotinine, atenolol and triclosan originating from the fall 2005 LMB application were detected in tile water nearly nine months after application (triclocarban was not measured in 2005). There were no significant differences (p>0.05) in PPCP mass loads among the two DMB land application treatments (i.e., SS vs. DI); although, average PPCP mass loads late in the study season (>100 days after application) were consistently higher for the DI treatment relative to the SS treatment. While the concentration of triclosan (approximately 14,000 ng g(-1) dw) in DMB was about twice that of triclocarban (approximately 8000 ng g(-1) dw), the average tile water concentrations for triclosan were much higher (43+/-5 ng L(-1)) than they were for triclocarban (0.73+/-0.14 ng L(-1)). Triclosan concentrations (maximum observed in 2006 approximately 235 ng L(-1)) in tile water resulting from land applications may warrant attention from a toxicological perspective.
    Science of The Total Environment 04/2009; 407(14):4220-30. · 3.16 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Application of municipal biosolids (sewage) to agricultural land is a common practice to improve soil physical quality and fertility. The chosen method of land application can have a strong impact on the extent of adjacent water contamination by nutrients and bacteria. Dewatered municipal biosolids (DMB) were applied to silt-clay loam experimental field plots in Ontario, Canada using two application methods: (i) surface spreading followed by shallow incorporation (SS) and (ii) a newly developed implement that directly injects DMB into the topsoil (DI). The objective of this study was to compare N, P, and bacteria quality of tile drainage and shallow groundwater associated with each land application technique. There were no significant differences (P > 0.05) in N, P, and bacteria tile mass loads among the application treatments for time periods <100 d postapplication, when the greatest peak loads and peak tile water concentrations were observed. Both land application treatments caused groundwater Escherichia coli contamination to at least 1.2 m depth below surface after the first postapplication rainfall event, and NO(3)-N contamination to at least 2.0 m depth below surface. The DI treatment did, however, have significantly (P < 0.05) higher tile mass loads of total Kjeldahl N (TKN), total phosphorus (TP), E. coli, Enterococci, and Clostridium perfringens relative to the SS treatment for time periods >100 d postapplication. Nevertheless, relative to tile effluent data collected <100 d postapplication (no application treatment differences), peak loads, and concentrations during this time were, overall, considerably lower for both treatments. This finding, along with no significant differences in N, P, and bacteria groundwater concentrations among the application treatments, and that the direct injection technique could potentially reduce vector attraction problems and odor, suggests that the direct injection technique should be considered a dewatered municipal biosolid land application option.
    Journal of Environmental Quality 01/2009; 38(3):1066-75. · 2.35 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Land application of municipal biosolids (sewage) is a common farming practice in many parts of the world. There is potential for transport of pharmaceuticals and personal care products (PPCPs) from agricultural fields to adjacent surface waters via tile drainage systems. In this study, liquid municipal biosolids (LMB) (total solids=11,933 mg L(-1)), supplemented with selected PPCPs and the fluorescent dye tracer rhodamine WT (RWT), were applied to tile drained fields using two land application approaches. Objectives included evaluating the relative benefits of land application practices with respect to reducing PPCP loadings to tile drains, evaluating PPCP persistence in tile water, and determining whether rhodamine WT can be used to estimate PPCP mass loads in tile. The PPCPs examined included an antibacterial agent used in personal care products (triclosan), a metabolite of nicotine (cotinine), and a variety of drugs including two sulfonamide antimicrobials (sulfapyridine, sulfamethoxazole), a beta-blocker (atenolol), an anti-epileptic (carbamazepine), an antidepressant (fluoxetine), analgesic/anti-inflammatories (acetaminophen, naproxen, ibuprofen), and a lipid-regulator (gemfibrozil). Maximum observed PPCP concentrations in the spiked LMB were about 10(3) ng g(-1) dry weight. PPCPs were shown to move rapidly via soil macropores to tile drains within minutes of the land application. Maximum observed PPCP concentrations in tile effluent associated with the LMB application-induced tile flow event were approximately 10(1) to 10(3) ng L(-1). PPCP mass loads, for the application-induced tile-hydrograph event, were significantly (p<0.1) higher for surface spreading over non-tilled soil (incorporation tillage occurring 20 h post-application), relative to aerating soil immediately prior to surface spreading using an AerWay slurry deposition system. PPCP concentrations that were detected above the limit of quantitation (LOQ) in tile water during several precipitation-induced tile flow events that occurred post-application, included: triclosan (max. approximately 1.5 x 10(2) ng L(-1)), carbamazepine (max. approximately 7 x 10(1) ng L(-1)), atenolol (max approximately 4 x 10(1) ng L(-1)), and cotinine (max approximately 2 x 10(1) ng L(-1)). In spite of their presence in biosolids, the other PPCPs were not observed above LOQ concentrations during these events. PPCP concentrations were predicted from RWT concentrations over a 40 day study period. Tile mass loads as a percent of PPCP mass applied to soil ranged from 4.2%+/-SD of 9.2% to 7.1%+/-10.9% for the AerWay system and surface spreading plus incorporation treatments, respectively.
    Science of The Total Environment 07/2008; 399(1-3):50-65. · 3.16 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This study examined bacteria and nutrient quality in tile drainage and shallow ground water resulting from a fall land application of liquid municipal biosolids (LMB), at field application rates of 93,500 L ha(-1), to silt-clay loam agricultural field plots using two different land application approaches. The land application methods were a one-pass AerWay SSD approach (A), and surface spreading plus subsequent incorporation (SS). For both treatments, it took between 3 and 39 min for LMB to reach tile drains after land application. The A treatment significantly (p < 0.1) reduced application-induced LMB contamination of tile drains relative to the SS treatment, as shown by mass loads of total Kjeldahl N (TKN), NH(4)-N, Total P (TP), PO(4)-P, E. coli., and Clostridium perfringens. E. coli contamination resulting from application occurred to at least 2.0-m depth in ground water, but was more notable in ground water immediately beneath tile depth (1.2 m). Treatment ground water concentrations of selected nutrients and bacteria for the study period ( approximately 46 d) at 1.2-m depth were significantly higher in the treatment plots, relative to control plots. The TKN and TP ground water concentrations at 1.2-m depth were significantly (p < 0.1) higher for the SS treatment, relative to the A treatment, but there were no significant (p > 0.1) treatment differences for the bacteria. For the macroporous field conditions observed, pre-tillage by equipment such as the AerWay SSD, will reduce LMB-induced tile and shallow ground water contamination compared to surface spreading over non-tilled soil, followed by incorporation.
    Journal of Environmental Quality 01/2008; 37(3):925-36. · 2.35 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Tillage action associated with liquid slurry application systems/management practices can modify soil infiltration properties. The degree or nature of such modification will depend largely on the type of tillage implement used, and the soil conditions at time of tillage activity. The specific objective of this study is to evaluate differences in soil infiltration properties, as measured using pressure infiltrometers and Guelph permeameters, resulting from the immediate tine action of two commonly used slurry application tillage implements (Kongskilde Vibro-Flex (S-tine) and the AerWay SSD (rolling aerator-type tine)) over a variety of silt–clay loam soil water content conditions. The results indicated that there were consistent negative correlations between field saturated hydraulic conductivity and soil water content for all tine-disturbed and undisturbed soil treatments. For Kongskilde, field-saturated hydraulic conductivity was, on average, lower in tine-influenced furrow bottoms, relative to those measured in undisturbed conditions at similar depths for most water content conditions. Generally, the Kongskilde tine-action reduced macropore-based infiltration in the bottom of the furrow for most soil conditions, albeit, this effect was most pronounced at the higher soil water contents. For AerWay, the tine-disturbed soils had generally higher field saturated hydraulic conductivities than undisturbed soil treatments over the observed water content range. This effect was manifested to a greater degree at higher, relative to lower observed water contents.
    Soil and Tillage Research 01/2007; 95:120-132. · 2.37 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Tillage associated with slurry applications, as well as soil physical properties at time of application, imparts strong control over resulting slurry application-induced infiltration patterns and contaminant flow pathways. This field-based study used Brilliant Blue-dyed water applied to tine-influenced silty-clay loam soil, at different antecedent soil water contents, to investigate the nature of infiltration patterns that might be expected to occur during a typical liquid manure or biosolid land application. The tines were associated with a furrow-based Kongskilde Vibro-Flex S-tine slurry application system and a soil pocket-forming AerWay® SSD rolling aerator-type slurry application system. For the furrow-based approach, liquid was applied to a small furrow stretch at a nominal rate of 180,000 l ha−1. For the AerWay treatment, a nominal liquid application rate of 180,000 l ha−1 was applied to individual soil pockets. Dye infiltration attributes were determined in 10 cm depth increments to over 1 m beneath the application area. Attributes included: dye infiltration depth, dye spread, and area coverage of dye. The attributes were determined for each depth via image processing software. Experiments were conducted at soil water conditions ranging from 15% v/v to 39% v/v. For furrow-based methods, dye was primarily absorbed above 30 cm depth (above a plough pan which, was approximately 20 cm depth) for all water content conditions. Dye spread:area ratios were generally larger below the pan than above it. Dye penetration depth for all water content conditions exceeded 60 cm depth. With the soil pockets caused by the AerWay treatments, the depth of dye penetration was non-linearly related to the soil water content where greatest dye penetration depth occurred at lower surface soil water contents (< 20% v/v) and at higher ones (> 29% v/v). Overall, for the lower soil water content conditions, desiccation cracks and soil fractures facilitated by tillage action augmented bypass-based preferential flow to continuous sub-pan macropore networks. The greater infiltration depths achieved for the wetter soil conditions were due to greater intrinsic pore sizes that are operative at lower soil tensions and reduced dye sorption. The area covered by dye was greater above the plough pan; but beneath the pan, discrete macropore-based flow (e.g., worm burrows, root channels) dominated infiltration to the deepest observed depths as supported by observations of relatively higher dye spread:area ratios. This study underscores the importance of basing liquid amendment timing regulations not only on an upper water content limit but also on a lower limit as well. In addition, the study supports the impact of plough pans augmenting sorption in the tillage layer, thus minimising the degree of preferential flow to depth during a typical land application.
    Biosystems Engineering - BIOSYST ENG. 01/2007; 98(2):235-247.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The least limiting water range (LLWR) attempts to incorporate crop-limiting values of soil strength, aeration, and water supply to plant roots into one effective parameter (on the basis of soil water content). The LLWR can be a useful indicator of soil quality and soil physical constraints on crop production. This study focused on assessing dynamic cultivation zone LLWR parameters between different cropping/tillage/trafficked clay loam plots at Winchester, Ont., to identify potential management impact on surficial soil physical conditions for contrasting growing seasons. This study also evaluated dynamic cultivation layer LLWR variables as indicators of corn (Zea mays L.) plant establishment and corn yield. The results suggest that no-till soils had lower average air-filled porosities (AFP) and O2 concentrations than respectively managed tilled plots for both years of study. Potential trafficking effects on aeration properties were most evident in no-till relative to till; preferentially trafficked no-tilled plots had lower AFP and O2 concentrations than respective non-preferentially trafficked no-till plots for both years of study. Corn establishment and yield variability were principally explained by cumulative differences between daily AFP and aeration threshold values, and the cumulative number of days daily AFP was below an AFP aeration threshold for specific corn growth stage periods. Lower AFP was linked to lower yields and plant establishments. Soil strength, as measured by cone penetration resistance, was important over certain sites, but not as important globally as AFP in predicting crop properties. Overall, conventional tilled soils that were not preferentially trafficked had most favorable aeration properties, and subsequently, greatest corn populations and yields. No-till soils were at greater risk of aeration limiting conditions, especially those in continuous corn and preferentially trafficked.
    Soil and Tillage Research. 01/2004;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cone penetration resistance (PR) is generally regarded as one of the best tools to assess soil strength. However, effects of soil water content (WC) on measured PR can mask or confound interpretations of treatment effects on soil strength. Correction of PR data to common water contents, via empirical PR versus WC relationships, could help reduce such problems. This study used a portable combination PR/WC instrument to evaluate and formalize growing season (multiple year) changes in cultivation zone PR versus WC relationships for different tillage (conventional and no-till), trafficked, and corn (Zea mays L.) cropping systems on clay loam soils in eastern Ontario, Canada. The results indicated expected negative linear and piecewise linear relationships between PR and WC for no-till soils. There was generally greater potential for higher PR at a specified water content for preferentially trafficked no-till soils, relative to no-till not receiving such a treatment. For tilled soils, negative linear relationships between bulk PR and WC were not as strong. Significant interactions between PR, WC, and days after planting (DAP), however, were uncovered using multivariate adaptive regression spline analyses. For non-preferentially trafficked tilled plots, linear negative relationships between PR and WC changed over the growing season and achieved strength/stability at approximately 90 days after planting; roughly 50 days after bulk density after planting effectively stabilized. For preferentially trafficked tilled plots, there were similar PR versus WC relationships, however, there were stronger interacting positive relationships between PR and DAP. The results from this work are promising for elucidating soil structural evolution over growing seasons for different tillage, trafficked and corn cropping systems on clay loam soils.
    Soil and Tillage Research 01/2004; 79(1):51-62. · 2.37 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The primary objective of this investigation was to evaluate some potential causal associations between draft derived from a 3-bottom mouldboard plow during normal fall field operations and soil-crop properties at a field site near Winchester, Ontario, Canada. A secondary objective was to investigate, in a preliminary manner, associations between draft and crop yield (corn, soybean, and wheat). Regression tree analysis indicated that draft variability was best explained by field location, crop type, soil cone penetration resistance in the plow layer, and soil texture in the plow layer. Draft was found to generally increase with cone penetration resistance in the plow layer and soil clay content. Corn yields were negatively associated with draft. The reverse was true for the soybean yields, and a combination of negative and positive draft vs. yield relationships existed for the wheat plots. The overall results indicated that draft data collected during normal field operations can be useful for producers interested in identifying areas in the field where soil strength/compaction might be problematic with regard to crop yields.
    Precision Agriculture 08/2002; 3(3):237-257. · 1.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Measurements of mouldboard plow draft can potentially provide a useful tool for continuously mapping, as a surrogate variable, crop limiting soil properties such as soil strength/compaction. Numerous researchers have shown that loading on tillage tools can be periodic. One source of higher frequency periodic loading has been related to failure modes in the soil. Lower frequency periodic loading on tillage tools, assuming tillage depth is relatively constant, more often reflects local spatial variability in soil physical properties such as soil moisture, soil texture, organic matter, and/or soil strength/compaction. This study presents a spectrum and cross-spectrum analysis of mouldboard draft recorded during normal fall plowing operations along adjacent transects. One objective of this study was to determine the dominant periodic components in order to elucidate meaningful frequencies which might be better related to variation in soil physical properties. Spectral densities were generally dominated by signals with a few cycles per 300-m transect. The cross-amplitude and squared coherency between draft recorded on adjacent transects provided further indication of the frequencies which characterized the signals because they provide an indication of correlation as a function of frequency. Spatial dependence in the data was quantified using spatial autocorrelation and cross-correlation. An additional objective was to use the spectral information to help design more physically meaningful filters for the raw draft data. Taking the Fast Fourier Transform of the raw draft data and filtering in the frequency domain using an optimal filter informed via the spectrum and cross-spectrum analysis, provided a convenient method for isolating a more physically meaningful signal.
    Precision Agriculture 08/2002; 3(3):225-236. · 1.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: For corn crops on soils with fine texture in eastern Canada, research has been ongoing on the relationships between corn grain yields and management practice, soil strength/compaction, and soil nutrient status. However, these variables can operate in a complex manner that may not be detectable via uni-structural models. This study used regression-tree analysis, in an exploratory context, to model corn grain yields over a relatively flat clay to silty loam field on the basis of several soil physical, soil nitrate, and management variables. It was found that corn grain yields were first subdivided by length of time under corn production (1st and 3rd year corn groups). These yield groups were further subdivided by cone penetration resistance, elevation, soil nitrate, and soil texture information. Generally, higher corn grain yields were associated with 1st year corn, lower relative soil strength/compaction, and higher post-growing season soil nitrate levels. The modeled results helped to identify equifinality, context dependent relationships, and spatial continuity in inferred formative mechanisms; issues important in many field and/or landscape studies of spatial processes.
    Soil and Tillage Research 03/2001; · 2.37 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Soil compaction can suppress crop yields. Thus, compaction indices such as cone penetration resistance (PR) can be useful to farmers and researchers interested in identifying areas in the field where soil strength/compaction, or governing soil properties reflected by PR measurements, might be problematic to crop yield. The general aim of this paper was to apply stochastic simulation to spatially delimit critically important soil strength patterns, the spatial disposition and uncertainty of those patterns, and to determine if broad strength/compaction spatial units defined via PR threshold probability patterns could be used to reflect corn yield variability under different rotation, tillage, and trafficking management treatments. Shallow (3–15 cm depth) linear PR patterns were strongly anisotropic while deeper patterns (25–40 cm depth) were more regionalized in character. Stochastic simulation produced very strong global patterns of low (2 MPa) PR values. Broad spatial units defined on the basis of these patterns were used to generate corn yield risk maps. It was found that yields, under the various treatments, reflected the risk patterns in an expected way 75% of the time over 5 years of observation. That is, under similar management treatments, lower risk areas (areas where there was lower probability of soil strength exceeding 2 MPa in the top 3 to 15 cm of the soil) produced higher yields than higher risk areas (areas where there was higher probability of soil strength exceeding 2 MPa in the top 3 to 15 cm of soil).
    Geoderma 01/2001; 104(3):325-343. · 2.35 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Tension infiltrometer (TI) measurements from a silty clay loam soil (Winchester, Ont.), a sandy soil (Hancock, WI), and a silt loam soil (Rosemount, MN) were used to: (i) characterise near-saturated hydraulic conductivity (K0) and flow-weighted mean radius of soil macropores (R0); (ii) distinguish differences in these water transmission properties between no-till (NT) and mouldboard plough (MP) continuous maize (Zea mays L.) production systems.The K0 values increased by about two orders of magnitude as the pressure heads (P0) set on the TI membranes were increased incrementally from the minimum values (P0=−10 cm or −15 cm) to the maximum value (P0=0 cm). This indicates that substantial networks of water-conducting soil macropores exist in continuous maize production systems, regardless of soil texture or tillage treatment. For each P0 value, the MP treatment had a consistently higher K0 than NT at the Winchester and Hancock fields sites, and a consistently lower K0 than NT at the Rosemount field site.Regardless of soil type, most R0 pores occurred in the 0.1–0.3 mm size range for both NT and MP soils, but NT had two to three times more of these R0 pore sizes, as well as smaller and larger R0 pores, than MP. This probably reflects a more consolidated soil matrix (enrichment of smaller R0 pores) and a greater number of large cracks and biopores (larger R0 pores) in NT soils, owing to the absence of annual loosening of the soil matrix and disruption of macropores that occurs with MP tillage.Relationships between K0 and R0 were complex but consistent within and between tillage treatments. A physical interpretation for this behaviour is given which employs capillary theory for water entry, and interactions among the size, number and morphology of water-conducting macropores during the infiltration process.It was concluded that the TI technique is effective for characterising differences in K0 and R0 between NT and MP continuous maize production systems.
    Soil and Tillage Research 01/1995; 33(2):117-131. · 2.37 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A no-tillage system was imposed on a structurally degraded fine-textured soil (Humic Gleysol) that had been under continuous corn with moldboard tillage for more than 20 years. After 3 years of no-tillage, several soil structural properties were compared with the conventional tillage treatment to assess whether the soil structure had improved.No significant difference (P<0.05) was found between tillage treatments for the saturated hydraulic conductivity, porosity and penetration resistance in the surface 5 cm. Measurements of soil penetration resistance and in situ saturated hydraulic conductivity (Kwp) using the well permeameter method were sensitive to structural changes that had occurred at 5–20 cm depth. The Kwp at this depth was significantly greater in the moldboard treatment than in the no-tillage treatment. Resistance measurements indicated significantly greater soil strengths at 10–20 cm under no-tillage. Aggregate stabilities were assessed by wet sieving twice during the growing season. No-tillage resulted in larger soil aggregates, especially at the surface, compared with the moldboard tillage.These data suggest that degraded soils with low structural stability may initially suffer further deterioration with the elimination of tillage, owing to the loss or reduction of mechanically formed pores.
    Soil and Tillage Research. 01/1993;