Soil health indicators after 21 yr of no-tillage in south coastal British Columbia

Publication: Canadian Journal of Soil Science
19 February 2019

Abstract

The lower Fraser Valley is one of the most intensively cropped regions in Canada. Yet, how soil health indicators respond to long-term intensive agricultural management is poorly documented in this region. Thus, we evaluated a suite of soil health indicators in response to 21 growing seasons of continuous silage corn (Zea mays L.) under conventional tillage or no-tillage (0–20 cm soil layer). Wet aggregate stability, available water capacity, active carbon (permanganate oxidizable, POXC), and extractable potassium and extractable magnesium were significantly greater with no-till than conventional tillage, whereas 8 of 13 indicators were similar. Soil health indicators responded more favourably to no-till than conventional tillage.

Résumé

La basse vallée du Fraser est une des régions les plus exploitées du Canada sur le plan agricole. Pourtant, on sait peu de chose sur la réaction des indicateurs de la vitalité du sol à une agriculture intensive prolongée. Pour y remédier, les auteurs ont évalué une série d’indicateurs pendant 21 périodes végétatives de monoculture du maïs d’ensilage (Zea mays L.), avec ou sans travail du sol (couche de 0 à 20 cm d’épaisseur). La stabilité des agrégats humides, la capacité en eau disponible, la concentration de charbon actif (oxydable au permanganate) ainsi que celle de potassium et de magnésium extractibles sont sensiblement plus élevées sans travail du sol qu’avec des labours ordinaires. Huit des 13 indicateurs subissent peu de modifications. Les indicateurs de la vitalité du sol réagissent mieux au non-travail du sol qu’au travail du sol usuel. [Traduit par la Rédaction]

Introduction

Sensitive soil health indicators serve as tools to monitor temporal changes in soil physical, chemical, and biological properties under various management practices (Congreves et al. 2015). Throughout North America, significant effort is being spent on identifying indicators that can detect changes in soil health induced by long-term cropping practices (Congreves et al. 2015; Morrow et al. 2016). The lower Fraser Valley of British Columbia is one of the most intensively cropped regions in Canada, while the climatic conditions are among the mildest in the country, with a plant hardiness zone 8. Given the long growing season and mild non-growing season, soil microbial activity throughout the year may help to increase the resilience of soil, but there is limited data on how intensive cropping practices alter soil health in the region and there has been no comprehensive effort to measure and monitor soil health indicators in the lower Fraser Valley. A field trial established in Agassiz, BC, in 1997 provided a unique opportunity to assess how soil health indicators responded to 21 yr of continuous silage corn (Zea mays L.), in which there is very little crop residue, under a conventional tillage or no-tillage system. The Cornell University, Comprehensive Assessment of Soil Health, was used as the framework. We hypothesized that most soil health indicators would have greater values under no-till than conventional tillage.

Materials and Methods

Study location and field site

The study site is located at the Agriculture and Agri-Food Canada, Agassiz Research and Development Centre in Agassiz, BC (49.242859 N, −121.763138 W, altitude 15 m). The region has a maritime climate with cool, wet winters, and relatively warm, dry summers with an average annual precipitation of 1755 mm (rainfall is 1689 mm). The soil is a moderately well to well-drained, medium-textured, stone-free Eluviated Eutric Brunisol with a silty loam texture (27% sand, 59% silt, and 14% clay), pH 6.1, 17 g organic carbon (C) kg−1, and 1.26 g total nitrogen (N) kg−1 (0–15 cm).
The study was established in 1997 as a split-plot randomized complete block design with tillage as a main factor and N source as a subfactor with four replicates (subplot size: 6.5 m × 3 m). The selected spring tillage treatments were conventional tillage and no-tillage receiving 180 kg N ha−1. Conventional tillage consisted of primary tillage with a moldboard plow to a 25 cm depth followed by two to three passes with tandem disks to a 20 cm depth with light harrowing a few days later. No-tillage consisted of controlling weeds prior to seeding by applying glyphosate at 438 g active ingredient ha−1 and seeding directly into the undisturbed stubble (<20 cm tall). Silage corn was planted in 75 cm spaced rows with a four-row planter (Max-emerge II, Deere & Company, Moline, IL, USA) with no-till attachments to close the seed furrows. The total N rate of 180 kg ha−1, included a side-banded starter rate of 20 kg N ha−1 at planting with 160 kg urea N ha−1 broadcasted. The starter phosphorus (P) rate was 40 kg P ha−1 applied as triple super phosphate. Other nutrients [potassium (K), sulfur, and magnesium (Mg)] were applied prior to planting based on local recommendations. Silage corn has been continuously grown for the duration of the study. Historically, tillage operations and fertilization have been conducted between late-April and mid-June, and planting has typically occurred shortly thereafter depending on seasonal weather conditions and staff availability. Given the wide planting window, silage corn varieties with different heat unit requirements have been grown over the years. Harvest has typically occurred mid-September to mid-October. This is within the range of practices used on local farms.

Soil sampling and analysis

Prior to tillage or pre-plant operations, soil was sampled on 7 June 2018 to a 20 cm depth at six locations with a soil auger and mixed well in a bucket to make a composite sample for each replicated plot. The soil was air-dried at 21 °C, and all visible plant material was removed. All soil health indicators were determined based on the Comprehensive Assessment of Soil Health — The Cornell Framework. In brief, wet aggregate stability was determined on 30 g soil using a rainfall simulator. Available water capacity was determined gravimetrically as the difference between soil water content at field capacity (10 kPa) and permanent wilting point (1500 kPa). Soil organic matter (OM) was determined by loss on ignition (LOI). The %LOI was converted into %OM using %OM = (%LOI × 0.7) − 0.23. Extractable protein was determined by a neutral sodium citrate buffer extraction. Heterotrophic soil respiration was measured in a 4 d incubation. Active C was determined by permanganate oxidation. Soil pH was measured in a 1:1 water to soil ratio (v:v). Macronutrients (P, K, and Mg) and micronutrients [iron (Fe), manganese (Mn), and zinc (Zn)] were extracted by a modified Morgan method (ammonium acetate plus acetic acid, pH = 4.8), and their concentrations were determined using an inductively coupled plasma emission spectrometer (SPECTRO Analytical Instruments Inc., Mahwah, NJ, USA).

Statistical analyses

The assumptions of analysis of variance (ANOVA) were confirmed with Shapiro–Wilk’s normality test and Brown–Forsythe equal variance test. One-way ANOVA was computed by the MIXED procedure using SAS software version 9.3 to assess whether the tillage system caused differences in the soil health indicators (SAS Institute Inc. 2010, Cary, NC, USA). Block was a random effect, and tillage system was a fixed effect.

Results and Discussion

Wet aggregate stability, available water capacity, active C, extractable K, and extractable Mg were significantly greater with no-till than conventional tillage (Table 1). No other soil health indicator was significantly affected by tillage system.
Table 1.
Table 1. Soil health indicators (mean values ± standard deviation) in response to 21 yr of continuous silage corn under conventional tillage or no-tillage near Agassiz, BC.
Wet aggregate stability was slightly more than double with no-till than conventional tillage, which is consistent with three of four long-term field sites in Ontario that had significantly greater wet aggregate stability with no-till than conventional tillage (Congreves et al. 2015). Conventional tillage primarily degrades soil structure by physically disrupting aggregates; the greater intact macro- and microaggregates in no-till promotes resistance to erosion and soil water retention (Six et al. 1999). The no-till plots were, therefore, less likely to be degraded by wind. Wind erosion can be a problem in the lower Fraser Valley due to intense Arctic outflows throughout the non-growing season. Fungi play an important role in promoting soil aggregation; arbuscular mycorrhizal fungi excrete copious amounts of glomalin, an insoluble, glue-like, hydrophobic glycoprotein, that may help to initiate and protect aggregates, which has been supported by a strong correlation between glomalin and aggregate stability (Wright and Upadhyaya 1998). At this location, greater arbuscular mycorrhizal colonization in the no-till than tilled plots has frequently been observed (unpublished data). Given that slaking can occur to macroaggregates in fields with conventional tillage (Six et al. 1999), this has important ramifications because the area is subjected to intense rainfall throughout the non-growing season, which subjects soils with weak aggregation to greater risk of runoff and erosion.
Available water capacity was 9% greater with no-till than conventional tillage. Similar to the current study, no-till was shown to have significantly greater available water capacity than a conventionally tilled clay loam in a dry subhumid region of Spain (Bescansa et al. 2006). Greater available water capacity may be linked to greater wet aggregate stability and be important in the study region because the area experiences significant water deficits in summer and crops respond well to irrigation. The greater available water capacity in the no-till soil may confer key advantages during the relatively dry summer months in the lower Fraser Valley, not only for crop production but also for water conservation. In general, available water capacity has received less research attention than the other soil health indicators. This may represent an important research gap for assessing the benefits of no-till compared with conventional tillage.
Active C was 24% greater with no-till than conventional tillage. This contrasts with findings from four long-term tillage field trials in Ontario, where tillage system was observed to have no effect on active C (Congreves et al. 2015), but it is consistent with long-term tillage trials in North Dakota (Weil et al. 2003), inland Oregon, and Idaho (Morrow et al. 2016). Given that active C is thought to represent a readily available energy source for soil microorganisms that can be highly correlated with microbial biomass C (Weil et al. 2003) and that greater microbial biomass C was previously reported for the no-till soils at this site (Lupwayi et al. 2010), the result of the current study is not entirely surprising. Interestingly, we found no effect of tillage system on soil respiration, which is an indicator of microbial activity. This may provide evidence that active C accumulates faster than microbes consume it in the no-till soils because microbes are apparently respiring at the same rate even though there is more microbial available C (active C) in the no-till soil. More frequent soil respiration and active C measurements may be needed to help validate their relationship. The increased active C with no-till in parallel with the lack of difference in soil respiration rates between tillage systems suggests that investigating the C-use efficiency by the soil microbial community is warranted.
Extractable-K and -Mg were 34% and 18% greater with no-till than conventional tillage, respectively. Although K- and Mg-containing fertilizer was applied to both the conventional and no-till plots, typically extractable-K and -Mg and other elements will tend to accumulate near the surface of no-till soils (0–5 cm), whereas mixing induced by mouldboard plowing will lead to greater extractable elements in the 15–30 cm soil layer (Ismail et al. 1994). Given that the mouldboard plow depth in the current study was about 25 cm, it is likely that mixing/inversion induced by conventional tillage led to lower extractable-K and -Mg concentrations in the 0–20 cm soil layer that was sampled. This is consistent with observations that long-term no-till led to elevated extractable-K or -Mg in some cases compared with conventional tillage in Ontario in the 0–15 cm soil layer (Congreves et al. 2015).
One statistically nonsignificant finding with respect to soil organic matter, based on the LOI method, is worth noting. The current study found that there was no significant difference in soil organic matter caused by tillage system (P = 0.1072). It is possible that this represents a type II error because previous work at the study site found that soil organic C (by dry combustion) was significantly greater (13%) with no-till than conventional tillage (Hunt et al. 2016). In this study, soil organic matter was 9% greater with no-till than conventional tillage. Conventional tillage typically leads to significantly lower soil total C than no-till above the plow layer because it disrupts aggregates exposing organic C to microbial decay (e.g., Six et al. 1999). As tillage effects on soil organic matter as measured by LOI have also not been observed in previous long-term tillage system studies (Congreves et al. 2015), we question the use of LOI for measuring changes in soil organic matter (and, by extension, soil organic C) as a soil health indicator and recommend the dry combustion method instead.

Conclusion

After 21 yr of continuous silage corn under conventional tillage or no-till in the lower Fraser Valley, British Columbia, wet aggregate stability, available water capacity, active C, extractable K, and extractable Mg were significantly greater with no-till than conventional tillage. The context of this long-term field trial may be seen as an intensively managed scenario because there is corn monoculture with little crop residue, no manure, and no winter cover crop. Long-term tillage was shown to negatively impact two important physical soil properties, wet aggregate stability and available water capacity, suggesting that adoption of no-till could be used to improve water-use efficiency and resistance to erosion. Overall, wet aggregate stability, available water capacity, and active C appear to be important soil health indicators for their sensitivity to tillage system in south coastal British Columbia.

Acknowledgements

The technical support of Dr. Wendy Clark is much appreciated. Field operations conducted by Frederic Bounaix, James Hall, and Jace LaFond are gratefully acknowledged. Funding for this work was provided by Agriculture and Agri-Food Canada.

References

Bescansa P., Imaz M.J., Virto I., Enrique A., and Hoogmoed W.B. 2006. Soil water retention as affected by tillage and residue management in semiarid Spain. Soil Tillage Res. 87: 19–27.
Congreves K.A., Hayes A., Verhallen E.A., and Van Eerd L.L. 2015. Long-term impact of tillage and crop rotation on soil health at four temperate agroecosystems. Soil Tillage Res. 152: 17–28.
Hunt D.E., Bittman S., Zhang H., Bhandral R., Grant C.A., and Lemke R. 2016. Effect of polymer-coated urea on nitrous oxide emission in zero-till and conventionally tilled silage corn. Can. J. Soil Sci. 96: 12–22.
Ismail I., Blevins R.L., and Frye W.W. 1994. Long-term no-tillage effects on soil properties and continuous corn yields. Soil Sci. Soc. Am. J. 58: 193–198.
Lupwayi N.Z., Grant C.A., Soon Y.K., Clayton G.W., Bittman S., Malhi S.S., and Zebarth B.J. 2010. Soil microbial community response to controlled-release urea fertilizer under zero tillage and conventional tillage. Appl. Soil Ecol. 45: 254–261.
Morrow J.G., Huggins D.R., Carpenter-Boggs L.A., and Reganold J.P. 2016. Evaluating measures to assess soil health in long-term agroecosystem trials. Soil Sci. Soc. Am. J. 80: 450–462.
Six J., Elliott E.T., and Paustian K. 1999. Aggregate and soil organic matter dynamics under conventional and no-tillage systems. Soil Sci. Soc. Am. J. 63: 1350–1358.
Weil R.R., Islam K.R., Stine M.A., Gruver J.B., and Samson-Liebig S.E. 2003. Estimating active carbon for soil quality assessment: a simplified method for laboratory and field use. Am. J. Altern. Agric. 18: 3–17.
Wright S.F. and Upadhyaya A. 1998. A survey of soils for aggregate stability and glomalin, a glycoprotein produced by hyphae of arbuscular mycorrhizal fungi. Plant Soil, 198: 97–107.

Information & Authors

Information

Published In

cover image Canadian Journal of Soil Science
Canadian Journal of Soil Science
Volume 99Number 2June 2019
Pages: 222 - 225
Editor: Newton Lupwayi

History

Received: 20 November 2018
Accepted: 13 February 2019
Accepted manuscript online: 19 February 2019
Version of record online: 19 February 2019

Key Words

  1. soil quality
  2. POXC
  3. active carbon
  4. wet aggregate stability
  5. available water capacity

Mots-clés

  1. qualité du sol
  2. POXC
  3. charbon actif
  4. stabilité des agrégats humides
  5. capacité en eau disponible

Authors

Affiliations

Ben W. Thomas* [email protected]
Agassiz Research and Development Centre, Agriculture and Agri-Food Canada, 6947 Highway 7, Agassiz, BC V0M 1A0, Canada.
Derek Hunt
Agassiz Research and Development Centre, Agriculture and Agri-Food Canada, 6947 Highway 7, Agassiz, BC V0M 1A0, Canada.
Shabtai Bittman
Agassiz Research and Development Centre, Agriculture and Agri-Food Canada, 6947 Highway 7, Agassiz, BC V0M 1A0, Canada.
Kirsten D. Hannam
Summerland Research and Development Centre, Agriculture and Agri-Food Canada, 4200 Highway 97, Summerland, BC V0H 1Z0, Canada.
Aimé J. Messiga*
Agassiz Research and Development Centre, Agriculture and Agri-Food Canada, 6947 Highway 7, Agassiz, BC V0M 1A0, Canada.
Dennis Haak
Agassiz Research and Development Centre, Agriculture and Agri-Food Canada, 6947 Highway 7, Agassiz, BC V0M 1A0, Canada.
Mehdi Sharifi
Summerland Research and Development Centre, Agriculture and Agri-Food Canada, 4200 Highway 97, Summerland, BC V0H 1Z0, Canada.
Xiying Hao
Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada, 5403 1st Avenue South, Lethbridge, AB T1J 4B1, Canada.

Notes

*
Ben W. Thomas and Aimé J. Messiga currently serve as Associate Editors; peer review and editorial decisions regarding this manuscript were handled by Nathan Basiliko.
© Her Majesty the Queen in right of Canada as represented by the Minister of Agriculture and Agri-Food Canada 2019. This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

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