Tillage or No-Tillage: Impact On Mycorrhizae
Tillage or No-Tillage: Impact On Mycorrhizae
Tillage or No-Tillage: Impact On Mycorrhizae
Zahangir Kabir
Department of Land, Air and Water Resources, 1150 Plant and Environmental Sciences
Building, University of California, Davis, One Shields Ave., Davis, California 95616, USA
(e-mail: kabir@ucdavis.edu). Received 14 October 2003, accepted 9 September 2004.
Kabir, Z. 2005. Tillage or no-tillage: Impact on mycorrhizae. Can. J. Plant Sci. 85: 23–29. Arbuscular mycorrhizal (AM) fungi
are ubiquitous in agricultural soils. These fungi play important roles in plant nutrition and soil conservation. The persistence of
AM fungi in ecosystems depends on the formation and survival of propagules (e.g., spore, hyphae and colonized roots). While
spores are considered to be resistant structure that may be view as “long-term” propagules when viable host plants are not present,
hyphae are considered to be the main source of inocula when host plants are present and the soil is not disturbed. Tillage is an inte-
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gral part of modern agriculture that can modify the physical, chemical and biological properties of a soil. Consequently, tillage
practices may also affect AM fungi. The various tillage practices used in the management of soil for maximum crop production
may negatively impact the survival of AM fungal propagules. In tilled soil, certain AM species may survive while others may dis-
appear. Because AM fungi are more abundant in the topsoil, deep plowing may dilute their propagules in a greater volume of soil,
thereby reducing the level of infection of a plant root. Tillage is particularly detrimental to AM hyphae if the soil is tilled in the
fall and the hyphae are detached from the host plant. Under no-till (NT), AM fungi survive better, particularly when they are close
to the host crop on which they developed. There is speculation that in NT systems, plants may follow old root channels and poten-
tially encounter more AM fungal propagules than plants growing in soil that has been tilled. Management of AM fungi in NT soil
is essential to maximizing benefits to crops. This review reports how tillage practices affect AM fungi species richness, surviv-
ability and infectivity, and how conservation tillage can increase AM fungi survival, consequently improving plant phosphorus
uptake and soil aggregate stability.
Key words: Arbuscular mycorrhizal fungi, conservation tillage, conventional tillage, P uptake,
soil aggregate stability, cover crops, crop yield
Kabir, Z. 2005. Travail ou non-travail du sol : incidence sur les mycorhizes. Can. J. Plant Sci. 85: 23–29. Les mycorhizes à
arbuscules (MA) sont des champignons omniprésents dans les sols agricoles. Ces champignons jouent un rôle important pour la
nutrition des plantes et la conservation du sol. Leur persistance dans l’écosystème dépend de la formation et de la survie des
propagules (les spores, les hyphes et les racines colonisées). Bien que les spores soient considérées comme des propagules « à long
terme » à cause de leur résistance en l’absence de plantes hôtes, les hyphes demeurent la principale source d’inoculum quand il y
a des plantes hôtes et que le sol n’est pas perturbé. Les labours font partie intégrante des pratiques agricoles modernes et peuvent
modifier les propriétés physiques, chimiques et biologiques du sol. De telles pratiques affectent donc aussi les MA. Diverses pra-
tiques employées pour parvenir à la production maximale d’une culture ont une incidence négative sur la survie des propagules
des MA. Certaines espèces de champignons survivront dans le sol retourné alors que d’autres périront. Les MA étant plus abon-
dants dans le sol de surface, un labour en profondeur diluera leurs propagules dans un plus grand volume, donc réduira le taux
d’infection des racines de la plante hôte. Les labours sont particulièrement néfastes quand le travail s’effectue à l’automne et que
les hyphes des MA se détachent de la plante hôte. Les MA survivent mieux avec le non-travail du sol, surtout quand ils se trou-
vent à proximité de la culture qui a servi à leur développement. On se demande si les plantes n’empruntent pas les anciens canaux
radiculaires dans les champs non travaillés, si bien qu’elles trouvent plus de propagules de MA que celles poussant dans un sol
travaillé. Une gestion des MA dans le sol non travaillé est essentielle si l’on veut que les cultures en profitent au maximum. La
présente étude explique comment les pratiques en matière de travail du sol affectent la richesse des espèces de MA, leur capacité
de survie et leur pouvoir infectieux et comment les pratiques de conservation accroissent la survie de ces cryptogames, donc
améliorent l’absorption du phosphore par les plantes et la stabilité des agrégats du sol.
Mots clés: Mycorhizes à arbuscules, conservation du sol, travail du sol classique, absorption du P,
stabilité des agrégats, cultures abris, rendement des cultures
Tillage, the mechanical manipulation of soil, is a common tional (CT) and conservation (at least 30% residue left on
practice in modern agriculture. Tillage is performed to the soil surface; Conservation Technology Information
enhance decomposition of crop residues through physical Center 1995). The general category of conservation tillage
breakdown and incorporation into soil. Tillage is also used includes specific practices such as no-till (NT), ridge-tillage,
to level soil, prepare seedbeds for planting, and incorporate reduced tillage (RT), shallow tillage and strip tillage.
fertilizers, manures and pesticides. Additionally, it can serve Reduced tillage systems are characterized by a reduction in
as a method of post-emergence weed control and as a man- the intensity or number of tillage operations compared to CT
agement tool to disrupt or reduce the incidence of diseases (generally autumn plowing plus spring disking). In RT sys-
and pests. While tillage is necessary in many situations, it
may also lead to soil degradation and environmental pollu- Abbreviations: AM, arbuscular mycorrhizal; CT, con-
tion. There are two main types of tillage systems, conven- ventional tillage; NT, no-till; RT, reduced tillage
23
24 CANADIAN JOURNAL OF PLANT SCIENCE
tems most of the crop residues remain on the soil surface, EFFECTS OF SOIL DISTURBANCE ON
and the tillage operation is normally done only in spring. MYCORRHIZAL FUNCTIONING
Thus, the soil remains undisturbed throughout the winter, as
is the case under NT systems. Concerns of environmental Impacts on AM Fungal Development
degradation through the transport of sediments, nutrients Soil disturbance has a negative effect on AM fungi and there-
and pesticides from farmlands to surface waters, as well as by reduces the benefits to crops and soil quality that are
the need to conserve soil water in dry areas, have prompted derived from mycorrhizae. Schenk et al. (1982) in Florida,
a switch to conservation tillage practices. These practices USA, reported an increase of mycorrhizal spores and root
may improve soil physical properties at the macroscopic colonization on several agronomic crops with minimum
level, which in turn affects chemical and biological proper- tillage compared with conventional tillage. Mulligan et al.
ties of soil at the microscopic level including AM fungi. (1985) in Michigan, USA, proposed that the negative impact
Arbuscular mycorrhizal fungi form symbiotic relation- of tillage on root colonization was due to lower root growth
ships with plants. In these associations plants provide car- of dry bean (Phaseolus vulgaris L.) caused by increased soil
bohydrates to the fungi in exchange for mineral nutrients bulk densities in tilled soils. In contrast, O’Halloran et al.
(1986) in eastern Canada found greater root growth but lower
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was hampered by lack of methodologies to examine AM to14-leaf stage. In the clay soil, however, P concentration
hyphae directly in the soil. Current research supports this was greater under NT both at the 12- to14-leaf and the silk-
hypothesis and addresses various mechanisms. ing stage. These results are in accordance with those of
O’Halloran (1982) who also observed higher P absorption
Impacts on AM Fungal Community Composition by corn in a NT system. McGonigle and Miller (1993), in
In a research field (Kabir et al. 1997a, 1998a) in Quebec, eastern Canada, observed that corn shoot P concentrations
Canada, the AM species diversity in a soil under 12 yr of CT were significantly greater under NT and RT than under CT.
practice was significantly lower than that of the NT soil In addition to P, Kabir et al. (1998a) found that Zn and Cu
(unpublished data). Hamel et al. (1994) in Quebec, Canada, concentrations in corn plants were sometimes significantly
reported the disappearance of Gigaspora margarita and G. greater under NT than under CT plots. A similar effect of
caledonium 3 yr after plowing and putting a previously soil disturbance on Zn and Cu was also observed for corn in
uncultivated field into cultivation. Similarly, Boddington pot studies (McGonigle and Miller 1996). Mozafar et al.
and Dodd (2000) observed a decrease in AM fungal species (2000) reported that the concentrations of P, Zn and Cu in
richness in tilled soil, relative to untilled soil, growing corn and those of P, K, Mn and Zn in wheat grown in
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Gliricidia sepium in Indonesia; Scutellospora sp. disap- Switzerland were greater in plants under NT than under CT
peared after soil disturbance. Significantly more AM spores at most of their sampling dates. While NT systems allow for
were also observed by Jansa et al. (2002) in soil growing greater nutrient uptake, in certain circumstances, crop yields
wheat under NT than under CT in Switzerland. Jansa et al. are reduced with NT. Thus the relatively minor economical
(2003) also found that Scutellospora was more dominant in benefits that derived from improved nutrient acquisition are
low-tillage fields, whereas Glomus was dominant in highly therefore, often dwarfed by the losses in crop yield.
tilled fields. Douds et al. (1995) found more G. occultum- However, considering the cost and benefit ratio, one could
like spores under NT corn-soybean-wheat rotations and argue that the profitability of NT is similar to CT even
more G. etunicatum-like and other Glomus spp. spores in though yields are reduced under NT. Furthermore, consider-
soils under cultivation in Pennsylvania, USA. Sieverding ing soil health and the environment, growing crops in an NT
(1991) observed that G. scintillans was sporulating earlier system far outweigh any short-term benefit of CT systems.
and was able to produce more spores than other AM species
in plowed soils in Columbia. The author reported that 75% Relationships among Soil Disturbance, AM Fungi
of the spores in plowed soils were belonging to G. scitillans and Aggregate Stability
while this species accounted for only 5% of the total spores Soil structure quality and aggregate stability in agricultural
in NT soils. This suggests that tillage practices may select fields are influenced by agricultural practices. Tillage gradu-
AM fungi with certain characteristics and eliminate others. ally reduces aggregate stability making soil more vulnerable
For example, soil disturbance created by tillage may favor to wind and water erosion. Arbuscular mycorrhizal fungi
fast-growing species that might be less mutualistic and less make direct contributions to aggregation and aggregate sta-
efficient in improving host plant nutrients uptake (Johnson bility (Bethlenfalvay and Barea 1994; Kabir and Koide 2000,
and Pfleger 1992). 2002) and therefore play an important role in soil conserva-
tion. AM hyphae have been positively correlated with soil
Differentiating Effects of Disturbance on Nutrient aggregate stability (Kabir and Koide 2002). Because AM
Acquisition and AM Functioning hyphal networks remain intact In NT soils, the density of
The most dramatic effect of AM fungal proliferation in the active hyphae is greater than under CT soils (Kabir et al.
soil is an increase in P absorption by the host plants (Koide 1997a). Hence, the importance of AM fungi for aggregation
1991). Phosphorus is found in very low concentration in the is greater in NT than in CT systems. Tisdall (1991) speculat-
soil solution as it has a high affinity for fixation onto soil ed that extracellular polysaccharides of fungi and bacteria
minerals (Lambert et al. 1984). The distribution of nutrients, provide a cementing agent for aggregates. Wright and
especially P, in the soil profile is affected by tillage intensi- Upadhyaya (1996) discovered “glomalin”, a glycoprotein on
ty (Dick 1983) and thus may impact P availability to crop the surface of active AM hyphae, which appears to act as a
roots. Research on the importance of soil disturbance on cementing agent for soil particles. The more abundant AM
AM colonization has been inconsistent, but P absorption by mycelium under NT may lead to a more abundant production
plants in disturbed soil has always been lower than those of glomalin under NT than CT. In contrast, in CT regimes,
grown in undisturbed soil (Miller 2000). This indicates the disruption of the hyphal network due to tillage operations,
importance of the AM hyphal network in potential tillage would likely lead to reduced glomalin production and
operations. reduced aggregate stability. For example, Bethlenfalvay and
Kabir et al. (1998a) in Quebec, Canada, found that in a Barea (1994) found an isolate of Glomus mosseae, which
sandy loam soil P concentration in corn plants growing improved soil aggregation by 50% when associated with pea,
under NT and RT was greater than under CT at the 12- to in a yellow clay-loam soil, and by 400% in a gray silt-loam
14-leaf and silking stages. At the grain filling stage, howev- soil. Wright et al. (1999) reported that both aggregate stabil-
er, plant P concentration was greater only under NT, and the ity and total glomalin were greater under NT than under CT
difference between P concentrations obtained under CT and in the top 0 to 5 cm of the soil. They also found that when
RT had disappeared. In another year in the same soil, NT soil was collected from the grassland adjacent to the tillage
increased P concentration in the corn plant only at the12- experiment, the structure of the top 0–10 cm of the grassland
26 CANADIAN JOURNAL OF PLANT SCIENCE
soil was more stable than that of the cultivated soil after sev- The vertical distribution is also influenced by tillage prac-
eral years under NT and 4 yr under CT. The production of tices (Kabir et al. 1998b). Mycorrhizal growth was mea-
glomalin was also greater in the grassland than under NT. sured within the top 0–25 cm of soil in NT and CT fields
Collectively, these results indicate that activities of AM under corn cultivation. Arbuscular mycorrhizal hyphae and
fungi are greater in NT than CT, and when mycotrophic spores were more abundant in the top 0- to15-cm layer of
plants are present, leading to greater hyphal densities, glo- the soil profile and decreased dramatically below this depth.
malin production, and aggregate stability. Similar results were reported for AM spores by An et al.
(1990) in Kentucky, USA, under soybean, and by Smith
OPTIMIZING THE AM FUNGAL BENEFIT VIA (1978) in an Australian wheat field under NT and CT oper-
CHNANGES IN CROPPING SYSTEMS ations. This suggests that tilling the soil to a depth of 15 cm
would affect most of the AM fungi and that plowing below
Tillage Practices this depth would dilute the AM propagules in the zone of
Some AM fungi are capable of free-living growth after the seedling establishment.
death of their host plant (Tommerup and Abbott 1981). Kabir and O’Halloran (unpublished data) observed lower
However, questions remain concerning how long the
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Fig. 1. Seasonal and vertical distribution of mycorrhizal hyphae in four corn-growing periods: 5- to 6-leaf stage (1), 10- to12-leaf stage (2),
silking stage (3), and mature stage (4) in conventional (CT) and no tillage (NT) systems.
Fig. 2. Seasonal and vertical distribution of mycorrhizal spores in four corn-growing periods: 5- to 6-leaf stage (1), 10- to12-leaf stage (2),
silking stage (3), and mature stage (4) in conventional (CT) and no tillage (NT) systems.
ng sweet corn, root colonization and shoot P content of the propagules by using cover crops for succeeding crops
plants were significantly greater in mycorrhizal cover improvement either under NT or CT operations.
cropped (oats and winter wheat) plots than in fallow plots or
non-mycorrhizal cover cropped (buckwheat) plots. This CONCLUSIONS
indicates that the mycorrhizal cover crop increased or main- Conventional tillage practices reduce AM hyphal survival and
tained AM fungal inoculum in soil. Accordingly, sweet corn proliferation thus reducing benefits of the symbiosis to associ-
shoot dry weight (14 and 31 days after planting) and plant ated plants and soils. Under temperate climates, it is beneficial
height (87 d after planting) were significantly greater in the to optimize survival of AM hyphae from fall to spring often in
mycorrhizal cover cropped plots. Similarly, sweet corn yield the absence of a living host plant. Fall tillage has been shown
was also greater in the mycorrhizal cover cropped plots than to adversely affect hyphal viability and host plant benefits in
in the fallow or non-mycorrhizal cover cropped plots the following year. Reduced tillage or ridge tillage systems
(Fig. 3). Boswell et al. (1998) and Kabir and Koide (2000) have less negative effects than CT on the abundance of AM
demonstrated that mycotrophic winter cover cropping with propagules because tillage operation in these systems are per-
wheat or dandelion increased subsequent sweet corn yield. formed in the spring and AM fungi remain intact throughout
Kabir and Koide (2002) observed that either single or mixed the winter. In my studies the greatest amounts of hyphae were
mycotrophic cover crops increased the following cash found in the crop rows and hyphal abundance decreased loga-
crop’s P status, and plant P status positively correlated with rithmically to the inter-row, suggesting that growing crops
vegetative growth, reproductive maturity and yield of sweet close to the previous years’ rows optimizes AM fungal bene-
corn. These results suggest that management of indigenous fits. Arbuscular mycorrhizal fungi were abundant in the upper
AM fungi is important to maintain or improve AM fungal 15 cm of the soil irrespective of tillage practices suggesting that
28 CANADIAN JOURNAL OF PLANT SCIENCE
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Fig. 3. Marketable sweet corn ear production growing in mycorrhizal cover crops (oats and winter wheat), non-mycorrhizal cover crop
(buckwheat) and winter NT fallow. Different letter indicate a significant (P < 0.05) difference between the treatment means.
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