IJERD – International Journal of Environmental and Rural Development (2014) 5-1

Research article
erd

Effect of Fallow on Arbuscular Mycorrhizal Fungi under
Maize Cropping System
PHAKPEN POOMIPAN*
Faculty of Science and Technology, Thammasat University, Phatum Thani, Thailand
Email: phakpen@tu.ac.th
Received 29 October 2013

Accepted 1 March 2014(*Corresponding Author)

Abstract Fallow had been reported to decline survival of arbuscular mycorrhizal (AM)
spore. The effect of fallow on AM fungi under maize cropping system was studied toevaluate its effects on population of AM fungal species in community, AM spore
abundance and biodiversity. A pot experiment was undertaken over two successive crops.
The crop 1 was maize planting in all pots for establishing a uniform AM community. The
crop 2 was maize planting and leaving pot soil as fallow. At the start of the crop 2, the AM
community in both topsoil and subsoil was composed of 12 species in 4 genera: 2 speciesof Acaulospora, 2 species of Entrophosphora, 7 species of Glomus and 1 species of
Scutellospora. Glomus spp. was dominant in the AM community. The spore number of
Glomus spp. was approximately 70 and 80% of total spore number in topsoil and subsoil,
respectively. The AM fungal biodiversity was 0.94 and 0.91 in topsoil and subsoil,
respectively. The AM spore abundance was approximately 1,600±50 and 750±70 sporesper 100 g-1 of soil in topsoil and subsoil, respectively. There were no differences in AM
spore abundance of all pots at the start of crop 2. The data collection at the end of the crop
2 was compared to those at the start of crop 2. The results showed that the population of
AM fungal species in community, the AM spore abundance and the biodiversity in the
topsoil and the subsoil did not change under maize crop. However, fallow treatment had
decreased the AM spore abundance by 30% and 15% in the topsoil and the subsoil,
respectively. It had greatly affected on spore number of Glomus spp. than the other AM
genera. The AM fungal biodiversity had declined to 0.79 and 0.84 in topsoil and subsoil,
respectively. Therefore, the results indicated that fallow had negative effect on AM fungal
community in soil. This may be due to life cycle of AM fungi was disturbed by absence
their host during fallow period.
Keywords arbuscular mycorrhizal fungi, fallow, Glomus, maize

INTRODUCTION
Symbiotic associations between arbuscular mycorrhizal (AM) fungi and plant roots are widespreadin the natural environment. It can provide a range of benefits to the host plant, soil and environment.
These include improved plant nutrient uptake (Marschner and Dell, 1994), enhanced tolerance todrought and salinity of soil (Schreiner et al., 2007), enhanced tolerance to nematode and soil-borne
pathogen (Sylvia and Chellemi, 2001), and provided stability of soil structure (Bedini et al., 2009).
In addition, AM extraradical hyphae itself and glomalin producing by the hyphae have highly
correlated with soil organic carbon and are the major component of soil microbial biomass (Rillig
et al., 2002). These are resulted in an important role of AM fungi in regulating carbon fluxes
between the biosphere and the atmosphere under climate change.
Thailand is an important country in South-east Asia for production of feed maize The global
feed maize demand will increase to around 50% by 2020 (FAO, 2004). This is due to increasing in
consumption of red and white meats which has resulted in an increase in demand for maize as feed
for livestock. Otherwise, some maize is also used industrially for ethanol production. Therefore,
research on enhancing sustainable maize yield in Thailand has value more broadly in the world.
However, the production of maize for animal feedstock occurs in more than 40 provinces in 3
regions: Central, North-eastern and Northern parts of Thailand. Nakhonratchasima is particularlyⒸ ISERD

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important production areas. On Pak Chong soil, high phosphorus (P) fixation presently limits
productivity, as many farmers do not have the finances to apply rates of fertilizer required for
optimum yields. Application of AM fungi might become a solution in this case. Due to AM fungi
are well known to enhance the P nutrition of crop plants and the importance of AM fungi for maize
production in Thailand has been discussed (Na Bhadalung et al., 2005).
However, the fallow period is another farming practice which can reduce the population of
AM propagules in soil. Harinikumar and Bangyaraj (1988) and Thompson (1994) observed that
low AM abundance following fallow led to reduced AM sporulation and colonization in the
succeeding crop. Otherwise, fallow is widely practiced in central Thailand and maize farmers also
are interested in crop rotation. Therefore, the pot experiment was undertaken to evaluate effects offallow on populations of indigenous AM fungi.
OBJECTIVE
To evaluate effect of fallow on population of AM fungal species composition in community, AM
spore abundance and biodiversity in topsoil and subsoil of Pak Chong soil series under maize
cropping system in Thailand.
METHODOLOGY
An experiment was conducted in large pots using a completely randomised design with 4
replications. The treatments were maize-maize crop and maize-fallow crop. The experiment was
conducted with two successive crops. In crop 1, all pots were planted with maize for 4 months. In
crop 2, maize and fallow were randomly applied to 4 replicate pots for 4 months.
The soil sample belonged to the Pak Chong soil series: clay-loam, kaolinitic, isohyperthermic,
Typic Paleustults (Soil survey staff, 1998). The soil was collected from field plots (14˚ 38΄ N, 101˚
19΄ E; elevation 354 m above sea level; National Corn and Sorghum Research Centre, Amphur Pak
Chong, Nakhonratchasima Province, Thailand) at two depths, 0-15 cm topsoil and 15-30 cm
subsoil. The soil was allowed to air-dry before use. The soil chemical properties are given in Table
1. The soils before potting were analysed for soil pH, soil organic matter (OM) (Kjeldahl method),available P (Bray II method) and exchangeable K, Ca and Mg (1N NH4OAc) using Black et al.
(1965)
Table 1 Chemical property of the topsoil and subsoil
Soil layer
Topsoil
SubsoilpH
1:1 soil:H2O
7.0±0.0
6.8±0.0

OM%
2.6±0.1
1.1±0.1P
9.8±0.6
4.8±0.5

KCa
mg kg-1
160.0±9.1 1920.0±32.7
57.5±4.8 1620.0±75.7

Mg225.0±5.0
175.0±5.0

The soil was crushed with a mallet, roots removed by hand and then well mixed. Five kg coarse
washed river sand was placed into glazed clay pots (32 cm diameter at the top, 25 cm diameter at thebottom and 30 cm in height) to enhance drainage and then 7 kg subsoil and 13 kg topsoil wereplaced, respectively. Each pot had a single, central drainage hole sealed to a U-shaped drainage pipe
(1.3 cm diameter) with the free end of the pipe being slightly below the bottom of the pot to reduce
air flow into the pot base. Between the crop cycles, the pots were left uncovered and exposed to rain.
Vertical plastic sheets (1.5 m high) were placed between pots to prevent rain-splash.
In crop 1, all pots were cropped with maize (Zea mays L., cv. Suwan 4452), one plant per pot.
This was undertaken to produce a uniform population of AM fungi under maize for testing
agronomic practices. N fertilizer was applied to the soil surface three times at the rate of 2.52 g ofurea per pot (on a soil weight basis, equivalent to 112 kg N ha-1), split equally at D7, D30 and D45.
This rate was used to ensure normal grain production since the volume per plant of the pot soil was
about a half of that in the field. P fertilizer was applied as triple super phosphate (TSP) at the rateof 1.67 g TSP per pot (equivalent to 32.75 kg P ha-1) by surface banding on one side of the plant atⒸ ISERD

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D14. Zinc (Zn) fertilizer was applied at the rate of 0.38 g of Zn per pot as Zn-EDTA (equivalent to30.4 kg Zn ha-1) at D40. Other nutrients were not applied as previous studies had shown that maize
growth in this soil is limited by N, P and Zn (Suwanarit et al., 1992).
In crop 2, maize and fallow were randomly applied to 4 replicate pots. In the cases with crops,
one plant was grown per pot. Fertilizer was applied for maize cropping; N fertilizer was applied
two times at the rate of 1.12 g urea per pot (equivalent to 50 kg N ha -1), equally split at D14 andD40. P fertilizer was applied as TSP at the rate of 1.12 g TSP per pot (equivalent to 21.8 kg P ha -1)
by surface banding on one side of the plant at D14 and Zn fertilizer was applied at the rate of 0.38 gof Zn per pot (equivalent to 30.4 kg Zn ha-1) at D40. The rates of fertilizers, lower than that used in
the preliminary crop but adequate for maize, was used to minimize the difference in nutrient status
in soil among cultural practices. Fallow treatment was not fertilised but was exposed to the weather(infrequent rain events).
Soil samples were collected from 0-15 cm depth for topsoil and 15-20 cm depth for subsoil
using a 2 cm diameter steel auger, 3 augers per pot at the start and the end of crop 2. The holes
were filled with sterilized Pak Chong soils that were stored at room temperature in laboratory
before use. The soil samples were left to air-dry for determining the AM spore number. The AM
spores were sorted into group using morphology and size traits and identified using the INVAM
species guide and manual for AM fungal identification (Schenck and Perez, 1988). The AM sporeof each species was counted for calculating AM biodiversity using the Shannon-Wiener index(Pielou, 1975).
All data were checked for normal distribution by Levene’s test. ANOVA was used todetermine effect of treatments. Duncan’s Multiple Range Test at P<0.05 was used for post hoc
testing.
RESULTS
The AM community in the soil (both topsoil and subsoil) at the start of crop 2 was composed of 12
species in 4 genera: 2 species of Acaulospora, 2 species of Entrophosphora, 7 species of Glomus
and 1 species of Scutellospora. The 12 AM species were described in Table 2.
At the start of crop 2, there were 1,637 and 765 AM fungal spores 100 g-1 in topsoil andsubsoil, respectively. Glomus spp. was dominant. It contributed 73 and 78% of the total spore
number in topsoil and subsoil, respectively. The spore of Glomus spp. was 1199 and 599 AM
fungal spores 100 g-1 in topsoil and subsoil, respectively. The spore of Acaulospora spp. was 232
and 94 AM fungal spores 100 g-1 in topsoil and subsoil, respectively. The spore of Entrophospora
spp. was 188 and 56 AM fungal spores 100 g-1 in topsoil and subsoil, respectively. The spore of
Scutellospora sp. was 18 and 16 AM fungal spores 100 g-1 in topsoil and subsoil, respectively. The
AM spore number of each species was shown in Fig. 1. The AM fungal biodiversity was 0.94 and0.91 in topsoil and subsoil, respectively.
At the end of crop 2, total spore number, spore number of each AM species and AM
biodiversity did not change under maize-maize treatment. However, under maize-fallow treatment,
there were 1166 and 649 AM fungal spores 100 g-1 in topsoil and subsoil, respectively. Comparing
to the AM spore number at the start of crop 2, fallow treatment had decreased the AM spore
abundance by 30% and 15% in the topsoil and the subsoil, respectively. It had greatly affected on
spore number of Glomus spp. than the other AM genera. The spore of Glomus spp. was 838 and
455 AM fungal spores 100 g-1 in topsoil and subsoil, respectively. The spore of Acaulospora spp.
was 190 and 140 AM fungal spores 100 g-1 in topsoil and subsoil, respectively. The spore of
Entrophospora spp. was 128 and 42 AM fungal spores 100 g-1 in topsoil and subsoil, respectively.
The spore of Scutellospora sp. was 10 and 12 AM fungal spores 100 g-1 in topsoil and subsoil,
respectively. The AM spore number of each species was shown in Fig. 2. The AM fungal
biodiversity of fallow treatment had declined to 0.79 and 0.84 in topsoil and subsoil, respectively.

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Table 2 Characteristics of the AM fungal taxa and their codes
AM fungal species
Acaulospora sp. 1 (A1)
Acaulospora sp. 2 (A2)

Entrophospora sp. 1(E1)

Entrophospora sp. 2 (E2)

Glomus sp. 1 (G1)
Glomus sp. 2 (G2)Glomus sp. 3 (G3)

Glomus sp. 4 (G4)

Glomus sp. 5 (G5)
Glomus sp. 6 (G6)
Glomus sp. 7 (G7)

Scutellospora sp. (S)Spore characteristic
Globose shape, 76-112.5 µm, white to orange, soporiferous succule(80-100 µm). Two layers of spore wall, combined thickness 3-7 µm.
Globose shape, 100-120 µm, yellow to orange, soporiferous succule (120130 µm) and fine spines present. Two layers of spore wall, combined
thickness 5-10 µm.
Globose shape, 165-208 µm, orange to dark orange, hyaline outer layer, andhyaline, subglobose soporiferous succule (180-220 µm) and thick spines
present. Three layers of spore wall, combined thickness 15-17.5 µm.
Globose shape, 60-80 µm, hyaline colour and hyaline subglobose
soporiferous succule (60-80 µm). Three layers of spore wall, combined
thickness 2-5 µm.
Globose shape, 80-125 µm, white to cream colour, single chlamydospore.
Four to five layers of spore wall, combined thickness 4-8 µm.
Sporocarp formation without peridium (200-1500 x 200-2000 µm), globose(80-140 µm) or subglobose (80-96 x 120-140 µm) chlamydospore, paleyellow, forms spores in roots. Three layers of spore wall, combined
thickness 4-5 µm.
Sporocarp formation without peridium (200-800 x 200-1000 µm), globose(60-120 µm) or subglobose (40-112 x 96-188 µm) chlamydospore, paleyellow to yellow, forms spores in roots. Two to three layers of spore wall,
combined thickness 2-4 µm.
Sporocarp formation without peridium (1-3 mm), globose (80-100 µm) or
subglobose (60-100 x 90-140 µm) chlamydospore, yellow to orange. Threelayers of spore wall, combined thickness 3-5 µm.
Sporocarp without peridium, globose chlamydospore (92-112 µm), white tocream. Three spore wall layers, thickness 5-7 µm.
Globose shape, 120-300 µm, pale yellow to yellow, recurved septum. Twolayers of spore wall, combined thickness 4-5 µm.
Globose shape, 124-180, yellow-brown to dark orange-brown, shiny andcontaining lipid content. Two to three layers of spore wall, combined
thickness 4-8 µm.
Globose shape, 168-240 µm, white to cream colour, germination shield andauxillary cell. Five layers of spore wall, combined thickness 4-8 µm.

DISCUSSION
Fallow had negative effect on AM fungal community in soil. The fallow period reduced AM fungal
spore number in the topsoil by 30%. This finding is consistent with many previous studies thathave been undertaken in containers or in the field. For example, in a field study (acid to neutralsoil), one year of bare fallow treatment reduced AM density by 80% compared to continuous maize
cropping for a range of sites in Iowa, USA (Troeh and Loynachan, 2003). Similarly, in Queensland,
Australia, viable propagules of AM fungi declined in cracking clay soils during long periods offallow (>1 year) resulting in poor root colonization and symbiotic effectiveness of subsequentcrops (Thompson, 1994). Ryan and Angus (2003) observed that the percentage of root colonizationof wheat and field pea grown after fallow in South-Eastern Australia was depressed compared tothose grown after clover, an AM host. One possibility for the reduction in AM populations during
fallow is a lack of host plant roots necessary to maintain viable spore populations for the next crop.
Alternatively, Pattinson and McGee (1997) suggested that periodic wetting and drying of soil
during fallow periods in agro-ecosystems may also reduce AM fungal propagules during the fallow
period.
Fallow affected the proportion of species composition in the AM community. Glomus species
were more sensitive to fallow than species of other AM genera. In general, AM fungal spores areable to germinate in the absence of host-derived signals. Soil edaphic conditions, such as moisture,temperature and pH, promote AM spores from a dormant to a germinating state, but they are unableⒸ ISERD

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to complete their life cycle without their host plant (Giovannetti, 2000). Therefore, the decrease inspore number in fallow treatment was likely the consequence of failure to establish a functional
symbiosis with a host plant during the fallow period.

Fig. 1 AM spore number in topsoil (a) and topsoil (b) at start of crop 2

Fig. 2 AM spore number of fallow treatment in topsoil (a) and topsoil (b) at end of crop 2
CONCLUSION
Fallow had negative effect on the proportion of species composition in the AM community.
Glomus species were more sensitive to fallow than species of other AM genera.

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ACKNOWLEDGEMENTS
Acknowledgements of the Thailand Research Fund and the Commission on Higher Education,
Staff development project for financial support.
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