Subject: [SANET-MG] On-farm production of AM fungus inoculum

From: Joel Gruver <[email-masked]>
Date: Tue, 9 May 2006 18:56:27 -0400

Hello folks,

I just ran across an article about "On-farm production of AM fungus 
inoculum..."  that may be of interest to some of you...

Joel

Bioresource Technology
Volume 97, Issue 6 , April 2006, Pages 809-818
doi:10.1016/j.biortech.2005.04.015

On-farm production of AM fungus inoculum in mixtures of compost and 
vermiculite
D.D. Douds, Jr.a, , , G. Nagahashia, P.E. Pfeffera, C. Reiderb and W.M. 
Kayserc

Abstract
On-farm production of arbuscular mycorrhizal (AM) fungus inoculum can reduce 
the cost of the inoculum and increase utilization of this symbiosis in plant 
production. Bahiagrass (Paspalum notatum Flugge) seedlings, colonized by AM 
fungi, were transplanted into raised bed enclosures. Media within the 
enclosures was vermiculite mixed with either field soil or yard clippings 
compost in Experiment I and vermiculite mixed with yard clippings compost or 
dairy manure/leaf compost in Experiment II. Compost and vermiculite mixtures 
yielded more propagules of AM fungi than soil-based mixtures in Experiment 
I. Growth of plants in a 1:4 (v/v) mixture of yard clippings compost and 
vermiculite produced more inoculum (503 propagules cm&#8722;3) than growth 
in 1:9 and 1:99 (v/v) mixtures (240 and 42 propagules cm&#8722;3, 
respectively). Water, inorganic nutrient solution minus P, and fish protein 
digest were added to inoculum production enclosures in Experiment II. 
Results indicated that supplemental nutrient addition was unnecessary. This 
method produces a concentrated inoculum of AM fungi in a form readily used 
as an amendment to horticultural potting media for the production of 
vegetable seedlings.

Keywords: Sustainable agriculture; Organic agriculture; Biofertilizer

<snip>

4. Discussion
Inoculum of AM fungi was successfully produced in compost diluted with 
vermiculite. Overall averages of 530 and 505 propagules cm&#8722;3 were 
produced in Experiments I and II, respectively, and up to 80 spores 
cm&#8722;3, in 1:4 (v/v) yard clippings compost and vermiculite. This 
greatly surpasses the target inoculum density of 80–100 propagules 
cm&#8722;3 to qualify as mass production (Feldmann and Grotkass, 2002). The 
lower average of 505 propagules cm&#8722;3 yields 37.57 × 106 propagules per 
0.61 × 0.61 m enclosure section. A target inoculation of 100 propagules per 
vegetable seedling to ensure colonization during growth in the greenhouse 
prior to outplanting means one enclosure section can be used to inoculate 
375,700 plants. This translates to 7.6 ha of tomatoes at a planting density 
of 49,400 plants ha&#8722;1, or five times that with use of the entire 
enclosure. Uniformly mixing such a small amount of inoculum into the potting 
media is difficult, so a more generous inoculation may be more practical.

On-farm production of AM fungus inoculum via different techniques has been 
described previously. Sieverding, 1987 and Sieverding, 1991 developed a 
procedure in Colombia whereby Glomus manihotis was introduced into fumigated 
soil. Direct comparison with the method reported here is difficult because 
total propagules were not estimated. After 4 months of growth of host 
plants, 42–96 spores cm&#8722;3 were produced (assuming an average bulk 
density of soil of 1.2 (Thompson and Troeh, 1973)). Only 9 spores cm&#8722;3 
were produced without fumigation. Dodd et al. (1990) used this method to 
produce inocula containing three AM fungi, including approximately 208 
spores cm&#8722;3 of G. manihotis.

Another method was developed at the Tata Energy Research Institute in India 
(Douds et al., 2000 and Gaur, 1997). One of a number of AM fungi was 
inoculated into furrows in raised beds of fumigated soil. Three crops, e.g., 
sorghum, corn, and carrot, were grown successively in the bed, each for 3 
months. The soil and roots were chopped and remixed prior to planting the 
next nurse host. This method produced an average of 22.7 infectious 
propagules cm&#8722;3 after three 1-year cycles. A modification of this 
method using one of three vegetable crops as a host plant produced 
approximately 1 propagule cm&#8722;3 in soil amended 1:1 or 1:2 (v/v) with 
compost (Gaur et al., 2000 and Gaur and Adholeya, 2002).

The method developed here is competitive with existing methods and, in 
addition to not requiring fumigation, offers several advantages to farmers 
in temperate climates. First, bahiagrass is a proven host plant that 
supports abundant colonization and sporulation by most, if not all, AM 
fungi. In addition, as a tropical C4 grass it is frost killed. This 
minimizes its potential to become a weed pest when the inoculum is used in 
the field. Also, bahiagrass is taxonomically unrelated to most crops and, 
therefore, is unlikely to allow the proliferation of crop pathogens. Second, 
all materials for the construction of the enclosures are readily available 
to farmers. The precolonized host plants could be purchased or grown on-site 
using commercially-available inocula. Another strength lies in the benefits 
of compost. Compost provides all the nutrients necessary for the growth of 
bahiagrass. The P concentration of compost, however, requires that it be 
diluted with a relatively inert material, such as vermiculite, prior to use 
because high levels of available P suppress the colonization of roots by AM 
fungi (Smith and Read, 1997). Compost also provides a broad spectrum of 
microbes to benefit the biological health of the soil and is known to 
suppress plant diseases (Hoitink and Fahy, 1986 and Kim et al., 1997). 
Lastly, a taxonomically diverse mixed inoculum can be produced when 
different AM fungi are inoculated into separate enclosure sections. Recent 
research indicates that there is functional diversity among AM fungi (Smith 
et al., 2000 and Stampe and Daehler, 2003). Though some AM fungi are 
beneficial in a wide variety of soil–plant combinations (Sylvia et al., 
1993), some data suggest that host benefits are greater with certain AM 
fungi than others (Blaszkowksi, 1993 and Pope et al., 1983). A diverse 
inocula increases the opportunity for an optimal match with the eventual 
crop host, and it also allows for the inclusion of Gigaspora spp. to aide 
soil aggregation (Miller and Jastrow, 1992 and Wright and Upadhyaya, 1996). 
Gigaspora spp. are typically absent from commercial formulations.

This inoculum production system targets vegetable producers who grow their 
own seedlings for transplant to the field. The most practical use for this 
inoculum is mixing it into horticultural potting media in which the 
seedlings are grown. Inocula produced by all currently available on-farm 
methods are not amenable to large scale direct application to fields via 
farm machinery. Direct application to the field is possible in labor 
intensive farming systems in the tropics (Gaur et al., 2000 and Sieverding, 
1987) or in small scale organic or community supported agriculture (CSA) 
farms.

Though plant response to AM fungus inoculation may vary from positive to 
negative in the presence of different AM fungi (Klironomos, 2003 and Marin 
et al., 2003), there are management situations in which the response to AM 
fungus inoculation can be more reliably predicted. Certain crops such as 
Cruciferae, spinach, and sugar beet do not become colonized by these fungi 
and will not respond to inoculation. Soil solarization and fumigation 
treatments adversely affect indigenous AM fungi, and inoculation with AM 
fungi has been shown to enhance plant growth and yield following these 
treatments (Wininger et al., 2003). Other situations in which AM fungus 
inoculation would be beneficial are after a long period of bare fallow 
(Thompson, 1987), following a nonmycotrophic crop such as rapeseed, or in 
soils with low available P.

The inoculum production method described here also may be used to 
proliferate indigenous AM fungi. Therefore, farmers may be able to 
re-introduce to their production fields the AM fungi adapted to their soils. 
Doing so may only require adding soil from an uncultivated part of the farm 
(e.g., fence row or natural wooded area), to the compost. No pre-inoculated 
plants would be required. Further, a contributing factor to the high yields 
found when native soils are first put under cultivation is the soil 
biological community (Aleman, personal communication), important members of 
which are the AM fungi.

We have developed a method for on-farm production of hundreds of millions of 
propagules of AM fungi within raised bed enclosures containing compost and 
vermiculite. More research is needed to develop formulae to predict the 
proper dilution ratio for optimum inoculum production given the nutrient 
analysis of specific composts and explore the production of indigenous AM 
fungi in similar enclosures.

Joel Gruver
Dept of Soil Science
NC State University
[email-masked]

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From: Joel Gruver <[email-masked]>
Date: Tue, 9 May 2006 18:56:27 -0400

Hello folks,

Joel

Bioresource Technology

Abstract

<snip>

4. Discussion

Joel Gruver
Dept of Soil Science
NC State University
[email-masked]