Farm-Grown Microbial Soil Inoculants: Effects on Bread Wheat Yield and Quality

Farm-Grown Microbial Soil Inoculants: Effects on Bread Wheat Yield and Quality

Summary

The aim of this project is to evaluate the efficacy of two ‘on-farm’ produced microbial inoculants and one commercially available inoculant in organic bread wheat production. A prominent Maine organic farmer asked us to test a purchased inoculant that he uses in wheat (MycoApply® from Mycorhizzal Applications Inc.). In addition, we are testing two emerging on-farm inoculant production methods: one developed by USDA-ARS researchers for arbuscular mycorrhizal fungi (AMF) (Douds et al., 2005), that has shown positive results in vegetables and fruit (Douds et al., 2007 and 2008); and one based on a South Korean practice of culturing indigenous microorganisms (IMO) from local organic matter and soil (Park and DuPonte, 2008; Prell, 2010).

We are evaluating these three inoculants (AMF, IMO, MycoApply®) in a greenhouse and field trial for their effects on bread wheat growth, nutrient uptake, yield and grain quality. To date we have completed a greenhouse trial and the first year of a 2-year field trial. Results from the greenhouse experiment show that the selected microbial inoculants do not enhance wheat growth, mycorhizzal colonization, or nutrient uptake as compared to their relative controls. Results from the 2012 field season are forthcoming.

We are also evaluating the production methods, costs and returns associated with producing on-farm inoculants. Outreach thus far has included oral presentations at University of Maine (UMaine) agriculture field days and a poster presentation for UMaine faculty and students. A hands-on workshop on microbial inoculant production is planned for March 2013 at UMaine. Overall, this project will help farmers and gardeners evaluate whether to use microbial inoculants and whether on-farm production of inoculants is appropriate for their farm. It addresses the sustainable agriculture goals of fostering healthy soil and productive crops while reducing off-farm inputs and maximizing on farm resources.

Objectives/Performance Targets

1) Evaluate the effects of 2 farm-produced and 1 commercially available microbial soil inoculants on bread wheat biomass accumulation, nutrient uptake, yield, and grain quality through field and greenhouse trials.

a) Completed a greenhouse trial in May 2012, which tested all 3 inoculants and their
relevant controls.

b) Completed one of two field trials in August 2012, which tested all 3 inoculant
treatments and their relative controls. The second field trial is planned for 2013.

2) Evaluate the costs and returns associated with producing and using the different inoculants.

a) Recorded expenses from inoculant purchase or production and application.

b) An assessment of relative returns due to inoculant treatments will be accomplished
when the data analysis from field and greenhouse trials is completed.

3) Provide results to researchers and farmers through a factsheet, presentations at field days and conferences, and a hands-on workshop.

a) Presented objectives, methods and results of the greenhouse and field trials at the
UMaine Sustainable Agriculture Field Day in July 2012.

b) Completed and presented a poster documenting the greenhouse trial (See Figure 1).

c) A hands-on workshop on farm production of microbial inoculants is planned for the
spring of 2013 at UMaine. This workshop will be open to students, farmers,
gardeners, and researchers.

Accomplishments/Milestones

Major accomplishments for 2012 included completion of a greenhouse and field trial, production of farm-grown AMF inoculant at the UMaine Roger Clapp greenhouse; and, completion of a poster depicting the greenhouse experiment. Overall the research project has progressed as scheduled and according to plan. Specific accomplishments and lessons learned in the field and greenhouse experiments are detailed below.

Greenhouse Trial:

The greenhouse trial was seeded in February 2012 and completed in May 2012. Microbial inoculants AMF, IMO and MycoApply were evaluated for their effects on wheat mycorrhizal colonization rates, biomass accumulation, and, nutrient uptake. Each inoculant was compared to its relative control, which was the inoculant autoclaved to sterilize microbial activity. Hard red spring wheat (var. Glenn) was planted into 1-gallon containers in a uniform soil media with nutrients balanced across treatments. The experiment was a Randomized Complete Block Design with 5 blocks. All containers were watered to 40% moisture based on a target weight and re-randomized within each block weekly. Greenhouse conditions were monitored with a mean temperature of 73 F, and a mean light intensity of 450 ?mol.

Two destructive sample dates were used to collect data. Aboveground biomass was cut at soil level, dried, weighed, ground and submitted to the UMaine Analytical lab for complete nutrient analysis to determine nutrient uptake. Belowground biomass was washed, weighed and subsampled to determine moisture content. Another subsample of roots was stained with the trypan-blue dye staining process of Phillips and Hayman (1970) modified to exclude phenol and then assayed to quantify mycorrhizal colonization rates. ANOVA with Tukey’s HSD (?=0.05) was used to determine if treatment effects existed among the inoculants and their relevant controls. In December, a poster was presented to UMaine faculty and students. The poster displayed the objectives, methods, results and conclusions of the greenhouse experiment.

Inoculants as compared to their relative controls did not produce measurable changes in wheat biomass, mycorrhizal colonization rates, or nutrient uptake. However, IMO+ increased aboveground biomass as compared to AMF- and MYAP+ at the boot and late-milk stages, and to AMF+/- and MYAP+/- at late milk stage only (Table 1). Additionally IMO+ increased Mg uptake as compared to AMF- and MYAP+. While there were no significant treatment differences in N, P, K, and Ca uptake, patterns similar to Mg uptake were seen for other macronutrient uptake responses (Table 2).

Further research is necessary to determine if increased biomass in IMO+ as compared to AMF and MYAP treatments at the late milk-stage was due to nutrient supply, microbial action, or the two factors acting in concert. Enhanced nutrient uptake of Mg in IMO+ treatment was likely due to increased biomass. The lack of treatment effects among the inoculants and their controls could be due to the lack of inoculant establishment based on immeasurable differences in mycorrhizal colonization rates. In addition, high variation (CV>20%) in mycorrhizal colonization, boot stage biomass, and, P and Ca uptake may have made it difficult to detect treatment differences. Results from our on-going field study will help determine whether the patterns seen in the greenhouse trial are replicable in a field setting.

Other considerations for testing microbial inoculants include growing wheat with and without inoculants in poor fertility conditions, which might reveal more treatment differences. Zhu et al. 2001 found that mycorrhizal inoculants enhanced phosphorus (P) uptake in certain wheat varieties and the effect of inoculation decreased as wheat P-uptake increased. Additionally, a 3-5 year study investigating inoculated versus un-inoculated fields might determine if microbial inoculants enhance soils for agricultural production over an extended period of time.

Field Trial:

The 2012 field trial was planted in May and harvested in August on UMaine’s research farm. We seeded hard red spring wheat (var. Glenn) and used a randomized complete block design with 5 blocks. Wheat aboveground biomass was sampled twice (peak biomass and harvest), dried, weighed, ground, and submitted to the UMaine Analytical Lab for complete nutrient analysis to determine nutrient uptake. A subsample of roots collected at peak biomass were washed, stained and assayed to quantify mycorrhizal colonization rates. In late August grain was harvested with a small plot combine. Field weights of the grain were recorded for each treatment and yield was converted to 13.5% moisture and lbs/acre. A subsample of grain for each treatment was ground and submitted to the UMaine Analytical Lab for complete nutrient analysis.

The results and data analysis from the 2012 field season are forthcoming and will be compared to the results of the greenhouse study. The 2012 field trial results will also be used to assess any changes necessary for the 2013 field trial.

Impacts and Contributions/Outcomes

The goal of the research project is to investigate the efficacy of 3 selected microbial inoculants in bread wheat systems by better understanding their affect upon wheat growth, nutrient uptake, and grain yield and quality. By empirically assessing the inoculants we intend to help farmers and gardeners determine the applicability of such inoculants for their agricultural systems. We hope this information will lead to further questions and research about the most effective and efficient applications for microbial inoculants in agriculture.

In the greenhouse, none of the inoculants had a significant effect on wheat mycorrhizal colonization, biomass, or nutrient uptake. We did detect differences among select treatments, although the implications of these results are unclear. Field studies will help us evaluate if the same patterns are replicable in a field setting, which more accurately reflect a wheat grower’s conditions.

Outreach in 2012 included a presentation of the research project at the UMaine Sustainable Agriculture Field Day to 32 farmers and agricultural service providers in July, and a poster of the greenhouse trial presented to faculty and students at a UMaine research display in December. Research on microbial inoculants is important because use of inoculants is a new and emerging aspect of sustainable agriculture that lacks a large base of scientific research. The results from this project contribute to the growing pool of scientific research on microbial inoculants in agricultural systems.

• References, Table 1 and 2

• Greenhouse Poster

Collaborators: