Dry Farming with Microbial Inoculants

Introduction

The plant microbiome plays an important role in mediating plant health and crop yield. In combination with a plant's genetics, the microorganisms present around and within the plant will affect its ability to acquire nutrients, resist pests and diseases, and tolerate environmental stresses. Plant microbiome management may become an important tool for sustainable agriculture, with promise of reducing over-reliance on fertilizers, pesticides, and other costly inputs. Though some microbial inoculants such as Rhizobia have been used for decades, the use of incoulants as a managment tool is still in its infancy, only recently coming to the fore of research thanks to advances in our understanding of the complexity of plant-microbe ecology. In addition to rood-nodulating bacteria and mycorrhizal fungi, plants associate with hundreds-to-thousands of species of bacteria and fungi, which inhabit nearly every imaginable space on the plant's surface and interior - epiphytes inhabit leaf surfaces, rhizosphere microbes inhabit the root zone - and endophytes inhabit areas within plant tissues, in between plant cells, and do not extend into the soil.

When plants are water-limited, such as in drought or dry farming systems, plants are more vulnerable to biological and environmental stresses such as heat. When stressed, plants will become less efficient at photosynthesis, water use, and thermal regulation, and will be more susceptible to pests and pathogens. With this in mind, researchers have studied plants thriving in extreme environments, such as thermal and saline soils, and arid climates. In some cases, these plants could not survive in their native environments without particular fungal endophytes. Crops inoculated with these wild-sourced fungal endophytes will yield more when exposed to stressful environments, though their yield is typically unaffected in ideal growing environments. Particular strains of these beneficial fungal endophytes have been developed into a product called BioEnsure, produced by Adaptive Symbiotic Technologies.

2018 Trials Summary

Experimental Design

In 2018, we trialed a single strain of Trichoderma harzianum fungus, one of several contained in the BioEnsure commercial product. We tested its effects on yield of corn, beans, winter squash (C. maxima), and tomatoes grown within the Dry Farming Collaborative. We trialed the inoculant in 3 different varieties of each of the four crops, for a total of 12 varieties. In addition to three main research sites managed by Lucas Nebert and Amy Garrett, twelve DFC participants trialed BioEnsure in at least one of these varieties on their farm. Inoculated seeds were grown in 100 ft2 plots, directly adjacent to non-inoculated control plots of 100 ft2 (Figure 1). These plots were replicated (2-3X) within the main research sites, and also replicated within some participant sites.

Corn, bean, and squash seeds were inoculated with a spore suspension using a rotary atomizer in a rotating drum, to uniformly coat the seeds with spores using minimal liquid. Inoculated seeds were thus kept dry until planting. Tomato seedlings were inoculated at 4 weeks of age, with a liquid spore suspension applied the base of the plant. In OSU research plots, inoculated and control corn, bean and squash seeds were soaked for 12 hours prior to direct-seeding (as is a common practice among dry farmers) in early May. Tomato seedlings were also transplanted at the time of direct seeding. Participants were given the freedom to soak seeds or plant them dry. They were encouraged to treat inoculated and control seeds identically, and to use practices to avoid contaminating the control treatments with inoculant.

Tomato yield was measured twice a week, and corn, bean and squash yield was measured all at once, during harvest at the end of September.

Results

Crop yield was not significantly affected by the inoculant on a yield-per-plot basis, partially due to variation in stand density per plot. When accounting for variable stand per plot by normalizing to a per-plant basis, the inoculant was shown to increase per-plant yield in all three corn varieties by 21% (Figure 2). Only one of the three trialed dry bean varieties, Whipple was affected by the fungal inoculant, with increased per-plant yields of 23% (Figure 3). Squash and tomato yields were unaffected by the endophyte (Figures 4 and 5).

Discussion

The fungal inoculant affected yield of field corn and one of the dry bean varieties, and none of the squash and tomato varieties (Figures 2-5). This inoculant product has been shown to prevent yield loss in plants that are undergoing stress. It may be that unaffected plant varieties were not experiencing sufficient stress to see a difference between the control and inoculated treatments. All tested crop varieties are grown by the Dry Farming Collaborative due to their purported robustness to dry farmed conditions, so these crops may not benefit from this inoculant as much as plants that are bred for ideal farming conditions.

The inoculant used in 2018 is comprised of a single strain of Trichoderma harzianum. called BioEnsure. Having multiple strains increases the chances of the inoculant becoming established in a plant. This particular fungus lives exclusively inside the plant roots and lower stem, and is very rare in the soil environment. Tests on harvested roots are ongoing to see how effective the fungus was at establishing in the 12 varieties tested.

Future research will include multiple strains of T. harzianum that comprise the commercial product, BioEnsure. Furthermore, we will test BioEnsure along with other microbial inoculants, such as rhizosphere bacteria and mycorrhizal fungi, to see if inoculating with multiple species with varying traits will boost dry farmed crop yield.