Investigating effects of beneficial microbial inoculants on potatoes

2011 Annual Report for FNE11-723

Project Type: Farmer
Funds awarded in 2011: $3,798.00
Projected End Date: 12/31/2011
Region: Northeast
State: New York
Project Leader:
Marina Michahelles
Shoving Leopard Farm

Investigating effects of beneficial microbial inoculants on potatoes


We proposed to study the effects of beneficial microbial inoculants on Red Norland potatoes. Previous research shows that symbiotic relationships exist between certain plants and various soil microbes, including some nitrogen-fixing bacteria and fungal mycorrhizae. We compared the emergence, growth, leaf sap and tuber Brix measurements, soil conductivity, plant longevity, yield, as well as tuber flavor and texture of potato plants treated with a mixture of beneficial microbial inoculants against an untreated control. A positive outcome would suggest a potential increase for farmers in plant health, yield, and nutritive value, all of which could result in increased income to producers.

Shoving Leopard Farm has been growing mixed vegetables and fresh cut flowers since 2006 on 1.5 acres of heavy clay. The potatoes for this trial followed were preceded by a crop of onions in 2010, and no cover crop over winter 2010-2011.

Marina Michahelles is the owner and grower at Shoving Leopard Farm, and was responsible for soil and bed prep, setting up and executing all aspects of the study except for the weekly data-collection. Marina did the weekly application of drenches and foliar sprays. She conducted the taste-test at a field day and at a Nutrient-Dense Crop Production course. When all the data was collected, she analyzed the results.

Sarah Ashcroft was hired as an assistant to the study. She was responsible for collecting weekly data, such as soil conductivity, leaf sap Brix, plant vigor, etc. She did not know which plots were control and which were test, so this study was single-blind. Sarah assisted in the harvest of the potatoes and the post-harvest measurements of spud Brix, quantity, and weight.

Wendy Su Harper was not able to continue as Technical Advisor, and Stephanie Radin at Cornell Cooperative Extension Dutchess County was able to take her place. Stephanie helped to advertise the field day, and was consulted for ideas for places to publish eventual results.


The study ran from April through September. In April, two 4’ x 60’ beds were prepared amended according to results of a soil test taken in fall 2010. Baseline measurements were taken in early May, and included a strong acid soil test, a Cornell Soil Health test, and soil conductivity of.
The two beds were divided into twelve plots, each with a blue field flag. Each plot was randomly assigned one of the four possible treatments. There were three plots of each treatment, five plants per plot for a total of fifteen plants per treatment. Only Marina knew which plot corresponded to which treatment.

May 3rd, potatoes were planted, and each week thereafter soil conductivity measurements were taken from the same three spots in each plot, (total of 12 weekly measurements per treatments per week) and when the plants emerged leaf sap Brix measurements were taken weekly from three plants per plot. Monthly measurements of stem girth and length were taken, and observations about predation and pests were made. Plants were given applications of soil drench and foliar feedings on alternating weeks. The control group received only water, T1 received water and liquid fertilizer, T2 received water, fertilizer and inoculant, and T3 received water and inoculant.

August 25th, the potatoes were harvested, cleaned, counted, weighed and measured for Brix. Taste tests were conducted at the field day in early September and at a Nutrient Dense Crop Production course.

Still to be done is the Cornell Soil Health test in April for a comparison to the baseline.

Impacts and Contributions/Outcomes

The hypothesis was that there would be a measurable difference in potato production – number and weight, in soil conductivity and Brix measurements between groups.

First, biological inoculant and liquid fertilizer did not have an effect on emergence of plants in the spring.

There is a moderate positive correlation between soil conductivity and plant sap Brix (Pearson = 0.78). As soil conductivity increased, so did leaf sap Brix. Analysis of variance (ANOVA) showed that the treatment had an effect on both soil conductivity (F=4.416, p=0.01) and leaf sap Brix (F=3.474, p=0.027). The plants that were given liquid fertilizer had higher soil conductivity, and the plants that received inoculant had higher leaf sap Brix.

Leaf sap Brix was not correlated with potato Brix, however, nor was the treatment appear to have an effect on the potato Brix. This was confirmed with the taste test, as scores were not significantly related to treatment.

Treatment did have a significant effect on the number of potatoes per plant (F=4.6, p=0.37), those plants that received inoculant produced 0.5% more than those grown without, but the weight of potatoes was not different.

Results from the Cornell Soil Health test will tell us if there are any long-term effects.

The 2011 season started off very wet and potatoes were slow to emerge. There was also much higher deer pressure than expected, and the problem was not solved before a number of the plants were eaten back a couple of times. As the deer did not eat from each of the treatment sections, the results may have been skewed by the predation.

Hurricane Irene caused a flood in the back part of the fields, but the potatoes were hilled and in a slightly higher part. Nonetheless, conditions were very wet for the last month of growth, and production was low overall compared to previous growing seasons. Had conditions been better, perhaps greater differences would have been found. A combination of small sample size and less-than-ideal conditions may have had an effect on results.

At our scale, a 0.5% increase in potato production may not be cost-effective.
About $25-worth of product (not including s+h) inoculates 100 lbs of seed. An 0.5% increase in production results up to 50 lbs more of potatoes sold at $1.50-$2.00/lb for a total of $75-$100 more per 50 lbs of potatoes sold, but this does not account for extra labor.

Labor cost is not very high for inoculating seed, which can be done with a slurry. Inoculant can be applied through drip irrigation along with fertilizers, but foliar feeding is time-consuming, and accounts for the greatest proportion of labor cost.

Larger operations will benefit from the economies of scale. Five thousand pounds of seed potato can be inoculated for $500. If growing 5000 lbs of potatoes, a $500 investment results in an increased yield of 2500lbs of potatoes.


Marina Michahelles

[email protected]
PI, Farmer
Shoving Leopard Farm
PO Box 657
Red Hook, NY 12571
Office Phone: 8457589961
Stephanie Radin

[email protected]
Ag/Hort Program Leader
Cornell Cooperative Extension, Dutchess County
2715 Route 44
Millbrook, NY 12545
Office Phone: 8456778223
Sarah Ashcroft

[email protected]
Research Assistant
Shoving Leopard Farm
PO Box 657
Red Hook, NY 12571
Office Phone: 9082688818
Wendy Sue Harper

[email protected]
Technical Advisor
PO Box 697
Richmond, VT 05477
Office Phone: 8024344122