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. The Real Food Campaign in the Northeast has been promoting the use of several microbial inoculants as part of healthy and sustainable soil fertility management.

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 correlation between soil conductivity and leaf sap Brix was found, supporting previous evidence that good soil health results in good plant health. Although yields did not vary according to treatment, we found the weekly use of the soil conductivity measured and the Brix reader to be an easy and effective way to quantitatively gauge what was happening in the field.

Introduction:

One problem every farmer faces is supplying adequate nutrition to the plants and animals he or she is raising. Not only do we have to compensate for our soil’s natural deficiencies and mineral imbalances, but we also have to re-supply nutrients we remove through harvest. A second problem, which Shoving Leopard Farm shares with many other farms, is limited space; we have to maximize production on our acre-and-a-half. To address both these limitations, we hope to enlist the help of beneficial soil microbial communities that have been shown to promote for plant nutrition and health.

Soil biologists now have a greater understanding of the role that living soil organisms - from bacteria, yeasts and fungi to actinomycetes and algae - play in plant nutrition. Some bacteria are responsible for fixing nitrogen; some are associated directly to legume root hairs and provide plants with useful nitrogen; others are free-living; while still others decompose chitin and cellulose. Several fungi are known to have strong symbiotic relationships with plants and in the absence of any of these, plants are shown to have lower yields and poorer quality. The activities of soil microbes increase plants’ access to nutrition, resulting in more pest-resistance, higher nutritive value, and greater resilience in drought and frost. Diverse soil biological communities in agricultural systems improve both yield and quality of produce.

Shoving Leopard Farm has been growing mixed vegetables and fresh cut flowers since 2006 on 1.5 acres of heavy clay. Save for the work the rototiller does to prepare beds in spring and fall, all work is done by hand. We have improved the soil tilth through applications of finished compost, green manure, and hay mulch and have seen an improvement over the years in terms of production and plant health. We want to study the effects on crop yield (measured in quantity and weight) and quality (measured in Brix) by the promotion of soil biological communities by inoculating seeds and soil with beneficial species of bacteria, mycorrhizae, and other microbes. If this study shows positive results, other farms could increase their crop production without increasing land-use, and possibly decrease their use of some fertilizers over time.

The Real Food Campaign has been offering courses in the Northeast on how to increase the nutrient value of the crops we raise by, not only addressing the underlying deficiencies and relative imbalances of nutrients in the soil, but also by introducing and promoting soil biology. Scores of farmers have already begun using the biological inoculants the associated company, Nutrient Density Supply Company, sells. This study is designed to evaluate the effect of these inoculants on Red Norland potatoes grown on our CSA farm.

There are studies that demonstrate the benefits to plant health and yields of applying compost and mulch, using cover crops, and limiting soil-disturbing practices to plant health and yields. Microbial inoculants applied through compost teas have been used to reduce the need for pesticides in grapes (SARE F NC03-467, 2003) and in 2007, a study demonstrated that inoculation of arbuscular micorrhizal fungi produced an increase in yields in carrots, strawberries, and potatoes (LNE03-179). A 2010 SARE-funded project (LS10-227) is looking at the use of inoculants on legume rhizobia, and whether the native populations of soil bacteria, mycorrhyzal bacteria, and microbes that mineralize legume residues have an impact on the success of these rhizobial inoculants.

Shoving Leopard Farm has been in production since 2006. We have a 30 member CSA, we sell flowers at two farmer’s markets, and offer a PYO flower labyrinth. There is one full-time grower and two work-trade CSA members, as well as many occasional volunteers. Though we are not certified organic, our practices go beyond NY state organic standards, and every effort has been made to grow the best possible produce and flowers while improving soil tilth. Finding biological ways to increase our crops’ health and nutritive value, and integrating these solutions into our management practices is in line with our mission to promote healthy agriculture from the ground up. If we can healthily and sustainably produce more and better food without expanding our acreage and without increasing our need to fertilize, we can improve our economic bottom line.