8.6: Inoculate With Beneficial Organisms?

The practices we discuss later in this part of the book—using cover crops, improving rotations, integrating animals and livestock, using composts and other organic materials, reducing tillage, reducing compaction, and so on—are all aimed at improving the soil’s biological, chemical and physical health. Many of these are the same practices that people refer to when they discuss “biological soil management” or “biological fertility management.” A result of following these practices should be soil rich in biological diversity with highly active organisms. In this soil condition there would usually be little advantage to applying beneficial organisms to seeds or transplant roots. However, even with high biological diversity with active organisms, it is still recommended to inoculate legume seeds with the appropriate nitrogen-fixing rhizobia bacteria. But there is growing interest in the possible use of other microorganisms that might promote plant growth by producing hormone-like chemicals to increase growth, helping plants defend themselves from diseases and insects, helping plants better access water and nutrients, and helping plants through stresses such as drought and wet conditions. A variety of growth-promoting beneficial bacterial and fungal species have been explored, but there are no general recommendations for their use. These types of inoculants may be especially helpful in situations in which plants might be under stress: in soils that are low in organic matter, in soils that tend to be dry and/or have moderate to high salinity, and in fields or plots newly used for farming, especially urban soils. And when transplanting vegetables, it might be worthwhile to dip into solutions containing mycorrhizae if the soil is one in which cover crops weren’t grown that year and, especially, if you’re planting following a brassica (which does not form associations with mycorrhizal fungi).