John Kempf

Forage legumes for disease suppressive soils

How often do you see rhizobium nodules the size of golf balls? I have only observed them on sun hemp.

The nitrogen fixation process of rhizobium bacteria in legume nodules has a reducing effect and shifts the soil microbial community in the direction of disease suppression. Forage legumes should be a part of our crop rotations and ecosystems for more reasons than just supplying nitrogen. Because of their reducing effect, they also increase manganese and iron availability from the soil reserves which are present in the oxidized form that plants don’t utilize.

Fixing nitrogen without Legumes

Legumes don’t fix nitrogen.

Only bacteria do.

And there are many more bacteria capable of fixing nitrogen than those associated with legumes.

We just need to stop killing them, begin encouraging and feeding them, and our soils and crops can be supplied with 100% of the nitrogen requirements at the highest yield levels.

A new report describes some of the rhizobia and other organisms found in the rhizosphere of plants other than legumes¹.

The important part, of course, is that these biology need an abundant energy source to be able to fix nitrogen. The more energy they have available, the more N will be fixed. A large part of their energy during the growing period is supplied by plant root exudates. When we have plants with optimum photosynthesis, producing large volumes of exudates, much more N can be sequestered, which leads to higher yields.

1. Yoneyama, T., Terakado-Tonooka, J., Bao, Z. & Minamisawa, K. Molecular Analyses of the Distribution and Function of Diazotrophic Rhizobia and Methanotrophs in the Tissues and Rhizosphere of Non-Leguminous Plants. Plants 8, (2019)