Hydrogen fertilization of soils – is this a benefit of legumes in rotation?

Hydrogen gas (H 2 ) is an obligate byproduct of the N 2 ‐fixing enzyme, nitrogenase, claiming about 5–6% of the crops’ net photosynthesis but most, if not all of the H 2 lost from nodules is oxidized by the soil surrounding the root system of the plant. When soils not recently used to support the growth of legumes were exposed to H 2 gas at a rate and duration similar to that of soil adjacent to legume nodules, the fertility of the soil was enhanced in comparison with soil treated with air. Under growth‐chamber and field conditions, H 2 ‐treated soils improved the growth performance of spring wheat, canola, barley and soybean (non‐symbiotic) when compared with untreated soils or with soils pretreated with air. The dry weights of 4‐ to 7‐week‐old plants were 15–48% greater in the H 2 ‐treated soil, and in barley and spring wheat, tiller number of 7‐week‐old plants were 36 and 48% greater in the H 2 ‐treated soils. These findings may contribute to an explanation for the persistence of H 2 evolving associations in agricultural legume symbioses selected for high yields (Uratsu et al ., Crop Science 22, 600–602, 1982) and suggest that it may be possible to isolate, identify and culture the micro‐organisms that are responsible for at least some of the benefits of legumes in crop rotation.