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

Abstract

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 (nonsymbiotic) when compared with untreated soils or with soils pretreated with air. The dry weights of 4-to 7-weekold 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.

Soil Formate Regulates the Fungal Nitrous Oxide Emission Pathway

“…Conversely, there was no difference between incubations with or without the inhibitor when soils were incubated under anaerobic conditions (i.e., soils at 70% WFPS with a nitrogen atmosphere), suggesting a bacterial source for the N 2 O. In the presence of formate, nearly all of the N 2 O emitted was derived from the labeled 15 …”

“…Either these water-shedding landforms, RG and CX, do not have significant fungal N 2 O emission, or the inhibitors were ineffective in these landforms. Thus, because our focus was on fungal denitrification, subsequent incubation studies designed to probe the regulation of fungal denitrification with 15 N-labeled nitrate and inhibitors was restricted to the CD and BC soils.…”

“…After 24 h, a 20-ml gas sample was withdrawn from the headspace using a 20-ml disposable syringe equipped with a 25-gauge needle and injected into a preevacuated 12-ml Exetainer vial (Labco Ltd., United Kingdom). Headspace N 2 O concentrations were determined using a gas chromatograph equipped with an electron capture detector (55 15 N studies were conducted under both aerobic and anaerobic conditions. Anaerobic systems were prepared by replacing the headspace air in the culture tubes with ultrahigh-purity N 2 (i.e., working in an anaerobic chamber under a N 2 atmosphere).…”

“…Gas samples were collected as described for SIRIN incubations, after which the soils were destructively sampled for ammonium and nitrate by extraction with 2 M KCl. 15 N-labeled N 2 O was analyzed by isotope ratio mass spectrometry at the University of California-Davis Stable Isotope Facility (Davis, CA). The fractionation of 15 N-labeled N 2 O was calculated as described by Arah (1) and Stevens et al (41).…”

“…15 N-labeled N 2 O was analyzed by isotope ratio mass spectrometry at the University of California-Davis Stable Isotope Facility (Davis, CA). The fractionation of 15 N-labeled N 2 O was calculated as described by Arah (1) and Stevens et al (41). The diffusion disk technique described by Stark and Hart (40) and modified by Bedard-Haughn et al (7) was used to concentrate soil ammonium and nitrate for 15 N analysis.…”