By Dr Mark Peoples, CSIRO Plant Industry
A new GRDC collaborative project aims to unravel the mechanisms by which
legume rotations increase plant growth.
It will build on findings by Canadian researchers involving soil fertilisation
by hydrogen gas, to discover whether their results can be reproduced under
Legumes have been widely used in crop rotations to enhance the growth
and yield of subsequent crops. While legumes can leave residual nitrogen
(N) in the soil, this cannot account for all the observed rotational benefits.
A variety of mechanisms have been proposed, including the ways legumes
alter soil structure or nutrient balance, break the disease cycle or open
channels in soil for deeper rooting. Recent research from Queen’s
University in Canada now suggests that soil fertilisation by hydrogen
gas may also be contributing to both legume growth and the subsequent
benefits to following crops.
Hydrogen (H2) gas is an obligate byproduct of the N2 fixing enzyme, nitrogenase,
in legume nodules. In some legume systems, the rhizobial bacteria produce
a hydrogenase uptake enzyme system (HUP) that is able to recover some
energy used in H2 production.
However, many legume nodules evolve H2 due to the absence (HUP-) or low
activity of the HUP system by the rhizobial strain. In these situations,
large amounts of H2 diffuse out of the nodule into the soil. For example,
every hectare of a N2-fixing HUP-legume might produce about 5000 litres
of H2 per day during peak growth.
This represents an energy equivalent of about five percent of the crop’s
net photosynthetic carbon gain for that day. Canadian researchers have
found that soil microorganisms multiply rapidly around the nodules that
are capable of using the H2 as an energy source in such systems.
They also discovered that the microbes appear to be very beneficial for
plant growth. Experimentation has shown that the biomass of non-nodulated
soybean plants, wheat, barley and canola can improve by 15 to 30 percent
when grown in hydrogen-treated soil.
The new GRDC project involving collaborative partnerships between CSIRO
Plant Industry, the University of Melbourne, the University of Western
Australia and Queen’s University, recently started field trials
to find out if the Canadian results can be reproduced in Australian soils.
The project aims to explain the mechanisms that are increasing plant growth.
A number of other important questions are also being tackled:
For more information:
Dr Mark Peoples, 02 6246 5244, firstname.lastname@example.org
GRDC RESEARCH CODE CSP00050, program 4