The Carrington Research Extension Center conducts annual soybean and field pea trials
to compare commercial and experimental inoculants of N2-fixing
bacteria to an uninoculated treatment and one or more levels of N
fertilizer. Inoculants are supplied by
manufacturers and distributors and include peat and liquid (seed applied) and
granular (in-furrow) formulations, as well as pre-inoculated seed. Root systems are visually evaluated for
nodulation during the growing season and data is collected on grain yield and
quality. Treatment effects are sometimes
quite small and sometimes relatively large.
In 2003, the yield of the best soybean inoculant treatment was 37% higher
than the uninoculated check. This
difference was not statistically significant at the 5% level of
probability. It seems odd that a 37%
difference is not significant. However,
nodulation and the nitrogen fixation process are very sensitive to environmental
conditions. This is frequently evident
among the different replicates of a given treatment or even in adjacent plants
within a row. All too often, one plant
may be well-nodulated and an adjacent plant will be sparsely nodulated. For this reason, 6-10 root systems are
examined to determine the nodulation score.
These differences may carry over to yield data, especially on a low-N
field which does not have the appropriate bacteria established in the soil. Every effort is made to eliminate data from
plots affected by non-treatment factors (e.g. deer predation). However, other sources of variability are not
as obvious.
