The soy is not a native plant in our country, so it is advisable to inoculate soybeans before sowing. The soybean inoculation and its bacterial treatment is primarily necessary where the soy has not been grown yet.
Bradyrhizobium japonicum is root nodule bacteria that can contribute on soybean growth.
During the symbiotic co-operation nodules are created on the roots, rarely on the stem of the host-plant where the transformed bacteria (bacteroides) “fix” the molecular nitrogen of the air namely convert it to ammonia which then can be utilised by the partner plant.
Thus, the plant does not depend on the nitrogen content of the soil as its nitrogen requirement is covered by the nitrogen compounds originating in the symbiotic relationship while the bacteria have access to a carbon source originating in the photosynthesis of the plant.
The symbiotic co-operation is favourable not only for the participants but has fundamental significance for the entire flora and fauna as well. Although 78% of the atmosphere of the Earth is nitrogen gas, the majority of living creatures cannot utilise it. Only a few prokaryotic organisms have the ability to reduce atmospheric nitrogen and thus make it available for other living organisms. Living independently or in loose association with plants some prokaryotes are capable of nitrogen fixation (e.g. Klebsiella, Azospirillum) while others perform this in a symbiotic relationship established with a host-plant (e.g. Rhizobia).
However, these latter systems are more efficient because of the closer relationship and co-operation thus providing the biggest organic nitrogen source in the nitrogen cycle. Biological nitrogen fixation produces in aggregate 44 x 106 tons fixed nitrogen on cultivated agricultural areas per year of which an estimated 35 x 106 tons are nitrogen reduced to ammonia by Rhizobia in the root nodules of papilionaceous plants.
That is why in most cases we also need to provide Rhizobium japonicum bacteria for soy growing. With the right process of inoculation, we contribute to the development of nodules on the root of soy.
What kind of factors can affect the inoculation of soybean seeds?
The shelf life of the product
The time between inoculation and sowing
The conditions under which the product is stored before use
The conditions under which soybean seeds are stored after inoculation
The inoculation should be carefully done because the bacterium Rhizobium is quite sensitive to environmental factors.
The product should be delivered to the seed, evenly and gently, according to the proposal for utilization.
Do not store the soybeans for a long time that have been inoculated.
Inoculation should preferably be carried out in a shaded or enclosed place protected from direct light.
The products and soybeans are also protected from direct light too.
In good cases the effectiveness of inoculation and atmospheric N-bonding can be shown in 4th and 5th week of vegetation. At this point we can find a knob-head-sized nodules. Later, the yellowish-pink incision surface of the larger nodules shows that an active atmospheric N-fixation is being carried out.
Despite technologies for soybean inoculation, nitrogen-binding nodules may only be formed in low proportions on the soy plant or may not be formed.
What sort of factors affect the formation of nodules on soy?
The bacterium Rhizobium japonicum is best grown in neutral soils with a pH 7 and in slightly acidic soil with a pH 6 to pH 7. The symbiosis is not created in soils with less than pH 5. (Although nitrogen-binding nodules may be formed in smaller numbers.) The extreme conditions of the soil limits the availability of nutrients.
The N-fixation is mainly suitable at 15-25 °C. The higher the soil temperature, reaching a soil temperature of 35-40 °C, the relationship between the Rhizobium bacterium and the plant may not be developed. In granular soils, the bacteria have a higher heat tolerance and survival rate.
Soil moisture content
The excessively wet soil, dry soil, airless and stagnant soil have a negative impact on the formation of nodules and nitrogen binding.
Soil nutrient sources
Calcium, phosphorus and molybdanolate in the soil are beneficial for the formation of nodules. High levels of N fertilizer should be avoided, the high nitrate supply of the soil may block the formation of nodules, it is more favourable for the plant to absorb sources from the soil in terms of energy use.
Plant protection products may also affect the viability of the Rhizobium bacterium, mainly fungicides.
Forrás: Dusha Ilona-Kondorosi Ádám (1999): Baktérium-növény jelcsere a szimbiotikus nitrogénkötésben. in: Balázs Ervin-Dudits Dénes (szerk.): Molekuláris növénybiológia. Akadémiai Kiadó, budapest / Balikó Sándor (2015): Szójatermesztés korszerűen, s-press 5 kft. gondozásában / gabonakutato.hu / agrarforum.hu