Crop rotation, choice of variety, soybean sowing technique
Agrotechnical measures are implemented in the production of soybeans in order to create optimal conditions for the growth and development of crops so that the genetic potential of the cultivated variety can be achieved. Based on years of extensive research and experience, a cultivation technology has been created for our production areas, which should be adopted in order to achieve the best possible results – a high and stable yield.
In the last few decades, intensive production has had a negative effect on the environment, especially on the most important resource – land. As a result, scientists around the world are once again focused on crop rotation as the standard way to achieve sustainable crop production and yield increase, as well as economic return which supports the production investments.
When it comes to soybean production, crop rotation must be considered because there are special requirements needed for soybeans. Too much nitrogen in the soil has a negative influence on the nitrogen fixation, and so soybeans should not be cultivated on lots where manure had been used or where legumes have been cultivated. Soybean rotation with plant species of the same family, or sunflower and rapeseed is not recommended, since the same diseases occur in these species. Soybean as an early arable crop and a legume is a good preceding crop for most cultivated plants. It makes the soil loose and free of weeds, and by choosing soybean varieties of different vegetation lengths, the harvest time can be fixed in order to prepare the soil for sowing the crops that follow it.
In addition to the corn – wheat – soybean crop rotation, the three-field system of corn – soybean – wheat crop rotation is becoming more widespread, since it is beneficial when it comes to nutrition for the crops, because soybeans use residual nutrients that remain in the soil after corn has been harvested, and wheat uses the positive balance of nitrogen in the soil that remains after soybeans.
Soybean monoculture cultivation leads to the accumulation of disease causative agents and insects, as well as a higher percentage of weeds resulting from hampered weed control, while the nitrogen remaining in the soil after soybeans have been harvested is more valuable for the crops that follow after.
CHOICE OF VARIETY
Key criteria for the choice of variety are:
Yield potential and sustainability – Certain varieties are better adapted to specific environmental conditions than others, making this a better choice of criterion than yield only. As a result of years of tests within macro-experimental networks located in the main regions of soybean cultivation in Serbia, as well as of extensive production feedback, the regionalization of varieties was carried out, and it was concluded that soybean varieties are well adapted to our agro-ecological conditions. Genotypes with a higher level of tolerance to adverse, stressful conditions were identified (Galina, NS Apolo, Luna/NS Rubin), as well as varieties with high yield potential that is evident in favorable cultivation conditions, in fertile soil, with the strict implementation of agrotechnology, in humid or irrigated regions (Zora, NS Maksimus, Trijumf).
Maturity group – a very important criterion for the choice of variety. If the variety is too early or too late for a certain locality, it will have limitations when it comes to realizing its yield potential, which will be lower than the yield of varieties adapted to that area. Also, the crops that come after it, i.e. crop rotation, should be taken into account, so that all agrotechnical measures can be implemented at the right time.
Sowing time – in our production conditions, soybeans are sown in two sowing periods: the regular sowing period and double-cropped sowing period. The variety should be chosen in accordance with the sowing time. Very early soybean varieties such as Kaća, Favorit, Fortuna, Mercury and Tajfun are used in double-cropped soybean production. It is very important to bear in mind that double-cropped soybean production is risky without irrigation.
Production purpose – it is necessary to define the purpose of production before beginning the production itself. If the soybeans are meant to be resold, the varieties which have the highest yield potential and which are best adapted to the given area should be chosen. If the soybean is to be used for animal feed at an owned property, the varieties containing a higher amount of proteins should be chosen, such as Luna/NS Rubin and NS Princeza, as well as the early varieties NS Kaća and Fortuna. There are also varieties for specific purposes, such as NS Pantera and NS Blackstar, which have black beans. These specific varieties are used in the pharmaceutical industry, and their beans can be used for the production of healthy snacks, mixed with other grainy products.
To ensure a high and sustainable soybean yield, it is necessary to choose quality declared seed. You must not try to save money on seed because the only certainty in production arises from quality declared seed.
The most frequent question and doubt of manufacturers is when to sow soybeans and what the right amount of seed is. The sowing of soybeans is carried out when the temperature of the sowing layer of soil settles at 10-12°C. In terms of dates, this period aligns with the end of March and the beginning of April. However, when deciding on the sowing time, the key criteria should be the meteorological conditions and the variety. It should be noted that a temperature of over 10°C is necessary for the biochemical processes and the translocation of the nutrients from the cotyledons to the growing zones, so sowing in cold soil may prolong the germination period by up to 25 days (in optimal conditions, germination lasts 6-7 days). Sowing soybean should begin with varieties with longer vegetation, which show the largest decrease in yield if the sowing is late.
Soybean varieties in the maturity group 00 are sown as a double crop by the end of June, while very early soybean varieties within maturity group 000 may be sown in the first ten days of July as well. It should be noted that very early soybean varieties also produce a significantly higher yield when sown earlier.
Crop canopy. Based on years of research into crop density for certain soybean varieties, the optimal values for maturity groups were derived: for medium early soybean varieties (maturity group 0) 500,000 plants/ha, for medium soybean varieties (maturity group I) 450,000 plants/ha, and for medium late soybean varieties (maturity group II) the optimal crop density is 400,000 plants/ha. Very early soybean varieties (maturity groups 00 and 000) are sown more densely, 550,000 – 600,000 plants/ha.
In a three-year study on the influence of crop density on soybean yield (Table 1), it was concluded that the highest yield of maturity group 0 varieties is produced at a crop canopy of 500,000 plants/ha, the highest yield of medium varieties (I) at a crop canopy of 400,000 plants/ha, while within maturity group II, the Luna/NS Rubin variety produced a higher yield at the recommended crop canopy of 400,000 plants/ha, while the Trijumf variety produced its highest yield at crop canopy of 500,000 plants/ha. The Trijumf variety has shorter internodia and it is shorter on the whole, and it can therefore be cultivated at higher densities in comparison with the soybean varieties in maturity group II.
Based on the produced yields, it can be observed that the yield decrease at a crop canopy of only 100,000 plants/ha was 22-30%, in comparison with the optimal canopy, and that a density higher than recommended leads to a decrease in yield, making the yield decrease at a crop canopy of 600,000 plants/ha 5-10%.
The recommended space between rows of soybeans is 45 or 50cm, but it is also possible to sow if the space between the rows is 70cm, on the condition that the optimal number of plants per surface unit is respected, in accordance with the maturity group.
Sowing depth. The optimal sowing depth for soybeans is between 4 and 5cm. The sprouting of soybeans begins with the development of the root system, so the root grows faster at the beginning; the hypocotyl also grows intensely, bringing the cotyledons to the surface. Water insufficiency or excess, lower temperature, or as the lack of oxygen may cause damage to seedlings and decrease the canopy. It is very important that the sowing depth is equal over the entire lot, since it is a precondition for synchronized germination and crop maturity, as well as for decreasing losses during the harvest. Sowing too deep, as well as cold soil, extends the period of sprouting and germination, and many seedlings are not strong enough for germination. Also, when it comes to this kind of sowing, the legumes are formed near the soil surface, which increases harvest losses.
It should be noted that all agrotechnical measures implemented before harvest determine the amount of harvest losses. The regularity of the sowing process and adhering to the experts’ recommendations are prerequisites for decreasing these losses as much as possible. Choosing the right variety, as well as good crop rotation, decreases the soybean production risk and increases the economic effect, i.e. the profitability.
Expert support: Institute of Field and Vegetable Crops Novi Sad, Soybean Department
Svetlana Balešević Tubić, PhD and Vuk Đorđević, PhD