1. Predecessor
When growing soybeans, we need to consider some factors:
a/ soybeans should be sown at three-year intervals because of the risk of sclerotinia. In some European countries there have been successful trials with two-year monoculture, but then the field should be allowed to rest longer. The advantage is that in the second year, due to the multiplication of nitrogen-fixing bacteria as a biofield, the yield and protein content of the soybean increases.
b/ after corn, soybeans may have a more significant attack of Rhizoctonia or show phytotoxicity to some herbicides used in corn
c/ It is best sown after cereals with a flush surface that leaves the soil relatively weed free. The soil should not be oversaturated with nitrogen as this makes it difficult for tubers to form with nitrogen-fixing bacteria.
Soybean itself as a precursor cannot be compared in quality with field peas, as the powerful above-ground mass extracts many nutrients, but still as a nitrogen-fixing crop and with a high protein content in the straw it leaves the soil enriched with nitrogen and fertilisation in the next crop could be reduced by 3-4 kgN/daa.
2. Soils
Soybean has a strong root system and thrives on all soil types, but does not reach its potential everywhere. It does not tolerate waterlogged, acidic or saline soils, or soils that are too heavy. The soil must be free of weed seeds, as soybean suffers severely from weed infestation in the early stages of development. Soybean yields best on rich, moisture-rich soils.
3. Soil treatment
Soybean does not respond significantly to tillage depth. It can be grown under any type of tillage - ploughing, loosening, minimal. As a result, however, we must have dealt with weed seed pods and the soil must be well settled and aligned. To avoid competition from weeds in the early development of soybean plants, the last pre-sowing treatment is carried out immediately before or at the same time as sowing. Soybeans set low, so for a successful harvest the area must be level and free of stones!
In soya beans, tillage with rotary hoes has a very good effect on emergence and initial development, especially if the soil is prone to crusting.
4. Seeding
a/ depth of sowing - on heavy soils 3-4 cm, on light soils - from 4 to 6 cm maximum.
Soya beans are not particularly vigorous at emergence. Water for germination is provided by good soil settlement and seed adhesion, not by sowing depth. Deep sowing can lead to seed failure as soybeans require a lot of heat to germinate.
b/ row spacing - best results are obtained with drill spacing of 15-25 cm. This provides the best light in the crop, but a herbicide screen is a must, the merged crop cannot be relied upon to shade out the weeds. Under irrigated conditions, 70 cm is recommended, but a more optimal arrangement with the possibility of mechanical hoeing is obtained at 45 cm. I recommend drilled.
c/ sowing density - it does not directly affect yield, as soya has a strong compensatory capacity, but when sown very sparsely, the plants branch out strongly and continuously, and then there is the problem of uneven ripening, and a tendency to lodging. In practice, it is customary to provide 40-50 germinating seeds per m2.
d/ decontamination - seeds are treated with fungicides against various soil pathogens and also with inoculants of nitrogen-fixing bacteria.
d/ sowing time - young plants are quite cold hardy, but for germination soybeans require a lot of heat to ensure a friendly and rapid germination, which is a crucial point for topping the seed and setting the yield. Uneven emergence and patchy moisture are already signs of soybean yield failure.
Due to climate variations and different years, we can assume that mid-April is the optimum time for sowing soybean in Bulgaria, regionally, climatic conditions should be respected and ranges from 5 to 20-25 April. It is important that the soil at 6-7 cm depth is warmed to 10-12 ⁰C.
f/ inoculants- it is desirable to use inoculants for seeds to stimulate the activity of tuber bacteria.
f/ rolling - recommended after sowing.
5. Fertilizing
For the formation of 100 kg of grain, soybean extracts 7-8 kg of N, 1.6-1.8 kg of P2O5 and about 2 kg of K2O per decare. With its powerful root system, soybeans are supplied with phosphorus and potassium as long as it is available in the soil, which means that it must be fertilised either in the fall before sowing or in the fall before planting.
Nitrogen fertilisation does not increase yield, as soybean manages itself by building tubers of nitrogen-fixing bacteria, and in practice a pre-sowing application of nitrogen to stimulate tuber formation is not recommended. In Europe it is the practice if the crop is not in a satisfactory condition in June
condition - there are not enough tubers on the plants and instead of being dark green it is light and chlorotic, nitrogen should be fed - 4-5 kg/daa, but provided that there is also rainfall.
A maximum of 3-4 kg/daa of nitrogen can be applied pre-sowing to feed the plants from germination until the first tubers form.
Of the trace elements, fertilisation with molybdenum is the most effective, generally based on soil availability and a balanced feeding regime for all elements.
Sulphur inputs generally have no proven effect on yield.
6. Weed control
In addition to good field preparation, it is desirable to seal the soybeans with a soil herbicide - e.g. Stomp at 400 ml/daa, Spectrum 80 - 140 ml/daa - after sowing before germination, etc.
During the vegetation, if necessary, Stratos Ultra can be used at a dose of 100 ml/daa against cereal weeds at the 3-5 leaf stage and 200 ml against rhizome blight at a blight height of 10-20 cm; Against broadleaf weeds during the vegetation, spray with Bazagran at a dose of 200ml/daa.
7. Fighting diseases
Of the diseases, bacteriosis, powdery mildew, phomopsis, anthracnose, virus mosaic, sclerotinia, etc. are the most common. In general, it is important that the seeds are treated with fungicides. In practice there is still no tradition of fungicide application during the growing season. A 3-year rotation interval is observed.
8. Pest management
The most economically important pests may be mites and aphids, and soybean can sometimes be attacked by atypical polyphagous pests.
When seed is stored for long periods, it must be fumigated against moths and grain eaters.
9. Harvesting
Grain soybeans are harvested directly with the combine harvester when the grain moisture content drops to 13-14%. The setting of the combine harvester is important, there are some fine adjustments in this respect. Due to the uneven ripening of the branches, senescence or desiccation of the soybeans can be practised, but this is decided at the time of ripening according to climatic and other conditions. New varieties are more resistant to splitting and ripen relatively amicably. Storage moisture - max. 14% per sample of milled grain.