In recent years, soybean growing is quite popular, its area is constantly growing, due to steady demand and high cost of grain of this crop.
In recent years, soybean has become quite popular, its area is constantly growing, due to steady demand and the high cost of a grain of this crop.
This attracts farmers who are trying to increase the profitability of their enterprises.
However, successful cultivation is impossible without knowledge of the biological characteristics of this culture, the sophistication of technology, and a creative approach.
One important aspect of soybean cultivation technology that is often neglected is the use of fertilizers. There is an opinion that soy does not need fertilizers. Moreover, it actively accumulates nitrogen in the soil due to the activity of nodule bacteria. Unfortunately, not everything is so simple.
Let’s try to figure it out in stages. The first thing to start is to select fields suitable for soybean cultivation in terms of soil characteristics. Soy can grow on a variety of soils. It can be successfully cultivated even in swamp silt. Although heavy clay soils are unfavorable for emergence, especially after rainy weather, soybean grows here better than many other crops.
Only salt marshes, highly marshy and acidic soils are unsuitable for it. Soybean growth on a variety of soils does not yet speak of its undemanding for fertility and soil type.
Soybean grows well at pH 6.5-7.0. The degree of soil fertility, its granulometry composition and the depth of the arable horizon have a great impact on productivity, especially with a lack of moisture. On unstructured soils with a small arable horizon, the effect of drought is much faster and stronger than on fertile soils with good water permeability.
Therefore, the best soils for soy are well-structured, quite moisture-intensive, with a powerful root-inhabited layer, highly fertile with an optimal supply of mobile elements of mineral nutrition, able to easily warm up, rich in humus, with a neutral soil reaction.
The need for soybean in nutrients is determined by its biological characteristics. At the beginning of the growing season, the culture develops slowly, from seedlings to flowering, it requires a few nutrients. From flowering to the mass filling of beans, the greatest need for batteries is observed (65% of NPK).
Critical periods for nutrients
The critical period for phosphorus for soy is the first month of life, for nitrogen 2-3 weeks before flowering and 2 weeks after flowering. The lack of nutrients in these periods leads to a noticeable decrease in soybean productivity and cannot be compensated by the introduction of fertilizers in the later phases of plant growth and development.
The soy fertilizer system, like any other crop, consists of three application methods: main, sowing and top dressing, and, most importantly, their correct combination.
Phosphorus and potassium as the main fertilizer are applied, as a rule, in the fall, and nitrogen in the autumn or better in the spring. Nitrogen in the main application should be 2 times less than phosphorus and not more than 30 kg.
It is appropriate to recall the biological features, namely the period of maximum nitrogen consumption.
Nitrogen, introduced in large doses at the beginning of the growing season, is not preserved by the flowering phase, in which it is especially necessary; therefore, its fractional use in the form of top dressing will be most effective.
Most studies confirm the positive effect of low doses of nitrogen on the yield and quality of soybean grain.
Nitrogen is especially necessary if one or more of the following conditions occurs:
- Crop do not have a uniform dark green color throughout the field (but their color does not contain signs of chlorosis);
- acidic soil (soil pH below 5.5);
- low organic matter, soil eroded or compacted;
- for some time, soybean was not grown on the field or the field was not provided with nitrogen to a sufficient degree for crops;
- active nodules (dark pink in the center) on the roots are absent or few;
- soy was not inoculated, there are symptoms of nitrogen deficiency.
It is necessary to create conditions in the soil for active legume-rhizobial symbiosis, in which case soybean will provide itself with nitrogen.
The opinion that soybean accumulates nitrogen in the soil is wrong. It does not accumulate nitrogen, it does not spend it. It works for own because to produce 1 ton of grain yield with the corresponding amount of by-products it needs only 16 kg of P2O5, 18 kg of K2O and as much as 70 kg of N. To get a lot of high-quality soy protein requires a large amount of nitrogen.
At initial phases of growing season, nitrogen fixation is weak, reaches its maximum during flowering and fruit formation, then the activity decreases as the plants approach maturation. In the case of successful symbiotic activity, soy will not need nitrogen, and if the nodules do not work, it becomes a powerful absorber of nitrogen from the soil.
The conditions for the best symbiotic activity of nodule bacteria are:
- Granulometric composition of soils – medium loam;
- The content of mobile phosphorus and metabolic potassium in the soil is not lower than average, pH not lower than 5.6;
- Inoculation of seeds on the day of sowing;
- Soil moisture – not lower than the air discharge factor (60% PPV);
- Refusal to use large doses of nitrogen.
The most important thing in main application is to prevent distortion in the ratio of batteries. Indeed, without sufficient provision with potassium and, especially, phosphorus, the activity of nodule bacteria decreases sharply.
The role of fertilizer application increases with soybean cultivation using minimum soil cultivation technology, with direct sowing, since in this case mineralization of nutrients in soil proceeds more slowly than with traditional soil cultivation.
Carrying out tissue diagnostics shows that soybean cultivated on untreated soil is more in need of phosphorus than when grown on fields cultivated from autumn and spring.
This article is jointly written by Fayaz Hussain, Syed Zeeshan Haider, Aftab Hussain Supervised by Dr Haroon Zaman Khan, Department Of Agronomy, University of Agriculture Faisalabad.