Leguminous crops - growth, selection of fertilizer dose

Pulses is a valuable food and feed crop. They are useful in that they independently absorb atmospheric nitrogen and enrich the soil with it. In addition, the straw of these cultures contains up to 15% of protein saturated with useful amino acids such as lysine, methionine, tryptophan. But even using pulses as a green fertilizer, you need to use fertilizers to get the most out of it.

Formed nodules supply the plant with nitrogen

As is known, nodule bacteria can develop on the root system of legumes. And the important task of the farmer is to create the most favorable conditions for their development.

The optimal conditions for the growth of nodule bacteria are neutral or slightly acidic reaction of the soil, normal temperature and humidity (not extreme values) and with a sufficient supply of carbohydrates, phosphorus, potassium and other elements to the nodules. If the soil acidity is less than 5.5, it is necessary to conduct its liming, which complicates the assimilation of boron and manganese, which can be solved by their foliar application. At the same time, liming increases mobility in the soil and the availability of molybdenum to plants.

It is recommended to monitor the molybdenum content on soils with acid reaction, which is well solved by pre-sowing seed treatment with ammonium molybdate. This metal is part of the enzymes involved in the fixation of molecular nitrogen by nodule bacteria.

Features of the use of nitrogen fertilizers in legumes

Despite the fact that this group is used to enrich the soil with nitrogen, at the beginning of growth, it also needs soil application of this mineral. However, it is very important not to overdo it in this matter, so as not to stop the process of natural assimilation of nitrogen from the atmosphere.

The main depth at which the roots of legumes do not exceed 20 cm. The introduction of a starting dose of nitrogen (20-60 kg / ha), especially on poor soils, accelerates the growth of legumes at the initial stage. The root system does not have nodules yet, so for the first three weeks only one source of nitrogen is available - the soil. But later you should be careful. Before it becomes possible to provide itself with nitrogen by yourself, legumes will take about 20-30 kg/ha of this mineral from the soil. If more is contributed, then there is no point for the plants to start the mechanism of nitrogen retention from the air.

Nitrogen-fixing bacteria can cover up to 70% of the plants need for this substance

It is believed that with good soil condition, up to 70% of the total nitrogen that will be used by a plant over its entire life can be produced by nodule bacteria. To start using nitrogen from the atmosphere a plant should face the following conditions:

  • Soil nitrogen deficiency;
  • Well developed sheet apparatus;
  • A sufficient amount of other minerals;
  • Normal humidity and temperature.

Under these conditions, in legumes, the assimilation of atmospheric nitrogen is started with the help of nodule bacteria. To assess the condition of the plants need to conduct an inspection of the root system. If the nodules are less than 5 per plant and are gray in the cut, this means that the nitrogen fixation process is disturbed and fertilizing with nitrogen is necessary. If there are more nodules, they are pink in the section, then everything is in order and additional nitrogen is not needed. To assess the population of the root system with nitrogen-fixing bacteria in soybean, the following scale is proposed:

  • Very weak colonization: 0-4 tubers/plant;
  • Weak: 5-10;
  • Good: 11-15;
  • Very good: more than 15 pcs.

Under optimal conditions, the biological fixation of nitrogen reaches 135 kg/ha in peas and 390 kg/ha in soybeans. These are the maximum values ​​that are not always achievable in reality.

The needs of legumes for other elements vary greatly in time. From the moment of emergence and before flowering, the requirements for the presence of phosphorus, potassium and other elements are minimal, although the lack of phosphorus can disrupt the development of the root system. As the flowering phase approaches, consumption begins to increase.

Mineral consumption of different crops kg/ha
Ele­ment Peas Vika Lupine Soya
Nitrogen 45-65 50-60 70-80 70-75
Phosphorus in the form of P2O5 15-20 12-16 15-25 18-20
Potassium in the form of K2O 20-30 16-20 40-50 20-25

Peas and lupins can absorb phosphorus even from poorly soluble compounds.

All legumes need sulfur in a dose of 30-40 kg/ha. With a lack of sulfur:

  • Reduced rate of protein synthesis;
  • Nitrogen accumulates in non-protein form or in the form of nitrates;
  • The activity of nodule bacteria decreases.


The choice of the dose for the introduction of sulfur depends on its content in the soil.
The content in the soil is mg/kg. The availability of plants is sulfur. The dosage of application is kg/ha.
<5 Very low 60
5-10 Low 45
10-15 Average 30
15-20 High 15
>20 Very high 0


Given the cost of soil analysis, with a possible shortage of sulfur it is cheaper to deposit a small amount of it (20 kg/ha) in the form of ammonium sulfate during presowing cultivation.

Before the development of beans, it makes sense to conduct foliar feeding by the mixture of UAN-32 with 0.05% boric acid, which reduces the abortion of the beans. At this stage, nitrogen deficiency can increase vulnerability due to drought. Boron is important at all stages, because it is responsible for the differentiation of cells and the formation of their walls. Its disadvantage naturally leads to the death of growth points.

Unlike nitrogen, phosphorus and potassium bean need to make timely

Phosphorus is especially needed on chernozem, potassium - on sod-podzolic soils of light particle size. Phosphorus is effective to make in the fall, under the tillage and with growing legumes - with leafy nutrition. Phosphorus in a dose of 10–20 kg/ha as a starting fertilizer has a good effect, which improves the development of the root system and plant growth in the future.

A lack of potassium is manifested in peas with yellow spots on the edges of the leaves, which then die off. To prevent this situation, it is better to use compounds without chlorine. Lupine is a typical chlorophobe that does not tolerate contact with this element at all. Therefore, chlorine-containing potash fertilizers for legumes should be applied in the fall.

A lack of potassium in an unexpected (at first glance) way reduces the yield of soybean, which in this case is more affected by soybean aphids. In addition to slowing the growth of soybeans, against the background of potassium deficiency, is under stress and begins to release more amino acids in the phloem, which becomes more nutritious for aphids. The harmful insect begins to multiply much faster and therefore the soybean harvest is reduced even more.

Sheet nutrition with magnesium should be early, it is especially useful to carry it out on acidic soils, at a dose of 30-50 kg/ha.

Table of recommendations for the use of trace elements for soybeans

Trace elements are better to introduce by foliar nutrition. This allows you to reduce consumption, because when introduced into the soil most will be lost, and the one that will be in the zone of root growth will be available for assimilation not very soon. In the case of sheet nutrition, the active ingredients from the solution become available to the plant immediately after application.

Summing up the use of microelements:

  • Bor promotes the formation of generative organs and growth points;
  • Cobalt improves nitrogen absorption, thereby accelerating growth in general;
  • Molybdenum increases the number and total weight of nodules.

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