“High doses of nitrogen (N) at the beginning of soybean development reduce nodulation…”
Lílian Angélica Moreira is a postdoctoral researcher, has a Ph.D. and a M.Sc. in plant nutrition from the University of São Paulo. Her postdoctoral research is focused on the efficiency of nitrogen fertilizers associated with bioinputs.
AgriBrasilis – To what extent does nitrogen fertilization in soybeans harm biological fixation?
Lílian Moreira – High doses of nitrogen (N) at the beginning of soybean development reduce nodulation. Therefore, in general, only a starter fertilization is recommended, that is, approximately 30 kg/ha of N when sowing. This N will be responsible for meeting the crop’s demand until Biological Nitrogen Fixation (BNF) is established. Another point is the foliar application of N, a practice about which there are still many doubts in the available research.
AgriBrasilis – Can Molybdenum (Mo) be recommended to improve nitrogen metabolism in the crop? Why?
Lílian Moreira – Yes. Mo is extremely important in plants that acquire N through the BNF process, because in addition to participating in the reduction of nitrate, as in all other plants, this element is a component of nitrogenase, an enzyme responsible for the BNF process. In other words, in the absence of Mo, the enzyme is not formed.
“The most common deficiencies in soybeans are Manganese, Boron and Zinc”
AgriBrasilis – What other elements interfere in N metabolism?
Lílian Moreira – In general, all nutrients interfere in N metabolism. But of course, some have more direct relationships, such as Molybdenum, Iron, Phosphorus and Sulfur.
AgriBrasilis – What are the most common nutritional deficiencies in soybeans and in which regions?
Lílian Moreira – The most common deficiencies in soybeans are Manganese, Boron and Zinc. They occur mainly in areas with high pH and high organic matter (complexation).
AgriBrasilis – How is it possible to distinguish the symptoms of nutritional deficiencies?
Lílian Moreira – The main characteristic of nutritional deficiency is symmetry in the leaf, plant and area. In other words, the symptom does not appear in random plants in an area, as can occur in the case of diseases.
The symptom of nutritional deficiency normally forms a gradient in the plant, unless it occurs very abruptly, which is not common in soybean farms. Sudden symptoms of disorder are usually related to incorrect applications and phytotoxicity. Another important point about nutritional deficiency is the location in the plant: the chemical elements have mobility characteristics and this allows us to observe the emergence of the symptom in a localized manner in old leaves (N, P, Mg, K) or young leaves (Ca, S, Fe, Mn, Zn, Cu).
Source: Lílian A. Moreira; Leaves collected from the lower part to the tip of a potassium-deficient soybean plant
AgriBrasilis – How to perform leaf sampling to detect these deficiencies?
Lílian Moreira – For soybeans, the first mature leaf free from disease and pest attack should be collected from the tip of the main branch at full bloom. The plant material is sent to the laboratory and the values generated are compared with reference values (high-yield crops). There are several calculation methods (DIRS, CND…) that can help in the interpretation of laboratory data. Visual diagnosis, that is, identification of the symptom, is an auxiliary method, but when performed it means that the deficiency is in an advanced stage. Therefore, monitoring the crop with leaf diagnosis is essential to obtain high yields.
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