Nitrogen is the most important plant nutrient for the soybean crop, and the one that is required in largest quantity. 80 Kg of N is needed to produce 1000 kg of soybean. However, most of the requirements for N are covered by the nitrogen from the air through the symbiotic fixation by the Rhizobium bacteria in the nodules on the plant’s roots.
In this process, molybdenum is a constituent of the enzyme nitrogenase in the nitrogen fixing bacteria, and together with cobalt it is essential for efficient nodulation and biological fixation. Thus, supplying these micronutrients has become a basic practice on most soils where soybean is grown.
The biological fixation can supply all the N required by the soybean plant, but due to price concerns it is normal to apply some N fertilizer, but it is important that this quantity does not surpass 20 kg N/ha.
Phosphorus has a function in the plants directly related to energy storage. It is essential in the absorption of nutrients from the photosynthesis and for its role in the buildup of organic compounds of high energetic value, and for soybean this means the oil.
Potassium is important for the for the construction and transport of carbohydrates, and it also has an effect on the reduction of diseases, hence a sufficient supply will help support a healthy plant.
Calcium, magnesium and sulphur are important nutrients for root growth, photosynthesis and the formation of the grains, respectively.
Of the micronutrients, special attention should be given to manganese, as there is an increase in deficiencies in the crops. Reduction in the uptake of this nutrient is due to the use of RR (Roundup Ready – Glyphosate tolerance) varieties, and excessive liming.
Boron has an important role in the pollen’s germination and the growth of the pollen tube. In the case of deficiency or hidden hunger for boron, the grain production will be adversely affected.