Denitrification is the process of conversion of nitrates and nitrites into nitrogen. This is done by bacteria called pseudomonas 

Pseudomonas converts nitrate salts into free nitrogen gas in nitrogen cycle. This process is known as denitrification.

Sodium is not generally regarded as an essential nutrient for plants. However, sodium can substitute for potassium to a greater or lesser extent in different plant species.

  Nickel is not an essential micronutrient.

 Deficiency of molybdenum causes mottling and necrosis of leaves.

 Boron is necessary for translocation of sugars in plants.

Magnesium ion is present in the center of a chlorophyll molecule. Its deficiency causes the yellowing or whitening of normal green plant tissue which is known as chlorosis. 

Death of the stem and root tips occurs due to deficiency of calcium.

 Root hairs do not play any role in both water and mineral intake.

Plant ash is an indication of mineral salts absorbed by the plant.

 Active mineral absorption depends on expenditure of energy.

Calcium is a macronutrient. It is an essential part of the plant cell wall and helps in the transport and retention of other elements.

Zinc can be absorbed by foliage. Zinc deficiencies can affect plant by stunting its growth, decreasing number of tillers, chlorosis and smaller leaves, increasing crop maturity period, spikelet sterility and inferior quality of harvested products.

In leguminous plants, leghaemoglobin regulates the supply of oxygen to nodule tissue. Therefore, it is essential for nitrogen fixation.

When working with plant tissue culture, we use EDTA as a chelating agent in order to keep magnesium and other elements in suspension, so that the plant tissue can easily absorb them (EDTA is ethylenediaminetetraacetic acid).