PLANT MINERAL NUTRITION [CSEC BIOLOGY]

SYLLABUS REFERENCE 

[B2.5] discuss the importance of minerals in plant nutrition using nitrogen and magnesium as examples.

Water is not the only nutrient that plants get from soil. 

Plants need mineral nutrients in order to make many different compounds. These nutrients are sometimes called mineral salts, salts, mineral ions, or just minerals. These terms refer to the elements plants need other than carbon, hydrogen, and oxygen. 

Most minerals are needed to make complex compounds, such as amino acids, proteins, chlorophyll and DNA. 

Plants absorb the mineral ions they require from the soil via active transport. Root hair cells provide a large surface area for the absorption of mineral ions. 

NITROGEN (N) 

Nitrogen is a macro-nutrient, essential to plant life in relatively large quantities. Nitrogen fixation (nitrogen gas → nitrates) or nitrification (ammonium →→ nitrates) makes nitrogen available to plants. The addition of fertilizer to the soil raises the nitrogen content of the soil, which is helpful to the plant. 

Plants use nitrogen to:

• synthesize chlorophyll, which is a pigment protein 
• make proteins and enzymes necessary for photosynthesis 
• increase their biomass. This, in turn, contributes to large crops 
• synthesize all the proteins that the plant needs 
• control and regulate the uptake of phosphorus (P) and potassium (K) 

Signs of Deficiency 

Nitrogen-deficient plants show the following signs:

• They are small and stunted, as they cannot make proteins 
• They are slow-growing 
• They are yellow, with weak leaves 
• They can over-mature, producing flowers and seeds before they have reached a sufficient size 

MAGNESIUM (Mg) 

This is a metallic element. Even though it is not needed in quantities as large as nitrogen, it is not officially considered a micro-nutrient. 

"Like calcium, magnesium is required by plants in large enough quantities that it's not considered a micronutrient, but rather a secondary nutrient. Only nitrogen, phosphorus and potassium (N, P, K) are needed in larger quantities by plants" (Yates, 2016) 

It is one of thirteen (13) mineral nutrients that come from soil. It is in a form that is dissolved in water, and then absorbed through the plant's roots. Sometimes, if the soil does not have enough of the nutrient, fertilizer can be added to make up the lack. 

"Magnesium deficiency in plants is common where soil is not rich in organic matter or is very light. Heavy rains can cause a deficiency to occur by leaching magnesium out of sandy or acidic soil. In addition, if soil contains high amounts of potassium, plants may absorb this instead of magnesium, leading to a deficiency." (Patterson, 2020) 

 Plants use this element...

• to synthesize chlorophyll. It is a crucial element.

The Chlorophyll Molecule 

• for carbohydrate metabolism 
• in cell membrane stabilisation 
• as part of various enzymes 

Signs of Deficiency 

• It appears on older leaves first. They become yellow between the veins and around the edges. One may also find purple, red or brown spots on the leaves. 
• Another key sign is interveinal yellowing, often referred to chlorosis. 

How Can We Investigate Nitrogen Deficiency? 

This is done using DEFICIENCY EXPERIMENTS. 

They are conducted using either washed sandy soil or hydroponics. 

Example of a Deficiency Experimental Procedure 

Materials 

• Bean or other seedlings
• Two trays of clean sand 
• Plant fertiliser containing nitrogen (Wash hands after using fertiliser!)  

Method 

1. Plant seedlings in both trays 
2. Add fertiliser (according to instructions) to the sand in one tray. This would be your control. 
3. Water the trays and place them in a sunny spot where they will not be disturbed. Leave them there for at least two weeks. 
4. Water both trays regularly during this time so that they do not dry out. 
5. Observe what happens to the plants in each tray. 

REFERENCES 

• Patterson, S. (June 2021) Gardening Know How [Blog] "Fixing Magnesium Deficiency in Plants: How Magnesium Affects Plant Growth" Understanding The Role Of Magnesium In Plants - How Do Plants Use Magnesium (gardeningknowhow.com) Accessed 26 Jan 2023. 
• Yates, R. (July 2016) Grower Talks [Blog] "Growing with Griffin: Magnesium Deficiency: Clues & Cures" Growing With Griffin: Magnesium Deficiency: Clues & Cures (growertalks.com). Accessed 26 Jan 2023