Plant nutrients in the soil

Plant nutrients

Plant nutrients are soil nutrients required by plants for proper growth, productivity, and protection against diseases. They play roles in enzyme production, hormone synthesis, and protein formation. Fertile soil supplies all essential plant nutrients in proper amounts.

Plant nutrients originate from the parent rock during soil formation and through manure or fertilizer application. Examples include nitrogen, iron, carbon, hydrogen, oxygen, manganese, cobalt, phosphorus, boron, and chlorine.

Types of plant nutrients

1. Micro nutrients: Trace elements required in small amounts.
2. Macro nutrients: Bulk elements required in large quantities.

Macro plant nutrients

Macronutrients are divided into two categories:

1. Primary macronutrients: Required in relatively large quantities. Examples: nitrogen (N), phosphorus (P), and potassium (K). These are essential for hormone and protein synthesis.
2. Secondary macronutrients: Required in smaller quantities compared to primary macronutrients. Examples: iron (Fe), hydrogen (H), oxygen (O), carbon (C), magnesium (Mg), calcium (Ca), and zinc (Zn).

Role of macro nutrients

1. Synthesis of hormones for metabolic activities (e.g., auxins, gibberellin, ethylene, abscisic acid).
2. Synthesis of proteins that promote plant growth.

Micro plant nutrients

These are nutrients required in small quantities but are essential for plant growth. Examples include cobalt (Co), boron (B), manganese (Mn), molybdenum (Mb), and copper (Cu).

Role of micro nutrients

1. Essential for enzyme synthesis, which controls metabolic activities such as digestion, respiration, and energy production.

Managing and preventing nutrient loss

Loss of plant nutrients

Plant nutrients may be lost naturally or through human activities. The primary causes include:

1. Soil erosion: Removal of the topsoil layer by wind, water, or animals.
2. Leaching: Loss of nutrients due to water movement through the soil.
3. Bad agricultural practices: Poor farming methods contribute to nutrient depletion.

Effects of soil erosion

1. Loss of soil fertility.
2. Deposition of waste in water bodies.
3. Death of soil organisms.
4. Formation of gullies.

Causes of soil erosion

1. Overstocking.
2. Cultivation along hills.
3. Deforestation.
4. Monoculture.
5. Burning of forests.

Prevention of soil erosion

1. Contour farming: Prevents water movement along hills.
2. Afforestation: Planting vegetation in open spaces to act as wind barriers.
3. Reforestation: Replanting trees in forests.
4. Destocking: Reducing livestock numbers to prevent soil structure damage.
5. Terracing: Constructing embankments to resist soil movement.

Good agricultural practices

Methods to preserve soil nutrients include:

1. Crop rotation: Alternating crops each season to maintain soil fertility and reduce pests.
2. Fallowing: Leaving land uncultivated to allow nutrient recycling.
3. Mulching: Covering the soil with organic materials like grasses or banana leaves.
4. Cover crops: Plants like beans or groundnuts that grow horizontally to prevent erosion.

Advantages of crop rotation

1. Destroys pests and diseases by disrupting their lifecycle.
2. Recycles nutrients at different soil levels.
3. Increases soil fertility through nitrogen fixation by leguminous plants.

Advantages of mulching

1. Increases soil fertility.
2. Reduces soil erosion.
3. Retains soil moisture by preventing evaporation.

Disadvantages of mulching

1. Risk of fire destroying crops.
2. May attract ants that damage plants.

Consumption of nitrogen by plants

Plants cannot use molecular nitrogen ($N_2$) directly because it is insoluble. Instead, nitrogen is converted into soluble nitrates ($NO_3^-$) that are easily absorbed by plant roots.