Nutrient cycling and soil fertility

Nutrient cycling is the movement and exchange of organic and inorganic matter back into the production of living matter.
The process is regulated by food web pathways, formerly known as food chains, and biogeochemical cycles.
Biogeochemical cycles include the carbon cycle, the nitrogen cycle, the oxygen cycle, the phosphorus cycle, the sulfur cycle, and the water cycle.

Soil fertility refers to the ability of soil to sustain plant growth by providing essential nutrients to plants.
Essential nutrients are broken into two categories: macronutrients and micronutrients.
Macronutrients are nutrients required by plants in large amounts: nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur.
Micronutrients are nutrients required by plants in smaller amounts: iron, manganese, copper, zinc, boron, molybdenum, and chlorine.

The nitrogen cycle is a biogeochemical cycle by which nitrogen is converted into various chemical forms as it circulates among the atmosphere, terrestrial, and marine ecosystems.
The primary steps in the nitrogen cycle are nitrogen fixation, ammonification, nitrification, and denitrification.
Nitrogen fixation is the process of converting nitrogen gas from the atmosphere into ammonia by bacteria in the soil.
Ammonification is the conversion of organic nitrogen into ammonia.
Nitrification involves the conversion of ammonia to nitrite ions, which are then converted into nitrate ions.
Denitrification is the conversion of nitrate ions back to nitrogen gas, completing the cycle.

Soil erosion is the process of wind, water, or other natural agents moving the top layer of soil.
Erosion can reduce soil fertility by removing nutrient-rich particles.
Effective erosion control methods include planting vegetation, building terraces, and making use of contour ploughing.

Soil conservation is the management of soil to prevent erosion and maintain fertility.
Conservation techniques may include crop rotation, cover crops, soil profiling, and the application of mulch or compost.
A healthy soil with good structure and plenty of organic material can hold more water and nutrients, supporting better plant growth.

Soil testing is important for identifying potential nutrient deficiencies and determining appropriate fertiliser applications.
Soil tests provide information on soil texture, pH, organic matter content, and the available amounts of various nutrients.
Applying too little or too much fertiliser can lead to poor plant health, therefore accurate soil testing is key to soil fertility.