Nutrient cycles in upland farms

Agroforestry aims to develop upland farms into self sustaining yet productive ecosystems. The key to this goal is an efficient cycling of nutrients within the system.

The nutrients required for plant growth consist of: Carbon (C), Hydrogen (H), Oxygen (O), which are all derived from air and water; the major nutrients: Nitrogen (N), Phosphonus (P) and Potassium (K), the secondary nutrients: Calcium (Ca), Magnesium (Mg) and Sulfur (S); and, the trace elements or micronutrients (around seven), which are all soilderives.

The soil-nutrient cycle operating in an upland farm can be viewed as a system consisting of stores, flows, gain, and losses.

Nutrient store:

- roots and shoots of all crops and trees
- plant residues
- soil organisms
- soil organic matter
- clay minerals (through fixation)
- soil solution Nutrient flows:
- plant uptake (via roots)
- mineralization (from plants to residues, via organisms to soil humus)

Nutrient gains:

- symbiotic, non-symbiotic fixation (for N only)
- rock weathering
- rain and dust
- organic materials from outside
- fertilizers

Nutrient losses:

- burning (for N and S)
- denitrification and volatilization (for N)
- leaching
- erosion
- harvest

Understanding these nutrient cycles is important for a farmer to be able to effectively manage them. This should also be the basis for determining what soil and water conservation measures are needed. Likewise, this should guide the farmer in a more rational use of fertilizers.

Nutrient cycle