INFORMATION SHEET 7
THEIR FUNCTIONS AND SOURCES
Nitrogen is important for the growth of the stems and leaves of home garden plants. It also contributes to the development of chlorophyll (a plant's green pigment). Chlorophyll is needed during photosynthesis; a process by which a plant makes carbohydrates (starch and sugars) from water and the carbon dioxide in the air. Pale green or yellow leaves, poor growth, leaf fall and pest problems are indications of nitrogen deficiency in plants. The application of green manure and compost can improve the nitrogen content of soil. Ground-up horns and bonemeal from slaughtered animals are rich in nitrogen and also contain phosphorus. They can be applied to the soil, but this form of natural fertilizer reacts slowly in soil. Shredded Ricinus (castor oil) plants are another source of nitrogen and phosphorus. They are particularly useful for crops with high nitrogen requirements (e.g. young plants of maize or sorghum).
Phosphorus reacts slowly and is important for root formation and the formation of seeds and fruit, as well as for the development of a plant's drought tolerance. Phosphorus deficiency symptoms are stunted growth and poor flower and shoot development. Rock phosphate, wood ash and animal bonemeal and manure supply phosphorus. Chicken manure is a good source of phosphorus, nitrogen and potassium, but it is quite strong and must be composted or diluted before application.
Potassium contributes to the development of roots, fruits and seeds and improves the storability of crops. Poor plant growth and uneven ripening of fruits and seeds are symptoms of potassium deficiency. Besides chicken manure, compost, ash and banana leaves also improve the potassium content of soil.