As promised, I’m starting this thread to compliment Mike’s excellent ‘The mystery of pH’ thread. I’ll keep it as simple as possible, otherwise it with develop into a chemistry class.
Basically NPK is: N=nitrogen P=phosphorous and K=potash, the three main food elements necessary for plant life. Nitrogen is required for foliage growth, phosphorous for root growth and potash for growth of flowers and fruit.
These elements can be applied in chemical or organic form…..the latter being preferred by most gardeners and the former mainly used by commercial growers.
Although there are several types in there chemical form, the most common available to us gardeners being, Sulphate of Ammonia = N (nitrogen) Superphosphates = P (phosphorus) and Sulphate of Potash = K (potash)
For an example, blood, fish & bonemeal (a favorite amongst gardeners) offers these properties.
Dried blood is a slaughter house by-product and is an excellent source of quickly available organic nitrogen, when used as a top dressing or watered in. Dried blood completely soluble and can be mixed with water and used as a liquid fertilizer.
Fish meal is a great natural fertilizer, high in phosphorous and high in organic nitrogen. Fish meal is quick acting, offering a sustained supply of nutrients.
Bone meal is used as a long-lasting source of phosphorous as well as low levels of nitrogen, potassium and calcium. The extremely slow availability of nutrients from bone meal makes it a very safe fertilizer, especially when planting of potting very young or new plants.