Agdex No. 200.21
Plants require up to 20 different elements to carry on their life processes. Of these carbon ©, hydrogen (H), and oxygen (O) are obtained from carbon dioxide and water. Fertilizers are added to soil to supply nutrients that are unavailable or depleted in the soil.
There are 6 macronutrients that are required in relatively large amounts: nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), and magnesium (Mg). Nitrogen, Phosphorus, and Potassium are the elements that most often require supplementing in the soil and are the basis of most commercial fertilizers. Calcium is supplied through calcitic limestone and Calcium and Magnesium are supplied through dolomitic limestone. Sulfur is usually available in adequate amounts in the soil.
There are 14 micronutrients that are required in small quantities in most plants. These are iron (Fe), manganese (Mn), molybdenum (Mo), copper (Cu), boron (B), zinc (Zn), chlorine (Cl), sodium (Na), cobalt (Co), vanadium (Va) and silicon (Si). These micronutrients are usually available in sufficient quantities in the soil and only supplemented if a deficiency is observed.
Commercially produced chemical fertilizers contain a guaranteed minimum analysis of nutrients that is stated on the bag. For example, the numbers 5-10-5 represent the Nitrogen (N): Phosphorus (P): Potassium (K) ratio. It indicates that the fertilizer contains 5% N, 10% P2O5, and 5% K2O. Fertilizer analyses vary with the purpose of the fertilizer.
Soil tests that give fertilizer recommendations for specific soils and crops are available through the New Brunswick Department of Agriculture, Fisheries and Aquaculture.
Fertilizers are available in dry and liquid forms. Liquid fertilizers are highly concentrated and water soluble; they are rapidly available and can be applied to soil or foliage. Dry fertilizers are available in various forms such as pellets, powders and slow release coated granules and each form has been developed for a specific use or a specific crop. Dry fertilizers are usually either broadcast on the soil or incorporated into the soil. Slow release fertilizers make nutrients available over a longer period of time and the nutrient release is governed by the coating of the granule and the nutrient source used. Nitrogen is the primarily controlled nutrient in slow release fertilizers.
Organic fertilizers are derived from living plant or animal sources. They supply a wide range of nutrients and have the added benefits of improving the soil structure and increasing the water holding capacity of the soil.
There are many organic fertilizers such as: barnyard manure, bonemeal, seaweed, composted plant residues, and green manure crops, etc. Green manure crops are crops grown and plowed in the soil. When legumes are used for this purpose they add significant nitrogen to the soil because these plants are able to fix atmospheric nitrogen into soil nitrogen.
Nitrogen is necessary for microbial decomposition of organic residues. High carbon organic residues such as straw and sawdust require nitrogen to decompose, therefore soils require an addition of nitrogen to maintain adequate fertility.
Nitrogen is a vitally important nutrient that is responsible for the vigorous vegetative growth and deep green colour of plants. Nitrogen is quickly leached from the soil so in most gardens it needs to be replaced every year.
Phosphorus has a double role in soil as a nutrient necessary for growth and because its presence influences the uptake of other nutrients. It is essential for seed formation, root development, crop maturity, and crop quality. Phosphorus is important for early growth (at transplanting) but it is not highly mobile in the soil so it should be incorporated into the soil.
Adequate potassium in soil is important in the health and vigour of plants due to its role in physiological functions such as carbohydrate metabolism, water movement, and growth of new tissues. It increases crop resistance to some diseases and encourages strong root systems.
Most soils in the Atlantic region are naturally acidic and require lime to raise the pH. Raising soil pH improves the efficiency of fertilizers by making the nutrients in the soil more available to the plants.