Soil fertility is an important part of healthy plant growth. Plants need sun and water, but the nutrients they uptake from soil are crucial to helping them perform the necessary growth functions, such as photosynthesis and respiration. Adequate soil nutrition is rarely found naturally. Often soils are rich in one main macro-nutrient and poor in another. Most fertilizers are comprised of the macro-nutrients nitrogen, phophorus and potassium in a variety of ratios. These plant foods also contain micro-nutrients and trace minerals.
History of Fertilizer
Early fertilizers were made from organic matter that was already on the farm. In the 1800's bird droppings, or guano, was a popular fertilizing agent. Bone meal has been used with good success and is still used today. Various other organic wastes and barnyard manure were used consistently and with good effect. It wasn't until the 1940's that scientists knew what basic compounds were needed for good growth. The middle part of the last century saw the formulation of specialized plant foods. Within a few decades the application methods were varied as well, and a huge industry was born.
Elements for Plant Growth
Plants need sixteen basic elements. Three of them are the ratio listed on a package of fertilizer and are referred to as NPK, or nitrogen, phosphorus and potassium. The secondary macro-nutrients are not needed in such large amounts as NPK. These include calcium, magnesium and sulfur and are usually found in sufficient amounts in soil. Some elements come from the environment such as oxygen, carbon and hydrogen. Finally there are seven trace elements or micro-nutrients, including boron and iron, among others. Soil that is adequately managed should have these required elements in large enough concentrations for plant needs. Granular fertilizers generally address deficiencies in the nitrogen, phosphorus and potassium areas.
Organic vs. Synthetic
Organic granular fertilizer is made up of natural items from a once living organism that compost into soil and release fertilizer components for plant uptake. The nutrients contained in organic fertilizers release slowly over time as they decompose. This is good if the soil is in adequate condition but not good if it needs immediate amendment for plant health.
Synthetic granular fertilizer releases nutrients quickly. Synthetic fertilizer is composed of chemical compounds that are suitable substitutes for organic nutrients. They are usually less expensive and readily available at garden centers. Synthetic fertilizer will not improve soil, but organic fertilizers add texture and balance to soil.
Granular fertilizers take more time to impart their compounds to the soil than liquid fertilizers that are saturated into the ground or onto plants leaves. Granular time- release fertilizers are a good way to feed plants over time. They are formulated to react to moisture in such a way that the granule breaks down over a specific period, slowly releasing the food to the soil. You can get granular time-release products that feed plants for three, six, or twelve months. This frees you from remembering to fertilize on schedule.
Granular vs. Liquid
Granular fertilizers are the most commonly used form of nutrition applied to soil. Granules vary in size but are sufficiently small to break down quickly and release food to the plant. They are extremely easy to apply and create a minimum of mess. Liquid fertilizer requires careful measurement and mixing. It also requires special equipment to spread the fertilizer. Liquid feeds are good for foliage fertilizing and transplanting new plants that need an immediate shot of nutrition.