Fertilizers are added to the soil to supply elements essential to the growth of plants. These elements include the major nutrients such as nitrogen, phosphorus, potassium, and sulfur, as well as the trace elements such as iron, zinc, and magnesium.
Organic fertilizers are made from materials derived from living things. Animal manures, compost, bonemeal and blood meal are organic fertilizers. Chemical fertilizers are manufactured from nonliving materials. Rock phosphate for example, is a common source of phosphorus in chemical fertilizers.
Organic fertilizers are not immediately available to plants. Before the plants can use them, they must be broken down by soil microorganisms into simpler, inorganic molecules and ions. In contrast, the nutrients in chemical fertilizers are already in inorganic form and so can be immediately used by the plants. It is important to understand that there is no fundamental difference in nutritional quality between organic and inorganic fertilizers.
It makes no difference to the beet root if the atoms of potassium it absorbs are from an organic fertilizer such as wood ash or an inorganic one such as muriate of potash.
Inorganic fertilizers – Although they are immediately available to plants, inorganic fertilizers have three main disadvantages. They are subject to leaching, which occurs when the fertilizers are washed by rain or irrigation water down below the level of the plant roots. Nitrogen is particularly susceptible to leaching. As well, a heavy application of chemical fertilizers can “burn” seedlings and young plants. This is actually a process of drying out, or desiccation, due to the presence of chemical salts within the commercial fertilizers. A third problem associated with the use of commercial fertilizers is that overly heavy applications can build up toxic concentrations of salts in the soil and create chemical imbalances.
Unlike chemical fertilizers, organic material does more than provide organic nutrients. It also improves the soil structure, or tilth, and increases its ability to hold both water and nutrients. As microorganisms in the soil break down the organic material into an inorganic soluble form, a slow release of nutrients is provided over a longer period of time. This is probably a healthier situation for plant growth in that an oversupply of a nutrient such as nitrogen can lead to lush, succulent tissue growth which is more vulnerable to fungal and bacterial entry, more appealing to some insects, and more prone to stress injury from heat, cold, or drought.
With organic fertilizers a buildup of toxicity in the soil is unlikely, as long as the amount of organic material incorporated into the soil is fully decomposed.
On the other side of the coin, there are some disadvantages to the use of organic fertilizers. As noted above, they are not immediately available to the plants. The manure which is applied to a vegetable garden in the spring may not be broken down into organic form by soil bacteria (and therefore available to plants) until midsummer. If organic nutrients have been added to soils continually on an ongoing basis, this may not be a problem. However, if you are just beginning to rely solely on organic material as a nutrient source, your garden may experience an initial nutrient deficiency until the system is in place.
The amount of nutrients and the exact type of elements available from a given amount of manure, compost or other inorganic fertilizer can only be guessed at. It is dependent on such factors as: the age of the manure or compost; its origin (chicken, cow, horse, sawdust, garden residue, grass clippings); and weather conditions such as temperature and rainfall. It is therefore a less exact way of providing for a plant’s nutritional needs. With inorganic fertilizers, the type and amount of any given element in the fertilizer formulation are known.
Organic fertilizers can be more expensive and less accessible than inorganic fertilizers. I think that is what stops some people from going organic.
Thanks to Steve the Gardenguy for sharing this information!