The Q&A Archives: Organic fertilizers

Question: How can I tell if a bag labeled as

Answer: When used in reference to fertilizers, the word organic generally means that the nutrients contained in the product are derived solely from the remains or a by-product of an organism. Cottonseed meal, blood meal, fish emulsion, manure and sewage sludge are examples of organic fertilizers. Urea is a synthetic organic fertilizer, an organic substance manufactured from inorganic materials.

When packaged as fertilizers, organic products have the fertilizer ratio stated on the package label. Some organic materials, particularly composted manures and sludges, are sold as soil conditioners and do not have a nutrient guarantee stated on the package, although small amounts of nutrients are present.

Some organic fertilizers are high in one of the three major nutrients (nitrogen, phosphorus, or potash,) but low or zero in the other two. Some are low in all three macronutrients. A few organic products can be purchased "fortified" for a higher nutrient analysis. The ingredients used to fortify organic fertilizers are organic materials; for example, rock phosphate to increase phosphorus, or greensand to increase potash.

Organic fertilizers depend on soil organisms to break them down to release nutrients; therefore, most are effective only when soil is moist and warm enough for the microorganisms to be active. Nutrient release by microbial activity, in general, occurs over a fairly long time period. One potential drawback is that the organic fertilizer may not release enough of their principal nutrient when the plant needs it for growth.

Compared to synthetic fertilizer formulations,organic fertilizers contain relatively low concentrations of actual nutrients, but they perform important functions which the synthetic formulations do not. They increase the organic content and consequently the water-holding capacity of the soil. They improve the physical structure of the soil which allows more air to get to plant roots. Where organic sources are used for fertilizer, bacterial and fungal activity increases in the soil. Mycorrhizal fungi which make other nutrients more available to plants thrive in soil where the organic matter content is high. Organically derived plant nutrients are slow to leach from the soil making them less likely to contribute to water pollution than synthetic fertilizers.

The bottom line is that if the package states the contents are organic, they must be organically derived.

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