What is npk used for

Plants in the bean family, legumes, have nodules on their roots where bacteria live that fix nitrogen from the air for use by the plant.

They provide their own nitrogen fertiliser this way. You can tell if your plants need nitrogen when their growth is stunted with weak stems and they will have yellowed or discoloured leaves. Nitrogenous fertilisers are quickly washed out of the soil by rain and need to be renewed annually.

With crops that require a lot of nitrogen over a period of time, like cabbages, adding nitrogen incrementally through the growth period is the most efficient application method. Phosphorus is essential for seed germination and root development. It is needed particularly by young plants forming their root systems and by fruit and seed crops. Root vegetables such as carrots, swedes and turnips obviously need plentiful phosphorus to develop well. Without ample phosphorus you will see stunted growth, probably a purple tinge to leaves and low fruit yields.

Phosphates remain in the soil for two or three years after application so the amount in a general fertilizer is probably enough. Add just before planting or top dress during growth periods. Potassium has the chemical symbol K from its Latin name kalium. It promotes flower and fruit production and is vital for maintaining growth and helping plants resist disease.

Because soil continually changes, you should have your soil tested every 2 to 3 years. Keeping records of test results, fertilizer applications, and any other soil amendments you make is always a good idea. Fertilizer providing the N-P-K nutrients mentioned above can come in both organic and synthetic versions. For the spring, some fertilizers combine the best of both worlds with an organically-based fertilizer mix that also contains small amounts of synthetic fertilizers to ensure the immediate availability of nutrients.

Note that the N-P-K ratio of organic fertilizers is typically lower than that of a synthetic fertilizer. By law, the ratio label can only list nutrients that are immediately available.

To build the long-term health and fertility of your soil, we recommend using granular organic fertilizers. Supplementing with an additional water-soluble fertilizer is a way to ensure that your plants have the nutrients they need when they need a boost during active growth.

Before buying bags or bottles of fertilizers, consider how you might add nutrients to the soil by improving its biology. Try compost tea, a liquid produced by extracting beneficial microbes bacteria, fungi, protozoa, and nematodes from compost.

Applying compost tea to both soil and plant foliage adds those beneficial microorganisms to the growing medium, which boosts plant health and encourages growth.

Compost tea is made using a brewing process similar to that used for making beer. Active compost, a brewing kit, and a little information can go a long way toward turning your landscape into a thriving ecosystem. See information on how to make compost tea.

Now that you understand more about fertilizers, see how to apply fertilizer to your garden! I would like to use cotton seed meal as fertilizer, but I am wary of the pesticides used in growing cotton residing in the seeds. I have not been able to locate organic cotton seed meal. Should I be concerned? Compost is great for adding organic matter to the soil, but pretty lousy when you need mineral fertilizer, the NPK the article mentions. Doesn't compost contain only about of NPK?

Certainly not much. In your terms look at it this way, compost is mostly filler, little mineral fertilizer. Another matter, to get enough compost for a small area takes a huge lot of raw organic matter. By the time it breaks down and is composted, very little quantity is available.

This element is essential for all plants to thrive, particularly in changing weather conditions. Potassium also has a tendency to remain in the soil, but is heavily used by growing vegetables, so should be supplemented as needed, based on a soil test. Along with nitrogen, phosphorus and potassium, fertilizers contain additional nutrients in much smaller quantities. Calcium Ca helps to build a plant's cell walls.

Iron Fe plays an active role in the creation of chlorophyll and in photosynthesis. Magnesium Mg aids in the creation of components of chlorophyll as well as in a plant's growth and repair process. Sulfur S helps to build proteins essential to plant growth and the maturation of fruit and seeds. Based in Atlanta, Valerie Liles has been writing about landscape and garden design since As a registered respiratory therapist, she also has experience in family health, nutrition and pediatric and adult asthma managment.

By Valerie Liles. Related Articles. Does the Sulfate of Potash Lower the pH? Reading a Fertilizer Label Fertilizer labels list three numbers; for example, indicates the relative amounts of nitrogen, phosphorus and potassium, or N-P-K.