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How much NPK does soil need

Dr. Sangeeta Soi
Dr. Sangeeta Soi

NPK fertilizer is a mixture of mineral contents composed primarily of the three primary nutrients required for healthy plant growth. The word NPK stands for Nitrogen, Phosphorus and Potassium which are the essential nutrient for any plant growth.

German scientist Justus Von Liebig was responsible for the theory that Nitrogen, Phosphorous, and Potassium levels are the basis for determining healthy plant growth. However, this theory, which dates to the 1800s, doesn't take into account the dozens of other nutrients and elements that are essential to plant growth such as sulfur, hydrogen, oxygen, carbon, magnesium, etc. Nor does the theory talk about the importance of beneficial soil organisms that help your plants to flourish and to fight off pests and diseases. Chemical fertilizers and organic fertilizers show their nutrient content with three bold numbers on the package. These numbers represent three different compounds: Nitrogen, Phosphorous, and Potash (Potassium), which we can also describe with the letters N-P-K. The agriculture industry relies heavily on the use of NPK fertilizer to meet global food supply and ensure healthy crops.

In the market, we usually find labels of NPK in fertilizers. They are usually important for the specific role they play. Understanding NPK (Nitrogen, Phosphorous, and Potash (Potassium) ratings on lawn and plant fertilizers is an important part of deciding whether or not fertilizers are appropriate or even necessary for your garden and landscaping. In addition to other properties, Nitrogen helps plant foliage to grow strong. Phosphorous helps roots and flowers grow and develop. Potassium (Potash) is important for overall plant health. Be aware that high nitrogen fertilizers will make for quick growth but weaker plants that are more susceptible to attacks by diseases and pests. Fast, showy growth is not necessarily the best thing for your plants.

Significance of NPK

The theory by  Justus Von Liebig has been found true but as the market is flooded with a number of chemical industries ready to produce a number of packets of a chemical composition containing NPK it has made it important to understand why are they really required for the soil.  It is clear that Nitrogen, Phosphorous, and Potassium are not necessarily the most important elements you need for your plants to grow well. In fact, elements such as carbon, hydrogen, oxygen, sulfur, magnesium, copper, cobalt, sodium, boron, molybdenum, and zinc are just as important to plant development as N-P-K  which can be made readily available for from the vermicompost we use as it may contain all these elements in natural form.

What is that number ‘NPK ratio’ on the pack

We will mostly find on the packets of Fertilizers the numbers in a ratio like 20:20:20 or it can be 5:10:20. What does that mean? Actually, it stands for the amount of each element present in the complete packet required for your soil. The higher the number, the more concentrated the nutrient is in the fertilizer. For example, numbers on fertilizer listed as 20-5-5 the four times more nitrogen in it than phosphorus and potassium. A 20-20-20 fertilizer has twice as much concentration of all three nutrients than 10-10-10.

The higher the number, the more concentrated the nutrient is in the fertilizer. For example, numbers on fertilizer listed as 20-5-5 have four times more nitrogen in it than phosphorus and potassium. A 20-20-20 fertilizer has twice as much concentration of all three nutrients than 10-10-10. The fertilizer numbers can be used to calculate how much of a fertilizer needs to be applied to equal 1 pound of the nutrient you are trying to add to the soil. So if the numbers on the fertilizer are 10-10-10, you can divide 100 by 10 and this will tell you that you need 10 pounds of the fertilizer to add 1 pound of the nutrient to the soil. If the fertilizer numbers were 20-20-20, you divide 100 by 20 and you know that it will take 5 pounds of the fertilizer to add 1 pound of the nutrient to the soil. A fertilizer that contains only one macro-nutrient will have “0” in the other values. For example, if a fertilizer is 10-0-0, then it only contains nitrogen. These fertilizer numbers, also called NPK values, should appear on any fertilizer you purchase, whether it is an organic fertilizer or a chemical fertilizer.

Side effects of using NPK

Inspite of the fact that the theory of  Justus Von Liebig has been followed since number of years which has lead to the pollution of our water bodies and soil in great way by incorporating huge amount of chemicals and spoiling the food chain. Many homeowners who aren't growing to make a profit end up inadvertently overusing chemical fertilizers (and pesticides too!). They think that if a little bit is good, then more must be better. It isn't! According to the National Academy of Sciences, even though farmers uses pesticides more widely, homeowners uses 10 times more fertilizer per acres. If you only take away one thing from this article, please let it be that you should only use the proper amount of any fertilizer, and not anything more. This will save you money, and it will also keep your yard and garden healthier at the same time. This is extremely important with chemicals, but it also applies to organics! Organic gardeners can look to the work of Sir Albert Howard for solid research and ideas on how to grow plants more naturally. His ideas consider chemical processes that occur in nature. He then applies them to agriculture and home gardening.

Organic versus NPK

As we all know the market is flooded with chemical fertilizers which has been used since long and has contaminated the food chain in the bad way. NPK which has paved its way in the market has made it possible to get results overnight. Its by the use of chemical fertilizers that flowering and production of plants can be made fast and productivity can be enhanced in a big way. When looking at both organic and chemical fertilizer labels, you'll notice that the NPK numbers don't add up to 100 percent. So, what is the rest of your fertilizer made up of? That depends on the fertilizer. Chemical fertilizers can have any number of additional ingredients including dirt, sand, and even materials that are potentially hazardous to your health and to the environment. These fillers for chemical fertilizers are required so that the nutrients aren't so concentrated that they will damage or "burn" your plants, your skin, and anything else they touch. Organic fertilizers don't necessarily contain fillers, as they are made up of a variety of natural components that in one way or another will benefit your plants.

How much NPK required for your soil

Soil nutrient levels vary from year to year, and frequently will vary within fields, even on fields that seem to be uniform. It is therefore necessary to follow certain recommended steps for soil sampling and testing to develop a sound ongoing soil fertility management program.

An understanding of general nutrient status can be obtained for a field if soil tests are conducted. Nitrogen soil testing is recommended annually as the available nitrogen can change considerably from year to year. Changes are dependent upon environmental conditions such as rainfall and temperature patterns during a growing season, type and yield of crop harvested, date of harvest, fall tillage, amount of fertilizer applied to the previous crop. Potassium and phosphorus levels do not change substantially in a soil over a period of several years. Therefore, sampling for phosphorus and potassium may be conducted every 2 or 3 years, or when changing crop type. Sampling for sulphur should be done annually, unless a previous test indicates that the available levels to 60 cm (24 in) are in excess of 55 kg/ha (50 lb/ac). In the latter case, a test for sulphur every 2 to 3 years is adequate.

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