Fertilizers are very important in gardening farming horticulture ect. If you want to start these activities here is a guide on What are fertilizers? Why to use them? How do they affect plant nutrition?  When and how to use them? What is soil fertilization? What is soil ph? What is nutrient pollution? Why to use organic fertilizers?

What is it?

A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply one or more plant nutrients essential to the growth of plants. 

Organic fertilizers are fertilizers derived from animal matter, animal excreta (manure), human excreta, and vegetable matter (e.g. compost and crop residues). Naturally occurring organic fertilizers include animal wastes from meat processing, peat, manure, slurry, and guano.

Plant nutrition


Boron deficiencyis a common deficiency of the micronutrient boron in plants. It is the most widespread micronutrient deficiency around the world and causes large losses in crop production and crop quality.

Calcium (Ca) deficiency is a plant disorder that can be caused by insufficient level of biologically available calcium in the growing medium, but is more frequently a product of low transpiration of the whole plant or more commonly the affected tissue.

Iron (Fe) deficiency is a plant disorder also known as “lime-induced chlorosis“. It can be confused with manganese deficiency. Soil iron concentration is high, but can become unavailable for absorption if soil pH is higher than 6.5.[1] Also, iron deficiency can develop if the soil is too waterlogged or has been overfertilised. 

Magnesium deficiency is a detrimental plant disorder that occurs most often in strongly acidic, light, sandy soils, where magnesium can be easily leached away.

Manganese (Mn) deficiency is a plant disorder that is often confused with, and occurs with, iron deficiency. Most common in poorly drained soils, also where organic matter levels are high. Manganese may be unavailable to plants where pH is high.

Nitrogen deficiency in plants can occur when organic matter with high carbon content, such as sawdust, is added to soil.[1] Soil organisms use any nitrogen to break down carbon sources, making N unavailable to plants.

Potassium deficiency, also known as potash deficiency, is a plant disorder that is most common on light, sandy soils, because potassium ions (K+) are highly soluble and will easily leach from soils without colloids.

Zinc deficiency occurs when plant growth is limited because the plant cannot take up sufficient quantities of this essential macronutrient from its growing medium.




Fertigation is practiced extensively in commercial agriculture and horticulture. Fertigation is also increasingly being used for landscaping as dispenser units become more reliable and easier to use. Fertigation is used to add additional nutrients or to correct nutrient deficiencies detected in plant tissue analysis. It is usually practiced on the high-value crops such as vegetables, turf, fruit trees, and ornamentals.

Green manure is created by leaving uprooted or sown crop parts to wither on a field so that they serve as a mulch and soil amendment. The plants used for green manure are often cover crops grown primarily for this purpose. Typically, they are ploughed under and incorporated into the soil while green or shortly after flowering. Green manure is commonly associated with organic farming and can play an important role in sustainable annual cropping systems.

In agriculture, a living mulch is a cover crop interplanted or undersown with a main crop, and intended to serve the purposes of a mulch, such as weed suppression and regulation of soil temperature. Living mulches grow for a long time with the main crops, whereas cover crops are incorporated into the soil or killed with herbicides.

Other benefits of mulches are slowing the growth of weeds, and protecting soil from water and wind erosion. Some living mulches were found to increase populations of the natural enemies of crop pests.[1] Legumes used as living mulches also provide nitrogen fixation, reducing the need for fertilizer.

Nutrient budgets offer insight into the balance between crop inputs and outputs. In short, they compare nutrients applied to the soil to nutrients taken up by crops. A nutrient budget takes into account all the nutrient inputs on a farm and all those removed from the land. The most obvious source of nutrients in this situation is fertilizer, but this is only part of the picture. Other inputs come with rainfall, in supplements brought on to the farm and in effluent – either farm or dairy factory – spread on the land. In addition, nutrients can be moved around the farm – from an area used for growing silage to the area used to feed it out, from paddock to raceway, and within paddocks in dung and urine patches. Nutrients are removed from the farm in stock sold on, products (meat, milk, wool), crops sold or fed out off farm, and through processes such as nitrate leachingvolatilization and phosphate run-off etc

Nutrient management is the science and practice directed to link soilcropweather, and hydrologic factors with cultural, irrigation, and soil and water conservation practices to achieve optimal nutrient use efficiency, crop yields, crop quality, and economic returns, while reducing off-site transport of nutrients (fertilizer) that may impact the environment.[1] It involves matching a specific field soil, climate, and crop management conditions to rate, source, timing, and place (commonly known as the 4R nutrient stewardship) of nutrient application.[2]

Important factors that need to be considered when managing nutrients include (a) the application of nutrients considering the achievable optimum yields and, in some cases, crop quality; (b) the management, application, and timing of nutrients using a budget based on all sources and sinks active at the site; and (c) the management of soil, water, and crop to minimize the off-site transport of nutrients from nutrient leaching out of the root zone, surface runoff, and volatilization (or other gas exchanges).



Soil fertility refers to the ability of soil to sustain agricultural plant growth, i.e. to provide plant habitat and result in sustained and consistent yields of high quality.[1] A fertile soil has the following properties:[2]

  • The ability to supply essential plant nutrients and water in adequate amounts and proportions for plant growth and reproduction; and
    • The absence of toxic substances which may inhibit plant growth.

The following properties contribute to soil fertility in most situations:

  • Sufficient soil depth for adequate root growth and water retention;
    • Good internal drainage, allowing sufficient aeration for optimal root growth (although some plants, such as rice, tolerate waterlogging);
    • Soil pH in the range 5.5 to 7.0 (suitable for most plants but some prefer or tolerate more acid or alkaline conditions);

In lands used for agriculture and other human activities, maintenance of soil fertility typically requires the use of soil conservation practices. This is because soil erosion and other forms of soil degradation generally result in a decline in quality with respect to one or more of the aspects indicated above.

Photosynthesis is the process whereby plants use light energy to drive chemical reactions which convert CO2 into sugars. As such, all plants require access to both light and carbon dioxide to produce energy, grow and reproduce.

While typically limited by nitrogen, phosphorus and potassium, low levels of carbon dioxide can also act as a limiting factor on plant growth. Peer-reviewed and published scientific studies have shown that increasing CO2 is highly effective at promoting plant growth up to levels over 300 ppm. Further increases in CO2 can, to a very small degree, continue to increase net photosynthetic output.

The quality of irrigation water is very important to maintain soil fertility and tilth, and for using more soil depth by the plants.[13] When soil is irrigated with high alkaline water, unwanted sodium salts build up in the soil which would make soil draining capacity very poor. So plant roots can not penetrate deep into the soil for optimum growth in Alkali soils. When soil is irrigated with low pH / acidic water, the useful salts ( Ca, Mg, K, P, S, etc.) are removed by draining water from the acidic soil and in addition unwanted aluminium and manganese salts to the plants are dissolved from the soil impeding plant growth.[14] When soil is irrigated with high salinity water or sufficient water is not draining out from the irrigated soil, the soil would convert into saline soil or lose its fertility. Saline water enhance the turgor pressure or osmotic pressure requirement which impedes the off take of water and nutrients by the plant roots.


Nutrient pollution

Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters, in which excess nutrients, usually nitrogen or phosphorus, stimulate algal growth. Sources of nutrient pollution include surface runoff from farm fields and pastures, discharges from septic tanks and feedlots, and emissions from combustion. Excess nutrients have been summarized as potentially leading to:

  • Population effects: excess growth of algae (blooms);[1]
    • Community effects: species composition shifts (dominant taxa);
    • Ecological effects: food web changes, light limitation;
    • Biogeochemical effects: excess organic carbon (eutrophication); dissolved oxygen deficits (environmental hypoxia); toxin production;[2]
    • Human health effects: excess nitrate in drinking water (blue baby syndrome); disinfection by-products in drinking water;[3]


Soil ph

Soil pH is a measure of the acidity or basicity (alkalinity) of a soilpH is defined as the negative logarithm (base 10) of the activity of hydronium ions (H+

 or, more precisely, H 3O+aq) in a solution. In soils, it is measured in a slurry of soil mixed with water (or a salt solution, such as 0.01 M CaCl2), and normally falls between 3 and 10, with 7 being neutral. Acid soils have a pH below 7 and alkaline soils have a pH above 7. Ultra-acidic soils (pH < 3.5) and very strongly alkaline soils (pH > 9) are rare.

Soil pH is considered a master variable in soils as it affects many chemical processes. It specifically affects plant nutrient availability by controlling the chemical forms of the different nutrients and influencing the chemical reactions they undergo. The optimum pH range for most plants is between 5.5 and 7.5;[2] however, many plants have adapted to thrive at pH values outside this range.


Why Fertilize?

Just like our bodies need nutrients to function and grow, so do plants. The soil contains many of the vital nutrients needed, but as plants use them, the soil can become depleted. Soil also can get depleted from erosion by wind and rain. Fertilizing is a way to replenish the fertility of the soil. The healthier the soil, the healthier the plants will be.

What do plants need? While there are at least 16 nutrient elements necessary for plant growth, the most important are nitrogen, phosphorous, and potassium (referred to by the elemental symbols, N, P, and K). Most soils contain large reserves of the other 13 nutrients — especially calcium, magnesium, sulfur, iron, zinc, and manganese — that might also hitchhike along when you fertilize with the “big three.”

To ensure that your soil has the right mix and balance of nutrients, you should do a soil test. Private laboratories and state cooperative extension services test garden soil for a nominal fee.

The Advantage of Organics

The purest form of organic fertilizer is a plant, animal, or mineral that is applied to the garden without any processing. Good examples of these are green manures, animal manures, and wood ashes. The advantage to this form of fertilization is that not only are main nutrients mentioned above added to the soil, but organic matter and humus, as well. Organic matter improves soil structure, moisture retention, drainage, and the microbial life of the soil. An adequate amount of organic matter in the soil can help ensure that nutrients are available to plants on a steady basis and that the soil structure enhances root growth. Organic fertilizers dole out the nutrients more slowly than chemical fertilizers, so plant roots are less likely to be burned by getting too high a dose.

Even if you use processed organic amendments, such as alfalfa meal, bonemeal, and greensand, you’ll still get many of the advantages. Plus, you can take care of the need for a specific nutrient by applying the appropriate fertilizer. For example, if your lettuce needs a shot of nitrogen, alfalfa meal would be a good choice. If you need more phosphorous to help your carrots grow, bonemeal would be a good addition.

Obviously, the best way to use organic fertilizers is to apply a combination of raw materials high in organic matter, such as manure, along with specific organic fertilizers to target crop needs. Another advantage of using raw materials, even leaves and straw, as part of your fertilizer program is you get to recycle materials that would otherwise end up in the landfill.


When and how to use them?


An exception to that “no dig” rule is when phosphorus levels are low, as indicated by a soil test or stunted plants that are purplish when young or late to ripen. (Cold soil in spring also can cause a phosphorus deficiency, a temporary one that abates as soon as soil warms and roots start reaching out.) Phosphorus moves very slowly in the soil, so the only way to get it quickly into the root zone is to mix it into the top 6 to 12 inches of soil.

Once a soil is up to snuff with phosphorus, periodic surface applications can trickle down through the soil fast enough to maintain adequate levels throughout the root zone.


When should you apply organic fertilizers? Remember that the nutrients in most of them are initially insoluble and in forms that plants cannot use. Account for the time lag between application and nutrient release by spreading organic fertilizers a few weeks before planting. Even a few months before planting, or way back late last fall.

A quick-acting fertilizer might also be needed when a plant is so hungry that it actually shows symptoms of starvation, such as yellowing, older leaves. Leaves can absorb nutrients directly, and for a really quick effect, you could spray a soluble organic fertilizer such as seaweed extract or fish emulsion right on leaves. Avoid plant injury by reading label directions and following specified rates carefully.

Consider using quick-acting fertilizers as quick fixes only. Build up good reserves of nutrients in your soil and such applications will be unnecessary.


The hungriest parts of the garden are vegetable and formal flower beds, so I like to feed the ground there with compost, which is an organic material relatively rich in nutrients. Less needy are trees and shrubs, informal flowers and wildflowers; here, any organic mulch, from wood ships to straw to pine needles, will suffice. Over the years, the compost or other organic mulches will enrich the soil to offer a spectrum of nutrients available to plants, a much wider spectrum that would be available from any chemical fertilizer.

In naturally poor soils, some additional, more concentrated, nitrogen fertilizer might — just might — also be needed for a year or more until the soil is up to snuff. Soybean meal or alfalfa meal is usually sold as an animal feed, but sprinkled over the ground just before some organic mulch is applied it’s a convenient, nourishing and organic “feed” for plants also. Apply a couple of pounds per hundred square feet.



Types of Organic Fertilizers

organic fertilizers can be grouped according to the source of their raw material. There are plant-based, animal-based, and mineral-based fertilizers available. I won’t be covering mineral-based fertilizers such as greensand, rock phosphate, and Chilean nitrate here, but will refer you to another article, Minerals for Soil, for a detailed explanation of this fertilizer group.

Here are some examples of plant- and animal-based products you might use in your garden.

Plant-Based Fertilizers

Plant-based fertilizers are usually high in nitrogen and sometimes potassium. Some crops are grown specifically to be made into organic fertilizer while others, such as cottonseed meal, are by-products of another industry.

Alfalfa Meal

This fertilizer is also available in pellets. It has a moderate amount of nitrogen (2 to 3 percent) and contains some trace minerals.

Corn Gluten

This by-product of the corn-processing industry contains 10 percent nitrogen in a form that’s quick to break down. It also has the unique ability to inhibit germination of seeds and is sold as an organic pre-emergent herbicide to control crabgrass in lawns.

Cottonseed Meal

This by-product of the cotton industry is made from the remains of cottonseeds after the oil is pressed out. It’s a slow-release fertilizer, moderately high in nitrogen (6 percent), with some phosphorous. It can acidify the soil. Since cotton is such a heavily sprayed crop, there are concerns about pesticides on the seed and in the meal. It’s best to buy low-residue or pesticide-free cottonseed meal.


Extracts of seaweed and kelp are found in meal and liquid forms. They are good sources of minerals, with some potassium and nitrogen. They also enhance the microbial activity in the soil. Liquid versions of seaweed can be sprayed directly on plants as a foliar fertilizer.


Soybean Meal

This high-nitrogen fertilizer (7 percent) is similar to alfalfa meal and contains more nitrogen than cottonseed meal.

Animal-Based Fertilizers

By-products from the dairy and meat processing industries produce a bevy of organic fertilizer products.

Blood Meal

This product is exactly what it sounds like; it’s a by-product of the slaughtering industry and is a rich source of nitrogen (14 percent). The smell may attract dogs and wild animals to your garden.


Another by-product of the slaughtering industry, bonemeal is a rich source of phosphorous (11 percent) and calcium (22 percent), and it supplies some nitrogen. “Steamed” bonemeal has less nitrogen but somewhat faster nutrient availability than “raw” bonemeal.

Fish Products

By-products from the fish industry yield organic fertilizer products such as fish emulsion and fish meal. These are high in nitrogen (up to 10 percent) and quickly available to plants.

Animal Manures

Manures can be derived from a variety of animals and even insects. Most are available bagged, composted, and sometimes sterilized.





Compost’s nutrient profile varies based on what is put into but it is often close to that of cow manure. It is a popular garden fertilizer. This is no doubt because it can be made for free and it works at a moderate pace. There are also a variety of ways that compost can be used in your garden. It can be used as a mulch or mixed with your garden soil. It can also be brewed into compost tea to use as a foliar feed. Gardeners who don’t have space for a large compost system can even get similar benefits from using worm compost bins under their sinks.

However, compost can be alkaline in nature. This characteristic negatively affects how well plants living in the soil can absorb nutrients. Compost also has a high weight to available nutrient ratio. Improperly tended compost pile can additionally emit bad smells, which can quickly get city dwellers in trouble with their neighbors.

If you still plan on using it, compost should be added before or after planting. It’s also a good soil refresher in between growing seasons for gardens that are constantly in use.  You’ll want to use half an inch to a full inch every time a new crop is planted.



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