Fertilizers, Types and use as Plant Nutrients

Fertilizers Nutrients for Plants – Types and Quantity

Agriculture is the activity of growing of various types of plants. Basic Fertilizers for plants to grow are water, soil, sunshine and food nutrients.

Soil and water are the major provider of food for the plants so that the plants can grow and produce.

Nutrients: Essential, Primary, Secondary and Micro

Growth and development of plants requires 17 Nutrients given through Fertilizers.

Carbon, Hydrogen and Oxygen are Essential Nutrients and supplied through water and air.

Nitrogen (N), Phosphorous (P), Potassium (K) are Primary Fertilizers Nutrients which are present in the soil and also supplemented before plantation occurs for any crop.

Secondary nutrients are Calcium (Ca), Magnesium (Mg) and Sulfur(S).

Iron (Fe), Manganese (MN), Zinc (Zn), Copper (Cu), Boron (B), Molybdenum (Mo), Chlorine (Cl) are Micro nutrients. Micro nutrients requirement is very small by the soil.  Supplement Micro nutrients  as per production program of any plant by the farmer.

Plant specific nutrient

A lot of study has gone into understanding the specific nutrient requirement by specific plants. This study determines what Fertilizers to be given. Crops require certain nutrients more than other type of crop. Knowledge of such study enables Farmers understand well what nutrients are required at what stage by their crops.  Otherwise the crops may not get what nutrient it should have had and other nutrient which has been given would go waste.

Primary nutrients i.e. nitrogen, phosphorous and potassium are normally freely given through appropriate Fertilizers. Little or no thought is given to balanced nutrition. A deficiency of the secondary nutrients and/or of the micro nutrients can lead to failure in achieving the desired yield.

It also goes without saying that any fertilizer use should be done only after studying the pH and E.C. of the soil. In fact it is best to do so at regular intervals and on their analysis modify the fertilization of the soil.

Fertilizers too much or too less ?

fertigation vs yield

fertigation vs yield

Too much of any Fertilizers is not good. As we apply fertilizers, yield increases but if we keep on increasing the fertilizers the laws of diminishing returns takes over. Yield goes down as soil becomes sodic. Timing of Fertilizers is important because what Fertilizers are required in the beginning of the plant cycle would not be same as when plants become productive.

Watch for soil pH, adjust fertilizers

absorption of nutrients is not uniform with pH

absorption of nutrients is not uniform with pH

The availability of these nutrients is highly dependent on the soil pH.  pH and EC are discussed separately by us. pH is expressed in a scale from 0 to 16, with values 6.5 to 0 as increasingly Acidic, values 7.5 to 16 as increasingly Basic and values 6.5 to 7.5 Neutral. For example, potable water and human blood have pH of 7.0. Absorption of all the nutrients  in the soil and  plants does not take place uniformly due to variation of pH value of the soil. The table below shows that the maximum availability of nutrients occurs between pH values of 6 to 7.5.

 

Mobility of nutrients in plants

Another aspect of Fertilizers that we need consider is the mobility of nutrients in the soil which affects absorption by the plants. The mobility also affects leaching, volatilization and runoff of fertilizers. Nitrogen in the form of NO3 is highly mobile in soil, Phosphorous is not. Nitrogen can be dispersed and still make it to plant roots but would leach, whereas Phosphorous needs applied closer to the root zone and would stay in upper zone.  Yellowing of new leaves shows deficiency of immobile nutrients. Yellowing of older leaves shows deficiency of mobile nutrients. Basic N P K nutrients are mobile in plants whereas Ca, Mg and most of micro nutrients are immobile in plants. So study of leaves gives an indication of deficiency.  The table below brings out deficiencies and symptoms.

Nutrient Mobility in Soil Mobility in Plant Role in Plant Growth Sign of Deficiency
Nitrogen Mobile in the form of NO3,immobile in the form of NH4+ Mobile Chlorophyll, amino acids, proteins Yellowing in the middle of the leaf, reduced and red-brown new growth
Phosphorus Immobile Somewhat mobile DNA/RNA, ATP, cell membrane Purple or reddish discolorations on leaves, poor growth, poor rooting, early fruit drop
Potassium Somewhat mobile Very mobile Plant metabolism, stress response, regulation of water loss Yellowing of leaf margins and veins, crinkling or rolling leaves, poor growth
Calcium Somewhat mobile Immobile Cell wall formation Yellowing new growth, localized tissue necrosis
Magnesium Immobile Somewhat mobile Photosynthesis, chlorophyll Interveinal chlorosis (yellow leaves with green veins)
Sulfur Mobile Mobile Amino acids, proteins, oils, chlorophyll Yellowing throughout the plant, necrotic tips on new growth
Boron Very mobile Immobile Cell wall, sugar transport, seed and fruit formation, hormone development Cell wall, sugar transport, seed and fruit formation, hormone
Copper Immobile Immobile Lignin production, photosynthesis, plant metabolism Pale green, withered new growth, yellowing, wilting
Iron Immobile Immobile Chlorophyll and enzyme production Yellowing in new growth
Manganese Mobile Immobile Photosynthesis, respiration, nitrogen assimilation Interveinal chlorosis on new growth, sunken tan spots on leaves
Zinc Immobile Immobile Chlorophyll, enzymes, proteins, growth hormones Interveinal chlorosis on new growth
Molybdenum Somewhat mobile Immobile Nitrogen cycle Yellowing of leaf margins on new growth
Chlorine Mobile Mobile Opening and closing stomata (respiration) Yellowing of leaf margins on old growth

 

Fertilizers Type:

Two types of Fertilizers are available to the farmers. Chemical and Organic. NPK values classify Chemical Fertilizers. N stands for Nitrogen content, P stands for Phosphorous expressed as P2O5 and K stands for Potassium expressed as K2O.

Chemical Fertilizers – Analysis and Composition

Some examples of available fertilizers are as below:

Fertilizer: Ammonium Nitrate

Grade: 37-0-0

Analysis / composition: 18.5% N-NO3, 18.5% N-NH4

Formula: NH4NO3

 

Fertilizer: Ammonium Sulfate

Grade: 21-0-0

Analysis / composition: 21% N-NH4, 73% SO

Formula: (NH4)2SO4

Fertilizer: Calcium Nitrate

Grade: 15.5-0-0 19

Analysis / composition: 14.4% N-NO3, 1.1% N-NH4, 19% Ca

Formula: 5Ca(NO3)2-NH4NO3*10H2O

 

Fertilizer: Magnesium Nitrate

Grade: 11-0-0 0-9.6

Analysis / composition: 11% N-NO3, 9.6% Mg

Formula: Mg(NO3)2

Fertilizer: Magnesium Sulfate

Grade: 0-0-0 – 0-9.1

Analysis / composition: 9.1% Mg, 14% S (42% SO4)

Formula: MgSO4

Fertilizer: Mono Ammonium Phosphate (MAP)

Grade: 12-61-0

Analysis / composition: 12% N-NH4, 26.5% P (61% P2O5)

Formula: NH4H2PO4

Fertilizer: Mono Potassium Phosphate (MKP)

Grade: 0-52-34

Analysis / composition: 22.5% P (52% P2O5), 28% K (34% K2O)

Formula: KH2PO4

Fertilizer: Potassium Nitrate

Grade: 13-0-46

Analysis / composition: 13% N-NO3, 38% K (46% K2O)

Formula: KNO3

Fertilizer: Potassium Sulfate

Grade: 0-0-52

Analysis / composition: 43% K (52% K2O), 18% S (54% SO4)

Formula: K2SO4

Fertilizer: Urea

Grade: 46-0-0

Analysis / composition: 46% N-NH2

Formula: CO(NH2)2

Fertilizer: Potassium Chloride

Grade: 0-0-60

Analysis / composition: 50% K (61% K2O)

Formula: KCl

Fertilizer: Copper Sulfate

Analysis / composition: 25% Cu, 13% S.

Formula: CuSO4*5H2O

 

Organic Fertilizers :

Organic Fertilizers are more commonly called manures. Animal dung and leaves of all kinds are composted to make organic Fertilizers i.e. manure. Manure made of cow dung and leaves after composting is much used by the farmers in India.  Sheep, Camel dung compost is also used in other parts of world. It is a rich source of nitrogen and potassium. Cow urine is also a good bio fertilizer. Vermi compost is another form of manure.  Vermicompost is a concentrated type of organic Fertilizer and so require little quantities to be given.

A mixture of  milk, curds, unclarified butter (ghee), cow dung and cow urine makes for effective rejuvenating bio fertilizer. It is a strong nutrient rich manure for soil and it contains earth friendly microbes.

The author has experimented and used mixture of cow dung, cow urine, besan floor, jaggery and a small fistful unfertilized soil in water and left to compost for until the mixture becomes clear and there is no odor left. This watery mix is then diluted and given to plants as manure.

Vermicomposting can be adopted by the farmers as they would have a constant supply of leaves. Stack alternate layers of leaves and dung, insert earthworms, occasionally moisten stack and covered up. The manure would be ready in about two to three months’ time.

 

 

 

 

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