Mixed Fertilizer

Mixed fertilizers

         "Mixed fertilizer" means a commercial fertilizer containing any combination, blend, or mixture of fertilizer materials designed for use or claimed to have value in promoting plant growth. When two or more fertilizers are mixed together to supply two or three major elements i.e. N, P2O5 and K2O is known as fertilizer mixture or Mixed fertilizer.  Or A mixture of two more straight fertilizer materials is referred to as fertilizer mixture. Sometimes, complex utilizes containing two plant nutrients are also used in formulating fertilizer mixtures. Complete fertilizer refers to the fertilizers containing 3 major plant nutrients, N, P2O5 and K2O.

Types of fertilizers: There are two types of fertilizer mixtures:

         a. Open formula fertilizer mixtures: The formulae of such fertilizers in terms of kinds and quantity of the ingredients mixed are disclosed by the manufacturers.

         b. Closed formula fertilizer mixtures: The ingredients of straight fertilizers used in such mixtures are not disclosed by the manufacturers.

Materials used in fertilizer mixtures: Different materials go in to production of mixed fertilizers. In accordance with their principle function in the mixture, the materials can be grouped into:

1.         Suppliers of plant materials: These are the straight fertilizers added to supply the plant nutrients mentioned in the grade, thus, are the primary materials most essential for preparing mixed fertilizers.

2.         Conditioners: These are the organic substances which prepare the fertilizer mixture in good drilling condition and reduce caking. E.g.: Tobacco stems, Peat, Groundnut hulls and paddy hulls (Husks), bone meal, oilcakes.

3. Neutralizers of residual acidity: The substances used to neutralize the residual effects are known as neutralizers. For example, if the ‘N’-ous fertilizers used are acidic in nature like Amm. Sulphate, Urea, a basic material like lime stone is added to counteract the acidity.

4. Filler: Filler is the make – weight material added to a fertilizer mixture. It is added to make up the differences between the weight of the added fertilizers required to supply the plant nutrients and the desired quantity of fertilizer mixture, such as sand, soil, ground coal ashes, sawdust and other waste products.

5. Secondary and micro – nutrients: Some times, secondary and micro – nutrient carrying fertilizers are added to correct its deficiency. An expression indicating the % of plant nutrient in a fertilizer mixture is termed as fertilizer grade and the relative proportion of major plant nutrients in the mixed fertilizer taking ‘N’ as one, called as fertilizer ratio. For example, in a fertilizer mixture of 6:12:6 grades, the fertilizer ratio is 1:2:1.

         The low analysis fertilizers contain less than 25% of primary nutrients and the high analysis fertilizers contain more than 25% of primary nutrients. On the other hand, the low analysis mixed fertilizers contain less than 14% sum of the primary nutrients and high analysis mixed fertilizers contain more than 14% sum of the primary nutrients.

         For over hundred years the mixed fertilizers are in use besides straight fertilizers.  Many fertilizer mixtures are made available now and this account for a major portion of the consumption of N, P and K.  Present day statistics show that numerous grades of fertilizers  mixtures  are  manufactured  and  the  fertilizer  mixing  industry  is  being considered as one of the major agro- industry.

         The  following  are  some  of  the  common  term  frequently  used  in  the  mixed fertilizer industry.

Fertilizer : The substance which is used for the supply of plant nutrients

Mixed  fertilizer  : A mixture of more  than one straight  fertilizer which can supply more than one plant nutrient element

Complete  fertilizer  : A single  fertilizer material containing  the entire  three major plant nutrients viz, N, P and K

Fertilizer  grade  :  This  refers  to  the  minimum  guarantee  with  regard  to  the  nutrient content of the fertilizer mixture in terms of N, P and K.

Fertilizer  formula  :  This  related  to  the  quantitative  expression  of  the  analysis  of  the different ingredients included in the mixed fertilizer in terms of N, P and K. 

Fertilizer  ratio  :  This  indicates  the  relative  percentage  of  N,  P2O5 and K2O  in  the manure mixture.

Acidic  fertilizer  :  Fertilizer  capable  of  increasing  the  acidity  of  the  soil  by  continued applications. 

Basic  fertilizer  :  Fertilizers which  increase  the  pH  and  the  soil  on  continued  use  by leaving a basic residue in the soil.

Neutral fertilizer : Materials which are neither  increasing nor decreasing  the pH of  the soil

Filler :   It  is called as  the  ‘make-weight’ material added  to  the  fertilizer mixtures. Filler materials  are  inert materials  like  sand,  saw  dust  etc,  are  added  to make  up  the difference between weight of  ingredients added  to supply  the plant nutrients  in a  tonne and the final weight viz., 1,000 kg.

Advantages

         All  the  three major  plant  nutrients  are made  available  in  one  and  the  same material.  There  is saving of  time and  labour. The residual effects will not be there.  The fertilizer mixtures are usually prepared taking into account the acidic or alkaline nature of  the ingredients,  and  other  chemical  reactions.   Hence,  some  of  the  residual  effects  like acidity will not be there.  Usually mixed fertilizer are prepared to suit a group of crops and soils.

Disadvantages

         Specific  needs  of  crops  and  deficiency  of  individual  nutrient  elements  cannot  be satisfied by using mixed fertilizers as efficiently as in the case of straight fertilizers.  

         The use of mixed  fertilizer  in such cases of specific needs will be a waste as other nutrients are also added to the soil.  

         Unit  cost  of  the  various  nutrients  contained  in  the  mixed  fertilizer  will  always  be higher  when  compared  to  the  unity  cost  of  nutrients  contained  in  the  straight fertilizers.

Improper  mixing  and  storage  of  fertilizers  can  result  in  large  nutrient  losses.  Some important aspects to consider in fertilizer mixing and storage include the following:

•  Urea  should not be mixed with ammonium  calcium nitrate  (CAN), KCl, SSP or TSP. 

•  Urea  can  be mixed with most  other  fertilizers  but  fertilizer mixtures  containing urea should be applied  immediately after mixing. Do not store  fertilizer mixtures containing urea. 

•  Ammonium  phosphates  and  super  phosphates  should  not  be mixed with  lime, slag, rock phosphate or CAN. 

•  Potassium chloride and sulfate of potash can be mixed with most  fertilizers, but mixtures of  these  fertilizers with urea and calcium ammonium nitrate should not be stored. 

•  CAN  should  not  be mixed with  basic  slag  but  can  be mixed with  urea,  single superphosphate, and ammonium phosphates immediately prior to application.

Do not store  fertilizers  in damp or dirty places. Make sure  that bags of  fertilizer  in  the store do not absorb moisture from leaky roofs or water seepage through walls and floors.

Preparation of mixed fertilizers

         Many kinds of materials are used  in  the manufacture of  fertilizer mixtures. The materials  are  found  to  be  highly  varying  in  their  properties. However,  only  a  limited number  of  materials  are  being  used  like  (NH4)2SO4,  CO(NH2)2,  Super  phosphate, ammonium phosphate, muriate of potash, limestone, gypsum and some fillers.  

         The  manufacture  of  fertilizer  mixtures  usually  involves  the  weighing  and proportioning of ingredients that are used,  sieving and sizing of the various ingredients, mixing  the  different  materials  and  packing.  All  the  above  operations  are  done  both mechanically and by hand operation.  Different kinds of machineries are being used.

Guide for mixing

To  determine  the  amount  of  individual  fertilizer  in  a  mixture,  the  quantity  is calculated as follows.

                               (Percentage of plant nutrient desired   in the mixture)  x (Weight of final mixture) 

 Quantity    =            ___________________________________________________________________                       

                                 (The Percentage of the plant nutrient in the straight fertilizer)  

                                                                                 R x    T

                                                               A   =            _____________            

                                                                                 P

 R   =  Percentage in the mixture,   T  =  Final weight of the mixture, P  =  Percentage in the straight fertilizer.

         To prepare a mixture of 10: 5: 10 using  (NH4)2SO4,  (20% N), Super phosphate  (16% P2O5) and muriate of potash  (60% K2O),  the  following quantities will be  required per tonne  (1,000 kg).

                                                              10x   1000                                                                           1.  Ammonium sulphate   =            ____________              = 500 Kg.

                                                                   20

                                                            5 x   1000 

     2.  Super phosphate  =                ______________              = 312.5 Kg.

                                                           16  

                                                          10 x   1000

    3.  Muriate of potash =      ________________             = 166.5 Kg.

                                                                   60  

 Total  =   979.0 Kg.

Filler   = 1000 – 979 = 21 Kg.  

 If the total calculated weight exceeds the final weight, a mixture of that ratio can not be prepared.

         Changes that occur while manufacturing mixed fertilizer.  The  ingredients  used  in  fertilizer  mixtures  vary  widely  in  their  physical  and chemical characteristics. When such widely varying materials  in physical and chemical properties are mixed together, naturally many changes are expected to take place during or  after  the  mixing.  Some  changes  will  be  of  physical  nature  and  some  will  be  of chemical nature.   The  following are  the most  important physical changes  that will take place during or after the mixing of fertilizers.

 Hygroscopicity 

         It is a property of any substance which absorbs  from air and gets converted  to semi- solid or liquid condition.  Fertilizer like Ca(NO3)2, NH4NO3, NaNO3 and CO(NH2)2 are  capable  of  absorbing moisture  from  air  and  become  hygroscopic. In  such  cases handling will be very difficult for such mixtures.

Caking up

         Moisture  present  in  some  of  the  ingredients  is  responsible  for  caking  up.  Moisture dissolves some of the easily soluble ingredients and forms a saturated solution.  This  saturated  solution  on  evaporation  gives  out  crystals  which  knit  together  forming larger lumps.  

         The caking up can be prevented by the use of certain kind of materials called as ‘conditioners’.  The  commonly  used  conditioners  are  groundnut  hulls,  lime,  clay  etc.  Another was of preventing the caking up is manufacture of granulated fertilizer mixture. The granulation aims at preparation of uniform sized particles with  reasonable stability, which presents caking up.

Segregation

         This  relates  to  separation  of  different  sized  particles  individually. When ingredients of different sizes and densities are included there will be the tendency for the segregation  (sorting  out  to  different  sizes)  to  take  place. To  prevent  this  bad  effect, granulation is conveniently followed. 

         The  following are some of  the most  important chemical changes  that  take place either during or after the manufacture of fertilizers mixtures. These changes are found to be influenced by temperature, moisture content and particle size of the in gradients.  

(a) Double decomposition

         The  reaction  is  between  two  compounds  without  a  common  ion  in  the presence  of  moisture. New  compounds  are  formed  which  may  have  different physical and chemical properties.

         Ca(H2PO4)2   + (NH4)2SO4    ------->      CaSO4   + 2 NH4 H2 PO4

         NH4 NO3   + KCl    ----------->      NH4 Cl  + KNO3

         (NH4)2 SO4 + 2 KCl  ----------->       2 NH4 Cl  + K2 SO4

(b) Neutralization

         This  reaction  takes place when  free acids present  in  some of  the  fertilizers are neutralized by alkalis or Ca containing salts included in the mixture.     

         H2PO4   + NH3  ----------->  NH4 H2 PO4  

         2H3 PO4 + CaCO3  ---------> Ca (H3 PO4)2   + H2CO3

(c) Hydration

         The  process  of tying up of water by the anhydrous form of salts is called hydration.  Some of the fertilizers are found to have this property.

   CaSO4  + 2H2O -------------> CaSO4 .2 H2O

   Ca HPO4  + 2H2 O  ----------> CaHPO4. 2 H2O

(d) Decomposition 

         Under certain conditions of moisture and temperature, there will be break down in the composition of molecules forming new compounds.

     CO(NH2)2 + H2 O  ----------->       2 NH3   + CO2 

         (NH4)2 HPO4   ----------->  NH4H2 PO4   +   NH3

 However,  the  following  important  principles  must  be  taken  into  consideration  while preparing mixed fertilizers.

1. All  fertilizers  containing  ammonia  are  not  mixed  directly  with  the  basic fertilizers (e.g. RP, limestone, basic slag, CaCN2) as reaction will take place resulting in the loss of gaseous NH3.

2. The water  – soluble phosphates are not mixed with those materials which contain free lime (e.g) lime stone, CaCN2) as  there will be reaction  towards the reversing of water – soluble phosphate to water – insoluble phosphates.  

3.  Hygroscopic fertilizers are not included as they will facilitate caking up.

4. The  acidic  fertilizers  are  likely  to  produce  some  free  acids  which  may damage the container or packing materials.

Manufacturing process

         The principal steps  in the manufacture of solid mixed fertilizers are calculating, weighing, sieving, sizing, mixing the materials and packing the product.

Calculating and weighing 

         With  a  good  weighing  device  the  calculated  quantities  of  the  various ingredients are weighed accurately for preparing mixtures.

(1) Seiving and sizing 

         If the raw materials have undergone too much of caking in the storage piles, it may be necessary  to subject  them  to preliminary grinding, sieving and sizing. The raw materials must be converted into uniform sized particles to have effective making and to avoid segregation during subsequent handling.

(2) Mixing 

         Many  kinds  of  fertilizer  mixing  machines  have  been  proposed  and  used  at  present. Rotary drum type is found to be more common than the vertical cylinder type.  Weighed quantities of different materials are introduced into the mixer and mixed thoroughly.

(3)  Packing 

         Equipments for packing fertilizer mixture range from the simplest types of hand operated facilities to highly sophisticated automatic machines. 

Granular mixtures

         Compared  to  pulverized  or  powdered  mixture,  the  advantages  of  granular mixtures are reduced caking up tendency, less dusting loss and easy handling.  Of late, attention is found in the manufacture of only granular mixtures.

1. All-Purpose Fertilizers

         The main ingredients in all-purpose fertilizers for use on gardens and potted plants are chemical or natural sources of nitrogen, phosphorous and potassium. A water-soluble plant food with the ratio 24-8-16 contains 24 percent nitrogen, 8 percent phosphorous and 16 percent potassium. The remainder of the mix is filler or trace nutrients. One tablespoon of this fertilizer would be mixed with 1 gallon of water and applied every seven to 14 days when plants are actively growing. A time-release fertilizer to be worked into the soil every three months will have a different fertilizer analysis, such as 10-10-10.

2. Lawn Fertilizers

         Mixed lawn fertilizers are typically sold in granular forms or as liquids that are applied when irrigating. For granular fertilizers, apply according to label directions, using a drop or cyclone spreader. Apply half the amount of fertilizer in one direction across the lawn, and then spread the remaining fertilizer in the other direction to avoid missing patches of lawn. Liquid fertilizers are often sold in a bottle that attaches to a garden hose and automatically dilutes the fertilizer as the lawn is watered. Lawn fertilizers contain high percentages of nitrogen and low levels of phosphorous. Typical ratios include 32-0-4 and 29-2-3.

3. Special Plant Foods

         Different types of plants have different fertilizer requirements. A time-release food for shrubs might have a fertilizer ratio of 18-6-8 with traces of minerals like magnesium, copper and iron. Rose mixes contain higher amounts of phosphorous with similar proportions of nitrogen and potassium, such as a 9-18-9 or 18-24-16 ratio. Vegetables can usually be fertilized with all-purpose plant foods, although there are specific mixed fertilizers for a few plants. Tomato food, for example, has a fertilizer ratio of 18-18-21 and can be used on other vegetables as well.