1. CS 351 Soil Management & Fertility
FERTILIZERS AND THEIR USE

2. Introduction Outline Introduction Terminology
Straight mixed or compound fertilizers
Superphosphates
Influence of Ammonium sulphate & Urea on soil acidity
Formulation of mixed/compound fertilizers
Fertilizer recommendation
Fertilizer application
Lime and liming
Organic fertilizers and manures

3. Why is it necessary to apply fertilizers?
When agriculture is practised, losses of plant nutrients occur through:
Crop removal and harvesting of crops
Leaching
Soil erosion
Such losses call for fertilizer use

4. Terminology What is a fertilizer?
It is any organic or inorganic material which is added to a soil (or plant) to supply certain elements essential for the growth of plants.
Straight, single or simple fertilizer
A fertilizer that contains only one of the 3 major nutrients – N, P or K
Mixed or compound fertilizer
A fertilizer that contains 2 or all 3 nutrient elements – thus NPK, NP, NK or PK
Straight or mixed fertilizer may contain other nutrients elements than N, P and K (e.g. S, Ca, Mg, Cl, etc)

5. Straight and mixed fertilizers common in Ghana
Straight fertilizers
N fertilizers
- Ammonium sulphate (21% N)
- Urea [(NH2)2CO] (46%N)
P fertilizers
- Single superphosphate, SSP (18% P205)
- Triple superphsophate, TSP (46% P205)
K fertilizers
- Muriate of potash, KCl (60% K20)
- Potassium sulphate (50% K20)

6. Mixed fertilizers , ,
, & others

7. Expression of fertilizer ingredients
By convention nutrient content of fertilizers is given by the percentage by weight of N, P2O5 and K2O contained in the fertilizer.
Conversions
%P = % P205 x 0.43
% P205 = %P x 2.29
%K = % K20 x 0.8
% K20 = % K x 1.2

8. Terminology
Fertilizer grade - Refers to the guaranteed percentage of plant nutrients contained in the mixture. It is stated in the following order: % Total N - % available P2O5 - % water soluble K2O.
A grade labelled would contain in every 100kg, 15kg total N; 15kg available P2O5 and 15kg of water soluble K2O.

9. Terminology
Fertilizer ratio - refers to the relative percentage of N-P-K or the proportion of each constituent in the grade.
A grade of , and would all have the same ratio of
An acid-forming fertilizer is one capable of increasing the acidity of the soil.
A basic fertilizer is capable of decreasing acidity of the soil.

10. Terminology
A filler is a make-weight material added to a mixed fertilizer or fertilizer material to make up a weight difference.
Fertilizer analysis
Fertilizer are commonly sold on the basis of the quantity and quality of their plant nutrients as determined by chemical analysis.

11. Fertilizer analysis
With straight fertilizers the analysis refers to the quantity of “active ingredient” in the fertilizer material.
E.g.
Sulphate of ammonia contains – 21% N and 24% S
Urea – 42-45% N
Single superphosphate – 16 – 21% P2O5
Triple superphosphate – 50% P2O5
Muriate of potash – 48 – 60% K2O

12. Fertilizer analysis
With mixed fertilizers – analysis refers to the composition and concentration of the fertilizers.
Low analysis grade: 15 to 25% total nutrients
E.g or
Medium analysis grade: 25 to 40% total nutrients
E.g or
High analysis grade: >40% total nutrients
E.g , , ,

13. Superphosphates Single superphosphate contains 16-22% P2O5
It contains gypsum (CaSO4) and other impurities.
RP [Ca3(PO4)2] + 2H2SO4 → SSP + 2CaSO4 + impurities
Triple superphosphate contains 42-50% P2O5
High grade RP [Ca3(PO4)2] + 4H3PO4 → TSP + impurities
Note: SSP and TSP are Ca(H2PO4)2 (monocalcium phosphate)

14. Superphosphates
The TSP differs from the SSP in that it contains more phosphorus and no gypsum.
TSP contains 2-3 times the phosphate in SSP.
SSP is desirable for sulphur demanding crops E.g. cowpea, groundnut and soybean.
The high P2O5 content of TSP gives it an advantage where it has to be transported long distances and at considerable cost.

15. Formulation of Mixed/Compound Fertilizers
Examples:
Question 1
Given: Sulphate of ammonia (21% N)
Single superphosphate (18% P2O5)
Muriate of potash (60% K2O),
Formulate a mixed fertilizer containing 5% N, 8% P2O5 and 10% K2O
Calculate the quantities required to give 1000 kg of mixed fertilizer.

16. Solution i.
Since the wt of mixed fertilizer is not specified, the formulation will be based on 100 parts of fertilizer.
21 parts of N are contained in 100 parts of (NH4)2SO4
5 parts of N are contained in 100 x 5/21 = 23.8 parts
(NH4)2SO4
18 parts P2O5 are contained in 100 parts SSP
 8 parts P2O5 are contained in 100 x 8/18 = 44.4 parts SSP
60 parts K2O are contained in 100 parts KCl
 10 parts K2O are contained in 100 x 10/60 = 16.6 parts KCl
Summary
23.8 parts (NH4)2SO4
+44.4 parts SSP
+16.6 parts KCl
84.8 parts mixed fertilizer
+15.2 parts filler
100 parts mixed fertilizer.

17. Solution ii. Required 1000kg of 5-8-10 mixed fertilzer
100 kg of mixture contains 5 kg N, 8 kg P2O5, 10 kg K2O
1000 kg of mixture contains 50 kg N, 80 kg P2O5, 100 kg K2O
21 kg N are contained in 100 kg (NH4)2SO4
50 kg N are contained in 100 x 50/21 = kg (NH4)2SO4
18 kg P2O5 are contained in 100 kg SSP
 80 kg P2O5 are contained in 100 x 80/18 = kg SSP
60 kg K2O are contained in 100 kg KCl
 100 kg K2O are contained in 100 x 100/60 = kg KCl
Summary
238.0 kg (NH4)2SO4
kg SSP
kg KCl
849 kg mixed fertilizer
+151 kg filler
1000 kg mixed fertilizer.

18. Question 1
Given: Sulphate of ammonia (20% N)
Single superphosphate (16% P2O5)
Sulphate of potash (48% K2O),
Calculate the quantities of these various fertilizers
required to give 500 kg of a 4 – 10 – 6 mixed
fertilizer.
What quantity of this mixed fertilizer must be applied
per small plot to supply 2 kg N, 5kg P2O5, 3kg K2O?

19. Solution i). Required 500kg of 4-10-6 mixed fertilzer
100 kg of mixture contains 4 kg N, 10 kg P2O5, 6kg K2O
500 kg of mixture contains 20kg N, 50kg P2O5, 30kg K2O
20 kg N are contained in 100 kg (NH4)2SO4
16 kg P2O5 are contained in 100 kg SSP
 50 kg P2O5 are contained in 100 x 50/16 = kg SSP
48 kg K2O are contained in 100 kg K2SO4
 30 kg K2O are contained in 100 x 30/48 = 62.5 kg KCl
Summary
100 kg (NH4)2SO4
kg SSP
+62.5 kg K2SO4
474.7 kg fertilizer
+25.3 kg filler
500 kg mixed fertilizer

20. Then 5 kg of P2O5 are contained in 500 x 5/50 = 50 kg
Solution ii).
If 20 kg of N are contained in 500 kg of mixed fertilizer
Then 2 kg of N are contained in 500 x 2/20 = 50kg of mixed fertilizer.
Similarly, if 50 kg of P2O5 are contained in 500kg of mixed fertilizer
Then 5 kg of P2O5 are contained in 500 x 5/50 = 50 kg
of mixed fertilizer
(Also 3 kg of K2O are contained in 500 x 3/30 = 50 kg of mixed fertilizer)
Note:
If 4 kg N, 10 kg P2O5, 6kg K2O are contained in 100 kg of mixture, then 2 kg N, 5 kg P2O5, 3kg K2O will be contained in 50 kg of mixture,

21. Fertilizer recommendation
Supposing a farmer has been advised to apply:
kg N, P2O5 & K2O /ha of Cassava
kg/ha Sugarcane
Available materials:
Sulphate of Ammonia - 20% N
T.S.P % P2O5
KCl % K2O

22. Solution: i).
20 kg of N are supplied by 100 kg sulphate of ammonia.
 75 kg of N are supplied by 100 x 75/20 = 375 kg sulphate of ammonia
45 kg P2O5 are supplied by 100 kg T.S.P.
60 kg K2O are supplied by 100 kg KCl
85 kg K2O are supplied 100 x 85/60 = kg KCl
Total = kg mixture /ha
NB. These three quantities of straight fertilizers are mixed and applied to a hectare of Cassava without adding a filler.

23. Solution: ii).
20 kg of N are supplied by 100 kg sulphate of
ammonia.
80 kg of N are supplied by 100 x 80/20 = 400 kg
sulphate of ammonia
45 kg P2O5 are supplied by 100 kg TSP
60 kg P2O5 are supplied by 100 x 60/45 = kg
TSP
60 kg K2O are supplied by 100 kg KCl
120 kg K2O are supplied 100 x 120/60 = 200 kg KCl
Total = kg mixture /ha
NB. These three quantities of straight fertilizers are mixed and applied to a hectare of sugarcane without adding a filler.

24. Fertilizer application
For efficient fertilizer application, it is necessary to consider
the selection of the right kind of fertilizers
rate
timing of application
method of application
The general factors that influence the selection, rate, timing and method of fertilizer application are:
a. Crop characteristics: - its nutrient demand
and its growth pattern
b. Soil Characteristics
c. Properties of the fertilizers
d. Climatic conditions
e. Economic considerations

25. Rate of fertilizer application
This is one of the most important parameters in fertilizer application technologies.
Various approaches are used for the determination of the rate of application:
Soil testing
Plant tissues analysis (particularly for perennial crops)
Field experimentation

26. Timing of Fertilizer application
Generally early application is better than late application.
When fertilizer is applied early, it accelerates the growth of the crop and increases root volume.
Split application of N fertilizer is generally recommended, since the amount of N fertilizer is usually large and losses may occur before it is absorbed by the crop.
In most cases the first dose (basal application) is given at planting and the 2nd dose (topdressing) is given about 4 to 6 weeks after the basal application.
P and K fertilizers are applied as single dose at planting or before planting.

27. Methods of fertilizer application
The proper placement of fertilizer is as important as choosing the correct fertilizer material. This is because proper placement -
minimizes losses by leaching, denitrification or conversion to unavailable forms.
enhances efficient and ready uptake by the roots of plants.
prevents salt injury or damage to the seedling.

28. Geometry of fertilizer placement
The geometry of fertilizer placement can be classified from two different angles:-
Localised placement
a. Horizontally
Broadcasting
b. Vertically
Surface application
Sub-surface application

29. Methods of placement into: Broadcasting
Generally methods of fertilizer placement are grouped
into:
Broadcasting
Localized placement in relation to the seed or plant.
1. Broadcasting: - includes all methods involved in the application of fertilizer uniformly over the surface of the soil. The fertilizer may or may not be subsequently worked into the soil.
Without crops i.e. before ploughing and planting.
With crops on the field. i.e. side dressing or top dressing
Broadcasting is easy but one of the least effective methods, particularly in cropping systems where plant density is low. In such situations, weeds compete with crop for fertilizer.

30. Localized placement – with special reference to the
seed or plant. Method requires more labour.
a. Band placement - fertilizer is placed in bands to one or both sides of the seed or plant. This is usually done in a definite space relationship to the plant or seed – usually 2-3 inches (5 – 7 cm) to the side and 2 inches (5cm) below the seed or plant.
5 – 7 cm
5 cm
Fertilizer
5 cm

31. b. Ring placement
Fertilizer
c. Point placement
Fertilizer ==

32. Lime and liming
Definition: In agriculture, the term – Liming means the addition to the soil of any calcium or calcium – and magnesium-containing compound that is capable of reducing acidity.
NB. Lime from strictly chemical standpoint refers to one and only one compound – Calcium Oxide.

33. Liming materials
The commonest compounds used in order of effectiveness are the following:
CaCO3 Equivalent
Calcium oxide, (CaO) 179
Calcium hydroxide, Ca(OH)2 136
Dolomite, CaMg(CO3)
Calcium Carbonate (limestone 100
Calcium silicate slag, CaSiO3 86

34. CaCO3 equivalent
Refers to the strength of the liming material in terms of CaCO3. i.e. its CaCO3 equivalent neutralizing value (where the effectiveness of CaCO3 is taken as 100).
The CaCO3 equivalent makes it possible to compare easily the neutralizing value of different compounds used in liming.
E.g. We can say that every 100kg of CaO is equivalent in neutralizing capacity to 179kg CaCO3.

35. Organic Fertilizers and Manures
These include all materials through which plant nutrients and organic matter may be added to the soil.
Organic manures – are composed mainly of wastes and residues from plant and animal life. E.g. FYM
Organic fertilizers – are usually wastes from industrial processing of parts of plants or animals. E.g. Bone meal, Dried blood, Fish meals.
The use of organic fertilizers and manures under tropical conditions is influenced by:
High temperatures which tend to encourage rapid decomposition and slow down the build up of O.M. in the soil.
The large quantities required to provide the total nutrients needed by plants in view of the generally low content of nutrient elements.

36. Organic Fertilizers and Manures
The bulkiness of organic materials in volume and weight which lead to transport and storage problems, demands that organic materials be used in areas close to where they are produced.
The inadequacy of organic materials
Competition for materials in alternative or
substitute uses:
E.g. - cowdung for fuel and building
- fish meal for human & livestock feed
- crop residue for livestock feed.
NB. These points should be considered in discussing the role of organic fertilizer/manures in Ghanaian Agriculture.

37. Role of organic fertilizers and Manures
Improve soil physical properties
encourage granulation or good structure formation for aeration and infiltration
reduce plasticity and cohesion, (features of importance in clayey soils)
increase water-holding capacity
reduce susceptibility to erosion in sandy soils

38. Role of organic fertilizers and Manures
Improve cation exchange capacity of mineral soils. Rapid decreases in organic matter results in sharp reduction in the CEC.
Supply and enhance the availability of plant nutrients in soil, particularly N, P, S and micronutrients.
Prevent leaching losses of nutrients (particularly micronutrients) by forming complexes.

39. Conclusion
It is in connection with some of these benefits that organic fertilizers and manures are of great importance in the maintenance of soil fertility.
Different organic manures have different contents of nutrients and thus provide different amounts of nutrients on decomposition.
Their composition therefore indicate their potential as manure or fertilizer, their efficiency and also suggest their management.