These are man made materials used to improve on plant nutrient levels in the soil.
- A good fertilizer should be able to supply the required nutrients readily to the soil.
- It should be easy to handle and store.
- It should be easy to apply.
Advantages of artificial fertilizers:
- They contain a high and definite level of nutrient concentration.
- They are not filthy and therefore are more conveniently to handle and store. However, a few of them are hygroscopic e.g. CAN
- They release nutrients readily in the soil so with in a week there will be a marked difference in the crop.
Disadvantages of artificial fertilizers:
- They are expensive especially the nitrogen fertilizers..
- There application requires some skill.
- They have a short lived effect in the soil.
- They are easily leached from the soil especially nitrogen fertilizers.
- When applied in excess, they become toxic to the plant.
- They can pollute the soil and water bodies e.g. frequent application of a fertilizer can change the soil PH.
Profitable use of artificial fertilizers will depend on the following:-
- Proper analysis of the soil to determine he nutrient level situation.
- Careful assessment of the nutrient requirement of the crop to be grown.
- Application of the right type of artificial fertilizer and at the correct rate.
- Fertilizer application should be combined with other agro-nomic practices if it is to be profitable e.g. pruning, weeding, mulching, irrigation e.t.c.
These are the fertilizers that supply nitrogen as the major nutrient.
Characteristics of Nitrogen Fertilizers:
- They are hydroscopic so can easily form lumps and this makes their storage difficult.
- They are very soluble in water therefore can easily be leached or lost through erosion.
- They are readily absorbed by plant roots.
- They have a short lived effect in soil.
- They promote fast growth of plants.
- Many o them may explode during storage.
- They have scorching effect on the plant especially the leaves.
Examples of Nitrogen Fertilizers.
Ammonium Sulphate (NH4)2 SO4
This contains about 21% Nitrogen and is a fine crystal (paleyellow / light ) its readily soluble in water. It has a rapid action when applied to the crops or fields and the disadvantage it has is that its easily leached out of the soil. It may lead to deficiency of calcium and magnesium in the soil. It has a great acidifying effect on soil.
This contains about 46% nitrogen and that is unique about it is that it can be dissolved in water and sprayed on leaves and plants take it in.
- Has very high nitrogen content.
- Leads to little loss of calcium and magnesium through leaching.
- It can provide both Ammonia and nitrate for plant use.
- It can easily be lost voltalisation inform of Ammonia.
- When applied in excess, it will kill the germinating seedlings and check root growth and development.
- Calcium ammonium nitrate (CAN) NH4 +NO3 +CaCO3
It has between 21 – 25% nitrogen.
- It has a less acidifying effect on soil as compared to the rest of other nitrogen fertilizers.
- It is less expensive than many of the other nitrogen fertilizers.
- It can stored in a large quantities.
- It is hydroscopic so tends to form lumps and this makes it application difficult.
- Ammonium nitrate
- It contain about 34%nitrogen
- It is quick acting.
- It can supply plants both inform of ammonium nitrate.
- It has a great acidifying effect on soil.
- It can easily explode under heat.
- It is highly hygroscopic and this makes it difficult to apply and store.
NPR (NITROGEN PHOSPHATE)
These are light brown granules a compound fertilizer than supplies the three nutrients.
It can supply 3 macro nutrients at the same time.
It is highly hygroscopic there fore not easy to store can easily form a cake are lump making it difficult to apply.
Methods applying nitrogen fertilizers band placement.
It is applied when then crop is already growing usually after the first weeding .it is putting ring a short distance in the crop as far as the branches stretch on top of the soil .
The method can easily be used where crop are widely spread.
The fertilizer is put in the root zone so can easily be taken up by crops.
It minimizes on fertilizer wastage since the fertilizer is applied only where the crop is growing
It discourages growth of weeds both .the crop raws
It is time consuming and labour intensive.
- Top dressing.
This involves dissolving the fertilizer into water before it is applied to the flied much nitrogen fertilizers have a burring affection leaves so should not get in contact. Urea can be sprayed safely on the leaves.
- Drip Application
It is first dissolved in a reservoir then carried through pipes to crops that are in rows. There is a device that will allow the fertilizer to drip out form the pipe in the root zone.
- Irrigation and fertilize application can be done at ago / during the same operation.
- There is no wastage of fertilizer since it will only be applied in the root zone of the crop.
- Doesn’t encourage growth of weed between the crop raws.
- It is expensive to buy and lay out pipes so the method s only recommended for high value crops.
Most poor crop production is mainly due to deficiency of phosphorus and nitrogen.
- They are not very soluble in water therefore can not easily be lost through leaching.
- They have a long residual of effect in the soil.
- Only beneficial when applied to acidic soils. When applied to alkaline soils, they form complex comps that are not soluble in water.
Examples of phosphatic fertilizers (SSP) single, super phosphate.
SSP is a whitish granule with an acidic /nell. It contains between 18 – 22% of the phosphate are has two major advantages.
- It can not be leached from the soil.
- It can supply calcium and sulphur on top of the phosphate.
- It is immobile in soil so it has to be very well worked in.
- It can only be applied before the crop is grown.
- Large amounts of the fertilizer has to be applied since only about 10-20% of what has been applied can dissolve in water and be taken up by crops.
- Double super phosphate (DSP)
It contains between 45-47% of the phosphate.
- Has a high percentage of the phosphate.
- (DAP/Double Ammonium Phosphate:
It contains between 48-50% of the phosphate and about 18% nitrogen.
It is extremely soluble in water therefore has a first acting effect on soil.
- Rock Phosphate CaPO4
It contains about 30% of phosphate.
Characteristics of Potassium Fertilizers:
- They have a scorching effect on leaves and germinating seeds.
- They are very soluble in water so can easily be last through leaching especially from sandy soil.
- They are not very mobile in soil as nitrogen fertilizers but more mobile as phosphate fertilizers.
Potash is usually a abundant (i) clay soils but usually deficient
Application of potash fertilizers:
- Band placement
- Broad casting
Example of potash fertilizers:
- Murate of potash
Factors that cause a soil to lose fertility
- Soil erosion which removes the top soil containing most of the organic maters, soil organisms and nutrients. It also leaves a hard stony soil preventing further infiltration of water into the soil.
- Burning which destroys organic matter and therefore soil structure leaving arch that can easily be carried away by running water.
- It kills beneficial soil organisms.
- It leads to loss of nutrients SNP
- Continuous cropping where land is not allowed to rest under bush fallow. Most of the nutrients are used up from the soil since the crops are harvested and continuous tilling of land will destroy the soil structure.
- Leaching especially in soils that lack organic matte and in sandy soils nutrients will be washed down to lower layers where they can not be used by plant roots.
- Changes in soil Ph which may either increase particular nutrients to toxic levels or lead to some nutrients being fixed and therefore unavailable for plant use.
- It will also affect presence and activity of soil organisms.