Mineral fertilizers
FERTILIZERS CHARACTERISTICS
- Concentration:
Fertilizer grade (concentration) is usually expressed as the percentage of N, P2O5 and K2O.
In view of the fact that costs of marketing, shipping, storage and distribution represents a high percentage of the fertilizer price, there is a trend towards the production of high-analysis materials.
This holds true for both straight (simple) fertilizers and compound fertilizers.
- Granulation:
Granulation of fertilizers is greatly improving the ease of handling and storage of hygroscopic and/or dusty products, but decreases the initial effectiveness of water-insoluble materials.
In general, courser granules are advantageous for water-soluble and finer granules for water-insoluble materials.
- Water-soluble:
Especially for phosphatic fertilizers to be used on a potato crop (short growing season crop, relative weak root system) it is necessary for phosphor in these fertilizers is to be water soluble.
- Soil reaction:
Another aspect of importance is the influence of fertilizers on soil reaction. Distinctions can be made between acidic, basic and neutral fertilizers.
FERTILIZER, SOIL REACTION, pH
FERTILIZERS
Main fertilizers used are nitrogen, phosphorus and potassium. Micro-elements become more important when land has been used for a longer time and fertilizer use changes, is reduced or used in excess.
Nitrogen fertilizers
- Nitrates give a quick but short crop response. Under conditions of high rainfall or irrigation on permeable soils,
the NO3 - ion quickly leaches out of the root zone.
Nitrate fertilizers NaNO3 and KNO3 - 16% and 14%are unsuitable for temporarily or permanently water-logged soils (rice). They are an advantage when used as a top-dressing, especially on calcareous and dry soils
- Ammonium salts are subject to volatilization losses as the ammonia (NH3) component escapes, mainly when surface applied on alkaline soils.
- Urea ( 42%N) is an excellent and cheap source of nitrogen. It has a slight residual acidifying effect on soils. Its bacterial decomposition into available nitrogen requires moisture, the reason why dry soils should be irrigated. Substantial losses may occur, when surface applied as a top dressing, particularly during dry weather, or on calcareous soils.Although some plants may show a certain preference for nitrates over ammonia-nitrogen, both fertilizers are equally efficient.
Phosphatic fertilizers
Water solubility is the main characteristic of phosphate fertilizers.
- Water soluble phosphates
are applied shortly before planting to ensure a quick start of the crop. Potatoes have a shallow root system and are highly responsive to water soluble phosphates. These fertilizers can best be drilled in bands near the seed, to reduce contact and avoid reaction with phosphate fixing sites in the soil.
- Citric acid soluble phosphates, like di-calcium phosphate and basic slag, have a low water-solubility and are not very suitable for potatoes, which are a short growing crop. If used they only should be applied on acid soils.
Potassium fertilizers
- Potassium chloride (muriate of potash) and potassium sulphate are the most important potash fertilizers. These are all water soluble and spread quickly through the soil moisture.
- Potassium chloride is the most common fertilizer and is a mixture of sodium- and potassium chloride.The lower grades contain substantial amounts of sodium and chloride per unit of potassium. Chloride has a negative effect on potato yield and dry matter content, the reason why low grade potassium chloride is not recommended for potatoes.
- Potassium sulphate contains no chloride, but is more expensive than potassium chloride fertilizers.
- Potassium magnesium sulphate
The magnesium in this fertilizer is often beneficial on course-textured slightly acidic soils.