Fertilizers

Natural fertilisers

• Organic matter/Green manure (unprocessed matter/unprocessed plant matter; whole plants)
• Compost/Humus (plant matter/feces in progress of processing/processed plant matter/feces)
• Compost tea (made with green manure)
• Animal manure/guano (unprocessed, is processed to humus in the soil)
• Night soil (unprocessed human manure, can cause illness so is banned in most countries)
• Bokashi liquid fertiliser (made from any kitchen scraps)
• Fermented animal/human urine
• Fermented manure/water mix
• Fermented plant/water mix
• Biochar
• Leaf Mold
• Limestone
• Seaweed

Chemical fertilisers

• Ammonia
• Ammonium nitrate
• Lime
• Urea
• Struvite

Organic fertilizers

Organic fertilizers are important as they:

• Improve the structure of the soil. On heavier soils de the adhesion of the particles is reduced so that the manipulatability is improved. On light soils, the adhesion between the particles is increased so that a stable crumb structure is obtained.
• Increase the water-holding capacity of the soil
• Promote soil life: soil organisms use organic materials as food
• Contain plantfeeding elements: the mineralization occurs slowly and is spread over several years (up to 3 years after administration), thus only a part is directly absorbable by the plant. The organic nitrogen compounds are first converted to ammonia and then further converted by microorganisms to nitrate, which is absorbable by the plant.

Soil improvers

As soil improvers, the following are usable:

• Compost
• Stable manure
• Green manure

These soil improvers also contain plant food, but in many cases it will be necessary to also use concentrated fertilizers. In the private garden, we can best work with concentrated, organic, slow-acting fertilizer like blood meal, bone meal, horn meal instead of fast-acting fertilizers.

Concentrated organic fertilizers

The shortage in certain nutrients can often not be remedied with the use of compost and old stable manure. We will then need to resort to fertilizers that contain specific nutrients in higher concentrations.

Manure, compost and wastes

When and how to fertilize

The timing: depends on the soil type. Sandy soils are best foreseen of compost or old manure in february. On clayish soils this is best done in autumn. When we would fertilise sandy soils in autumn, a large part would be rinsed to deeper soil layers, where it is unreachable by the plant roots. This is an issue specific to light/sandy soils due to their already loose structure. On clayish soils with a a dense structure, the trough-flushing is low. By already fertilising in autumn, the clods produced by the soil improver can freeze-break in winter.

The digging-in of the manure. In most gardens the manure is simply dug in, this is however not recommended. By simply digging-in, we destroy many of our soil organisms. Each type of micro-organism lives at its own depth in the soil. By digging and turning the soil around, we bring the topsoil a depth where many micro organisms suffocate. A good way to process manure and compost, without disturbing the soil too much is to dig shallowly. It is sufficient to dig in the fertilizer in the 5 to 10 cm-layer under the soilsurface.

Artificial fertilizers

Nitrogen: several N-compounds exist: - Nitric N: works fast, but washes out easily - Ammoniacal N: works slow (needs to be converted to nitrical first), washes out less easily (locked to clay-humus-complex) - Urea N: works rather slow (needs to be converted to ammoniacal and then to nitric N first) - Amidic N: works very slow (needs to be converted to ureum, then to ammoniacal, and then to nitric N first)

Phosphor cycle

Phosphor: phosphor= directly absorbable by H₂PO₄^- (phosphate)

For magnesium limes: see lime and soil improvers

• If the base-equivalent is negative, the fertilizer is acidifying

Complex compound fertilizers

Complex compound fertilizers contain NPK (Mg) in each pellet. eg: 10-15-20(5) means 10% N, 15% P, 20% K, 5% Mg

Calculation of quantities

Eg: A crop like cauliflower requires 3 kg of N per are 100 kg of ammonia contains 20 kg of N 10 kg of ammonia contains 2 kg of N To obtain 3 kg of N, we thus need to provide 15 kg of ammonia.

Workings of lime in the soil

• Structure: Ca makes heavy clayish soils less stiff, and improves the coagulation.
• pH: lime fertilizers increase the pH when the soil is too acidic
• Enriching of the soil with N: a reduction of the level of acidity promotes the development of N-binding bacteria , hereby improving the the binding of N
• Mobilization of plant nutrition: the present food supplies are rendered absorbable

At a low pH, the uptake of N, K, Mg, S decreases and the solubility of trace elements is increased with a too acidic pH. At a high pH, the uptake of Fe, Mn, Cu, Zn decreases.

Liming is more focused on improving the soil structure and soil pH then the supplying of crops with Ca.

Lime fertilizers

• Slaked agricultural lime powder Ca(OH)₂: abv= 50-60
• Calcium carbonate lime such as marl lime, chalc, carbonated agricultural lime CaCO₃ abv= 35-52
• Calcium and magnesium carbonates such as dolomitic lime MgCO₃ and CaCO₃ abv= 45-60
• Magnesium lime powder Mg(OH)₂ -Ca(OH)₂ abv= 50-60
• Foaming soil CaCO₃ abv= 20-40

Acid binding value

In a liming advise, the lime dosage is given in kg abv per ha. Eg: calcium dosage of 1000 kg abv per hectare, with the use of agricultural lime powder with a abv=50 means the administration of 2000 kg/ha .

When to administer

Repair liming: When the pH is too low and a lot of lime needs to be administered, it is best done in late summer or autumn, and spread over 2-3 years. The lime needs to be scattered and well mixed with the soil. Maintenance liming: slight limings to supplement the lime store is best done in early spring after plowing and then well mixed.