How can I provide enough nutrients for my crops by supplying organic material?

1. Nitrogen:

• The supply of nitrogen (N) in organic farming is usually provided by legumes. Through a symbiosis with nodule bacteria, these plants are capable of fixing atmospheric nitrogen and making it available to plants.
• There are other bacteria that can also fix nitrogen (Actinomyceten which are present in dead wood, soil-bound Azotobacter or Beijerinckia bacteria, which live in association with the tropical fodder-grass Paspalum notatum and other Gramineen).
• In paddy rice, the bacteria Anabena azollae is used, which forms a symbiosis with the water fern Azolla, and CAN, under tropical conditions, fix up to 400 kg N/ha and year, and which is very often used as a green manure for rice crops.

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2. Phosphorous

• The phosphate content of the soil vary just as much as the availability of phosphates (P) for the plants (e.g. tropical soil with its high acid, iron and aluminium content has a very high rate of P fixation, thus applied P-fertilisers become unavailable for the plants).
• On organic farms emphasis is placed upon increasing the availability of the phosphate content of the soil for the plants. This is achieved by a biological conversion of unsoluble to soluble P-compounds in the soil (enzymes and plant acids):
• Fertile soils with a high organic substance content encourage the growth of VAM, a fungus that lives in a symbiosis with plants having a high capacity to dissolve fixed P-compounds.
• Use of plants that are particularly capable to break up fixed P- compounds (e.g. onions in mixed crop systems with cotton, palms and vanilla in agroforestry systems).
• Organic matter (mulching material, compost) increases the availability of Phosphates.
• High pH values and poor phosphate availability can be alleviated by applying silicates.

3. Potassium

The following strategies are important in organic farming to ensure a sufficient supply of K for the plants:

• Regular applications of organic matter will improve the absorption of potassium in the upper soil layers, where it can be reached by the plants’ roots.
• Use of deep-rooting plants to mobilize K in lower soil layers.
• Integration of plants with a high K-uptake in mixed cultivation systems (e.g.bananas on coffee plantations).
• A permanent mulching layer, especially in the wet tropics in order to reduce leaching of K.
• In arid regions with soils poor in K, it can be useful to mix pulverized rock containing mineral clay into the compost (e.g. as. practised in Egypt, Israel).

In case of potassium deficiencies showed by soil analysis it is permitted to use certain potassium salts with a low chlorine content (Muriate of potash/ potassium chloride is not allowed). Wood ash from untreated wood is also allowed .