Which fertilizers are used in organic farming?

How is fertilization used in organic farming?

Material cycles and fertilization in organic agriculture

In stable natural ecosystems, the material cycles are largely closed. Humus degradation and humus build-up from dead plant parts and animal excrement are roughly in balance. In organically managed farms, attempts are made to close material cycles. However, due to the sale of plant and animal products, this is not possible for all material cycles in the company. So reinforced z. B. the associated removal of bases, the slowly progressing natural soil acidification. Sustainable soil management must counteract this process through regular liming. Unavoidable nutrient losses can partly be supplemented naturally through the weathering of the soil's own minerals and through biological nitrogen fixation. Organic farmers promote these processes, e.g. B. by growing suitable catch crops. These are grown between two main crops and are not harvested. Instead, they are worked into the soil as green manure. Nutrients that cannot be supplemented in this way must be supplied from the outside as required.

Legumes as a natural source of nitrogen

For organic agriculture, pulses (legumes) are the most important source for naturally introducing nitrogen into internal business cycles. These are fodder legumes (e.g. in perennial clover or alfalfa grass), catch crops (e.g. vetch in a mix with non-legumes) and grain legumes as fodder or as food (broad beans, peas, lentils, soybeans). The roots of the legumes live in symbiosis with Rhizobium bacteria, which can fix nitrogen from the air. In the root nodules, this nitrogen is converted into amino acids and is thus available to the host plants. The annual nitrogen fixation can be between 65–150 kg / ha for grain legumes and up to over 300 kg / ha for fodder legumes [2]. When legumes are grown as catch crops, nitrogen fixation in the very short vegetation period after a main crop is very variable, but can be up to 150 kg / ha in individual years [3]. With the remaining root mass or the incorporation of the plant into the soil, the nitrogen nourishes the subsequent crop.

Humus management as the basis of plant nutrition

Humus plays a key role in soil fertility. Elements of humus management, with which humus is preserved and increased, are sensible crop rotations from main crops and catch crops with balanced proportions of humus-increasing and humus-consuming crops as well as adapted organic fertilization. As farm manure, fertilizers of organic origin come primarily from the farm's own production. The manure comes first, but manure and liquid manure are also used. The amount of manure produced is of course limited due to the area-based animal husbandry in organic agriculture. Only in organic vegetable cultivation may more organic nitrogen be fertilized to cover the very high, short-term nutrient requirements than in other arable crops.

The purchase of fertilizers of organic origin, especially those of non-ecological origin, is strictly regulated. Sewage sludge and garbage compost are strictly prohibited for reasons of hygiene and because of potential contamination with heavy metals and organic pollutants. The use of organic compost (from separate collections), green waste compost and peat substitutes is permitted by some cultivation associations after prior analysis for pollutants [4; 5]. In addition to the humus and nutrient effects, compost also naturally suppresses fungal plant parasites [6].

Mineral fertilization only for need-oriented nutrient supplementation

Certain mineral fertilizers are also allowed in organic agriculture to supplement nutrient stocks in the soil. The phosphorus intake is of particular importance in companies with negative phosphorus balances [7]. Phosphorus deficiency can have significant undesirable effects on biological nitrogen fixation [8]. Against the background of the world's very limited phosphate deposits, however, the return of phosphates from waste products and wastewater must be discussed as an important means of closing regional cycles in organic agriculture - especially with regard to undesirable secondary components, heavy metals and organic residues in compost and recycling fertilizers.

Other mineral fertilizers permitted in organic farming are rock flour, lime, potassium sulfate, various naturally occurring minerals, sulfur and trace element fertilizers. The use of some of these fertilizers is only permitted if there is a proven need based on soil analyzes, plant observations and nutrient balances as well as after consultation with the advice or control body.

Chemical-synthetic nitrogen fertilizers (ammonium, nitrate) as well as Chile nitrate and urea are prohibited in organic agriculture. Highly soluble phosphorus fertilizers (e.g. triple superphosphate), which are produced from rock phosphates by digestion with acids, are also taboo [9]. In the restrictive use of mineral fertilizers, the difference to fertilization in conventional agriculture becomes particularly clear.


[1] Mäder, P. et al. (2002): Soil fertility and biodiversity in organic farming. Science 296, pp. 1694-1697,

[2] Coyne, M.S. (1999): Soil Microbiology: An Exploratory Approach. Delmar Publishers, Columbia, p. 365.

[3] Müller, T. and Thorup-Kristensen, K. (2001): N-fixation of selected green manure plants in an organic crop rotation. Biological agriculture & horticulture 18, 4/2001, pp. 345–363

[4] Bioland (2012): Bioland guidelines. Bioland e. V. Association for organic-biological agriculture, Mainz.

[5] Naturland (2012): Naturland standards. Naturland e.V., Graefelfing.

[6] Schüler, C., Biala, J. and Vogtmann, H. (1998): Antiphytopathogenic properties of biogenic waste compost. Agriculture, Ecosystems & Environment 27, pp. 417-482.

[7] Lindenthal, T. (2000): Phosphorus stocks in soils, operational phosphorus balances and phosphorus supply in organic farming. Dissertation, Institute for Organic Agriculture, University of Natural Resources and Life Sciences, Vienna.

[8] Römer, W., J. Gerke and P. Lehne (2004): Phosphate fertilization increases nitrogen fixation in legumes. Ecology & Agriculture 132, 4/2004, pp. 37-39

[9] Regulation (EU) 889/2008 Annex I.