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Organic vs mineral fertilisers

Fertilisers

Fertilisers are applied to crops and ornamental plants to promote plant growth. The main nutrients they provide are nitrogen, phosphorous and potassium as well as a range of trace minerals. They can be applied to plants through the watering regime or as a foliar spray. Fertilisers are generally classed as either organic or inorganic, however in many cases a blend of organic and inorganic sources is used. There is a lot of debate on the benefits of organic versus inorganic food and produce at the moment, we will highlight some of the issues and try to give you a better understanding of them.

Mineral Fertilisers

Mineral fertilisers are synthetically produced or mined and are designed to provide rapidly available nutrients. They are blended differently dependent on the type of crop to be grown and are made from a huge range of specific fertilisers. Some of the popular mineral fertilisers used to make complete fertilisers are calcium nitrate, mono-ammonium phosphate and magnesium sulphate. These are actually used as supplements on their own in some cases where plants may be exhibiting specific nutrient deficiencies. For details about specific mineral elements and their roles in plant health see our Nutrients and Their Functions table. Mineral fertilisers are usually produced via unsustainable methods, with phosphorous and potassium being mined and extracted from salt lakes which are both finite resources. Nitrogen, which is the most widely used element in fertilisers, is commonly made artificially using fossil fuels (coal and natural gas), these again are limited resources. There are studies being conducted to allow these artificial nitrogen fertilisers to become more sustainable, however this is a long way off.

Organic Fertilisers

Organic fertilisers are made from a range of naturally occurring organic sources including worm castings, bat guano, compost, manure and various aquatic plants. Organic nutrients are excellent in increasing the biodiversity and longevity of soil life. As well as feeding the plant directly they also provide micronutrients and other organic matter for different beneficial microbes such as trichoderma and mycorrhizae fungi which are excellent for your plant’s root system. It terms of its sustainablity, organic fertilisers generally involve minimal processing and recycling/reusing of resources.

Health Aspects

Many studies have been done into the health effects of organic versus inorganically produced foods. In some cases higher levels of vitamins and antioxidants and lower levels of heavy metals, pesticide residues and mycotoxins have been observed. There have also been many tests which have resulted in no significant findings for either side. Due to the popularity of organic foods only gathering serious momentum in the last 10 years it is still too early for any definitive health findings. Although, the numerous environmental issues which organically sourced foods deal with will continue to increase its popularity into the future.

Plant Growth

Inorganic fertilisers have a higher solubility, nutrient content and nutrient availability/release rate than organic fertilisers. In making organic fertilisers there are various decomposition and digestion techniques which can create variables from batch to batch. The consistency and instant availability of mineral fertilisers allow for faster growth rates in all soil-less mediums and they are the popular choice for most hydroponically grown crops. In soil gardens it is a different story. Growth rates are quite similar between organic and inorganic nutrients, but after nutrient application has ceased gardens that have used organic fertilisers start to have faster growth rates. This is due to the increased biological activity encouraged by the organic fertilisers and the residual effects of steadier long term availability. In essence, the choice is yours.