Fertilizer is defined by Tom Stevenson (2011) as ‘a chemical product used to enrich the soil with one or more of the three basic requirements for all plant life: potassium (for fruit development and general plant metabolism), phosphorus (for root development), and nitrogen (for leaf development). Technically, the term also refers to manure, compost, and other natural means of soil enrichment.’
NPK Soluble fertilizers | The initials of the three chemical elements in manufactured soluble fertilisers mean they are often referred to the acronym NPK (nitrogen, phosphorus, potassium). NPK fertilisers are not permitted for either organics or Biodynamics. Soluble fertilizers date from the 19th-century and Justus von Liebig. See Haber-Bosch for how this type of fertiliser was invented. Craig Sams (2003, p.23-25) points out that in 1947 the UK passed am Agriculture Act which paid subsidies on soluble fertilizers for farmers. After the UK joined the EEC the latter’s Common Agricultural Policy authorised subsidies for crops (rather than fertilizers), with guaranteed prices. This led to over-production and dumping. Sams says subsidies were never paid to fields of clover which increase the nitrogen and humus content of the soils.
The organic fertility approach | Craig Sams (2003, p.26-8) says organics helps prevents the loss of topsoil and the leaching of nitrates, and builds humus which captures carbon. Sams (ibid.)
Cascade effect | Using soluble fertilizers create a ‘cascade effect in which:
– nitrates wipe out the nitrogen-fixing bacteria and encourage bacteria whose role is to break down organic matter and humus
– loss of humus = loss of water retention = more irrigation needed and more run-off causing flooding after heavy rains
– loss of humus = loss of organic matter and nutrient holding capacity, the soil becomes more acid, salts build up, and erosion occurs.
– the depleted soils need higher levels of ‘chemical’ inputs just to maintain yields, but this also produces more weeds and weak, sappy crops prone to disease
– herbicides end up in ground water, higher cancer rates and hormonal changes in wildlife
– insecticides are used which are non-selective
– there is a loss of habitat and species
– nitrous oxide (a powerful greenhouse gas) is generated from fertilised fields and nitrous acid contributes to acid rain (see file on nitrous oxide).
Problems with NPK | N fertiliser is made from fossil fuel – mainly natural gas. N fertiliser is the largest source of carbon dioxide (C02) emissions in agriculture.
As conventional fertilisers are soluble they contribute to algal blooms. Manufacture of fertilisers also emits large amounts of a long-lived greenhouse gas called nitrous oxide, a far more powerful greenhouse gas than CO2. Alternatives to fertiliser used in organic and Biodynamic farming include compost and cover crops.
Sir Patrick Holden says ‘the use of nitrogen fertiliser has liberated [farmers] from the need to build soil fertility, as a result of which post-war farming has become a soil carbon asset-stripping operation.’ He goes on to say that if farmers were forced to pay for the cost of the damage such fertilisers cause (outlined above) farmers would once again contemplate reintroducing crop rotations to build soil fertility, adhering to the “law or return”, meaning the recycling of all organic matter and other nutrients in line with the principles of the circular economy, composting animal manures and other surplus biomass, and practicing of holistic grazing. All these things can ‘in combination dramatically speed up soil formation,’ Holden says.
Patrick Holden, ‘Evolving food and farming’, Star and Furrow, Issue 130, January 2019 p7.
Tom Stevenson, The Sotheby’s Wine Encyclopedia 5th Edition (Dorling Kindersley, 2011), p694.
Soil Association, ‘N fertiliser and climate change’, (unknown author) in Living Earth, Spring 2006, p.8, published by the Soil Association.