Fertilisers

Fertilisers

The big development in Anthropocene times has been the massive increase in chemicals on soils. The fertilisers - the NPK, are the most widespread, followed by pesticides - insecticides, herbicides and fungicides being the most frequent. Figures for chemical increase

In 2020, fertilizer consumption for World was 146.4 kilograms per hectare. Applications are growing nearly 2%/yr.

Nitrates

Prior to 1960, the nitrogen cycle was roughly balanced across the world. Since then, the use of nitrogen fertilisers has increased some 800%. [5] Usage has roughly doubled since pre-1980.

Too many nutrients can be just as harmful as too few – excess nitrogen is washed into rivers and streams where it can cause devastating algal blooms, killing off other water life

We have more than doubled the total amount of N introduced into the global biosphere, greatly altering the natural N cycle. This has led to a web of pollution problems, including a rapid increase of toxic algae, known as algal blooms, which deplete oxygen in water and can create coastal dead zones affecting underwater life. Nitrogen pollution is the most influential global driver of human-made biodiversity decline after habitat destruction and the emission of greenhouse gases.[6] Certain plants thrive on nitrogen fertilisers keeping out many other species.

The change is the largest the nitrogen cycle has experienced in 2.5 billion years and it could have serious consequences for our food supply, soils and climate. Disruptions to key nutrient cycles in the soil are particularly worrying because our soil systems tend to respond slowly to change – any harm done by humans now may take decades, even centuries to repair.

The United Nations considers the ‘Nitrogen Fix’ to now be one of the main emerging issues of environmental concern - in  ‘Frontiers 2018-19’

“In the first decade of the 20th century, two German chemists – Fritz Haber and     Carl Bosch – developed a way to produce synthetic nitrogen cheaply and on a large scale. Their invention spurred the mass production of nitrogen-based fertilizers, and thus transformed farming around the globe. It also marked the beginning of our long-term interference with the Earth’s nitrogen balance. Every year, an estimated US$200 billion worth of reactive nitrogen is now lost into the environment, where it degrades our soils, pollutes our air and triggers the spread of “dead zones” and toxic algal blooms in our waterways.” [7]

Nitrogen fertilisers are said to be responsible for feeding an extra 2 billion people oo the planet. Just look at those fields of lush green crops and grass, and you know they have been fertilised with N. Growing demand on the livestock, agriculture, transport, industry and energy sector has led to a sharp growth of the levels of reactive nitrogen – ammonia, nitrate, nitric oxide (NO), nitrous oxide (N2O) – in our ecosystems,

A UNEP Report warns: “Altogether, humans are producing a cocktail of reactive nitrogen that threatens health, climate and ecosystems, making nitrogen one of the most important pollution issues facing humanity. Yet the scale of the problem remains largely unknown and unacknowledged outside scientific circles.”[8] The energy consumption and nitrous dioxide pollution from nitrogen fertilisers means they make up more than a 1/3 of all GHG emissions from farming, according to the influential Stern Report[9]

Obviously the effects of nitrogen fertiliser on soil fauna vary widely according to soils and fauna. However a global meta analysis effects of nitrogen on a range of soil animals showed “An overall negative effect of N addition on soil fauna. However, the effect varied among soil faunal taxa. Specifically, N addition had no significant effects on the abundance of collembolans and mites in any ecosystem. On the other hand, N addition significantly reduced the abundance of all nematode trophic groups except bacterivores. “[10]  That is obvious at one level - the increase in crop roots would provide food sources for collembolans, but why the consistent drop in nematodes. I would propose that  it could be something to do with water. Nematodes need pretty constant water.

Phosphates

https://www.nature.com/articles/s41893-024-01385-9#Abs1 Impacts of global trade on cropland soil-phosphorus depletion and food security

"global data on international trade and soil-P reserves and deficits from 1970 to 2017, we demonstrate that the contribution of trade to global soil-P deficits increased from 7% in 1970 to 18% in 2017, with 54% of this impact driven by non-food consumption. Over these 48 years, developing regions exported a net of 5.8 Mt P through agricultural trade, resulting in a net increase of 13 Mt soil-P deficits. These deficits are primarily concentrated in regions with low soil-P reserves, such as sub-Saharan Africa, Latin America and Southeast Asia 

In the industrialised countries, there was a gradual increase in the annual use of P fertilizers from the mid-1850s; which then increased rapidly between in the 1950s to mid-1970s , before stabilizing or declining slightly thereafter. . Total phosphorus is about 0.1 percent by weight of the soil, but only one percent of that is directly available to plants.

The problems with phosphates involves what goes in, on and comes out of soil. There are finite amounts of rock phosphate that can go in, and what goes on in soils is the subject of much fertiliser research,  and what comes out can cause water pollution problems.

Global supply is finite, but we have enough for 600-100 years [11]  . However these global phosphorus sources may be not always be available. Prices of phosphate fertilisers doubled in two years to Sep22 making for a total worth of over US$60 billion, the cost to farmers. Only four countries control around 70 per cent of the annual global production of phosphate rock from which phosphorus is extracted China, Morocco and USA are the biggest three producers. China are already controlling exports. The supply of phosphate is consolidated into a very small group of suppliers, and prices are settled through bilateral negotiations; there is no central and transparent market.

The UK has no domestic source of phosphorus. Most of the phosphorus fertiliser used in UK comes from phosphate rock mined in Morocco and Moroccan-controlled Western Sahara.  As a result of the Russian invasion of Ukraine, the EU has sourced more phosphate from Morocco, whose production has gone up by over ¾.

Look  what is going on in Ukraine today, perhaps all due to its fabulous soil. Look at the depth of that black soil with all the roots showing how deep they go.

However this poses its own problems in that the state-owned rock miner had sought to increase supply to sub-Saharan Africa as part of a broader diplomatic deal to control Western Sahara as it joined the African Union in 2017. Other African countries are feeling part of a ‘second Cold War’ as their fertiliser supplies tighten.[12]

Tensions like this are becoming ever more important as phosphates demands increase but supplies flatten.. In the UK alone, less than half of the 174,000 tonnes of imported phosphate are actually used productively to grow food, [13]with similar phosphorus efficiencies measured throughout the EU where often phosphate efficiency is less than 40%[14]. People are recommended to 1.2 grams per P per day. Yet it requires 50 X this -around 22 kg of phosphate rock to deliver this. As the price goes up, so farmers, used to just putting more phosphate on to make the soil work, are questioning whether this is the best, most efficient and cheapest way

Why is P conversion from rock to plate so inefficient? Do you remember, over 350 mya, that vital relation between plants, mycorrhizal fungi and  PSBs about phosphate availability - one of the most important relations in soil?  The PSBs change insoluble phosphates, from the rocks in soil, into forms plants can absorb. That helps both the plants grow and the fungi in the roots to grow , to help absorb more phosphates

And the, do you remember those fabulous fertilisers called ‘super phosphates’, stolen from remote islands, tested at Rothamsted, or manufactured by Fisons out of fossil dung, which transformed crop growth nearly 200 years ago?  They made sure plants got an adequate supply the plant got the energy, stored as ATP in its mitochondria, to build the plants and hence feed many people. Cheaper. Phosphates are considered ‘limiting elements’ - without certain amounts, the plant does not grow. But When artificial phosphate is applied , most of it - certainly over ¾ , is quickly adsorbed. We saw what that meant nearly 400mya.

But  when we apply inorganic phosphate fertiliser to help grow plants, something affects that four hundred million year old plant/fungi/bacteria relationship. When there is high plant phosphorus (P) status, as occurs with fertilisers, the mycorrhizal P uptake pathway is almost completely repressed and the mycorrhiza-inducible Pi transporter genes are ‘down-regulated’[15] . Increasingly we are finding that the supply of exogenous (ie applied as fertiliser) phosphate leads to a rapid -- within hours, suppression in arbuscule fungal development in roots and temporarily inhibits the growth of fungal colonisation [16]  It has been known for over 50 years that the AMF colonization level is remarkably decreased by the intense application of phosphorus fertilizer [17] and is called “phosphate inhibition”[18].With reduced mycorrhiza, the ability of plants to take in phosphate causes all sorts of problems. The dominant response to this is to put on more artificial phosphates. This vicious cycle reduces the ability of plants to absorb phosphates - essential for fungal growth[19] This is the Catch 22 in the fertiliser role on a global scale. We keep topping up phosphate which increasingly ends up in water courses.

There is enough phosphates in UK soil (and river beds) already to feed next crops, but it is making that P available that is the problem - ie turning on the PSBs and mycorrhiza. The issue of phosphate availability, variable and controlling, is being studied carefully, especially fertiliser organisations. Many look to maintain ‘critical value’, enough for plant growth without over fertilising. It is thought that this critical value is similar to the amount of plant phosphate taken away in the crops[20].

Farmers use of too much phosphorus on their land; the excess flows from the farmland into rivers, lakes, and coasts, damaging aquatic ecosystems. Added to the river concerns are the phosphates leaching into rivers from poultry and dairy units. This increase in phosphate river pollution is leading to XS feed source leading to eutrophication. The cost of responding to water-based phosphorus pollution in the UK alone is estimated at £170 million per year and a projected yearly clean-up bill of over US $300 billion to remove phosphorus from polluted water courses globally.[21]. 

Most famous in Britain is that of River Wye caused, in part, by intensive poultry production.[22] We always knew bird dung was a good source of phosphates, so it is a shame we can’t use that in the river. Phosphates are a major source of river pollution. There is a phosphate standard for soil and it should be ‘2’, otherwise expect runoff.

“The PSBs actually stimulate biological N-fixing bacteria (BNF). If we add phosphorus fertiliser round plant roots, then we don’t have PSBs that are stimulated by the plant, as just given the plant phosphorus, so plant doesn’t bother to produce exudates. And if they don’t stimulate PSBs in order to get the phosphorus, then don’t get the BNF either. And without the two we don’t get well structured soil”[23] Without exudates, there are no mycorrhiza, along with loss of bacteria, there is no food for springtails and mites which produce the poo to glue the aggregates.

[5] https://www.bbc.co.uk/programmes/p02544td

[6] https://www.unep.org/news-and-stories/story/four-reasons-why-world-needs-limit-nitrogen-pollution

[7] https://wedocs.unep.org/bitstream/handle/20.500.11822/27543/Frontiers1819_ch4.pdf

[8] https://www.unep.org/news-and-stories/press-release/it-time-fix-broken-nitrogen-cycle-says-un-environment-frontiers

[9] https://webarchive.nationalarchives.gov.uk/ukgwa/20100407172811/https:/www.hm-treasury.gov.uk/stern_review_report.htm Annex 7.g

[10] https://onlinelibrary.wiley.com/doi/full/10.1111/geb.13528

[11] https://www.fao.org/3/a1595e/a1595e.pdf

[12] https://www.euractiv.com/section/agriculture-food/news/europe-searches-for-alternatives-in-fertiliser-supply-battle/

[13] https://www.sciencedirect.com/science/article/pii/S0301479722005941?via%3Dihub

[14] https://link.springer.com/article/10.1007/s13280-019-01255-1

[15] https://nph.onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2008.02721.x

[16] https://www.frontiersin.org/articles/10.3389/fenvs.2018.00159/full

[17] https://nph.onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.1967.tb06001.x

[18] https://academic.oup.com/plphys/article/68/3/548/6077750?login=false

[19] https://www.frontiersin.org/articles/10.3389/fenvs.2018.00159/full#B64

[20] https://www.fao.org/3/a1595e/a1595e.pdf

[21] https://www.ceh.ac.uk/press/scientists-offer-solutions-global-phosphorus-crisis-threatens-food-and-water-security

[22] https://www.ems-geotech.co.uk/news/phosphate-pollution-herefordshire/

[23] https://www.youtube.com/watch?v=Yv288F4TXbo