Add a little P, get a load more Poo! Part 5: P reserves and productivity!!

More on the reserves of P!

Van Vuuren et al.’s (2010) highlights predicted use of P from 1970 to 2100. Clearly they think that P reserves are going to last a while; they come to the conclusion that:

• There are no signs of short-term to medium-term depletion
• In the longer term, the depletion of low-cost and high-grade resources will have consequences for future production trends
• Given the impact of resource uncertainty on the assessment of risks associated with P depletion, it is important to pay more attention to data on P resources. Uncertainty was found to play a role in data on P production,
• Phosphate rock depletion may lead to concentrating production to a few countries, thus increasing production costs.
• Major reductions in the use of fertiliser P can be achieved by improving plant nutrition management, better integrating of animal manure and recycling P content in human and/or animal excreta

What is most interesting about the article is that it highlights the different scenarios of P depletion; the figures show their findings:

Cordell et al. (2009) also look at the geopolitics; inequality; economics and relative irony of it all – peak oil has received a lot of attention and it is only necessary for energy and cars (I know hear me out!) whilst P is integral to crop growing, and that ever vital necessity that is food.

The figures below (taken from Cordell et al. 2009) include a pretty graph showing Phosphorous sources over time; it just shows how dependant, or as Cordell et al. puts it ‘addicted’ (2009, 292). 

With high grade P reserves being depleted (Cisse and Mrabet, 2004), and our addiction (Cordell et al. 2009), the debate as to where the next lot of P will come from, which just adds to increased food insecurity and environmental degradation due to a potential in greater mining; this leads to:

• Greater energy use – fossil fuels and GHG emissions.
• Greater waters usage and wastage – particularly in countries where safe water supplies are already an issue.
• Rising prices – of P, fertilisers, agriculture and fundamentally the cost of food).

Inorganic fertiliser alone is not sufficient in restoring soil organic carbon (SOC) that forms through decomposition in situ of organic materials , and attaining the highest yields in crop production  (Su et al, 2006; Liu et al., 2010). SOC is an integral part to the soil and provides plants with capacity to grow due to its properties or absorbing water and nutrients. Fertilisers cannot provide that level of SOC; just another benefit of using manure and other waste material to fertilise the soil.

Turnerand Leytem (2004) looked into phosphorous compound sequestration from, of all things, urine. Their success in fractionating the compounds in two steps furthers the research in attaining P from readily available resources, excrement. Admittedly, this is a much more energy intensive way as well as poorly cost-effective; but it opens the doors to greater utilisation and indeed valuation of what we all poop and pee out.

So a variety of sources point to manure and other forms of excreta as a sustainable and beneficial source of P; not to mention an eventual necessary source!

Happy New Year!!! Lets hope there are a lot less cows farting this year!