Soil and Climate - Soil: Reflections on the Basis of our Existence - page 128

Sustainable Fertiliser Use
Forests have a much higher carbon content than arable land. Growing more trees
would help to sequester atmospheric carbon dioxide, though at global level this would
have a negative impact on food production. There is, however, a debate on whether
forests should be fertilised in order to increase tree growth and sequester more carbon.
Fertiliser increases biomass production. Not only could some of this biomass be used
to make renewable fuels, some of it would end up in the soil. Organic matter breaks
down more slowly if fertiliser is added to the soil, which would increase the amount
of soil carbon. This may sound compelling as a climate change strategy, but there
are drawbacks. Walking through a fertilised young spruce forest is almost impossi-
ble. I kept getting sharp needles in my eyes when taking soil samples for one of my
research projects. Fewer types of plant and fungus can survive in dense forests of this
sort, creating a trade-off between positive climate impact and reduced biodiversity.
Moreover, we are unlikely to be able to afford to apply fertiliser to forests on
the scale required. Producing nitrogen-based fertiliser is an energy-intensive pro-
cess and a global shortage of phosphorus is also looming, as reserves in North
Africa's phosphorus mines are projected to last for only 50-130 years. Phosphorus
Exemplary vehicles . We cannot continue wasting resources as we have in the past. Phosphorus
is a prime example. It is a vital ingredient in agricultural fertiliser but natural deposits are dwin-
dling and will soon be exhausted. And yet we excrete large quantities of phosphorus in our
urine—only a fraction of which are recovered in water treatment plants. If we can recycle Coca-
Cola cans, as in the photo, surely we can also recycle the phosphorus in our urine