Plant Nutrients - Soils and Food Security - page 183

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Plant Nutrients

DAVID A. C. MANNING

School of Civil Engineering and Geosciences, Newcastle University, Newcastle
upon Tyne, NE1 7RU, UK
E-mail: [e-mail]

ABSTRACT

All plants require nitrogen (N), phosphorus (P) and potassium (K) as
major nutrients, from a range of possible sources including artificial
fertilisers. Both P and K (and almost all minor and trace nutrients) are
derived from mined sources: P from phosphate rock and K from
potassium salts such as sylvite (KCl). The reserves of P and K are
equivalent to up to 400 years production at current rates, and resources
have life expectancies of 1800 and 7500 years, respectively. Prices of K
fertilisers are currently very high (US$ 500 per tonne), in part reflecting
the cost of mining. However, nutrient audit studies for the end of the
20 th Century show that although N is approximately in balance, 30%
more P and twice as much K needs to be mined to compensate for that
removed by crops. With growing global populations, world production
of K needs to triple by 2050 to feed the expected population, whereas P
production needs to increase by 70%. In these circumstances, there is a
pressing need to broaden the range of available sources of K, especially
for farmers who cannot afford conventional fertilisers. Candidates
include the silicate minerals, such as feldspars, feldspathoids and micas.
Mineral dissolution rates show that feldspathoids dissolve 10 5 -10 7
times more rapidly than feldspars, and in contrast micas release K by