• undefined supplements such as coconut milk etc. (which, when used, contribute some of the five components above and also plant growth substances or regulants);
• buffers (have seldom been used, but the addition of organic acids or buffers could be beneficial in some circumstances).
Finally, it should be noted that minerals may also have a signalling role altering developmental patterns. This is most obvious in root architecture (Lopez-Bucio et al., 2003) which is logical as roots have a principal function in ion uptake and the root system should be such that uptake is optimal. So growth and branching of roots should be affected by mineral concentrations in the soil. Ramage and Williams (2002) also argue that minerals appear to have an important role in the regulation of plant morphogenesis as opposed to just growth. Some reviews of whole plant mineral nutrition will be found in Grusak (2001), Leiffert et al., (1995), Mengel and Kirkby (1982), Hewitt and Smith (1975) and Epstein (1971).
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