Supplementary memorandum submitted by
Professor William McKelvey (F 54)
The Committee asked me to determine whether
they were any biochemical differences in the conversion of organic
and inorganic nutrients, to yield. I have consulted my colleague,
Dr Christine Watson, on this and her reply is as follows:
"Plants take up the majority of their nutrients
in inorganic forms. Using nitrogen as an example, if a plant is
grown in a soil with manure, the chemically organic forms of nitrogen
present in the manure will be converted to inorganic forms eg
nitrate or ammonium, by micro-organisms in the soil. In a conventional
system large quantities of nitrogen will be supplied in inorganic
forms by fertiliser. But, when plants have mycorrhizal associations
(ie a symbiosis between the plant and a mycorrhizal fungus) the
story is not so simple. Mycorrhizae have the ability to access
simple organic forms of nitrogen (eg glycine). Thus, in organic
farming systems, where mycorrhizae are likely to be more prevalent
(no fungicides to get rid of them) plants will also take up organic
forms of nitrogen through mycorrhizal associations.
Once the nutrients are within the plant, however,
there is unlikely to be any biochemical difference in the conversion
of those nutrients into yield."
18 July 2000
|
