193 
and nitrogen, the ground would be completely exhausted of the 
first in 6U0 years, of the second in 16 years, and of the third in 
3,000 years. 
This assumption, however, would be entirely unsupported in 
practice. The high percentage of salt is an indication that the 
land in question is badly drained; in fact, it is often waterlogged, 
and the soluble salts, instead of being washed out uf the ground, 
accumulate to an alarming extent. The roots, then, of the more 
tender crop plants instead of feeding on a layer of soil one foot 
deep, would rot and corrode and only penetrate to a few inches. 
The mass of plant food revealed by chemical analysis is in practice 
found to be beyond the reach of the crops, and, besides, whatever 
amount of that plant food lies within reach of the shallow roots of 
the crop is of such a crude and raw quality that it is not in a fit 
state to act as plant food. 
“AVAILABLE” and “ToTaL” PLANT Foon. 
Bernard Dyer stated as a result of the Rothamstead experi- 
ments conducted over a period of 50 vears the following definite 
conclusions could be drawn :— 
That soil containing as low as .01 per cent. of phosphorie acid 
“available” required phosphorie manuring, but when the proportion 
reached .03 per cent. the necessity no longer existed. 
The corresponding limits for potash he placed at about .0057 
per cent. and .01 per cent. respectively. Judged by this standard 
many of our Western .Australian soils would seem to contain suffie- 
jent potash, but as the bulk of it is locked up and insoluble, and not 
“available” to the roots of plants, an additional dressing generally 
shows notable results. 
A soil may, on analysis, be shown to contain a high “total” 
percentage of nitrogen, phosphates or potash, and vet even under 
favourable climatic conditions yield poor crops. It is important 
that it should contain an adequate amount of “available” fertiliser 
or mineral to be utilised by plants, as food, immediately or within 
a few years. 
DIFFERENT SOURCES OF FERTILISERS. 
According to their origin or the sort of food stuff thev supply 
to plants, manures are spoken of as: 
“Animal Manures.’—These are characterised by the large 
quantity of nitrogen they contain, and the ease with which thev 
decompose and vield their fertilising matter in available form—e.g. 
guanos. desiccated blood. bones, and superphosphate. 
“Vegetable Manures,” which undergo decomposition more 
slowly; some, as the leguminous plants, having a large percentage 
of nitrogen—e.g., green manuring, farmyard manure, sea-weeds, 
and oil-cakes. 
