From England comes interesting information about "Tree Nutrition"[5].
Evidence shows that the healthy growth of trees such as pines and
spruces is intimately bound up with an association between their roots
and fungi present in woodland soil. Poverty in mineral nutrients is no
longer regarded as a necessarily critical factor in the failure of
growth of trees of this kind, since the associated fungi have at their
disposal sources of supply inaccessible to the roots of higher plants.
Experiments carried out during the past ten years at Wareham in England
fully confirm the opinion expressed long ago by Professor Elias Melin,
Upsala, Sweden, that the growth of trees and other plants on poor soils
of the raw humus type is greatly influenced by the root-fungus
association. By fostering the appropriate combination it has been
possible to carry out successful afforestation of heathland so poor that
ordinary cultural methods prove inadequate for the least exacting tree
species. Satisfying the mineral requirements of the trees by direct
application of fertilizers is not in itself sufficient treatment to
ensure continued healthy growth; biological factors also play an
essential role in promoting soil fertility. The experiments have shown
that failure of the trees to establish a satisfactory biological
equilibrium with the necessary fungi is due in this case, not to the
absence of these fungi in the soil, but to their inactivation by toxic
products of biological origin. The factors inhibiting the activity of
the fungi can be removed by the application of comparatively small
amounts of organic composts which produce dramatic and lasting effects
on the growth of roots and shoots.
The special composts used are prepared from organic materials such as
straw, hop waste and sawdust. The mechanism by which they stimulate
growth is still obscure. All of them contain small amounts of directly
available plant foods such as phosphates and potash, but careful
investigation both in laboratory pot cultures and in the field, has
shown that these can account for only a relatively temporary effect on
growth. It is suggested that the composts act mainly by modifying the
course of humus decomposition, thus bringing about drastic changes in
the biological activities of the organic substrate of the soil.
This demonstration of the profound influence of biological factors on
the nutrition of trees challenges the attention of foresters and has
important practical applications. By making use of suitable composts, it
will be possible to carry out the successful afforestation of land
formerly regarded as wholly unproductive.
For further information see "Problems of Tree Nutrition"[5].
From the two foregoing examples it is seen that in the case of banana
blight, fungi had to be suppressed by bacteriae, but that for pine trees
on poor English soils fungi had to be activated for proper tree
nutrition.