46 
G. A. PFISTER : 
are as yet far from being complete, and I do not want to 
formulate any hasty conclusions which later on may prove 
to be wrong. 
The fact that fallowing increases the yield of our crops 
considerably is well established. Fallowing is one of the 
best means of conserving moisture in the soil, as evaporation 
and capillarity in the top-layer of the soil are lessened. It 
also aerates the soil, and by doing so not only furthers 
chemical changes by which the plants are benefited, but 
also stimulates the growth and activity of the nitrifying 
bacteria so that a larger amount of nitrogen will be stored 
up for the next season. 
There is, however, another way in which fallowing helps 
to increase the fertility of our soils. Fallowing prevents 
denitrification to a great extent. We apply the term 
denitrification to the reduction of nitrates to nitrites, am- 
monia or gaseous nitrogen, which is brought about by the 
action of de nitrifying bacteria under certain conditions. 
De-nitrifving bacteria are widely distributed. They normally 
require oxygen, which they mostly obtain from the air. If, 
however, they are deprived of oxygen in the form of air, 
or if the oxygen supply is not sufficient, then they will ob- 
tain it by breaking up organic matter at the expense of the 
nitrate, i.e., they will by assimilating the oxygen from the 
nitrates reduce these to nitrites, ammonia or gaseous nitro- 
gen, with the result that the nitrogen in these forms will 
be lost to the plants for which we desire it. 
By fallowing we loosen and aerate the soil, providing 
an abundant supply of air (and consequently oxygen) for 
these de-nitrifving bacteria. These will then not have to 
break up the nitrates to procure the oxygen, which they 
normally require. As you see, by fallowing we help nitri- 
fication, and we prevent to a large extent rle nitrification. 
Fallowing is therefore not only an advisable but an 
absolutely necessary operation where intense cultivation 
and rotation of crops are not the practice, and for climatic 
reasons in our W.A. wheat areas it is likely to prove of 
comparatively higher value than elsewhere. 
