Transpiration as a Factor in Crop Production. 201 
result in production at the lowest water cost, or in other words 
the least water is required per unit dry matter. This does not 
mean, however, that under these optimum conditions less water 
is required per plant or per acre. In fact, it appears to mean 
just the reverse. For example, as you add manure to an infertile, 
unproductive soil, you may greatly reduce the water required 
per unit dry matter produced, but at the same time you also 
actually increase the total amount of water transpired. The 
ratio of water loss to dry weight is lower because the plants grow 
in a more normal manner. Anything below the optimum fertility 
approaches a pathological condition. In this condition the plants 
lack the thrift and vigor characteristic of a fertile soil, and con- 
sequently the elaboration of carbohydrates and the accumulation 
of dry matter are less for a given water usage. The plants grow 
more luxuriantly in fertile soil, having a greater leaf-area, and 
consequently each plant requires a greater total amount of avail- 
able water. Under conditions where the rainfall is limited, what 
would be the result of adding fertility? It would not mean that 
the plants could endure dry weather better by requiring less water, 
but it would mean a greater total water requirement per plant, 
and the crops would tend to withstand the shortage of moisture 
less well than if no fertility had been added. The addition of 
manure to an infertile soil would not appear to offer any hope of 
growing crops in territories too dry to grow crops without it, 
by virtue of reducing the amount of water consumed by the 
individual plant, as is commonly stated, for in fact the total 
transpiration would be increased. Thus, in regions of limited 
rainfall where corn is now grown but suffers from lack of moisture, 
an application of manure or other fertilizer might be expected to 
cause even greater injury from a lack of moisture provided the 
same rate of planting was practiced, thus giving a greater total 
vegetable growth and greater leaf -area per acre from which water 
would evaporate. 
COMBINATION OF INCREASED FERTILITY AND REDUCED 
RATE OF PLANTING. 
There is one manner suggested by these experiments in which 
this reduced water requirement in the production of dry matter 
by the plant due to increased fertility may be taken advantage 
of under the above conditions of limited available moisture. If 
the plants were spaced farther apart upon the land so that a 
thinner stand would exist even after the greater amount of stool- 
ing which usually follows a reduced rate of planting has taken 
place, relatively more water would be available in the soil for the 
