376 
Journal of Agricultural Research 
Vol. XXVII, No. 6 
host not only does not usually increase susceptibility, but may decrease 
it. The relationship between host and parasite is so intimate that it is 
difficult to generalize about it. As a rule, however, plants which grow 
normally are likely to yield best, regardless of rust. And the yield must 
be the real test of the value of fertilizers. 
Tor practical purposes much can be done to increase yields when stem 
rust is prevalent. The old principle of avoiding excessive applications 
of nitrogenous fertilizers is sound. But some soils need them and on such 
soils wheat will yield better when they are supplied. Acid phosphate 
and potassium often are valuable in increasing stiffness of straw and 
promoting early maturity. It is useless to add them, however, to soils 
which do not need them, or in which they do not become available. 
The opinion that they have an actual immunizing effect against stem 
rust does not seem to be justified, although the indirect effect may be 
very great. The problem of fertilization, in order to reduce losses from 
rust, varies with soil type and climate. The writers are forced to the 
conclusion that, while the direct effect of fertilizers on the susceptibility 
of wheat to stem rust under field conditions is slight, the indirect effect 
on rust and the direct effect on yield may be very great. Give the soil 
those fertilizers which the wheat needs, but avoid too much nitrogen, 
add potash and phosphates judiciously, and the best results are likely 
to be obtained. 
SUMMARY 
Experiments and observations, covering a period of eight years, have 
been made to determine the effect of artificial and natural fertilizers on 
the amount of stem rust developed on susceptible and resistant varieties 
of wheat, when grown on several soil types in different parts of Minnesota. 
The plants were grown under heavy artificially induced epidemics, and 
under natural field epidemics. 
The effect of barnyard manure, clover soil, alfalfa soil, and cabbage 
soil, with and without fertilizers, was tried in the field. In addition, va¬ 
rious amounts of sodium nitrate, acid phosphate, and potassium chlorid 
or potassium sulphate, alone and in combinations with each other, were 
added to soils to determine the effect on infection of wheat by rust. 
The degree of physiologic susceptibility of susceptible and resistant 
varieties apparently was not changed directly by the use of different 
fertilizers, although morphologic resistance may be changed slightly. 
Plants growing in plats heavily fertilized with nitrogenous manures 
sometimes were more heavily attacked by stem rust than those in other 
plats. This apparently was an indirect effect due to increased density of 
stand and delayed maturity, which made conditions for infection more 
favorable and lengthened the time during which the plants could become 
infected. In hot, dry weather, plants heavily fertilized with nitrogen 
may burn out, thus indirectly causing a decrease in the amount of rust. 
There is some evidence that the amount of orange leaf rust may be 
increased by the use of nitrogenous fertilizers. 
The direct effect of fertilizers on the character of plant growth and 
yields seems to be much more important than their effect on the severity 
of stem rust. 
The date of maturity, degree of lodging, crinkling, shriveling of seed, 
percentage of yellow-berry, and yield of straw and grain may be affected 
profoundly by different fertilizers. 
