Feb. 9, 1924 
Effect of Fertilizers on Stem Rust of Wheat 
359 
per acre and the highest was 31 bushels. In 1916 the lowest yield was 
only 0.3 of a bushel per acre and the highest only 7.1 bushels. Either 
the drought alone caused much of the damage in 1916, or the drought 
aggravated the rust damage. As Weaver (40) has shown that the rate 
of transpiration of rusted cereal plants is considerably greater than that 
of rust-free plants, it seems probable either that the loss of water or the 
water requirement is an important factor in rust damage. This would 
explain why plants fertilized with nitrogen apparently or actually are 
injured more by rust than are other plants. The susceptibility of the 
plants to rust is not necessarily increased by the nitrogen, but the rust 
is especially dangeous to such plants, because it increases the water re¬ 
quirement which already is too high for safety. That the great damage 
to the? Haynes Bluestem in the commercial fertilizer plats was caused by 
a combination of drought and stem rust, and not by drought alone, is 
suggested by the fact that the resistant hybrid yielded from two to about 
twelve times as much as the Bluestem. (See Table VI.) It is possible, 
however, that the hybrid may be somewhat drought resistant. While it 
is difficult to differentiate clearly between drought injury and rust injury, 
it is quite evident that the degree of rust infection is not necessarily an 
index of the amount of injury it will cause. 
The results obtained in 1915 and 1916 indicate clearly that wheat may 
yield well in spite of heavy stem-rust infection, if weather conditions are 
favorable to the crop. On the contrary, a moderate rust attack either 
causes or appears to cause severe damage when weather and soil condi¬ 
tions are unfavorable to the wheat. It is probable also that the effect 
of fertilizers may be different under different climatic conditions. In a 
hot, dry year, wheat fertilized with nitrogen may “burn out,” thus 
checking the spread of stem rust; while in a cool, moist season, maturity 
may be delayed by nitrogenous fertilizers, thus giving the rust more 
time in which to develop. 
EXPERIMENTS WITH COMMERCIAL FERTILIZERS PLUS NATURAL FERTILIZER 
IN 1916 
The general plan of the plats treated with commercial plus natural 
fertilizer is shown in Table VII. The plats were on heavy Hempstead 
clay loam on University Farm, which had grown alfalfa for several years 
previously. Haynes Bluestem and the same hybrid wheat which was 
used in 1915 also were used in this experiment. Each variety occupied 
1 full square rod instead of half that area as in 1915. The general con¬ 
ditions of the experiment were the same as those for the commercial 
fertilizer experiments in 1916. 
