Feb. 9, 1924 
Effect of Fertilizers on Stem Rust of Wheat 
363 
It will be noted that the effect of nitrogen m a year like 1917 may be 
quite different from that in a year like 1916. In 1916 the weather 
became very hot and dry shortly after the plants headed. The plants 
in the nitrate plats suffered more from the drought than did those in 
any of the other plats. The result, of course, was that the development 
of the rust was checked by the premature ripening of the plants. In 
1917, on the other hand, the growing conditions were good, there was 
but little real burning out the stand in the nitrogen plats was very 
heavy, the individual plants were succulent, and maturity was greatly 
delayed, thus making conditions especially favorable for the develop¬ 
ment of stem rus . 
The date of maturity often has a great influence on the degree of rust 
infection. It is a very commonly observed and well-known fact that 
early maturing varieties often escape rust, while late maturing ones may 
be injured severely. In certain years the rust epidemic appears just 
after the earlier-maturing variety has ripened, but early enough to attack 
the late variety while it is still susceptible. The plants in the plats heavily 
fertilized with nitrogen in 1917 matured several days later than those in 
the other plats, and the opportunity for infection was thus increased. 
The rust percentage on a given date was uniform in all of the plats, but 
the weather was still favorable for the development of rust after the earlier- 
maturing plants were harvested and while the later-maturing plants still 
were green. Naturally more rust developed on the latter. This is illus¬ 
trated in Table XII with data taken from the plats on the Quinn farm. 
The residual effect of the potassium and phosphate fertilizers applied 
to the plats prior to 1917 apparently had little or no effect on the sus¬ 
ceptibility or resistance of the plants to stem rust. (Table IX.) The 
percentages of rust in the plats which had received only acid phosphate the 
previous year actually were slightly higher than those in the control plat. 
There clearly was no protective action in the potassium plats, nor in those 
which had received both acid phosphate and potassium sulphate. It was 
possible to note the residual effect of the fertilizers applied in 1916 only 
on one character, that of yellow-berry, which was very high in some of 
the plats which had received no nitrogen. The results from the seven 
plats receiving 2,000 pounds of acid phosphate are illustrated graphi¬ 
cally in figure 4. 
It will be seen from Table X that there was a great increase in the 
amount of straw on the nitrogen plats. In some cases it is almost 
double that on certain potassium plats. Just the reverse is true of the 
total weight of seed per plat. The average yield of grain for all plats 
receiving applications of nitrogen was 20.7 bushels per acre, while the 
average yield for all those not receiving nitrogen was 29.9 bushels per 
acre, a difference of 9.2 bushels in favor of the plats not receiving nitro¬ 
gen. The ratio of weight of seed to weight of straw shows clearly the 
effect of the fertilizers applied to the soil on the growth of the plant. 
Likewise, the yields from the nitrogen plats is inversely proportional to 
the amount of nitrogen applied. 
There appears to be little correlation between rust percentage and 
yield. This is especially clear when one compares the data for the plats 
which received 500 pounds of sodium nitrate with those for the plats 
which received 250 pounds (Table IX). The highest yield was obtained 
on the untreated control. The ratio of seed to straw for all plats 
receiving applications of nitrogen is 1:4.6; while the ratio for all plats 
not receiving applications of nitrogen is 1:2.5. The nitrogen clearly 
