1196 
Journal of Agricultural Research 
Vol. XXXI, No. 12 
moisture content of the soil to a depth of 3 feet could be the controlling 
factor in bringing about the difference both in yield and in protein 
formation. The fact that there is more available nitrogen in the 
summer-fallowed plots than in those continuously cropped indicates 
quite strongly that the available nitrogen in the soil is the more 
important factor. 
EFFECT OF CLIMATIC CONDITIONS 
The yearly variations in yields and percentages of nitrogen found 
in grain and straw are undoubtedly influenced by climatic conditions. 
An inspection of Table II shows that the year 1917 was the driest year 
recorded during the seven-year investigation, and it shows also that 
the temperatures for July and August of that year were considerably 
above the average. A lack of moisture accompanied by high tem¬ 
peratures during these months was undoubtedly the controlling factor 
Fig. 3.—Nitrate nitrogen found in the soil of four summer-fallow plots at different periods of plant growth 
in producing small yields. The yields for 1914 were quite certainly 
affected by a low precipitation during July and August and a high 
temperature during July. The year 1915 gave, in general, very good, 
yields. The precipitation for the months of June and July was 
considerably above the average, but the temperature for the same 
months was below normal. These conditions were favorable for 
plant growth and were important factors in producing larger yields 
that year. There does not seem, however, to be any constant ratio 
between the protein content of the wheat and the yield on the con¬ 
tinuously cropped plots for the different years, nor is there any 
decided difference in the protein content of the wheat grown on the 
alternate fallow and crop plots in favor of the dry years. The most 
pronounced difference was with spring wheat in 1914. 
The data on the formation of nitrate nitrogen in the soil, given in 
Figure 3, show that there was a decided loss in June in the first 3 
feet of soil. It is possible that the ground water carried some of the 
