4 
BULLETIN 976, U. S. DEPARTMENT OF AGRICULTURE. 
PHYSICAL FACTORS. 
The more important physical factors which usually influence crop 
production are (1) the soil, (2) the annual and seasonal rainfall and 
its distribution, and (3) the seasonal evaporation and temperature. 
SOIL. 
The soil at the Amarillo Cereal Field Station is a dark clay loam, 
which is known on the Plains as ''tight" land. It bears a close turf 
of buffalo and grama grasses. The soil is productive, which results 
in high yields when the moisture is distributed so that crops can make 
proper use of it. 
RAINFALL. 
Precipitation and its distribution probably are the prime factors in 
crop production in the section of the Plains in which the Amarillo 
Cereal Field Station is located. There is usually moisture enough to 
grow a crop, but it is not always so distributed that the crop can make 
the best use of it. When it is not, crop yields are low, and in extreme 
cases total failures result. 
MONTHLY AND ANNUAL PRECIPITATION. 
Table I shows the monthly, annual, and mean annual precipitation, 
in inches, at Amarillo, Tex., during the 28-year period from 1892 to 
1919, inclusive. The mean annual precipitation at Amarillo for 
these 28 years was 20| inches, of which 15f inches fell during the 
growing season, or from April to September, inclusive. 
Table I. — Monthly and annual precipitation at Amarillo, Tex., during the ^8-year 
period from 1892 to 1919, inclusive. 
[Data (in inches) furnished by the observer of the United States Weather Bureau at Amarillo, Tex. 
T.=trace.] 
Year. 
Jan. 
Feb. 
Mar. 
Apr. 
May. 
June. 
July. 
Aug. 
Sept. 
Oct. 
Nov. 
Dec. 
An- 
nual. 
Mean 
an- 
nual. 
1892 
0. 42 
0.57 
2. 10 
0. 21 
2. 70 
1.49 
1.85 
1.93 
0.24 
2. 85 
.03 
0. 16 
1.08 
15. 60 
1893 
.09 
2. 03 
T. 
.16 
2. 19 
2. 03 
2. 05 
2. 67 
5. 27 
.28 
.43 
17.23 
16.42 
1894 
.02 
1. 15 
.05 
.85 
1. 30 
3. 59 
1. 82 
3. 41 
2. 41 
.59 

.82 
15.- 81 
16. 21 
1895 
1.60 
1.92 
.16 
1.31 
1. 78 
6. 84 
2. 08 
3.87 
.57 
2. 26 
.81 
.79 
24. 79 
18. 36 
1896 
.76 
.41 
.21 
1.95 
2. 20 
2. 31 
7. 04 
.63 
2. 45 
3.09 
.35 
2. 68 
24. 28 
19. 54 
1897 
2 26 
.65 
.47 
1.08 
4. 44 
2. 32 
2. 16 
2. 71 
.73 
1.63 
.08 
.63 
19. 16 
19.48 
1898 
.86 
.82 
.36 
.98 
3. 52 
4. 81 
3. 88 
4.03 
.48 
.41 
.34 
2.06 
22. 54 
19.91 
1899 
.29 
.07 
.17 
.23 
3. 12 
4. 45 
6. 96 
.51 
6.09 
1. 15 
3.24 
1. 11 
27. 39 
20.85 
1900 
.59 
.47 
.48 
5. 47 
4. 53 
1.84 
3. 21 
.83 
5. 25 
1. 58 
.98 
.07 
24. 40 
21.24 
1901 
.03 
.48 
.02 
4. 90 
5. 99 
.92 
1.66 
3.03 
2. 19 
3. 26 
2. 00 
.04 
24. 42 
21. 56 
1902 
.04 
T. 
.74 
1.83 
9. 14 
2. 01 
1. 45 
2. 42 
.95 
1. 74 
2. 24 
.55 
23. 11 
2L70 
1903 
.12 
2. 93 
.26 
.90 
1. 79 
2. 83 
3. 38 
4.67 
.82 
2.58 

T. 
20. 28 
2L 58 
1904 
.16 
.08 
T. 
.63 
2. 88 
5. 53 
2. 48 
4.69 
3. 55 
.44 
.20 
.69 
21. 33 
21.56 
1905 
1.00 
1.52 
2. 62 
4. 52 
6. 16 
2. 19 
3. 76 
.63 
3. 08 
.30 
5. 09 
1.45 
32. 32 
22. 33 
1906 
.41 
.51 
.64 
3. 23 
1. 18 
2. 07 
2. 90 
6. 76 
1. 96 
2. 49 
2. 58 
. 19 
24. 92 
22. 50 
1907 
1.11 
.24 
.02 
1. 25 
.99 
1. 97 
1. 49 
6. 20 
.91 
1. 79 
.66 
1.46 
18. 09 
22.22 
1908 
.26 
.72 
T. 
1.90 
3. 55 
1. 75 
5. 40 
2. 75 
1. 83 
.40 
.51 

19. 05 
22. 04 
1909 
.07 
.22 
1. 20 
.50 
1. 08 
4. 72 
3. 63 
. 87 
2. 19 
1. 18 
3. 25 
.54 
19. 59 
21.90 
1910 
.05 
.17 
.34 
.59 
2. 99 
.66 
3. 57 
2. 19 
.05 
.26 
.28 
T. 
11. 15 
21. 34 
1911 
.13 
2. 88 
.50 
2. 76 
5. 88 
.20 
3. 85 
2. 97 
.85 
.84 
.94 
.95 
22. 73 
21.41 
1912 
T. 
1.94 
.82 
.72 
1. 67 
1.90 
1. 88 
2. 28 
2. 28 
.39 
.02 
1. 18 
15. 08 
21. 10 
1913 
.11 
55 
.59 
1. 76 
1. 41 
2. 32 
1. 80 
.61 
4. 19 
.61 
1.98 
2. 84 
18. 97 
21.01 
1914 
.06 
.10 
.15 
.95 
4. 43 
.84 
3. 07 
2. 97 
1. 07 
4. 46 
T. 
1.17 
19. 27 
20. 93 
1915 
.72 
1.60 
1.00 
5. 05 
1. 70 
1.04 
4. 14 
5. 85 
4. 69 
1. 55 
.18 
. 13 
27. 64 
21.21 
1916 
.36 
.02 
.57 
1. 71 
.89 
2. 18 
.94 
3. 82 
1. 76 
2. 90 
.40 
.88 
16. 43 
21.02 
1917 
.69 
.22 
.25 
.71 
2. 49 
.83 
2. 68 
6. 17 
2. 05 
.34 
.59 
.04 
17. 06 
20. 89 
1918 
I. 01 
.26 
1.06 
.48 
2. 23 
1.43 
2. 23 
2. 36 
.64 
2. 47 
1. 16 
2.78 
18. 11 
20.74 
1919 
T. 
.73 
1. 73 
2. 56 
2. 08 
2. 94 
1. 75 
3. 21 
4.58 
.67 
1. 26 
.50 
22. 01 
20. 81 
Average. 
.47 
.83 
.59 
1.72 
3. 01 
2.43 
2.96 
3.04 
2. 25 
1. 47 
1.05 
.89 
20. 81 
