234 Report OF THE HorTICcCULTURAL DEPARTMENT OF THE 
The average daily increase varied from 0.2° to 6.7° with an 
average increase for the whole period of observation of 2.8°. 
The differences in temperature are very unevenly distributed 
through the day. The greatest difference, according to the 
records, was obtained at noon, when it varied from nothing on a 
day of heavy rainfall to 14° on a very bright day, with an average 
for the whole period of 6.1°. The least difference was at 7 a. m., 
when it varied from 4.5° cooler to 3° warmer under the cover 
than outside. At 6 p. m. the difference in temperature varied 
from 0.5° cooler to 11° warmer. 
EFFECT OF THE COVER ON SOIL TEMPERATURE. 
The effect of the cover on the temperature of the soil was 
also to raise it. In this case, however, the greatest difference 
was in the morning, when the soil underneath the cover averaged 
1.4° warmer than that in the check, the differences ranging on 
different mornings from 0° to 2°. Through the day the differences 
eradually decreased until at night it averaged only 0.1° warmer 
under the cover than outside. 
The optimum soil temperature for most cultivated crops, ac- 
cording to Ebermayer as quoted by King,* is 68° to 70° F. Hence 
the increase in soil temperature is advantageous as long as the 
soil temperature is below that point and not otherwise. Examin- 
ing the records of observed soil temperatures in Table II, we 
find that only in occasional instances during the period of obser- 
vation did the soil temperature reach the optimum. Hence the 
increase in soil temperature may be set down as beneficial to the 
plant. 
EFFECT OF THE COVER IN CONSERVING SOIL MOISTURE. 
Soil moisture determinations were made May 22, which was 
after a period of protracted drought, and July 10, which was 
after a period of abundant rainfall, to determine the effect of the 
cover on the moisture content of the soil. Composite samples 
showed the following percentages of moisture: 
May 22. | July 10. 
Per ct Per ct 
Cheek—ITmuinow: 22'< sit. diete ot Se Tike es oe Ona et aren tet ue eens | 11.0 14.4 
Gheck—Between! TOWS: jas..:-c)sin siete 2 eh ee eine rece ie tare ere 14.4 |} 16.9 
Shaded Tro wis sins ahi sts ae cv nd « oh snacestevaetensieechenere Erato bas ah ec re | eG 14.5 
Shaded—Between rows ik .'2 cede ee Ree cle Sees 14.8 | 17.0 
*The Soil, p. 220. 
= allt Lee ae 
