4 BULLETIN 157, U. S. DEPARTMENT OF AGEICTJLTUEE. 



with snow. When there is no snow, however, winterkilling of fall 

 sown cereals is not uncommon. 



Only two months of the year, July and August, have been free 

 from frost. Normally, however, there are from 90 to 100 days in the 

 frost-free period, extending from June 15 to September 15. 



EXPERIMENTAL WORK. 



All experiments were conducted under field conditions, the treat- 

 ment differing from common farm practice only in the tillage method 

 under test. 



DESCRIPTION OF PLATS. 



Rectangular tenth-acre plats were used for all experiments except 

 one, in which fifth-acre plats were used. The tenth-acre plats were 

 36 by 121 feet, while the fifth-acre plats were 72 by 121 feet. The 

 plats lay in series running north and south. The series were in pairs, 

 the two in each pair being separated from each other by a 5-foot alley, 

 while between the pairs of series there were roads 13 feet wide. The 

 plats within each series were separated by 5-foot alleys. Thus, each 

 plat was separated from the others by a 5-foot alley on two sides and 

 one end and by a 13-foot road on the other end. 



Two sets of plats were used for each experiment, except in the case 

 of the continuous-cropping test. These two sets of plats permitted 

 the alternate cropping and fallowing of each plat, a practice which was 

 followed regularly. 



SOIL-MOISTURE DATA. 



Soil-moisture data were collected on most fallow plats and on 

 some cropped plats. The number of samples taken varied with the 

 plan of the experiment. Soil tubes were used in sampling, the soil 

 being taken out in foot sections to depths of 6 to 10 feet. Each foot 

 section was placed in a soil can, which was immediately covered 

 with a close-fitting lid and taken soon after to the laboratory. From 

 two to four cores were taken from each plat on each day that it was 

 sampled. 



The moist weight of each sample was obtained soon after its 

 arrival in the laboratory. In no case was the weighing delayed 

 more than half a day, the sampling usually being done in the fore- 

 noon and the weighing in the afternoon. After the moist weights 

 were obtained, the samples were placed in an asbestos-board oven, 

 where they were subjected to an average temperature of 110° C. 

 They were left in the oven until constant weight was reached and 

 then the dry weight of each sample was determined. The difference 

 between the moist and the dry weights of the sample was then 

 divided by the dry weight of the sample, to get the percentage of 

 moisture. An average of the moisture content of all samples taken 

 on a plat was considered the average moisture content of the plat. 



