CHEMICAL AND BACTERIOLOGICAL STUDY OF WHEAT SOIL. 9} 
(b) A field till quite recently cropped with lucerne, on 
which barley was growing during ‘the earlier months 
of the investigation, designated “‘lucerne.’’ This soil 
has a different physical constitution from the other 
soils. (See Table I.) 
(c) Wxperiment plots under rotation including— 
(1) An uncultivated fallow—P A. 
(2) A wheat plot, the straw to be left on the plot and 
ploughed in after harvest—P B. 
(3) A cultivated fallow—P C. 
(4) A wheat plot, the straw to be burned off after 
harvest and the land to be ploughed soon after-PD. 
Owing to climatic conditions neither of the wheat plots 
had been ploughed when observations came to an end. 
Sampling. 
The June samples were taken toa depth of 6 inches with 
a spade and trowel, but for all later bulk samples a post- 
hole auger was used and samples taken to a depth of 9 inches 
and 9 to 18 inches, while 18 to 27 inches sections were 
taken in July and August. In June all the samples from 
the experiment plots, which up to that time had received 
the same treatment, were taken together, and in July the 
two fallow pilots were treated as one, and the two wheat 
plots as one, but from August onward each plot was 
sampled separately. Special samples were taken in sterile 
glass tubes for the more delicate estimations. The actual 
dates of sampling were:—14/6/21; 14/7/21; 17/8/21; 15/9/21; 
BaflO/20; 16/41/21; 15/12/21; 11/1/22; 15/2/22. 16/3/22: 
Physical Examination of Soils. 
Mechanical analyses were made of the soils designated 
“‘grass’’ and “‘lucerne,’’? and of a bulk sample from the 
experiment plots. The method employed was the simple 
elutriation method with two amplifications for separating— 
(a) coarse and fine sand. (b)-silt and clay fractions. 
