A Cover Crop Program for Florida Pecan Orchards 37

part of the soil is called humus, and is different from the rough
organic material. In these samples the humus content was
determined.
 VOLUME SOIL SAMPLES
 In 1934 volume samples were taken from the same location
as those of different depths in A of each plot with a volume
sampler which took out a cube of surface soil 6 x 6 x 6 inches,
each having an average weight of about 10 pounds. The soil
was passed through a two millimeter sieve and the nitrogen
determined; it was then placed in jars and nine plants of Sudan
grass were grown in each so as to determine its relative pro-
ductive ability following the different treatments. The data
obtained from these samples are presented in Table 9.
 Nitrogen:-The nitrogen content of the volume soil samples
averaged 0.049, 0.059, 0.047, and 0.055 percent, respectively, for
Plots 1, 2, 3, and 4. It was highest, therefore, in Plot 2 in which
hairy vetch and Crotalaria spectabilis were grown, second in
the winter non-legume and summer legume plot, third with
Austrian peas and C. spectabilis, and lowest where no planted
crops were grown. Nitrogen in the volume samples was slightly
higher than it was in the 0-9 inch depth taken in 1933, for all
plots except the winter non-legume in which it was slightly
lower. However, it followed the same general trend as in 1933
and was in practical agreement with the 0-9 inch tube samples,
the differences not being significant.
 Organic Matter:-The organic material as determined by loss
on ignition in the volume samples did not vary materially from
those of the 0-9 inch depth for 1933 as shown in Table 8, except
that it was slightly higher in Plots 2 and 3 and lower in 4.
Therefore, the organic content in the volume soil samples fol-
lowed rather closely the general trend of the 0-9 inch tube
samples.
 Sudan Grass Growth:-Growth made by the Sudan grass was
 heaviest in soils from the legume plots and lightest from the
 unplanted plot. Soil from the oats plot grew plants almost as
 heavy as those from the soil of the Austrian peas plot. (See
 Table 9.) While there was only a slight difference in the weight
 of the Sudan grass growth in favor of the Austrian peas over
 the oats, apparently there were significant differences in favor
 of the cover crops over the unplanted soil. This indicated that
 soil in the planted plots was more fertile than in the unplanted
 check, and that soil from Plot 4 where oats were grown during