Florida Agricultural Experiment Station


and total nitrogen and the pH of each were determined. Data
obtained from the soil analyses are presented in Table 8.
 Soil Reaction:-The soil samples at all depths and from all
 plots in 1928 and 1933 were acid in reaction. The acidity of
 the surface 0-9 inches decreased during the period over which
 the experiment was conducted. This decrease was greatest where
 no planted cover crops were grown, and least where the summer
 legume and the winter non-legume were returned to the soil.
 Nitrogen:-Available nitrogen in the soil is important in plant
 growth, and orchard practices that will maintain it will produce
 best results with pecans. Analyses do not necessarily show
 what a certain soil may require; but they can be employed to
 show changes that may take place over a definite period, and
 they were so used here in determining the nitrogen content of
 the soil at the beginning of the experiment and six years later.
 It was not intended that they show the percent of available
 nitrogen in the soil for the two sampling dates, but rather that
 they show the totals only.
 Data in Table 8 show that from 1928 to 1933 the nitrogen
 content of the surface soil increased where planted cover crops
 were grown and decreased in the unplanted plot. At the lower
 depths there was practically no change in the nitrogen content.
 Samples of surface soil taken in 1928 and 1933 from the winter
 legume Plots 1 and 2 contained 14.28 and 16.32 percent more
 nitrogen at the latter date. This was slightly less than the
 increase where the winter non-legume was grown. The nitrogen
 content of the 0-9 inch soil samples, although differing slightly,
 was consistently higher in 1933 than in 1928 in all planted plots,
 and likewise lower in the unplanted plot. This indicated rather
 positively that nitrogen can be maintained and even increased
 in the surface soil with the proper use of suitable cover crops
 in winter and summer.
 This is in agreement with the findings of Fowler and Lewis
 in Georgia (6). They reported increases of total nitrogen in
 the surface of Norfolk sandy loam soil where winter legumes
 consisting of either Austrian peas or Monantha vetch were
 grown.
 For the period of the experiment, data in Table 2 show that
 the most nitrogen per acre was returned to the soil by hairy
 vetch and Crotalaria spectabilis in Plot 2 and amounted to a
 total of 603.4 pounds; Austrian peas and C. spectabilis in Plot 1
were second, returning 414.7 pounds. In Plot 4 in which one
crop of vetch was grown at the beginning of the experiment