PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest

Z
w
2
w
J
w
3
0
Table 2. Average total precipitation increased sharply from winter to spring ,
across all plots by season slightly decreasing from spring to summer .
Season
Precipitation
Calcium and P reached low points during th e
spring, at which time 92 percent of the tota l
pre pitation had allen, and increased fro m
spring to summer. Magnesium input was great -
centimeters
est from fall to winter and remained approximately
the same from winter to summer.
Fall
70.89
Nitrogen input slightly increased from fall to
winter, decreasing from winter to sprin g
Winter
92 .0 5
reaching a low point during the summer .
There appears to be no difference in term s
Spring
57.9 6
of net kg per hectare per year between plot s
1 to 4 for each element with the exception o f
Summer
18 .0 8
plot 3 (table 3) . Plot 3 had more K + and les s
Ca++ than plots 1, 2, and 4 .
Total 238 .98
100
8 0
20
Figure 2. Total average kg per hectare of plots 1
through 4 for each element by season .
Throughfall Discussion
In general, the total nutrient input an d
throughfall concentrations were highest in th e
summer and fall and lowest during the winte r
and spring months. This seems to indicate
that each tree or canopy has a constant fraction
of elements which can be removed fro m
the foliage through leaching elements . Once
the rains start in the fall, the majority of eac h
nutrient is leached out . As the rains increase
in quantity and duration during the winter
• and spring months, the available fraction of
nutrients is further depleted. Decreasing
precipitation from spring to the end of summer
allows the nutrient fraction to increase
•
again until the total fraction of leachabl e
nutrients is reached .
Variations found between plot 3 and plot s
1, 2, and 4 with respect to K + and Ca++ coul d
be due to differences in soil types (data no t
available yet) . If soil types are different with
respect to nutrient availability, the difference s
between plots could be explained by luxur y
consumption .
Another possible source of the nitroge n
found in the throughfall samples is nitrogen -
fixing bacteria . Jones (1970) in his study o f
nitrogen fixation by bacteria in the phyllo -
sphere of Douglas-fir (Pseudotsuga douglasii)
in England isolated bacteria from the leaf
surfaces of Douglas-fir. He found that th e
bacteria could fix atmospheric nitrogen whe n
provided with a carbohydrate source . The fat e
13 7