278 
IOWA ACADEMY OF SCIENCE You XXIX, 1922 
TABLE 7 
.CORN — FULL CULTIVATION 
Soil moisture 15.2 per cent 
Designation 
No. or 
PLANTS 
Aver. 
Height 
CM. 
Green 
Weight 
gm. 
Amount 
Water Giv- 
en Orr eor 
Growing 
Season gms. 
Corn — tasseling out, strong and 
healthy 
2 
192 
Portulaca oleracea (weed total) 
6 
5 
8 
474.13 
Total for all weeds 
6 
were only 71 cm. in height while in the full cultivation experiment 
the height was 192 cm. 
In the same area, there is recorded a water outgo of 164,774 
grams of water from the uncultivated plot as compared to 474 cm. 
for the full cultivation plot. For the plot given four cultivations, 
there is of course a greater amount of water given off by the corn 
plant due to a larger leaf surface. 
In field experiment No. 2 (table 4) the weeds were removed at a 
distance of 30 cms. from the hill at time of planting and then 
allowed to grow. The average height of the corn was 91 cms., 
total number of weeds 171, and water loss of 70,489.8 gms. 
But even under this meager treatment there were 66 less weeds 
and a difference of 94,285.20 grams. Proceeding in order from 
table 4, each additional cultivation measure gives a smaller tran- 
spiration loss and at the same time, corn plants of greater height 
and vigor. It is clearly evident that cultivation is beneficial. 
Usually the leaf area is an accurate index of water loss. How- 
ever such weeds as the two common bindweeds, Convolvulus 
sepium and Polygonum convolvulus are climbing and as such 
compete by this particular means as well. 
As to the. kind of treatment it is interesting to note the effective- 
ness of hoeing. In experiment 4 (table 6) -the plot was hoed twice 
while in Field Experiment 5 (table 7) there were four cultivations. 
In the former there are seven weeds, while in the latter there are 
six. However, there is considerable difference in size and develop- 
ment, for the hoed plot (table 6) evaporates 1,424.57 grams, 
while for the full cultivation there is an evaporation of 474.13 
grams. The data of these two tables at least indicate that two 
hoeings are not, under these conditions, as effective as four culti- 
vations. But at the same time one hoeing isi superior to one 
cultivation (see tables 5 and 6). Throughout it is clear that the 
