Mar. 34, 1933 
Summer Irrigation of Pima Cotton 
931 
was allowed between irrigations of these borders. This period was 
known to be much shorter than usual, as irrigation records of these 
borders for previous years showed that intervals of 20 days or more had 
been used with good results. 
‘ ‘ Medium-heavy ’ ’ irrigation was planned to be intermediate, as nearly 
as possible, between the “normal’* and “heavy” treatments. These 
periods varied, of course, with the “normal” irrigations and ranged 
between 14 and 23 days, while the periods of the “normal” borders 
varied from 14 to 44 days. 
In applying the water the borders were flooded to a depth of several 
inches, as uniformly as possible. In the absence of any means of meas¬ 
uring the amount applied, there were some fluctuations in the quantity 
a border received, but such differences were not considered sufficient to 
modify the results, in view of the generally uniform behavior of the cotton. 
This plan of irrigation was adhered to in the months of July and 
August, during the period of maximum plant growth and the setting of 
most of the bolls. After the first of September the effects of irrigation 
were considered only in relation to the maturing of the crop, there being 
no advantage in further growth of the plants. Bolls that set later than 
September 10 at Sacaton, even if they reach mature size, are likely to 
be frozen and then not open. 
APPLICATION OF WATER 
All the borders were irrigated on July 2 for the first time after planting. 
At this time the plants were from 14 to 20 inches high and were just 
beginning to flower. The next application of water was on July 13 to 
the three “heavy” borders, although they showed no signs of needing 
more moisture. A week later, July 20, the “medium-heavy” borders 
were irrigated, before any indications of wilting could be detected. The 
“heavy” borders had their third irrigation on July 23, when they were 
still visibly wet and there was no practical need of more water. 
About July 28 limited areas of plants in the “normal” borders in 
series II and III began to show wilting of the leaves in the middle of the 
day, although the plants were growing rapidly and not showing flowers 
at the top. With this indication of the need of water, these two plots 
were irrigated on July 30. 
It was apparent from the behavior of the plants that the “normal” 
border of series I would not require irrigation as soon as the “normal” 
borders in series II and III. As a result, the irrigation of both the 
“normal” and “medium-heavy” borders of series I was later. For the 
“heavy” border of series I the 10-day interval of irrigation was main¬ 
tained, as in the other series, until August 24, when this border was not 
watered because the plants showed unmistakable signs of distress by a 
yellowish green color and an almost complete cessation of growth, while 
the soil obviously was too wet. 
After August 13, no further irrigations were required to mature the 
crop of the “normal” and “medium-heavy” borders in series I, but the 
corresponding borders of series II and III received* two irrigations in 
September. The need of water in September was indicated by a more 
yellowish color of the foliage, although the leaves did not wilt in the 
cooler weather. The “heavy” borders in all three sections were irri¬ 
gated once in September, but water was needed earlier in series I than in 
series II and III. 
