The Soil Tensiometer 

Vaouum Gauge 15 inohes mercury vacuum 
Sorew removed to allow water escape 
Blook of wood 2%x2"x5" with 1 1/8" hole 
Tensiometer oup No. K9MS 
Brass nipple 1/4" ID x 1 1/2" 
Koroseal 5/16 ID - 1/8" wall 
Air trap glass tube 1OMM ID 
Rubber stopper No. 00 
Zashvaw, 
foenrronne 
is held around the soil particles. A peat 
soil may hold 200 per cent water and a sandy 
soil only 25 per cent water, yet both may be 
at the same capillary tension. The plant 
would remove the water from both soils with 
the same ease because the water is held by 
the soil at the same tension. 
If it were found desirable to water a 
given soil type at a tensiometer reading of 
1 inoh, any other soil of similar depth and 
growing the same crop should be watered at 
the same tension. We soon found that some 
eoil mixtures and some soil types required 
watering when they looked wet. Soil that 
had been mulched with manure looked wet wher 
it had a high tensiometer reading that showed 
4t was in need of water. In general, clay, 
eilty, and peaty soils look wet when the ten- 
siometer shows they need water; sandy soils 
look dry before the tensiometer registers. 
It is doubtful whether any person can 
tell when soil should be watered by the feel 
unless he hae had considerable experience 
with it. When we were comparing soil mix-. 
tures it would have been impossible to keep 
them at the same capillary tension without 
tensiometers. Our work shows clearly that 
differences in growth of roses in various soil 
mixtures are likely due to the amount of water 
available or to Sunt ere oet ee nutrition. i 
ou are not sure you are waterin our soi 
Rervanti geet a tensiometer and follow it. 
Follow the diagram in putting together your 
tensiometer. Have the rubber connections as 
short as possible and use plenty of compound 
in the joints. 
When setting the tensiometer make a hole, 
the size and shape of the cup, with a soil- 
sampling tube or trowel and fit the coup into 
it firmly. Don't jam the cup into the soil. 
Set the tensiometer in the bench where 
the soil dries at an average rate for the 
bench. Usually between the first and second 
rows of plants from the south side of the 
bench and at least 5 feet from the end is near 
average. Don't move the tensiometer frequent 
fe: A correct reading cannot be had in less 
two hours after the cup is set. 
One tensiometer is enough for each bench © 
operating individually if the bench ia level 
lengthwise of the house. If several beds are 
the same level and conneoted to operate fron 
one valve, one tensiometer is enough for the 
section. This is assuming you are injecting 
water to keep the soil at a low tension (not 
more than 3 inches). The diagram shows how 
to wire a tensiometer to an automatic valve 
for automatic injection. 
Tensiometers are not used when the con- 
stant water level is maintained. 
Soil tensiometers ready to set are now 
obtainable through your florist-supply deal- 
ers. Robert T. Geary, Plant Products Co., 
Blue Point, New York, and Lord and Burnham 
Co., Irvington, New York, are making and dis- 
tributing them direct. 

The soil tensiometer for operating an auto- 
matio valve. Produced by Lord and Burnham Co. 
