Product Manual

12
Irrigating with IRROMETERS
Your charts enable you to determine how soon and how much to irrigate after a rain. Most growers
find surprising differences in penetration in different areas, due to variations in soil type and
topography. Even in the same areas, infiltration rates often vary considerably depending upon how
recently the soil has been cultivated and how wet the soil happens to be at the time rainfall occurs.
Wilt starts at the roots. By the time the leaves indicate stress, plant growth has either stopped or
slowed. Unless the stress is severe, growth will resume following an irrigation, but some loss of
production and delayed maturity will result. For this reason, most research workers recommend that
irrigations start well before there is any evidence of stress.
Be sure to maintain plenty of soil moisture in the vital feeder root zone. Note that about 70% of the
plants’ moisture requirements are taken from the upper half of the root zone. Adequate soil moisture
in the lower root zone helps to tide over temporary periods of stress but is not sufficient to promote
maximum growth. IRROMETERS installed at two or more depths register soil moisture conditions at
different root horizons and thus give a more accurate picture of the moisture profile than composite
soil samples taken with a soil tube or auger.
With crops grown for the seeds or fruit, the same recommendation applies during the period of
vegetative growth. For instance, research has demonstrated that yields with corn are reduced
materially by even short periods of stress from seeding up through the dough stage. With some of
these crops, research work indicates that irrigations should be reduced during the ripening period of
growth. The amount that irrigation is reduced varies with the crop and climatic conditions.
With seasonal crops, you can expect to effect marked improvement the first year with IRROMETER
control. With tree and perennial crops, that are in poor condition, it may take longer. In any case, you
will find that IRROMETER control eliminates the most important variable affecting production —
irrigation. This enables you to concentrate on improving other cultural practices that may be necessary
to improve production.
Finally – if you have been irrigating by rule of thumb methods, based on the calendar, acre inches of
water per crop or per year or any of the older concepts, be prepared to make very radical changes.
They are usually indicated. The degree of change is often an index of the degree of improvement. You
can rely upon the accuracy of your IRROMETERS in making these changes.
Discontinuing Irrigations
As soon as irrigation water penetrates to the ceramic tips, gauge readings will go down. Discontinue
irrigations when the readings on the shorter instruments drop to the 0-15 range and readings on the
36" to 48" instruments drop to the 10-15 range. It is not necessary to continue irrigating until the
readings reach 0. In poorly drained soils, discontinuing irrigations at reading of about 30 is advisable
to avoid any possibility of water logged soils.
The gauge readings should begin to rise after gravity water has had time to seep down and the roots
begin to take up moisture from the soil. Continuous readings in the 0-20 range indicate poor drainage
and saturated soil. Irrigations should be discontinued or reduced until this condition is corrected.
Waterlogged Soils
Where there is poor drainage, three IRROMETERS per “station” are used in critical areas. The third
IRROMETER is of extra length and usually extends below the normal root zone. It provides a
continuous check on the water table and helps to prevent over irrigation and waterlogged soils.
Increasing Profits
Investigate the possibility of using IRROMETER control to increase plant population per acre with your
particular crops. Various agricultural experiment stations have demonstrated that this is possible with