Em4885 irrigation management practices to protect ground water

4 CHAPTER
ECe
LF = .......................... x 100
(5 * ECe) - ECiw
where:
LF = that percentage of applied water that must be deep percolation
ECe = the electrical conductivity of the average saturation extract from the root
zone - this number will usually be assumed as the maximum salinity allowable
before yield reductions will be expected. These “yield reduction threshold
salinities” are listed in a number of publications. Local agronomic consultants
should know the values for crops grown in their areas.
ECiw = the electrical conductivity of the irrigation water
SCS National Practice 610 addresses leaching for salt control.
IP 2.01.05 - Use Irrigation Scheduling as an Aid in Deciding
When and How Much to Irrigate
Objective
Irrigation scheduling techniques can aid in improving overall application efficiency by
either improving the timing of irrigations, more closely estimating the correct amount
of water to apply during the irrigations, or both. Thus, implementing irrigation scheduling
would normally tend to reduce water diversions.
However, in those cases where a crop was proved to be under-watered, diversions may
actually be increased. Note that this does not mean that application efficiencies were
necessarily reduced.
Description
Irrigation scheduling is the general name given to a number of different techniques. All of
these techniques will help the irrigator in deciding when to irrigate, how much water to
apply with the irrigation, or both. Generally, some method is used to measure or predict
the soil or plant water content. At some pre-determined water content an irrigation is
indicated. Some form of irrigation scheduling is applicable to any combination of crop
and irrigation system.
Application efficiency can be improved either because individual applications are reduced
or, in extreme cases, some irrigations avoided entirely. This Practice should be used in
conjunction with IP 2.01.03, Irrigation System Evaluation, so that the increased knowledge
of how much to irrigate can be utilized properly.
26