The key factor that determines whether flood irrigation
is effective and efficient, is the producer and his labourer. If the producer ensures that his borders, furrows or
basin are correctly constructed, the irrigation done correctly and faults corrected, then he is using his system
to the optimum.
Land levelling, smoothing and shaping the field surface
is as important to the irrigation system as the design of
laterals, manifolds, risers and outlets is for sprinkler or
micro irrigation systems. It is a process for ensuring
that the depths and discharge variations over the field
are relatively uniform and, as a result, that water distributions in the root zone are also uniform. These field
operations are required nearly every cropping season,
particularly where substantial cultivation following harvest disrupts the field surface. The preparation of the
field surface for conveyance and distribution of irrigation water is as important to efficient surface irrigation
as any other single management practice the farmer
employs.
There are perhaps two land levelling philosophies:
to provide a slope which fits a water supply; and
to level the field to its best condition with minimal
earth movement and then vary the water supply for
the field condition.
The second philosophy is generally the most feasible.
Because land levelling is expensive and large earth
movements may leave significant areas of the field
without fertile topsoil, this second philosophy is also
generally the most economic approach.
Land levelling always improves the efficiency of water,
labour and energy resources utilization. The levelling
operation, however, can be the most intensively disruptive practice applied to the field and several factors
should be considered before implementing a land levelling project. Major topographical changes will nearly
always reduce crop production in the cut areas until
fertility can be replaced. Similarly, equipment traffic
can so compact or pulverize the soil that water penetration is a major problem for some time. The farmer
has many activities which contribute to his productivity
and therefore require his skill and labour.
The irrigation system should be designed with the producer in mind. A field levelled to high standards is generally more easily irrigated than one where undulations
require special attention. Land forming is therefore very
important for improved sustainable flood irrigation.