Page 56 - soil-plant-water relationship and water requirement

SOIL-PLANT-WATER RELATIONSHIP AND WATER REQUIREMENT

The interval should be as large as possible without detriment to growth, quality
and yield of crops. Also, it has to be ensured that available water resources are
utilised efficiently in crop production. The water requirement of crop is
affected by soil, plant and climatic factors.

The schedule of irrigation has therefore to be prepared on the basis of these
factors:
a. Soil Factor:

Available soil moisture content at which irrigation should be applied is a
good criteria as it indicates moisture content present in the soil and its
availability for plant growth. Soil moisture can be considered extending
full root zone of the crop or at least 60 cm from ground level because
most of the roots are concentrated in these layers.

The limit to which the soil moisture content is allowed to be depleted is
determined by field experiments. For cereals and grain crops around 50
to 60 per cent of available soil moisture may be allowed to be depleted
for good crop growth. The field experiments for soil moisture
determination require extra labour and time.

b. Plant Factor:

Plants have distinct growth stages. For example, for wheat crop various
growth stages are crown root initiation, tillering, jointing, flowering, milk
and dough stage etc. Certain stages of crop growth are more critical than
others so far as demand of water is concerned. While following criterion
of critical stages it is necessary to apply irrigation sufficiently before the
particular stage of growth is reached so that optimum moisture
conditions prevail during that stage.

c. Climatic Factor:

At a place climatic conditions influence the evapotranspiration.
Knowledge of amount of evapotranspiration during various intervals
serve as a best criterion to know the soil water balance in the field.

In addition to the above factors timeliness, adequacy and cost of
irrigation water supplies greatly influence the irrigation scheduling of
crops. Other considerations like pest control, temperature control (e.g.,
by maintaining submerged in case of rice), field preparation and
harvesting etc., also influence irrigation schedule. Considering the
availability of water resources and cultivated land two approaches could
be mentioned for irrigation scheduling.

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