Question

Given below are two statements:
Statement (I): The soil moisture depletion method is usually employed to determine the consumptive use of unirrigated field crops grown on fairly uniform soils when the depth to the ground water is such that it will not influence the soil moisture fluctuation within the root zone.
Statement (II): The field experimental plots technique though satisfactory for computing seasonal water requirements, does not provide information on intermediate soil moisture condition, short term use, profile use, deep percolation losses and peak use rate of the crop.
In light of the above statements, choose the most appropriate answer from the options given below:

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

To measure short-term, precise daily consumptive use, researchers use high-precision weighing lysimeters rather than soil moisture depletion or open field plots.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Consumptive use (or evapotranspiration, ET) is the total quantity of water used by crops for transpiration and evaporation from adjacent soil.
Determining consumptive use is essential for planning irrigation projects.
Methods to measure it include soil moisture depletion monitoring and field experimental plots.

Step 2: Detailed Explanation:
Let us evaluate Statement (I):
The soil moisture depletion method calculates ET by measuring the decline in soil moisture within the crop's root zone between successive irrigations or rain events.
For this method to be accurate, the soil must be uniform to ensure consistent moisture readings.
Additionally, the water table must be deep enough so that capillary rise does not supply water to the root zone, as this would cause the depletion readings to underestimate actual water use.
Thus, Statement (I) is correct.
Let us evaluate Statement (II):
The field experimental plot method measures the water balance (\( \text{Water Applied} + \text{Rainfall} \pm \Delta \text{Soil Moisture} \)) over a small test plot.
While this method provides a reliable estimate of the total seasonal water requirement under typical field conditions, it is a macro-level approach.
It does not easily measure short-term water use, deep percolation losses beneath the root zone, daily peak water use rates, or moisture movement within the soil profile.
Thus, Statement (II) is correct.

Step 3: Final Answer:
Both Statement (I) and Statement (II) are correct.