Question

If irrigation water is NOT limited, groundnut grown in a sandy loam soil should be irrigated throughout crop period using which of the following schedule

• A. 50 % depletion of available soil moisture or IW/CPE ratio of 0.6
• B. 25 % depletion of available soil moisture or IW/CPE ratio of 0
• C. 25 % depletion of available soil moisture or IW/CPE ratio of 0.6
• D. 50 % depletion of available soil moisture or IW/CPE ratio of 0.75

Hint:

To select the correct irrigation schedule:
- Under unlimited water conditions \(\rightarrow\) Choose low soil moisture depletion (\( 25\% \)) and a high IW/CPE ratio (\( 0.8 \text{ to } 0 \)).
- Under limited water conditions \(\rightarrow\) Choose higher depletion (\( 50\% \)) and a lower IW/CPE ratio (\( 0.6 \)).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Irrigation scheduling is the process of determining when to irrigate and how much water to apply.
It is designed to maximize crop yield and water use efficiency based on soil moisture depletion or climatological approaches such as the IW/CPE ratio (Irrigation Water depth to Cumulative Pan Evaporation ratio).
Groundnut (Arachis hypogaea) is highly sensitive to soil moisture deficits, particularly during its critical growth stages such as flowering, pegging, and pod development.

Step 2: Detailed Explanation:
When irrigation water is not a limiting constraint, the primary objective is to maintain soil moisture at a high level to prevent any moisture stress.
Let us analyze the two common scientific approaches to irrigation scheduling:
Available Soil Moisture Depletion (ASMD) approach: This method schedules irrigation when the available soil moisture in the root zone is depleted to a pre-determined level.
Under non-limiting water conditions, keeping the soil relatively wet by irrigating at a low depletion level, such as \( 25\% \) depletion of available soil moisture, is optimal for groundnut.
This frequent, light irrigation prevents the hard crust formation common in sandy loam soils, which otherwise hinders peg penetration.
IW/CPE Ratio approach: This climatological approach matches the irrigation depth to cumulative evaporation.
A higher ratio (such as \( 0 \)) means that irrigation is scheduled frequently, keeping pace with evaporation losses.
For a sensitive, high-yielding crop like groundnut under non-limiting water conditions, a high IW/CPE ratio of \( 0.8 \) to \( 0 \) is recommended to sustain rapid transpiration and cell turgor.
Therefore, scheduling at \( 25\% \) depletion of available soil moisture or an IW/CPE ratio of \( 0 \) represents the most intensive and optimal schedule when water is abundant.

Step 3: Final Answer:
The correct irrigation schedule when water is not limited is 25 % depletion of available soil moisture or IW/CPE ratio of 0.