Step 1: Understanding the Concept:
Irrigation efficiency is a measure of how effectively the applied water is used. Application efficiency ($E_a$) specifically measures the ratio of water stored in the crop root zone to the total amount of water applied to the field.
\[ E_a = \frac{\text{Water stored in root zone}}{\text{Water delivered to the field}} \times 100% \]
The question asks for the typical application efficiency of "conventional surface irrigation" methods.
Step 2: Detailed Explanation:
1. Conventional surface irrigation methods include flood, furrow, border, and basin irrigation. In these methods, water is applied to the surface of the field and allowed to flow across it by gravity.
2. These methods are known to have significant water losses, which lower their efficiency. The main losses are:
Deep percolation: Water percolating below the crop root zone, where it is unavailable to the plants.
Runoff: Water that runs off the end of the field without infiltrating.
3. Due to these losses, the application efficiency of traditional, unimproved surface irrigation systems is notoriously low.
4. Let's compare typical efficiencies of different irrigation systems:
Surface Irrigation (Conventional): 30% - 60%. A commonly cited average range is 40% to 50%. With significant improvements (like land leveling, surge flow, cutback streams), it can be higher, but the question asks about "conventional" methods.
Sprinkler Irrigation: 60% - 80%.
Drip (Trickle) Irrigation: 85% - 95%.
5. Looking at the options, the range of 40 to 50% is the most representative average for conventional surface irrigation methods under typical field conditions. The provided key indicates (C) 40 to 50%. However, the solution in the image shows (B) 30 to 35%. Let's reconsider. In many poorly managed traditional systems, efficiencies can indeed be as low as 30-35%. However, a more general and widely accepted range for average performance is 40-50%. Given the ambiguity, both B and C are plausible depending on the assumed level of management. If the key is B, it implies a focus on less efficient, traditional practices. If the key is C, it represents a more general average. The checkmark in the image is on option 3, which is 40 to 50%. I will follow the checkmark.
Step 3: Final Answer:
The typical field level application efficiency of conventional surface irrigation methods is in the range of 40 to 50%. Therefore, option (C) is the correct answer.