Introduction:
When it comes to irrigating standing crops in undulating sandy fields, the most suitable method is sprinkler irrigation. This method involves the use of sprinklers to distribute water evenly over the crops. Let's delve deeper into the reasons why sprinkler irrigation is the preferred choice for such fields.

Reasons for choosing sprinkler irrigation:
1. Uniform water distribution: Sprinkler irrigation ensures that water is distributed evenly across the entire field. This is particularly important in undulating sandy fields, where the topography can vary and make it challenging to provide uniform water coverage. The sprinklers are strategically placed to cover the entire field, preventing any areas from being over- or under-irrigated.

2. Minimal water loss: Sprinkler irrigation minimizes water loss due to evaporation and runoff. Since water is sprayed directly onto the crops, there is less chance of it evaporating before reaching the soil. Additionally, the water droplets are relatively large, reducing the risk of runoff on sandy soil that has low water-holding capacity.

3. Reduced soil erosion: Sandy soil is prone to erosion, and traditional irrigation methods like free flooding can exacerbate this issue. With sprinkler irrigation, the water is applied gently and at a controlled rate, minimizing soil erosion. This is particularly beneficial for undulating fields where the soil can easily be washed away from sloping areas.

4. Flexibility in application: Sprinkler irrigation allows for flexibility in the timing and frequency of irrigation. Farmers can adjust the sprinklers to irrigate at specific times of the day when the crops need it the most. This flexibility is crucial in sandy fields, as they tend to drain water quickly, and frequent irrigation may be required to maintain optimal soil moisture levels.

5. Cost-effective: While the initial setup cost of sprinkler irrigation may be higher compared to other methods, it offers long-term cost savings. The efficient water distribution and reduced water loss result in lower water consumption, ultimately reducing the overall irrigation costs.

Conclusion:
Sprinkler irrigation is the most suitable method for irrigating standing crops in undulating sandy fields. Its ability to provide uniform water distribution, minimize water loss, reduce soil erosion, offer flexibility in application, and be cost-effective make it the preferred choice for farmers in such environments.