Which factor primarily determines the efficiency of an irrigation system?

The efficiency of an irrigation system is primarily determined by the uniformity of water distribution across the field. This aspect is crucial because effective irrigation relies on delivering the right amount of water to each part of the field to meet the plants' needs. Uniformity ensures that all areas receive adequate moisture, which can prevent issues such as overwatering or underwatering specific zones, leading to improved crop yield and health.

When water is distributed uniformly, it reduces the chance of waterlogged areas that can negatively affect crop growth and minimizes water waste, ultimately promoting a more sustainable irrigation practice. In contrast, factors like installation cost, crop type, and size of the system, while important, do not directly influence the effectiveness with which the water is applied across the entire area. Uniformity in water distribution is thus the key factor that determines how well an irrigation system serves its intended purpose.