What should be observed during a test spray on pavement to check boom height?

Observing how evenly the spray dries is crucial when testing boom height on pavement. This factor allows for an evaluation of coverage uniformity and the effectiveness of the spray pattern produced by the boom. If the spray dries evenly, it indicates that the application was consistent across the treated area, suggesting that the boom height is appropriate to achieve effective herbicide distribution.

When the spray dries unevenly, it could suggest that adjustments are needed in boom height or nozzle configuration to ensure that the entire area receives the correct amount of herbicide. This can impact the efficiency of the herbicide treatment and the control of target weeds.

Evaluating the other aspects mentioned in the options can provide additional context but does not directly measure the effectiveness of the application in terms of coverage. For example, observing how much liquid splashed may indicate issues with pressure or nozzle type but does not relate directly to the evenness of coverage. Similarly, the speed of evaporation might be impacted by environmental conditions rather than the performance of the sprayer itself, making it less relevant for assessing boom height. Lastly, measuring how far the spray travels is important for understanding drift potential but doesn't directly relate to the uniformity of application.