Nozzle spacing and boom height: Spray nozzles used for broadcast spraying do not deliver a uniform quantity of material over the width of the spray pattern (Fig. 6). The distribution pattern is determined by nozzle design, nozzle wear, nozzle clogging and pressure at the nozzle.
When a number of nozzles are spaced on the boom, the individual nozzle spray patterns must overlap to obtain more uniform distribution over the entire boom width. Nozzle manufacturers recommend a boom height for each particular nozzle and nozzle spacing. Improper boom height will result in uneven distribution patterns (Fig. 7). Anything that changes boom height such as rolling land that causes the boom to tilt and rough land that causes the boom to bounce up and down as well as forward and back will affect the distribution pattern.
Effect of pressure: Pressure may also affect distribution patterns. In tests conducted at the Prairie Agricultural Machinery Institute in Canada, poor distribution was obtained at 20 pounds per square inch (PSI) (Fig. 8). The actual application varied by more than 40 percent above and below the recommended application rate. However, when the pressure was increased to 40 PSI, a good distribution pattern was obtained (Fig. 9). This illustrates that if the pressure is changed, boom height should be checked to make certain uniform distribution is being obtained.
Double application or skips can result from either the boom overlapping or not matching with the boom pattern of the previous trip across the field. Boom markers that spray a readily visible material will help solve this problem.
Uniformity of distribution can be checked by operating the sprayer as it is crossing a dry, smooth surface such as concrete and observing the drying pattern.