There should be no sags in the lines, particularly after the final distributor. If there are low points in a line, the cold liquid accumulates there until the line fills, and then the pressure builds enough to force the full line to empty. This results in overapplication for some distance along the seed row, causing poor or no crop emergence for several feet of that row. Controllers need to be calibrated for ground speed and for flow through the meter. All monitors come with instructions for calibration and for setting up the control unit for the desired application.
Controllers account for changes in daily temperature and changes in travel speed.
Application rate controllers can change the application rate on the go if the need for more or less nitrogen in certain areas of the field is known. Recent controller designs have a computer communication port so that a computer, with the necessary program information and real-time global positioning, can set the NH 3 meter to a preplanned nitrogen rate for each area of the field. The addition of NH 3 to a direct planter results in many more hoses, fittings, manifolds and so on. These have to be carefully arranged, so the wings of the planter lift without causing kinking or pinching of the lines. Cooling by NH 3 causes frost to form on the lines.