 
If the container
spacing in a typical nursery bed is one foot by 2 feet in an unjammed situation, and the container has
a top diameter of 10 inches, what is the theoretical interception efficiency
for the crop? A similar question could be asked for a greenhouse crop on a bench.
If the container spacing is 1 foot by 2 feet, then the centers of the containers will be the points at the corners of a rectangle 1 foot by 2 feet.
The most difficult calculation is determining the open area on the top of the container; the open area is calculated using the outside diameter of the top of the container. The area of a circle is the constant (Pi= 3.14) x (diameter / 2) 2. The (diameter divided by 2) is substituted for the radius of the circle. This equation can also be expressed simply as:
Convert the diameter, given in inches to feet, by dividing by 12. If using inches is easier for you, then divide the result by 144 to convert to square feet. Just be careful to watch the units! Thus, in our example,
The area of the ground area (rectangle) is length times width.
The Interception Efficiency equals the top container area divided by the total surface area times 100 to convert to percentage.
So, for this spacing, about 27% of the overheadapplied water will fall into the containers and 100  27 = 73% will fall onto the ground. Part of the 73 percent will evaporate, some may infiltrate, and the rest will runoff from the site.
Extra: Container volume calculation: This is useful information to calculate the number of containers that can be filled by a cubic yard of substrate.
