Nursery Irrigation Continued

Growing in the field

Don't make the mistake of buying pipe, pumps, and other equipment without knowing what you really need. What your neighbor did my not work in your situation. This seems to be the most common mistake growers make.

We must first determine the factors on which we will base the design. These include information such as row spacing and plant spacing down the row, length of row, soil structure, water requirements of the plants being grown. It is to the grower’s advantage to group plants with similar water requirements in the irrigation area.

It is important to have accurate information about the dimensions of the site that has been chosen. We use this information to determine both the quantity of dripperline per acre and the flow rate per acre. Since our goal is to replace the water used by the plants on a daily basis, called ET (or evapotranspiration), we must know how much we can expect them to use.

Depending on your location’s climate (see chart above), we choose a target amount of water to be applied. This is stated in inches per acre per day (TIP: 1 acre inch equals 27,154 gallons of water). For most of the Deep South, the target amount is .3” per acre per day, or approximately 8150 gallons per acre. This amount must then be modified by what is called a crop coefficient for your particular crop. This is simply a reference crop that is used as a basis for determining relative water requirements to the reference crop: either more, the same as, or less than. Let's say your crop coefficient is 1.1. Multiply 8150 by 1.1 to get 8961. You need to apply 8961 gallons per acre per day to meet your crop's requirement. If your crop coefficient is .7, multiply 8150 by .7 to get 5705. You need to apply 5705 gallons. This amount of water represents the net volume that needs to be applied on a daily basis per acre.

Properly designed drip irrigation systems are about 95% efficient in delivering the water to the root zone. We must divide by .95 the amount of water we desire to put on per day. This figure will give us the gross amount of water required to supply the net amount desired. Since most of the feeder roots of commonly grown woody ornamentals are found in the top 12 to 15 inches of soil, this is the area in which we must manage our moisture. The soil type, along with the tree spacing, will determine the spacing and flow rate of the drippers selected.