Bobbi Stevenson-McDermott August 21, 2016 publication
It’s been a long, hot and now humid summer, and we are still not through it. The farm fields that have been between crops since mid July are beginning to be prepared for the fall produce crops. Some crops, like head lettuce are still planted using seed and as soon as the planters leave the field, the sprinklers are set up.
In the late 80’s and early 90’s, after the lettuce was planted, the fields were flooded and the water held in the field continuously for 6 to 10 days, a practice called ‘subbing’, until the water moved into the lettuce beds and caused the seed to germinate. As time went on and more acreage was being put in produce, the irrigation districts started to have problems proving all the ‘sub heads’ to the farmers who needed them. The irrigation district delivery systems only have a limited capacity and to spread the water where it was needed became a challenge.
While some farmers were already using sprinklers to germinate their crops, it was not the normal practice. With the difficulty of watering thousands of acres at the same time, the irrigation districts encouraged the use of sprinklers, since it took less water to keep the sprinklers operating than flooding. The grower uses a portable pump and pumps water from an irrigation ditch on the farm that serves as a reservoir for the sprinkler water during the germination process.
One of the best byproducts of the use of sprinklers was the amount of water saved during the germination process. When fields are subbed, holding the water in the furrows used up to 3 feet of water, depending on the weather. Sprinklers encourage rapid germination, 2 to 3 days, and normally only use about 6 inches of water. The result was almost 30 inches of water saved on every acre sprinkled. This helped reduce water table problems from deep percolation and speeded up the germination process.
In addition, sprinklers create a cooler microclimate when they are running. Even though the air temperature may be 105 plus degrees, under the sprinklers the temperature is 75 to 85 degrees, perfect for seed germination. The August-September planted crops also have greater insect pressure than crops planted in the cooler months. The white fly is a particular problem in early Fall. The sprinklers keep the bugs from the plants and wash them off if they happen to land.
Sprinklers are also used on transplanted crops such as cauliflower, broccoli and cabbage. As soon as the transplanter leaves the field, the sprinkler pipe is laid and the water turned on. Growers are experimenting with different transplanter designs that allow the sprinklers to be placed in the field prior to transplanting, making the process more efficient and getting water to the little plants immediately.
In the beginning, many growers rented pumps and sprinklers. As time has gone on, most have purchased their own systems to better manage their irrigations. To keep track of whose pipe was whose, growers initially painted their equipment. With the tremendous amount of pipe now used, growers have identification numbers etched into their pipe. It is not uncommon though, to still see pink, green or blue sprinklers in fields.
Several years ago, a letter appeared in the Phoenix paper from someone who had traveled through on the freeway and saw the sprinklers running in the middle of the day. They were protesting the ‘waste’ of water in Yuma. Nothing was further from the truth.
Locals can be confused by the fact that when it rains, the sprinklers are turned on the small produce. One drawback of the sprinkler is our 10 foot per year evaporation rate. When the irrigation is done, the evaporation of water from the soil surface leaves calcium and other salts on the soil surface. When the plants are young, those salts need to be diluted before they reach the plant root zone. The amount of rain Yuma County gets in one event is often only enough to drive the salts into the plants roots, not past them. This can cause the little plants to die, so when it rains, the sprinklers run.