Special Focus – Irrigation 2012
Todd Posted March 21st 2013
Irrigation is yet another integral part of our farm operation. Unless there is a good rain fall, irrigation management is a daily task that follows a flexible weekly rotation based on areas of highest priority. The farm is divided into blocks that reflect the maximum amount of watering achievable within the operational pressure. A block is watered for a determined amount of time before being turned off and moving to the next. Within these blocks, there are basically three ways that we set up lines to accomplish our watering needs. All lines follow this order: the well pump to the main lines, main lines to sub-main lines, sub-main lines to drip lines.
Field crops: 200 foot beds each planted with two rows. A single line of drip tape is used for these beds. A spool of drip tape is held horizontally in a wooden stand on a piece of rebar. It is stationed at the start of the bed and the line is pulled from this down the middle of the two crop rows to the far end. Attention is given that the tape is tucked beneath all plants. The tail end is then capped by cutting a section of the drip tape two to three inches long to act as a sleeve. The new end of the line is then folded over a couple times and inserted it into the sleeve (see picture). These lines are then secured to a thumb valve in the sub-main. Our flowers in the “579 field” also require only one line of drip tape.
See Photo set for more detail
Big garden beds: 100 foot permanent raised beds usually very tightly planted. For these five lines of drip tube are used. This task is most easily accomplished with two people, starting with the center line and working outward to either side. One person at each end pulls the line taught then lays it straight and evenly spaced down the length of the bed. These lines are secured to a thumb valve in the sub-main and capped on the end with a plastic end cap. This could be a pressure valve that bleeds the line and automatically closes or a repurposed thumb valve. There are two beds of fruit trees, black berries, and asparagus. Each has two lines of drip tube that are treated the same way.
Green houses: We have two green houses for production, one 50 feet long the other 75. Each has four beds typically planted with two rows each and trellising down the middle. Two lines of drip tube are laid just outside of each crop, secured to a thumb valve in the sub-main, and capped with plastic end caps. Again this could be a pressure valve or a thumb valve. Our strawberry beds and the permanent beds in the “corner garden” area share the same configuration of two lines of drip tube.
The well pump is turned on at the begging of the season and off at the end. The main line always remains in the same location. Sub-main lines along with the drip tubes are disconnected and stored together in the fields over winter. These lines are reassembled as we proceed through the planting secessions. When the season is in full swing the lines move very little, so irrigation is a matter of turning the correct valves on and off in the appropriate timing and making any repairs. Starting in the morning the main valve is turned on. This comes directly from the well. When starting a block the sub-main line is connected to the main line. All of the desired thumb valves are opened and the undesired valves are closed. Finally the valve from the sub-main to main line is opened. The lines will fill with water and begin to drip. It will take a few minutes for the system to pressurize and some air will be forced out of the end. The very end of all the lines must be checked for full pressure. Steady dripping can be seen at these furthest points. If all lines are functioning properly then the pressure gage at the sub-main main line connection is read and this information is recorded in the log along with the date, location, and duration. This log also contains any rainfall data that we have collected, which plays a role in our rotation.
If the line fails to pressurize and begin dripping, it is then walked backwards to the beginning. In this process all connections and valves are checked, along with checking for any holes or damages. The issue usually become obvious and is promptly resolved. Watering in the seedling greenhouse is typically done manually by the green house manager. This will result temporarily in a lower pressure reading but will not greatly disturb the irrigation rotation. If pressure still cannot be achieved and all lines have been checked and rechecked, then it could be that water is being used somewhere else however irrigation is usually given priority. The worst case scenario in the irrigation system would be a failure of the well pump. I did not experience anything like this.
On the more sophisticated side we have used water sensors that are buried in specific locations around the farm. Most times though, the soil moisture is assessed by picking a representative spot for a specific watering block, digging down a few inches to retrieve some soil, and pressing it between your fore finger and thumb.
Damage and Repair
Damage to irrigation will make its self known when turning on the water and walking the lines. Often the damage can either be seen or heard. All repairs are rather easy; it is a matter of assessing the damage and making the fewest and most affective repairs or alterations. Simpler is better. After that it comes down to timeliness for rejoining the crew with the other tasks at hand. Holes in lines are cut out and replaced with sections of new line where necessary and spliced together with an inline connecter. Often cutting out the hole and putting an inline connecter will fix it without having to add new drip tube or tape.
Most damage is due to the mower hitting lines, no irrigation components will withstand this. It is most common that the mower may take off the end caps of lines in the big garden beds, or hit lines that have been moved or stored in vulnerable locations. It is less common that the mower should hit component of a main or sub main. Repair requires removing damaged sections of lines or fixtures and replacing them.
The weed-wacker will break the red tabs on the thumb valves and the pressure gauges. The sun will also make the plastic tabs brittle. One way or another they will eventually break off. They will still be usable but it is important to note that the plastic can be sharp enough to cut ones figure when turning on an off. We prolong the life of thumb valves by using them as end caps when they are too difficult to turn.
Drip tape is far more easily damaged than drip tube. This most commonly occurs during harvesting with the harvest knives. This year an interesting issue was the amount of small holes chewed by animals in the drip tape of our furthest field. This happened during the hottest and driest time of the summer. We attempted to address it by providing water for the wildlife is an old sink that we set up on the edge of this field. Many of these lines still required repeatedly repaired.
Water lines: Main lines, Sub main line, drip tube, drip tape
Hardware: Main ball valves, aluminum quick connects and end caps, thumb valve, end caps, in line connects, pressure gage, main valve, hose clamps, 1” and ¾” plastic elbows, tee’s, reducers, and end plugs.
Tools: The tools consist of a utility knife, a hexagonal head screw driver for the hose clamps, the hole punch for adding thumb valves to sub main lines, and a roll of Teflon tape. These items are always carried in a small “job bucket”, hardware is added according to task.
Timing is important. I have forgotten and turned off irrigation late. This resulted in some flooding. Thankfully it was never too bad. On the other hand, by the time we are done transplanting a row in the fields in the middle of summer, all the plants look pretty wilted and sad. Irrigation must be available for them right away. By the time that they are turned off, they are standing up looking much happier and eager in their new homes. Also, turning the well pump on and off gives a clear sense of begging and ending to the season.