It has been reported that more than 4,500 years ago the hanging gardens of Babylon were drip irrigated. Modem drip irrigation as we know it today is about 50 years old. In this short period of time many system designs have evolved. Some of the major installations are surface, subsurface, permanent and disposable systems as well as household, commercial landscape and agricultural applications.
Types of System Designs
The four (4) systems we are going to deal with are as follows:
• Surface Drip Irrigation (SDI)
• Subsurface Drip Irrigation (SSDI)
• Permanent, and
SDI has probably been around the longest period of time and is generally used in orchards, vineyards, and permanent plants. SDI is also used as a supplemental system where a sprinkler system is used to sprout the crop to be grown. After stand establishment, the sprinkler is removed and then the drip lines are laid down on top of the ground on every other row and are then used to finish growing the crop. The surface drip lines are then removed just before harvest.
SSDI found its general acceptance in sugar cane fields and other large field applications where some machine operations were necessary, such as cultivating and spraying. Most of these SSDI systems were considered disposable and as a result where used only to grow one or two crops and then removed from the field and thrown away. Strawberries provide a classic example of an SSDI system that is used once and then disposed of.
In recent years there has been considerable effort expended to permanentize SSDI by using thicker walled drip tape, burying it deeper and also developing specialized equipment to till the soil above and between the buried drip lines.
Starting in 1980 Sundance Farms and Arizona Drip Systems in Coolidge Arizona began working on these two problems with some degree of success. One of the first things that had been done, at Sundance Farms, to help permanentize SSDI was to design an injection shank that would bury the drip tape 8' to 12'deep to provide for some tillage above and between the tapes. This machine was developed in 1986 and was granted U.S. Patent # 4,637,755,.
The next problem that needed to be addressed was how to deal with the crop residue to go to the next crop and still respect the buried drip tape under the bed of each row of crop plants. Since cotton was the principal crop grown on Sundance Farms, some method or machine was needed to pull the plants up by their roots and to incorporate the whole plant residue in the first 4' of the soil.
After several years of work, several experimental models were developed with a lot of patience and some luck. A Sundance root puller and disk was invented and patented.
The invention of these two machines made it possible for a broad range of crops to be grown on a permanently buried drip tape. This became a major break through because it eliminated the need and associated cost of an annual removal and
replacement of the drip tape.
SSDI systems can be installed at various row spacing. Most melon installations are spaced anywhere from 60' to 80' apart, depending on the crop to be grown and a grower's personal preference. Other row crops are grown on rows as narrow as 30' and as wide as 42' again depending on the grower's preference.
On the 60' to 80' drip tape spacing, and when the grower wants to rotate out away from melons, other row crops such as cotton and grain can be planted on either side of the drip tape. By pre-irrigating the beds and driving the salt to the surface and then using a peel-off disk to remove the salt and any dry soil, the seed is placed in good moisture and salt free soil, both of which will ensure a perfect stand. This procedure allows for a crop rotation on buried drip lines.
Another major break through that took place about the same time was the development of the turbulent flow emitter by Netafim Irrigation which was built into the drip tape to reduce the chances of the emitter orifice becoming plugged with sediment or other contaminates that might be present in the water.
The first of this type of drip tape was installed at Sundance Farms in April of 1987. After 13 years of use the orifices show lime or no plugging. Other factors that helped to prevent plugging are proper filtration, acid treatment, and periodic chlorination of the water, flushing out the system and finally maintaining proper operating pressure on the system. Flushing of individual drip lines made much more cost effective by manifolding the lines so that the whole field could be flushed by opening the valves at the end of the flush line. Instead of taking several hours to flush the individual lines in a field, it can now be done in a few minutes. Another benefit of the collector flush line is that it equalizes the pressure on the drip block and also can be used as a submain to feed the drip tapes from the lower end of the field.
There are other products on the market today such as fiberglass sand media filters equipped with either stainless steel or polyethylene pipe manifolds, and PVC or plastic valves which deliver the water into black polyethylene drip tape buried under the ground which help to complete the almost indestructible irrigation system.
At Sundance Farms and Arizona Drip Systems, we say, 'a properly designed, installed, operated, and maintained SSDI is the cheapest irrigation system on the market today, when amortized over the life of the system'.
Another quite popular SSDI is the disposable one. The design of this system utilizes much thinner walled drip tape, lay-flat submain or thin walled PVC pipe and the use of a portable filter station thus eliminating all main water delivery lines. None of the drip tapes are manifolded which further reduces cost.
Crops such as melons and tomatoes that need to be rotated to new ground after each crop use the disposable system quite effectively, especially when it is installed on leased ground.
The issue of salt and salt accumulation in the soil profile usually comes up when SSDI is mentioned. Since the drip tape is placed 8' to 12'below ground, the water is offered to the soil under pressure so that even the most alkaline parts in a field will take as much water as the more porous portions of the field. The movement of the salts is to the terminus of the wetted front. This then leaves the root zone relatively salt free with the salt accumulating on the surface of the bed. Sundance Farms, working with Arizona Drip Systems, has developed a peel off disk which is used to remove the top one or two inches of the bed which contains the salt.
Sundance Farms started with EC levels as high 12; after one year of SSDI, the salt levels have dropped to an EC of three and have stabilized in that range for more than 20 years. Because of these results we have concluded that an SSDI system is the best way to manage salt yet devised. Because the water is delivered 8' to 12'below ground under pressure of 10 - 15 psi, thus forcing the salts out of the root zone and to the periphery of the wetted front.
With a broad range of products on the market for every aspect of a drip system, designs can be made to fit almost any need.
Drip systems are not just water savings devices. They also provide for a number of other benefits that increase profits through higher yields and better quality as well as reducing the amount of fertilizer being used along with other chemicals needed to produce various crops. For a number of crops, the SSDI system provides for timely field accessibility which is vital to obtain high yields and top quality.
By performing minimum tillage over the SSDI system, significant savings have been realized along with better tilth and higher organic matter in the soil. According to Dr. R. Lal at Ohio State University, five times as much C02 is released into the atmosphere when soil is moldboard plowed as compared to stubble-mulch or minimum tilled soils.
Through the use of minimum tillage, Sundance Farms has doubled the organic content of its soils. SSDI systems are generally considered as a primary irrigation system that is used to sprout the crop grow the crop and allow for a free and unencumbered harvest without regard to any components of the irrigation system being in the way. However, when small seeded crops such as lettuce and broccoli are grown, whose seeds are placed no deeper than 1/8' below ground, sprinklers are recommended to sprout the crop and wash the salt out of the seed zone. By sprinkling and drip irrigating at the same time, the salts are driven to the surface so that the sprinkler can wash them away. Usually 1.5' of water through the sprinkler and 1'of water from the drip will produce an outstanding stand. The valve tree used for the drip system can be retrofitted with a valve for the sprinkler booster pump. This hookup provides the opportunity to sprinkle and drip irrigate at the same time.
In order for irrigated agriculture to succeed in the 21st century, production costs will have to be cut and yields increased. The only way Sundance Farms has been able to deal with these problems is with permanently installed SSDI, minimum tillage and a diversified crop mix.