The Evolution of Subsurface Drip Irrigation on Sundance Farms

Transcription

1 The Evolution of Subsurface Drip Irrigation on Sundance Farms Item Type text; Article Authors Wuertz, Howard; Tollefson, Scott Publisher College of Agriculture, University of Arizona (Tucson, AZ) Journal Cotton: A College of Agriculture Report Download date 30/06/ :40:15 Link to Item

2 The Evolution of Subsurface Drip Irrigation on Sundance Farms Howard Wuertz and Scott Tollefson, Sundance Farms Sundance Farms has been involved in the development of drip irrigation for cotton since Initially the farm started with a one -acre test plot and has presently expanded the acreage to over 1,500 acres for Much of the technology incorporated into the systems was previously established by drip pioneers in Hawaii, California, and Israel. Unlike our predecessors, however, Sundance Farms attempted to expand subsurface drip from high value crops to field crops such as cotton and grain. In order to establish the feasibility of drip for cotton, it was essential that we first determine if significant water savings could be realized, and more importantly if the yield plateau of 2.5 to 3.0 bales per acre could be broken. Historically, our drip yields have ranged from 3.25 to 4.50 bales per acre and have surpassed furrow yields by 12% to 50% over the past six years. (Table 1) Management strategies formulated for drip cotton have also been transferred to furrow irrigated fields. Light and frequent irrigations, coupled with carefully timed fertilizer applications, have resulted in substantial yield increases for furrow cotton, typically averaging 25% to 30% over the state average of 2.25 bales per acre. Table 1. Cotton Yield Comparisons - Bales /Acre Year Sprinkler Furrow Drip % Increasea apercentage Increase of Drip over Furrow NOTE: Furrow Cotton Rotated with Wheat in 1981, 1982, and Drip Cotton Fields Rotated With Cotton on Cotton in 1982 and Water use, our most expensive crop input, has consistently been reduced by more than half when compared with furrow irrigation. (Table 2) Fertilizer use, specifically nitrogen, has been comparable for both furrow and drip. Table 2. Cotton Water Use Comparisons - Ac.In. Applied Water Year Sprinkler Furrow Drip Differencea adii Terence is Drip Versus Furrow NOTE: 1983 Water Cost - $3.15 acre /inch March, 1987 Cotton Report Page 122

3 In Arizona, there are two schools of drip irrigation: Surface systems patterned after technology developed in Israel, and subsurface or buried drip systems. The above ground systems utilize 40 mil in -line emitter tubing placed on the surface every 80 ", or in other words every other row. Upon completion of the crop, drip lines and submains are retrieved and the field tilled conventionally, i.e., plow, disk, landplane, etc. The tubing is then replaced prior to planting the next crop. Subsurface systems typically have 10 to 15 mil drip lines buried 2 to 12 inches deep and spaced every row or every other row. The key to Sundance Farms' success has been the ability to permanently bury drip lines every row to a depth of 8 to 10 inches, and then farm around the system with a minimum ammount of tillage. Since removal of the irrigation system is no longer necessary, a considerable amount of time, energy, and labor is saved. Another advantage to subsurface irrrigation is that PVC and polyethylene materials are shielded from temperature extremes, harmful UV light, and mechanical damage. The oldest tubes on the farm have been buried for six years, produced seven crops, and show no signs of deterioration. In the past six years, we have developed maintenance strategies essential to clog -free, top performing tubes. Another major concern has been the maintenance of soil productivity in spite of intensive farming practices associated with drip. DRIP SYSTEM MAINTENANCE In order to make drip economical for field crops, it is critical that equipment be maintained and stand the test of time. Filter stations should last 12 to 15 years, PVC pipelines 30 years, and drip tubing 10 years plus. Historically, most drip irrigators have had little trouble maintaining filters and PVC pipelines, but have failed to get more than a season or two out of the lighter weight (6-20 mil) drip tubes. Proper tube maintenance starts with irrigation system design. At Sundance Farms, we utilize water from deep well turbines which pump directly into the system. Sediment is initially settled out as it passes through 20,000 gallon surge tanks. Inorganic materials such as rust, sand, silt, and clay are further removed in banks of sand media filters. To assure filtration in excess of 200 mesh screen, 20 silica sand is used in all media filters. The filtration system is equipped with automated backflush to purge tanks on a timely basis. The pressurized, filtered water is conveyed to the fields via buried PVC pipelines and electric control valves. Mainlines which range in size from 10 to 15 inches in diameter are equipped with valves or removable end caps to facilitate flushing. Drip tubes receive water from submains consisting of 6 to 8 inch PVC pipe, which usually extends 1200 feet. At the end of submains, the 6 inch pipe is reduced in size to accommodate 4 inch flush valves. The polyethylene drip tubes are buried 8 to 10 inches in every row. Although standard flow Hardie bi -wall tubing is designed to run lengths in excess of 800 feet, we prefer 600 to 650 foot runs which aids flushing. In order to minimize hand labor, the ends of tubes are manifolded in groups of 100 to 2 inch PVC flushing lines. Another advantage to manifolding ends is water flow now occurs from both ends resulting in reduced contamination when lines break. Chemical treatment of water is another aspect of system maintenance that must not be overlooked. Sulfuric Acid (H2SO4) is used to keep salts such as calcium carbonate and bicarbonates in solution. Acid is also used in conjunction with chlorine treatments and has been found to synergize the biocidal activity. Chlorine must be administered frequently to subsurface tubes regardless of the water quality. We have discovered that almost all of our plugging occurs from the outside and is the result of bacteria native to our soils. Upon shut down of the system, soil born bacteria is drawn into the orfices and begin breaking down silicate particles. The bacteria excrete a slime which bonds soil particles together forming an impervious block. Researchers from Hardie Irrigation Systems discovered that strong solutions (1000 ppm) of hydroflouric (HF) acid plus a surfactant could remove plugs. The treatment was administered to several fields with a high rate of success reported. In spite of the ability to remove plugs with HF, the process was deemed too expensive and hazardous to use on a routine basis. March, 1987 Cotton Report Page 123

4 Sundance Farms has adopted a form of preventive maintenance utilizing bi- weekly applications of 7 ppm chlorine at a ph of 6.5. The use of gas chlorinators and H2SO4 supplied in bulk from copper mines make the treatment simple and inexpensive ($2.50 per acre per year.) MAINTENANCE OF SOIL PRODUCTIVITY It was realized early that water savings and system longevity were without question very important but fell short of the mark when it came to paying for a $1,200 per acre drip system. The primary objective in converting drip was to increase yields. To accomplish this goal it was necessary to address four critical areas: (1) Crop rotations; (2) salts; (3) minimum tillage; and (4) soil born parasites and pathogens. CROP ROTATION Before ever embarking into drip, it was realized that our success as cotton farmers was closely tied to crop rotations. Most of the soils farmed are classified as sandy barns with sand levels nearing 80% in some fields. Caliche (CaCo3) layers limit the effective root zone to 3 feet or less. It was not surprising to learn that a rotation with small grains was essential for high yielding cotton on drip. Because of Arizona's exceptionally long growing season (3,800 heat units) and the ability to push early maturing varieties of barley and cotton, double cropping became a profitable alternative. Proper variety selection coupled with intensive management has enabled the production in excess of 5,000 pounds of grain and 3 bales of cotton in double crop mode. Normally, one crop of grain is rotated with every two crops of cotton. SALT MANAGEMENT Subsurface drip, if used properly, can have a dramatic impact on salt management. Ina short term, we have been able to establish excellent stands of grain and cotton on soils with EC levels that ranged from 6 to 12. By placing tubes below every listed bed, salts have been pushed away from the seed with the wetted front when irrigating up. Experience has shown that salty fields should be irrigated during rains to further protect plants after emergence. In addition to establishing stands in salty soils, we have also noted substantial declines in salt levels from year to year. (Table 3) As noted earlier, since half the water is applied with drip irrigation, half the salts are also applied. Application of water every row at the root zone pushes salts away from the plants and into the furrows. Irrigation during rain continues to push salts out of the effective root zone. The use of sulfuric acid as an amendment to the water helps to maintain an open soil profile, further enhancing leaching. Table 3. Soil Salt Levels (EC) In Drip Fields vs. Furrow Field No. Field Before Drip Field After Drip Conversion * * Field 50 is a Surface Drip Installation, i.e., Lines Are on Top of Ground at 80 in. Centers. All Other Fields Are Subsurface Drip Installations. NOTE: Pump Water Salt Level for Fields 50 and 55 are 450 ppm. All Other Fields have Pump Water Salt Levels Ranging from 800 to 3000 ppm. March, 1987 Cotton Report Page 124

5 MINIMUM TILLAGE The advent of subsurface drip irrigation on Sundance Farms had a profound impact on the way fields were tilled. While four -wheel drive tractors, plows, disks, and landplanes became obsolete, it also forced us to adopt the concept of minimum tillage. The objective was to shred stalks, kill roots, and incorporate residue in the top 4 to 6 inches of soil just above the drip lines. Initially, commercially available minimum tillage rigs were evaluated. On paper, these rigs were designed to do all required in one pass over the field. In general, the machines were complicated, slow, and most importantly did not kill 100% of the roots, a requirement set by the Agriculture and Horticulture Commission of Arizona. Over the past three years, through extensive testing and experimenting, the "Rolling Root Puller /Cutter" was developed. The rig incorporates a set of disks oriented at a 90 degree angle to one another to form a V- shaped pulling action and/or cutting edge capable of destroying all the roots 3 to 4 inches below the soil surface. A typical sequence of operations to till grain or cotton would be as follows: 1. Shred stalks with a four -row, flail -type shredder. 2. Root pull/cut roots with six -row rolling root puller /cutter. 3. Re -list beds with a disk lister. 4. Peel off top of beds and incorporate herbicide with six-row rotary mulcher. 5. Plant. The shift to reduced tillage has resulted in less compaction, has had no effect on yield, and has cut tillage costs by more than half. NEMATODE AND PLANT PATHOGENS A review of existing literature reveals a re- occurring plant pathogen /nematode problem associated with both minimum tillage and intensive drip irrigated farming. At Sundance Farms, an increase in the incidence of root knot nematodes has been particularly noted. Since cotton fields are no longer summer fallowed but double cropped with grain, the host free period is insufficient to break the cycle of nematodes. The more consistent moisture regimes associated with drip irrigation also favors nematode survival. To cope with the problem, we have had to switch to tolerant cotton varieties i.e., semicluster types, and utilize chemical control. Drip irrigation provides a perfect vehicle to deliver a variety of chemicals directly to the root system. Early on in the farm's experiments with drip, we dabbled with several forms of fertilizer, such as UN 32, centrifuge grade phosphoric acid, NPK mixtures, and micronutrients. The excellent results achieved with fertilizers prompted us to experiment with herbicides, insecticides, nematistats, and fumigants. The injection of herbicides and insecticides is still experimental, but the commercial use of nematicides has been an absolute necessity. Portable injection rigs built on the farm have enabled the delivering of nematistats such as Vydate, Lannate, and Nemacur quickly and safely. To make our control program complete, fumigants have also been used and excellent results with EDB has been attained in years past. (Table 4 and 5) Most recently, a rig has been designed capable of emulsifying and injecting Telone into drip systems. The use of Telone should reduce control costs considerably and aid in the production of nematode susceptible crops such as cantaloupes. SUMMARY In summary, Sundance Farms has developed a subsurface drip irrigation system which can be used to grow cotton, small grains, and a variety of specialty crops economically. Proper management and maintenance of the drip system has enabled the 15 mil bi -wall tubing to be permanently buried 8 to 10 March, 1987 Cotton Report Page 125

6 inches below ground. The yield history and cost analysis of the farm's oldest drip field (Table 6) lends credence to these statements. Table 4. Drip Fumigation Trials for Control of Root Knot Nematode (meloidogyne incognita) TREATMENTS Untreated Soilbrome Check Vapam 90 EC No. of Nematodes Per 250 cc of Soil 1, NOTE 1: Fumigants Injected Into the Drip Lines Directly With.25 Inches of Water as a Carrier NOTE 2: Soil Temperature at Time of Injection -58 deg. F NOTE 3: Rates: Vapam - 25 gal /ac. at $100 /acre Soilbrome -1 S gal/ac. at $16 /acre Table 5. Fumigation Trials - Yield Comparisons Untreated Check TREATMENTS Vapam Soilbrome 90 EC Lint Lbs/Acre 1,123 1,430 1,596 NOTE 1: First Pick Yields Only NOTE 2: DPL 90 Variety Year Table 6. Production Records on Subsurface Drip -Field 17 Yield Per /Acre Price Per Pound Value Of Crop Production Cost Net Income Bales $.70 $1575 $750 $ Bales $.70 $1260 $750 $ # Wheat $6.50 /cwt $442 $300 $142 $.65 $913 $550 $ Bales $.62 $1395 $750 $ # Barley $6.00 /cwt $300 $ Bales $.60 $900 $550 $350 March, 1987 Cotton Report Page 126