Unlike other irrigation systems, subsurface drip applies water directly to the crop root zone using buried polyethylene drip tapes that come in various diameters and thicknesses. The smaller diameter tapes are used for short lengths. As the run length increases, larger diameter tapes are needed. The thickness of the tape wall is directly related to its durability. Thin tapes are mainly used for temporary installations such as surface drip irrigation of high value crops. The thicker tapes are used for permanent installations. The cost of the tape is directly related to both diameter and thickness.

Small holes called emitters are spaced every 8 to 24 inches along the length of the drip tape. When the tape is pressurized, water passes through the emitters to the soil, drop by drop. The movement and wetting pattern will depend on the soil’s physical characteristics. For instance, in a heavy soil water will tend to move laterally and upward to a greater degree compared to a sandy soil where it tends to move downward. The amount of water that can be delivered through the system depends on tape diameter and spacing, operating pressure, and emitter spacing, size, and design. You can choose from a variety of tapes to fit specific design requirements.

One of the main advantages of subsurface drip irrigation is that it has the potential to be the most efficient irrigation method available today. I stress the word potential because irrigation efficiency not only depends on the type of irrigation system, but also on its design and management.

Since the tapes are usually installed every other row, the system only wets a fraction of the soil, requiring less water and leaving space in the soil to store water from rainfall. Also, since the drip tapes are buried -- about 16-18 inches for corn -- the soil surface stays dry. A dry soil surface means that practically no irrigation water is lost from evaporation or runoff. In addition deep percolation losses can be eliminated. The only small inevitable water losses are those needed for flushing the drip tapes and filtering system. Therefore, subsurface drip irrigation can deliver water with an efficiency of 95% or higher. This means that for every inch of water that is pumped, 0.95 inch or more stays in the crop root zone. Because of the potential high efficiency of this system, it may be especially beneficial where water is limited. Water savings, however, should not be the only factor to consider when selecting an irrigation system.

Water savings

How much water can be saved by switching to subsurface drip irrigation? Furrow irrigation efficiency is usually 65% or less. Assuming that the net seasonal irrigation requirement for corn is 15 inches (taking into account water inputs from rainfall and residual soil moisture), the furrow system would need to apply 23 inches while the subsurface drip system would need to apply 16 inches, a savings of 7 inches.

A reel of the type of tape which is placed underground as part of a subsurface drip irrigation system.

When compared to center pivot irrigation the water savings is not as dramatic. Assuming a center pivot with an irrigation efficiency of 90% and a net irrigation requirement of 15 inches, the producer would need to apply 16.7 inches, a difference of less than 1 inch.

Therefore, changing from center pivot to subsurface drip irrigation does not provide significant water savings; however, switching to it from furrow irrigation will result in significant water savings. Subsurface drip irrigation can be automated for frequent applications of water, fertilizers, and other chemicals such as acids, chlorine or pesticides. Research has documented that spoon-feeding water and nutrients to vegetable crops can result in increased yields; however, the results for corn have not been as fully researched.

Keeping the soil surface dry

Because subsurface drip irrigation keeps the soil surface dry, seed germination may be a problem, especially in sandy soils, since water has difficulty moving up in the soil profile. Additionally, rodents like gophers may chew on the tapes and leaks can be difficult to repair since they require digging the tapes out.

Having the irrigation system underground and keeping the soil surface dry also means that farm equipment can enter the field during irrigation, and there is less potential for weed germination and growth. Subsurface drip irrigation adapts well to fields of any size and shape, unlike center pivots. However, it does not work well in rolling terrain.

Energy savings

Energy savings is another advantage of this irrigation method. Subsurface drip irrigation systems operate at low pressure and deliver small flow rates. Emitters usually require a pressure of 4 to 15 psi and flow rates of 0.16 to 1 gallon per hour. Less energy is required to achieve the low water pressure and a smaller pump than those used for either center pivot or furrow irrigation is needed to achieve the small flow rate.

Cost

Installation equipment Irrigation tape is spooled from overhead down through a tube and into a slot cut in the soil. Tapes used for drip irrigation vary in size and thickness, depending on the intended use and length of row.

The largest disadvantage of subsurface drip irrigation is its high initial cost, which varies from $600 to $1200 or more per acre, depending on field size and level of automation. In Nebraska, an average cost of $800 per acre is a good estimate. This includes the cost of installation, which is around $200 per acre. For a large field, the $800 cost of installing subsurface drip irrigation cannot compete with the cost of installing a center pivot, which costs about $400 per acre.

Economic comparisons of center pivots and subsurface drip irrigation conducted by Kansas State University researchers, however, showed that as fields get smaller, subsurface drip irrigation becomes more cost effective as compared to pivots. Determining the economic break-even point, however, is complicated since the analysis is sensitive to expected crop prices, value of the water saved, expected yield increases, field size, and the life expectancy of the system. Some of these factors are relatively uncertain. For instance, subsurface drip irrigation is a relatively new technology and the life expectancy of system components is unknown. There is a 12-year-old system in Colby, Kansas, where the drip tapes still look and function like new. There are even older systems in California. Design and maintenance of the system also will affect its life expectancy.

In general, center pivots make more economic sense for large areas. Subsurface drip irrigation could be a good alternative for small, odd-shaped fields, especially when irrigation water is limited. Future cost-share programs may make subsurface drip irrigation more economical as the need to save water increases and as concerns about the environmental impacts of irrigation becomes more important.

Aside from cost, it is critical that these systems be properly designed and maintained. Decisions made during the design phase cannot be reversed after system installation. Decisions like tape diameter, length, emitter diameter and spacing, lateral spacing, mainline diameter, type of filtration and injection systems, etc, need to be made by both the farmer and an experienced irrigation system designer. This is particularly important since the recovery value of an abandoned subsurface drip irrigation system is very low.

Clogging

Proper maintenance is absolutely necessary for these systems to be successful. The main problem with drip irrigation systems is emitter clogging. Since the emitters have very small diameters, they can be clogged by very small particles. And once emitters are clogged, there’s no easy way to unclog them.

Soil particles, chemical precipitates, and biological particles all can cause clogs. That’s why the filtration system is one of the most critical parts of the system. When the water’s pH is too high, chemical precipitates, like calcium carbonate, can form inside the tapes. To avoid the formation of chemical precipitates, acid is usually injected in the irrigation water to lower its pH. Biological particles like algae and bacteria slime are eliminated by chlorine injection.

The filtration system will block most soil particles, however some very small particles may still pass through and settle inside the tapes. These particles need to be eliminated by periodically flushing the system. This is why the design must include a good filtration system as well as a proper flushing system. This usually includes connecting the drip tapes to a PVC flush line at the end of the field.

Crop roots growing around the drip tapes also can plug emitters, especially when the soil is dry. Keeping the soil around the tape sufficiently wet and injecting chemicals to kill those roots can eliminate this problem. When water in the drip tapes is drained after irrigation, a negative pressure can be created inside the tapes. Under this negative pressure, soil particles from outside the tapes can be sucked in through the emitters. This can be avoided by adding air/vacuum release valves at strategic points in the system.

NDEQ regulations Although one advantage of this system is that fertilizer and other chemicals can be applied with irrigation water, the producer needs to be aware of some legal issues involved. Before injecting any chemical, the producer will need a chemigation license from the Nebraska Department of Environmental Quality (NDEQ) and comply with all legal regulations. Regulations may even affect where a drip irrigation system can be installed. If you’re considering installing a system, contact the NDEQ to inquire about legal requirements.

Summary

All things considered, subsurface drip irrigation is a highly efficient system, which can be used to help improve the management of both irrigation water and crop nutrients. Because of economics, it has mainly been used to produce high value crops like vegetables and fruits, but its use in row crops is beginning to spread. Here in Nebraska, some farmers are irrigating small fields of row crops and are satisfied with the results. Other farmers have tried it and failed. Causes of failures include cutting corners on key system components, like filtration systems and flushing lines.

1. If the low temperature was above 28^oF, I expect little significant impact on any alfalfa except for some singed leaf edges. Remember, though, that 28^oF at the farmstead may not mean the same temperature in the field. Low spots easily could have been 3 to 5 degrees colder and for a longer time period.

2. New seedlings generally are very tolerant of cold temps, partly due to heat arising from the soil and partly due to natural plant tolerance. Seedlings no older than first trifoliolate growth stage probably handle temps in the low 20s. As they grow, cold tolerance lessens so any seedlings at 4th or 5th trifoliolate stage may be injured similarly to alfalfa seeded late last summer (see below).

3. With well-established stands, if external canopy parts are the only parts showing freeze damage (wilting), there will be little impact. If the growing point froze (the growing point of alfalfa is in the tight cluster of emerging leaves at the top of the stem) and plants are wilting below that cluster, a significant delay in recovery is likely. During the next week, watch for:

   a) new growth emerging from the tip. This means the plant is recovering nicely and no action is needed.

   b) new growth emerging as branches below the tip. This means the growing point was killed, slowing plant development significantly, however, recovery is occurring. Take no action.

   c) new shoots emerging from crown buds. This means the growing point was killed and very little new growth can be expected from existing shoots. Cut or graze if sufficient growth is available for economical harvest before new shoots get tall enough to be damaged by the harvest. CAUTION -- cutting or damaging new regrowth shoots will cause severe, sometimes even fatal, damage. Otherwise, just let the new shoots develop and expect to take first cutting much later than normal.

   d) nothing happening. If the growing point cluster froze and has wilted severely, additional growth from the existing plant is highly unlikely. Harvest or shred plants to encourage new shoots from the crown as quickly as possible. Or wait -- new shoots will come eventually, but slower than if existing plants are removed. If growing point cluster appears healthy, stands straight, and remains green with little or no wilting, the plant may be stunned but should start growing again with warmer temperatures. Do not take any action, but continue observing the plant. If nothing happens after 10 days of favorable temps, harvest or shred.

4. With last year's planting, response is likely to be the same as with well-established stands except recovery, especially from crown buds, is likely to be much slower due to small root and crown containing low level of nutrient reserves. It might be wise to give plants an extra week to start recovering before taking any cutting, shredding, or grazing action that removes green leaves.

5. With plants of any age frozen to ground level, well-established, healthy plants should start regrowing from new shoots emerging from the crown within seven days of favorable temperatures. Old diseased plants and last year's planting will take longer to start regrowing and some may not survive at all. New seedings frozen to ground level are dead -- reseed as soon as possible or plant to another crop.

6. Any plants damaged beyond singed leaf margins can be expected to become ready for first harvest later than usual. Plan accordingly.

Alfalfa weevil scouting This map shows accumulated growing degree days base 48 as of April 28. Most of the state has passed the 350 GDD threshold where feeding damage is likely to be visible and scouting should be underway. Keith Jarvi, Extension entomologist at the Northeast REC, reminds producers to not let down their guard. Recent cool weather has slowed insect developement and their appearance may be a little delayed in some areas, leading to an unwelcome surprise if scouting stops short. (Graphic by Al Dutcher, State Climatologist)

Precipitation data and percent of normal precipitation is provided for all of the sites, for these periods: the last 7 days; April 1 to current date; January 1 to current date, and September 1 to current date. Data is organized by districts and includes district and state averages for each of the categories.

Among the findings in this year's analysis, a drop in farm income of nearly 25%. Bredensteiner blames lower-than-expected market prices and an overall increase in farm expenses for the decline.

“The expenditures are the key,” Bredensteiner said. Farmers who can keep expenses low enough, he says, can better weather low market prices. In fact, says Bredensteiner, the ability to hold down expenses is what differentiates high-profit farms from all the rest. Off-farm income and farm size also play a role. Also on the May 9 broadcast, farmer Gene Watermeier of Unadilla provides a real-world example of how NU's annual analysis can be used in financial planning. He uses it to set his financial goals year-by-year.

“The Nebraska Farm Business Association analysis is a critical tool in analyzing my operation every year,” said Watermeier. “It’s dependable, realistic and unbiased.”

Weed infestations in pasture usually point to a management problem. Pastures are unique systems that do quite well when managed properly. Grazing livestock is a key component of pasture/range management. However, when overgrazing and abuse occur, favorable perennial forages are replaced by a host of invaders and/or exotic plants. When pastures are grazed, vegetative material is removed and openings are left in the grass canopy. When overgrazed, favorable forages are weakened and slow to regrow, providing a good opportunity for weeds to move in and establish.

Chemical control

There are several pros and cons to chemical control of weeds in pastures. For most broadleaf weeds, chemicals work quite well. Depending on the specific weed, either Ally, Tordon, Banvel, 2,4-D and/or combination herbicides such as Grazon, Curtail, Redeem, or Transline will control most infestations. Producers should remember that more than one application may be needed for complete control. Also, in pastures with legumes, such as clover, there is really no good way to selectively control broadleaf weeds without damaging the legumes. Spot treatments may provide acceptable control while reducing the amount of injury to desirable species.

Timing of weed control is also important. If annual weeds are present, including ragweed, sunflower, prostrate vervain, catchweed bedstraw, beebalm and annual sage, control should occur early in the season before the plants are large and go on to produce seed. Perennials such as Canada thistle, hoary vervain, ironweed, goldenrod, and curly dock generally respond better to fall applications when the plant energy reserves are translocated down to the roots.

Specific rates for troublesome weeds can be found in the 2002 Guide for Weed Management for Nebraska (EC-130) available from your local University of Nebraska Cooperative Extension office.

Grazing

Perhaps no other management factor has as great an impact on the species composition of a pasture as grazing. When well managed, livestock can be very beneficial to the overall vigor and health of a pasture. Of course, when timed incorrectly or if the stocking rate is too heavy, livestock can be hard on pastures, leading to weed infestations.

Livestock, like all animals, have certain preferences for some plants. For instance, little bluestem may not be grazed readily but eastern gamagrass is very desirable to cattle. It does not take long to figure out which one will disappear first. Good management will focus on redistributing livestock to minimize overuse of desirable forages.

Warm vs. cool-season pastures

Warm and cool-season grass forages are mixed in pastures throughout Nebraska. While this provides for ideal grazing schedules, this can make grassy weed management quite difficult. If cool-season grasses are a problem in a warm season pasture, remove cool-season grasses early in the spring before the warm season grasses break dormancy. Glyphosate does well here, provided the warm-season grasses are dormant. Remember, switch grass breaks dormancy about April 15. Another technique is to heavily graze the cool-season forage in the spring and late summer, allowing the warm- season grasses to remain dominant. Fire has been used for centuries in early to mid spring. This is perhaps one of the most efficient management tools the producer can use. Burning pastures heavily infested with cool season grasses and woody plants in the spring will do a lot for the overall health of warm-season forages and provide some weed control. Heavy grazing also can work well to remove warm-season grasses from a cool-season pasture, provided the grazing occurs in mid summer.

Remember that range management should be based on integrated pest management. Livestock, herbicides, a working knowledge of plant ecology and common sense can be used to maintain pastures in a desirable stage. This balance is delicate and will not be maintained with improper management. The producer has a narrow window each year to implement changes that will have an impact for several years. Weeds in a pasture are a signal of management problems. While controlling them is important, be sure to understand what's contributing to their development so management can be adjusted accordingly.

Aatrex/atrazine, the least expensive of these herbicides, provides fair control of foxtails but poor control of most other grasses. It provides fair control of large seeded broadleaf weeds and good control of small seeded broadleaf weeds. Dual II Magnum, Frontier, Outlook, and Micro-Tech provide good control of many annual grasses and small seeded broadleaf weeds but poor control of large seeded broadleaf weeds. The combination products containing both a grass herbicide and atrazine, Bicep II Magnum/Lite, Bullet, and Guardsman/Max, provide good control of many annual grasses and small seeded broadleaf weeds, and fair control of large seeded broadleaf weeds.

All of these herbicides require a good rain after application or mechanical incorporation to ensure good performance. Even with a good rain large seeded broadleaf weeds often require additional control. Several effective postemergence herbicides are available for broadleaf control and one, Paramount, provides postemergence grass control in sorghum.

In general, the bill slightly raises the government safety net, even after including emergency payments of the past four years. The exact amount of increased support will vary by commodity. It also will depend on cropping history (bases) and yields on individual farms.

Take corn, for example. For a typical dryland producer in eastern Nebraska, the government's guarantee appears to go from about $2.22 a bushel in 2001 to $2.37 a bushel in 2002. In relative terms, that's a 6.8 percent increase. (Last minute changes in the bill necessitated by budget concerns brought the gain down from 9.6%.)

Soybean supports will rise the least among Nebraska's major crops, at least in percentage terms. On that same hypothetical dryland eastern Nebraska farm, support increases from $5.16 a bushel in 2001 to $5.32 a bushel in 2002, or 3.1%.

Wheat and sorghum, the two other primary crops in Nebraska, fare somewhat better. For wheat, support increases from $3.29 per bushel to $3.55 per bushel. For sorghum, the gain is from $3.56 per hundredweight to $3.84 per hundredweight. Both are up about 7.9%.

The estimates above, which apply to 2002 and 2003 crops, include the three distinct parts of the new support system: marketing loan rates, fixed payments and target prices. Beginning in 2004, support levels will change slightly for the remaining four years of the legislation. At first blush, the 2004 shift appears to be slightly positive for crops grown in marginal-production areas and slightly negative in better areas.

As in the past, loan rates will apply to all production of program crops on participating farms. However, direct payments and payments under the target price mechanism will be based on predetermined crop bases and yields. A conversion has been made in my estimates to approximate the per-bushel value of all supports as applied to a typical year's production.

Individual producers may have the opportunity to improve on estimated support levels by carefully choosing between current and updated crop bases. Skillful use of the marketing loan program also can help cash flow. Even better, perhaps prices will improve at some point. Direct payments and payments under the target price mechanism will continue without regard to the cash market.

Finally, the farm bill provides for an approximate 80% increase in conservation program spending. For many Nebraska farmers, this may be an ace in the hole. As conservation rules and regulations are announced, why not see if one or more conservation programs won't fit on your farm?

Roy Frederick
Extension Public Policy Specialist

The name of the event was changed to better reflect a new schedule. This year not all the tour will occur in the same week, allowing participants to have a better opportunity to see even more demonstrations at each site due to environmental differences between locations. This year the "tour" will begin at the South Central Research and Extension Center near Clay Center.

These field days will provide a hands-on look at university herbicide research trials. While most participants are from the agricultural chemical industry, the tour is free and open to the public. Individuals may attend all or part of it. The itinerary is as follows:

Tuesday - June 18

9:00 a.m., Clay Center, South Central Research and Extension Center
Wednesday - June 19

8:30 a.m., North Platte, West Central Research and Extension Center

3:30 p.m., Sidney, High Plains Agricultural Laboratory
Thursday - June 20

8:30 a.m. (MDT), Scottsbluff, Panhandle Research and Extension Center
Tuesday - June 25

9:00 a.m., Lincoln, Havelock Research Farm
Wednesday - June 26

1:00 p.m., Concord, Haskell Agricultural Laboratory

In most years, grazing cool-season grasses in spring should be easy. There is lots of grass and the animals do well. In fact, most springs we have so much grass that much of it goes to seed and is wasted. To avoid this, I usually recommend starting to graze early to keep up with grass growth. However, when subsoils start out as dry as they are this spring, early grazing will lower grass yields and yearlong carrying capacity.

If your subsoils are dry underneath your pastures this spring, turn cattle out to grass about two weeks later than normal. This should increase forage production on those pastures from 10% to 20% compared to starting at the normal turnout date.

Don't let some extra early spring green-up fool you into starting too early. Many pastures in eastern Nebraska look like they should already be grazed, but that might not be the best practice in the long run. This year, with the dry soils, let the calendar be your guide. If you usually turn cattle out about May 1, this year wait until May 15, feeding carryover hay if necessary. Then quickly move animals through all your pastures once. When you start your second rotation, slow down the movement so each paddock has at least six weeks to recover before the third pass. After that, let rainfall and grass growth be your guide.