Sticking To the Basics:
High Plains Cotton Production Considerations for 2002
Dr. Randy Boman
Texas Cooperative Extension
Some producers have been asking questions concerning optimizing inputs. We are again faced with low commodity prices, but escalating production costs. I recommend that producers who are interested in managing input costs consider reading the reports from the AGCARES facility at Lamesa, or other Extension materials available at their county offices. Many good projects have been conducted over the last several years, and the data have a wide range of applications from dryland production to LEPA irrigated systems. Producers should spend dollars on inputs that have a high likelihood of returning the most lint production. It is important to consider the following management criteria.
Minimize tillage where feasible. This is one management factor where producers should consider their specific situation. Data from the AGCARES facility at Lamesa have shown that reduced tillage was the most profitable system for dryland, while a terminated small grains cover crop system was most profitable for irrigated land. Based on multi-year results from AGCARES, conventional production systems may not be the most profitable for sandyland conditions in west Texas. Moisture level does make a difference, and a terminated small grains cover cropping system appears to be more suitable for irrigated land. For dryland, the terminated system does not appear to work as well, since the cover crop consumes precious moisture. A minimum tillage system is better under dryland conditions. Under 0.75 ET (evapotranspiration) deficit LEPA irrigation, continuous cotton has averaged about 2 bales per acre production in three systems studied since 1990. Conventional Tillage resulted in a five-year average yield of 909 pounds of lint per acre, with net returns of $225 per acre. The Conventional Tillage system includes shredding stalks, breaking, listing and furrow diking, rodweeding and diking, sandfighting, and cultivation and diking. The Minimum Tillage system produced 916 pounds of lint per acre and had net returns of $235 per acre. Minimum Tillage practices include shredding stalks, relisting of old rows to incorporated preplant herbicides and furrow diking, rodweeding and diking, sandfighting, cultivations and diking, and drilling small grains after harvest. After the 1996 crop, there is some indication that deep tillage
is needed on the minimum tillage system after several years of that cropping systems practice. Terminated Rye/Wheat-Cotton produced the highest yields and net returns over the five-year
period, at 1025 pounds of lint per acre and $282 per acre in returns. A cover crop of wheat/rye is planted into cotton stalks after harvest each year and chemically terminated about 2-4 weeks before planting cotton in the spring. The cotton is planted directly into crop residue. Fewer field operations
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are used, but more herbicide inputs (Roundup and Caparol) are required. Wind erosion potential is reduced considerably due to the high level of residue remaining on the soil surface. For dryland, over the five-year period the Minimum Tillage system produced 354 pounds of lint per acre, and generated $93 per acre in net returns. The other systems did not fare as well, with Conventional Tillage resulting in 199 pounds of lint yield per acre, with only $2 per acre in net returns. The Terminated Wheat/Rye-Cotton system produced 195 pounds of lint per acre for a net return of only $14 per acre.
Fertilize for a realistic yield goal. Remember that soil testing can pay. Many times we may have had an outstanding fertilizer management program on a specific farm. Other farms may have had less than desirable soil fertility management. The best way to determine which farms require higher expenditure of fertilizer dollars is simply by checking the soil fertility status by using soil testing. A one bale cotton crop will remove about 45 lb of actual nitrogen per acre. The same yield will remove about 25 lb of phosphate per acre. If the previous crop was well fertilized and yielded poorly due to drought, then it is very likely that residual nitrate-nitrogen will be present in the soil profile. Determination of the amount in the upper profile can result in reduction in nitrogen fertilization requirement in many cases, where soil residual nitrate levels are great enough. Where possible, nitrogen fertilizer (UAN, 32-0-0) can be applied through center pivots or “fertigated”. This results in lower application costs. One should consider whether a LEPA system with drop hoses is used vs. a spray system. If a pivot rigged with spray nozzles has marginal water quality and extremely hot, dry conditions are encountered, then some salt burn may be encountered on foliage. In order to reduce front-loading of expenses, dryland fields may be sidedressed with fertilizer after establishment. Applications of nitrogen are more likely to stimulate growth and promote fruit retention. Adjust nitrogen rates to fit yield potential. Generally speaking, about 30-50 pounds of actual nitrogen per acre are adequate for dryland cotton. The higher rates should be used if the yield potential (stored soil moisture) is adequate for higher lint yields. Sidedressing should be completed before blooming, with extreme care taken to not prune roots during the application. Benefits from low rates of foliar fertilizers are questionable.
If the Bray1-phosphorus test exceeds 30 ppm (do not use if soil pH > 7.6), the Olsen-phosphorus test exceeds 10 ppm, or if the Texas Cooperative Extension phosphorus soil test exceeds 44 ppm, then an economic return to phosphate fertilization may not be realized from a particular field. Multi-year, soil fertility research data from a high-yielding irrigated, terminated small grains cover system at AGCARES indicates that if soil test values are high enough, economic returns to phosphorus fertilization may not be realized. The money spent on phosphorus fertilization is not “completely lost” even if it is not required to boost yields. The phosphorus fertilizer is put into the “soil phosphorus bank” and a percentage can be drawn upon in later cropping years. Some reductions in phosphorus fertilizer availability will occur over time due to reactions with calcium and other soil constituents, and soil testing should be used to determine the “plant available” amount. Potassium fertilizer requirement should be based on soil testing. Most laboratories report ammonium acetate-extractable potassium. Other labs report Mehlich extractable. In general, it is difficult to document economic potassium fertilization responses in west Texas. The exceptions might be intensively managed sandy soils with high crop yields. A soil test value of 125 ppm extractable potassium is considered 100 percent sufficient for cotton yields. As with other immobile nutrients such as phosphorus, the potassium soil test values can increase over time with continued fertilization. Sulfur nutrition is also important and producers should consider the following comments concerning sulfur. Sulfur requirement is related to the crop requirement nitrogen to sulfur ratio. For every 10-20 pounds of nitrogen required by a crop, about 1 pound of sulfur is required. Sulfur is mineralized from soil organic residues. Atmospheric deposition also results in up to 6 pounds per acre per year in our region. In general, about 5-15 pounds of sulfur per acre can meet the needs of bumper crops of most crop species. A considerable amount of sulfate-sulfur is applied through irrigation waters high in sulfates. Zinc is a micronutrient that should be assessed using soil testing. Zinc is extracted using a chelating agent called DTPA. For cotton in west Texas, DTPA extractable zinc should be at least 0.30 ppm. If a soil tests less than that, then 3-6 pounds per acre per year of zinc sulfate (resulting in 1-2 pounds per acre of elemental zinc) should be applied until subsequent soil testing indicates adequate amounts. If soil test phosphorus is extremely high in some High Plains soils (high pH), then zinc uptake by the plant may be reduced, indicating possible problems with zinc nutrition.
Variety selection considerations. Many good varieties are currently available to High Plains producers. Consult you local county Extension offices if you have questions concerning performance of a particular variety in your area. Generally speaking, it is important to consider multi-year and multi-site performance averages. However, many transgenic varieties are beginning to show up in the marketplace without multi-year university testing. Transgenic varieties are protected by federal patent laws, and seed from them cannot be legally saved and replanted by producers. When selecting a variety, careful consideration of the following factors is important. Yield potential is probably the single most important factor. Producers sell pounds of lint. How much each pound of lint is worth is a function of fiber quality, so the two are very closely linked, but production is still very important. Adaptability is also important. Several companies are entering the cotton seed market in the High Plains region. Many are selling full-season picker type (open boll) varieties perhaps better adapted to other locations in the Cotton Belt. It is important to carefully weigh the benefits that may be derived in terms of yield, fiber quality and vigor, but boll type should not be overlooked. Stormproof bolls can be extremely important with our stripper harvesting methods and “meteorological events” that dominate the High Plains. Make inquiry into the stormproofness of new varieties. If an open boll type is selected, one should plan ahead and budget for an appropriate harvest aid program on the back side of the season. Many times, we can PRODUCE the lint, but can we HARVEST it? Full-season, open boll type varieties have been extremely productive and more popular in the last few years, especially where adequate irrigation exists. Due to extremely warm September temperatures allowing us to mature many late-set bolls, record yields were sometimes obtained. The key to success is appropriate irrigation termination, and timely harvest aid application and harvest. One should not leave an open boll type cotton to be conditioned for harvest by a freeze due to the high probability of considerable preharvest lint losses. “Value added” traits (such as Roundup Ready, BXN, Bollgard) should be selected based on need or potential for economic return. We know the value of transgenic herbicide programs in foul fields, but the value of transgenic worm resistance is yet to be fully determined. Obviously, if producers traditionally spend a lot of money on bollworm/budworm or pink bollworm control, the technology can be a bargain, but in the High Plains, our bollworm problems tend to be lighter than in other production regions. Economic benefits from sub-threshold worm control are still being investigated in the High Plains. Disease tolerance is still important and fields with historical verticillium wilt or fusarium wilt/nematode problems should be targeted with tolerant or resistant varieties when possible.
Target optimum plant density. Various workers have demonstrated that plant populations can be adjusted based on the overall situation. Use good quality seed and plant SEEDS PER FOOT not POUNDS PER ACRE. One should adjust seeding rates based on SEED SIZE. Cotton varieties may vary by as much as 1500 seed/lb. Many High Plains varieties contain about 4500 seeds/pound. The optimum plant population for 40 inch rows is around 2 – 5 plants per foot of row. Target the low end for dryland, and the high end for irrigated fields.
Factors to consider to obtain an optimum plant population
1) Acceptable population range for yield is 2 to 5 plants/ft of row in 40 inch rows
2) Seed size – some varieties differ by up to 1000 to 1500 seed/lb, with large seeded types having over 3000 seed/lb, while small seeded types may have over 5000 seed/lb (Paymaster HS26 and HS200 each have about 4400 seed/lb)
3) Germination percentage – purchased seed is guaranteed at about 80% germination
4) Seedling survivability – quality seed treatments can increase seedling survivability during stand establishment if environmental and disease pressures occur. This may run 50% or lower during cold, wet periods, but as high as 80% if high quality treated seed are planted into warm soils and environmental stresses are not observed. A seedling survival rate of 60 to 70% can generally be estimated.
Scenario for obtaining an optimum plant population. Target stands for upper portion of optimum production range. This will give a “cushion” for stand loss. For a “target stand” of 5 plants/ft of row, you would have to plant about 6 seed/ft, if 80% germination is expected. If the environment causes a loss of 1/3 of the plants, then one would still have about 4 plants/ft of row. If losses were one-half of the stand, then one would obtain about 3 plants/ft of row.
For Paymaster HS26 at 4400 seed/lb, and 40″ rows (13068 ft = 1 acre) one would have to plant:
6 seed/ft x 13068 ft/acre = 78,408 seed/acre
78,408 seed/acre / 4400 seed/lb = 18 lb of seed/acre
For early planting into soils with marginal soil temperatures, higher seeding rates may be justified since a higher probability of observing stressful environmental conditions exists. For later planting into warmer soils, lower rates may be justified. Dryland fields will likely obtain optimum production at lower plant populations than irrigated fields, thus reduced seeding rates may be in order.
Excessive plant populations have been shown to increase the node location of the first fruiting branch on the mainstem. This may cause a shift from nodes 5-6 up to 7-8. Each increase in one node may delay maturity 3 – 5 days, since 3-5 days is required to produce a mainstem node on the cotton plant. Increases in plant population can also result in more barren plants per acre. Each unproductive plant is a “weed” and competes for sunlight, water, and nutrients with the productive plants. Another consideration is seed costs. If one is considering planting a Roundup Ready variety, then the following table delineates the cost per acre from various planting rates. If we assume a seed cost of $44 per bag plus a $26.20 per bag Roundup Ready tech fee. This results in a total cost of $70.20 per bag of seed.
Seeding Rate, lb/acre
Acres per bag
Use of high quality and fungicide-treated seed. The Cool Warm Vigor Index (CWVI) consists of a warm germination test which cycles daily for 16 hrs at 68oF, then 8 hrs at 86oF. The seedlings are counted after 4 days. The cool germination test is conducted at 64oF and is counted after 7 days. The index is calculated by adding germination percentages of both tests together. The following criteria are used for determining the quality of the seed:
Excellent: 160 or above
Good: 140 – 159
Fair: 120 – 139
Poor: less than 120
The CWVI test is available from the Texas Department of Agriculture facilities in Lubbock. Ideally, producers can use the CWVI to sort seed lots and to determine planting sequence. This allows one to start planting with higher vigor seed under cooler soil temperatures and then end with lower vigor seed when warmer soil temperatures may be encountered. It may also be used to screen seed lots to establish seeding rates. The high vigor seed lots may justify a lower seeding rate, while low vigor seed may justify a higher seeding rate. When in question concerning seed quality, pull a one-pound sample that represents the seed lot and send it to TDA for CWVI analysis. Stay with basic seed treatments for control of rhizoctonia, pythium, fusarium, and thielaviopsis (black root rot). Other seed treatments may not pay dividends. Fungicide treatments generally enhance stand establishment, minimize stand losses, help maintain healthy roots and vigorous plants, thus reducing the possibility of replanting. Seed treatments and materials which control Pythium, Rhizoctonia, and Thielaviopsis (Black Root Rot) are important. Apron is recognized as a good Pythium control product, while Nu-Flow M, Vitavax-PCNB, Demosan, and Baytan or Nu-Flow M at ½ oz / cwt are effective for Rhizoctonia. For Thielaviopsis control, Baytan or Nu-Flow M at 1 oz / cwt are effective. Research conducted by Dr. Terry Wheeler in 1997 indicates that Black Root Rot at low infection levels may be responsible for more negative yield impact than once thought. The combination of high quality seed with chemical seed treatments reduces planting risk, results in plants more tolerant to early season stress (cold, soil crusting, etc.), stronger emergence with deeper planting, a more uniform stand, and vigorous early plant growth.
Plant at appropriate time. Planting in our region is often related to soil moisture availability in the seeding zone. This is obviously the prime consideration in many locations. Based on work conducted by USDA-ARS researchers at Lubbock, the cotton plant requires more than 100 hours above 64oF at the seed level to emerge. The optimum soil temperature target is to have a 10-day average soil temp of 65oF at the 8-inch depth. If poor quality seed is planted, then 70oF may be a better target. Since soil temperatures generally lag air temperatures by about 3 hours in the seed zone, at a minimum, the following criteria for planting should be considered.
Soil temperatures in the seed and root zone should exceed 60oF and the five day forecast should predict overall temperatures on the upswing and low air temperatures forecast above 50oF. During critical germination times, soil temperatures below 50o F can result in chilling injury to seedlings and result in malformed seedlings, reduced vigor and stand establishment, and increased likelihood of seedling disease problems. Emergence will generally occur after accumulation of 60-80 DD60 heat units after planting. If as few as 25 heat units are forecast over the next five days, it is not recommended to plant. At Lubbock, the long-term average air temperatures and corresponding DD60s for various dates in May are listed below:
Day High Low Average DD60s per day (or average – 60)
May 1 79 51 65 5
May 10 82 54 68 8
May 20 84 57 70.5 10.5
May 30 87 60 73.5 13.5
When considering long-term average temperatures for May, one should consider waiting until after at least May 1 to plant. By delaying planting until May 10, at least 8 DD60s per day would result in a total of about 40 over the next five days.
Thrips management decisions. Problems with thrips do not necessarily disappear during dry years or when prices are low. Fields in close proximity to small grains should be carefully watched for thrips infestations. Where thrips have been a problem, there are several control options to choose from. Temik applied in the seed furrow at planting is the “Cadillac” treatment providing the greatest returns for the investment. One way to reduce cost is to use the 2.0 to 2.5 pound per acre rate where nematodes are not a problem. Thimet is another soil-applied systemic insecticide but based on High Plains trials, generally provides less return than Temik for every dollar spent. This is not due primarily to its lower efficacy compared to Temik but rather its phytotoxic effect on the cotton plant itself. While Thimet costs significantly less than Temik at useful rates, its use does not produce the larger yield increases commonly associated with Temik. When using Thimet, make sure you use excellent quality seed. This practice may overcome some of the Thimet phytotoxicity problems. The best performing preventative treatments have been in-furrow Temik treatments and recently, the new Syngenta Cruiser seed treatment in the High Plains area where western flower thrips are the main species. Orthene seed treatments have been highly erratic in performance, sometimes working well and other times failing to deliver control. An Orthene seed treatment is a low cost option to the soil-applied systemics but it provides 1-2 weeks less control. Foliar application of Bidrin, Orthene, Address or dimethoate insecticides can also be effective if applied in a timely matter. They can also be inexpensive if applied as a banded treatment. Weather and large acreage can hamper timely applications leading to poor yield response to the treatment. Sometimes a second foliar application is needed when thrips problems persist over extended periods. One should consider scouting and adding a foliar insecticide when thrips numbers equal to 1 per true leaf are present. A straight foliar program is also an option but requires a speedy application when needed. The primary application usually is needed within a couple of days following emergence. A second application may be required based on scouting reports. Under dryland conditions, the lower cost options are the best.
Use an appropriate weed control program. The weed spectrum present in a particular field should be the main concern. Don’t skimp on this one. Everyone knows the kinds of problems that can be encountered when herbicide programs fail. Utilize transgenic varieties where needed. We have several good Roundup Ready and BXN (Buctril-tolerant) varieties that can be used. Look to these variety/weed control systems as being tools in a tool box. Pick the weed control system that best fits a specific field with specific weed challenges. Conventional cotton varieties employing our routine arsenal of herbicides including yellow preplant herbicides, Caparol, Staple, and grass herbicides can get expensive quickly, especially if the weed spectrum present consists of weeds easily controlled by transgenic weed control systems. Under conditions where a specific farm does not have hard to manage weeds, a conventional program may be more economical. A generic approach to using various weed control systems may not necessarily be the most sound approach in terms of economic returns. The Buctril/BXN system probably best fits in fields with cocklebur, devilsclaw, and morningglory problems. Pigweeds are not as easily controlled with Buctril, so in fields with heavy pigweed pressure a Roundup Ready program may be the best choice. Some varietal adaptation limitations (full-season and/or open boll types) should also be carefully considered by the grower. Generate a budget sheet that shows what kinds of herbicide/technology fee inputs you would anticipate in a particular field based on your weed spectrum for Roundup Ready, BXN, and conventional varieties.
Properly time Roundup applications on Roundup Ready cotton. Roundup UltraMax offers good control of a large weed spectrum and will take out grasses. Best control is generally obtained from Roundup when most weeds are 1 to 3″ in height. Applying about half the normal rate of Staple herbicide with early over the top Roundup applications in Roundup Ready cotton will help control morning-glories and add some residual control. High winds and wet conditions can result in challenges for timely Roundup application in the High Plains. One concern we have is proper crop staging for termination of over-the-top Roundup applications on cotton that has been “ragged up” by environmental conditions such as wind/sand damage and by thrips pressure. These factors can result in mainstem leaf loss, severe stress, and “stacked nodes” and thus make staging the seedling plants more difficult. Where leaves have been lost or badly damaged, it is imperative that mainstem nodes be counted in order to properly stage the cotton. A node is a bump or knot on the mainstem where leaves, vegetative and fruiting branches arise. Nodes at the bottom of the plant are called cotyledonary nodes because the cotyledons, or “seed leaves” are attached there. The two cotyledons are always opposite one another. Always count this as node zero. Over-the-top applications of Roundup cease once the plants have 5 mainstem nodes, or potential for yield loss will be increased. Proper staging for termination of applications is important, as late applications can result in poor early season fruit retention – exactly what we DON’T want in our short season environment. As we move into June, a lot of early planted fields should be nearing the end of the over-the-top application window. If late applications are made, then yield losses can be encountered. Results from small-plot field research conducted on several Roundup Ready varieties planted at the Lubbock Center over the last three years indicated that when Roundup was applied over-the-top late, corresponding yield reduction ranged from about 5% up to nearly 20%.
Getting the most from available water under dryland conditions. The use of furrow diking has been one of the best ways to improve storage of rainfall during high intensity, short duration rainfall events which abound in Texas. Multi-year dryland cropping system studies from the Rolling and High Plains indicate that furrow diking can successfully reduce surface runoff and increase infiltration, and thus the amount of water stored in the soil profile. In an 8-year experiment conducted at the Texas Agricultural Experiment Station in the northern Rolling Plains near Chillicothe, a furrow-diked system (shredding stalks, reworking beds, subsoiling and diking furrows) produced 390 pounds of lint per acre compared to 320 pounds of lint per acre produced in a conventional system (disking, chiseling, sweeping with no diking). Similar results from the Texas High Plains were reported for a 4-year experiment where furrow diking resulted in 340 pounds of lint per acre versus 290 pounds for the conventionally tilled. These studies conclusively show that furrow diking is a sound management strategy for dryland production, resulting in approximately 20 percent average increase in lint yields compared to conventional management.
Timely irrigation. Furrow irrigation continues to be practiced on considerable acres in the High Plains even though it is not as efficient as other methods. Use of LEPA irrigation has shown tremendous benefits over several seasons, especially at AGCARES.
LEPA Irrigation. This system works very well in areas with near level land with low irrigation capacity. LEPA is an overall philosophy of irrigation management and includes farming in a circle, dragging hoses in alternate and diked rows, and high-frequency (up to 2-day interval) deficit irrigation based on ET (evapotranspiration) replacement.
Preplant Irrigation. The High Plains irrigation period is typically divided into “preplant” and “in-season” irrigation periods. Preplant irrigations are an attempt to “bank” water in the soil profile prior to planting for later use in fields where in-season irrigation capacity cannot meet the evaporative demand of the crop. However, high wind speeds and low relative humidity can cause sever water losses during preplant periods. A recent study conducted at the Research Center at Halfway documented water resource losses (both irrigation and rainfall losses) over the past three years at 67, 60, and 47 percent for low elevation spray, LEPA, and subsurface drip irrigated treatments, respectively. Water losses were from evaporation and from movement below the root zone. Based on this limited study, recommendations for preplant irrigation with different irrigation systems are as follows:
Subsurface drip irrigation – apply sufficient irrigation to insure seed germination. Based on the study, attempting to fill the profile resulted in water loss below the root zone and generally failed to increase lint yield compared to treatments receiving less preplant irrigation.
LEPA – apply sufficient irrigation to fill the “effective” root zone just prior to planting. This should be done with multiple pivot passes in a “wedge” of the field in quantities that do not cause runoff. The “effective” root zone and, therefore, the effective water holding ability of LEPA irrigated soil profiles are comparatively small. Because water is applied in alternate furrows and irrigation water tends to move down instead of laterally, the effective root zone of a LEPA-irrigated field may be only half of a spray-irrigated field. If the water holding capacity of a 4-foot deep soil is 2 inches/foot of depth, the effective root zone of a spray-irrigated field could hold 8 inches of water compared to a LEPA-irrigated field holding only 4 inches. Irrigations in excess of the effective water holding capacity will be lost below the root zone. Experiments show that failing to fill the effective root zone of LEPA treatments prior to planting resulted in significant yield losses over the 3-year test period.
Spray – yield results are strongly dependent on timing and amounts of rainfall. Field operations (apply phosphorus, listing, and install furrow dikes) should be completed prior to initial irrigations. In general, do not initiate preplant irrigations prior to April 1. In low irrigation capacity areas, adequately irrigate (bring to 75% of field capacity) one-quarter to one-third of the pivot area by “windshield wiping” the area, applying the largest irrigation possible per pass without causing runoff. Irrigate the next pivot quadrant using the same application plan after the first portion of the pivot is sufficiently wet. As soon as an area is reasonably dry, mulch the area with a rotary hoe or sand fighter. With low irrigation capacity, there is not sufficient time prior to planting to irrigate the entire pivot area, however, the probability of receiving 2 inches of rainfall in May is over 60 percent. Experiments show significant yield reductions by eliminating preplant irrigations in areas with low irrigation capacity, however light preplant irrigations generally waste water. At irrigation capacities greater than 0.2 inches per day, heavy preplant irrigations failed to significantly increase yield over treatments where in-season irrigations began early in the crop year.
In-Season Irrigation. Producers are encouraged to use the High Plains PET (potential evapotranspiration) network data that is published in local newspapers and on the Lubbock Center homepage (http://lubbock.tamu.edu) to determine how much irrigation water to apply. This can be especially useful in determining the start of the initial seasonal irrigation and when to restart irrigation following significant in-season rainfall. As we get into the season, the cotton crop will draw upon the subsoil moisture, and we can use 0.75 ET replacement with high-frequency application to keep the cotton moving along and ultimately produce good to excellent yields year in and year out.
LEPA versus Spray. Results from a 4-year study in the High Plains show that when using a 75 percent ET replacement level for both LEPA and low elevation spray, the LEPA system was 180 pounds of lint per acre superior to spray. The value of 180 lb/ac of cotton at $0.50/lb is $90 per acre. At this rate, the potential increase in gross receipts from a 120-acre pivot would be $10,800 and would easily justify a one-time LEPA conversion cost of $4,000.
In years of extreme drought, differences in yield between LEPA and conventional spray systems have been very large in favor of the LEPA system. Data from the AGCARES facility at Lamesa showed that we made 250 pounds more lint per acre in 1998 when LEPA was used (910 lb/acre) versus low elevation spray application (660 lb/acre) with the same amount of water. A study conducted from 1999 to 2001 at Halfway showed a 21 percent increase in lint yield by applying water by the LEPA method (761 lb/ac) compared to low elevation spray (628 lb/ac) at a 0.1 inch per day irrigation capacity.
Subsurface Drip. Subsurface drip irrigation systems also resulted in high yields in the High Plains over the last few years, especially where irrigation capacities were very low, but some concerns exist about the high capital expenditure in our region. An economic study based on data developed at the Halfway Research Center showed subsurface drip irrigation may be a good alternative to LEPA irrigation when irrigation capacities are very low (2 gpm/acre), when initial drip installation costs are significantly less that $800/acre, or when initial LEPA costs exceed $350/acre. The prime situation for conversion to subsurface drip irritation is on areas irrigated by furrow or non-pivot sprinkler systems that are too small for a quarter-mile pivot.
Early boll set will regulate plant growth and allow early cutout. Basically, the main decision criteria for mepiquat chloride use are plant size, early season square retention, and continued growth potential. In the High Plains we do not normally have overly large cotton due to our ability to control plant growth with timely irrigation and accurate fertigation of nitrogen through the use of center pivot irrigation systems, especially LEPA. An exception to this might be areas that are still furrow irrigated with extremely large amounts of water applied per irrigation. Lint yield response to most mepiquat chloride plant growth regulator materials in High Plains replicated testing has been variable, but plant size is consistently reduced. Mepiquat chloride may best fit in a situation where fields have more than adequate soil moisture and producers are trying to keep vegetative growth in check. This is especially true north of Lubbock when fields may have excessive residual nitrogen – perhaps following corn, and when they have more water.
Maintain yield and quality with a timely harvest aid program. Timely harvest of cotton is important to maintain yield and quality. Leaving cotton “on the stalk” until adequate freeze conditioning for stripper harvest is not necessarily the best approach. Based on large-plot field trial results of harvests conducted from September to January, color grades were degraded over time, with 11 dominating until significant rainfall events occurred. After that time, color grades 42 and 52 were predominant. Staple length was reduced by about 1/32nd in harvests after rainfall events. Fiber uniformity also was reduced by one percent. HVI strength was also significantly reduced by field exposure by about one g/tex over the harvest period. Leaf grades in early harvests averaged about 2, and subsequently were reduced in quality to 3 and 4 in later harvests. Bark incidence was not observed before October weather events and increased to between 50% and nearly 100% after rainfall events. USDA loan value for the lint was about $0.44/lb with the early harvests and ultimately reached a low of $0.38 in January. This is equivalent to about $28.80/bale in terms of loan value losses. Proper harvest-aid timing and harvest are generally required to fully capture yield and quality of open boll (picker) varieties in the High Plains. Preharvest lint losses of stripper varieties are more difficult to document, but losses of up to 10% have been noted after extended field exposure and high-intensity rainfall events.
Personnel from the Texas A&M University Research and Extension Centers at Lubbock and Halfway who contributed to this publication include:
Mr. Jim Bordovsky, Research Agricultural Engineer-Irrigation, Halfway
Dr. Kevin Bronson, Soil Fertility Research, Lubbock
Dr. John Gannaway, Cotton Breeder, Lubbock
Dr. Norman Hopper, Seed Physiologist, Lubbock
Dr. Harold Kaufman, Extension Plant Pathologist, Lubbock
Dr. Wayne Keeling, Systems Agronomist, Lubbock
Dr. Jim Leser, Extension Entomologist, Lubbock
Dr. Terry Wheeler, Plant Pathology Research, Lubbock