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Published in Agron J 91:922-927 (1999)
© 1999 American Society of Agronomy
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Agronomy Journal 91:922-927 (1999)
© 1999 American Society of Agronomy

INTEGRATED SOIL AND CROP MANAGEMENT

Water Budget and Yield of Dryland Cotton Intercropped with Terminated Winter Wheat

R.Louis Baumhardta and Robert J. Lascanob

a USDA-ARS, Conservation and Production Res. Lab., P.O. Drawer 10, Bushland, TX 79012-0010 USA
b Texas Agric. Exp. Stn., Route 3, Box 219, Lubbock, TX 79401-9757 USA

lbaumhar{at}ag.gov


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 Materials and methods
 NOTES
 Results and discussion
 Summary and conclusions
 REFERENCES
 
A Texas South Plains production system for reducing wind erosion in irrigated cotton (Gossypium hirsutum L.), a low-residue crop, is to plant winter wheat (Triticum aestivum L.) after cotton harvest, chemically terminate the wheat in the spring, and plant cotton using conservation tillage. The terminated wheat–cotton system (TWC) utilizes fall rain to grow wheat residue. This system has increased irrigated cotton lint yields compared with continuous clean-tillage cotton (CCC), but there is limited information on the annual water budget and adaptability of TWC under dryland conditions. This study compares CCC and TWC effects on (i) runoff and infiltration of rain, (ii) the annual water balance, and (iii) cotton lint yield under dryland conditions. The water budget of TWC and CCC was measured in 3- by 30–m subplot watersheds from May 1992 to December 1995 on an Amarillo sandy loam (fine-loamy, mixed, thermic Aridic Paleustalf) at Wellman, TX. Compared with CCC plots, the TWC residue reduced average annual runoff by 43 mm, but increased average fallow water use by 28 mm (for growing wheat). The use of TWC did not significantly increase either water conservation or cotton lint yields compared with CCC. Cotton establishment was problematic, due to limited soil water at planting in 1993 for TWC and CCC. This prevented 1994 TWC cotton establishment, thus offsetting improved establishment in 1992, when residue protected cotton seedlings during above-average rain. In semiarid regions, inadequate soil water for crop establishment is an uncontrolled risk with dryland TWC production. Because no significant gains in water storage or cotton lint yield were observed under dryland conditions with TWC compared with CCC, undertaking the greater crop establishment risk with TWC cotton production is not recommended in the Texas South Plains.

Abbreviations: CCC, continuous clean-tillage cotton • DOY, day of year • ET, evaporation and transpiration • P, precipitation • R, runoff • S, soil water • TWC, terminated wheat–cotton • WUE, water use efficiency


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
Materials and methods
 NOTES
 Results and discussion
 Summary and conclusions
 REFERENCES
 
HIGHLY ERODIBLE SOILS

of the Texas South Plains region are intensively cropped with cotton, a crop that does not produce adequate plant residues to protect the soil against wind erosion (Bilbro and Fryrear, 1985). Wind erosion is often controlled, as mandated by the 1985 Food Security Act (Federal Register, 1987), with reduced tillage of residue crops such as wheat seeded after cotton harvest and chemically terminated in the spring (Keeling et al., 1989a). This green fallow system is possible in the Texas South Plains because fall and spring rain may be adequate to establish and grow wheat and to recharge the soil water profile before cotton is planted. Two primary hazards challenge this cropping system, however: (i) fall rains may be insufficient to establish wheat for residues and (ii) spring rains may fail to provide adequate water to establish cotton. With timely irrigation, these risks are controlled and so wheat residues are present to protect young cotton plants against blowing sand and to increase the amount of water available to the cotton (Lascano et al., 1994).

The impact of TWC residue cover on improved soil water management through increased infiltration and reduced soil water evaporation, has been studied. Baumhardt and Lascano (1996) found that infiltration of simulated rain increased with increasing TWC residue. They concluded that increasing residue intercepted rain drop impact and prevented the formation of a soil seal or crust, which reduces water infiltration (Duley, 1939; McIntyre, 1958; Morin and Benyamini, 1977; Baumhardt et al., 1990). Compared with other crops, raindrop interception and infiltration are decreased in cotton, due to limited residue production (Baumhardt et al., 1993a). Field water balance studies by Baumhardt et al. (1993b) related increased soil water content in plots having greater residue cover to reduced evaporation and increased rain infiltration resulting from residue interception of rain drop impact. While these studies established the value of residue in reducing evaporation from soil and increasing rain infiltration, we found nothing in the literature that contrasts overall water conservation with the amount of water consumed to produce residue except under the limited irrigation conditions reported by Vorheis (1997).

A review by Steiner (1994) demonstrates the value of residue management systems for conserving soil water through reduced soil water evaporation. The TWC system, when used for cotton production, provides residues that limit growing season evaporation and conserve water. Lascano et al. (1994) showed that growing season (100 d) soil water evaporation (100 mm) for cotton planted in wheat residues was about 40% less than from bare soil (160 mm), while evapotranspiration from both CCC and TWC was the same. Surface residues repartition evapotranspiration by reducing water evaporation from the soil, allowing increased transpiration by the crop (Lascano and Baumhardt, 1996). The advantage of interseeding residue-producing winter cereals after cotton may be negated under dryland conditions, however, due to increased water demand to establish and grow residue.

There is limited information on the annual water budget and adaptability of the TWC system for dryland cotton production in the Texas High Plains. We hypothesized that the fall–winter rain used to grow a TWC cover crop will be less than the spring–summer runoff and evaporation savings compared with CCC. The objectives of this study were to compare (i) runoff and infiltration of natural rain, (ii) annual water balance, and (iii) adaptability, based on lint yield, of the CCC and TWC management systems under dryland conditions.


   Materials and methods
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
NOTES
 Results and discussion
 Summary and conclusions
 REFERENCES
 
The water budget of continuous cotton grown with (i) conventional tillage (CCC) or with (ii) conservation tillage of terminated-wheat residue (TWC) was measured from May 1992 to December 1995 at the Texas Agricultural Experiment Station near Wellman, TX (102°25' W, 33°1' N). The study was conducted on an Amarillo sandy loam having 739 g kg-1 sand and 194 g kg-1 clay, a 1% slope, and other physical, chemical, and hydraulic properties as described by Lascano and Onken (1989) and Baumhardt et al. (1995). Water budget measurements were taken from a subset of 48- by 100-m field plots installed in 1990 as part of an ongoing regional assessment of cropping systems originally described by Keeling et al. (1989a). These two treatments were compared using unpaired t-tests of triplicate measurements within the original study's randomized block design.

Cultural Practices
The CCC system required annual shredding of stalks after harvest, a spring chisel and disk primary tillage (to a depth of 0.10 m), and a second disk tillage for incorporation of pendimethalin1 [N-(1-ethlypropyl)-3,4-dimethyl-2,6-dinitrobenzamine] applied at 0.7 kg a.i. ha-1 for seasonal weed control. The soil received 60 kg N ha-1 and was disk bedded to form 0.25-m-tall seed-bed ridges on 1.0-m intervals. Cotton (Paymaster cv. HS-26; Cargill Research, Plainview, TX) was planted in single rows on freshly cultivated ridge tops at a rate of 7.0 x 104 plants ha-1 using Max-Emerge unit planters (John Deere, East Moline, IL). Date of planting varied annually, according to the available soil water, resulting in planting dates of 7 May 1992 (DOY 128), 29 May 1993 (DOY 149), 19 May 1994 (DOY 139), and 2 June 1995 (DOY 153) (where DOY is day of year). Repeated failures to establish cotton seedlings due to damaging rain in 1992 necessitated planting a catch crop. A listing planter was used to terminate cotton and plant grain sorghum [Sorghum bicolor (L.) Moench] (cv. DK-46; Dekalb Inc., De Kalb, IL) in single rows at a rate of 1.0 x 105 plants ha-1 with 1 m between rows on 30 June (DOY 182).

The TWC tillage plots received no primary tillage of the standing cotton stalks for weed control. After cotton harvest, a residue-producing crop, wheat (cv. AgriPro Mesa; Helena Chem. Co., Memphis, TN), was seeded at 2.5 x 106 plants ha-1 in rows 0.20 m apart, except for the row where cotton would be planted. Wheat planting dates were 20 Oct. 1991 (DOY 293), 11 Nov. 1992 (DOY 316), 23 Sept. 1993 (DOY 266), 17 Nov. 1994 (DOY 321), and 1 Nov. 1995 (DOY 305). Growing wheat was chemically terminated with glyphosate [N-(phosphonomethyl)glycine] applied at a rate of 0.4 kg a.i. ha-1 when wheat was about 150 mm tall on 24 Mar. 1992 (DOY 84), 18 Apr. 1993 (DOY 108), 29 Mar. 1994 (DOY 88), and 17 Mar. 1995 (DOY 76). Cotton was later seeded directly into predominantly erect wheat and cotton residues in single rows using unit planters to obtain 7.0 x 104 plants ha-1 after broadcast application of 60 kg N ha-1. Planting dates were 7 May 1992, 29 May 1993, 1 June 1994 (DOY 152), and 5 June 1995 (DOY 156). These dates vary from those for CCC because of differences in surface soil water content and the availability of planting equipment adapted for use with residue. Control of growing season weeds in the interrow was by cultivation, and near the planted row by pendimethalin applied at 0.35 kg a.i. ha-1 during planting as a 0.30-m-wide band above the seed row and incorporated using steel cage rollers attached behind the press wheels.

Measurements
The soil water balance was determined for the CCC and TWC production systems by measuring rain, runoff, and changes in soil water content. Rain was measured using dual tipping bucket rain gauges and electronically recorded. Runoff was measured from each of the 3.0- by 30.5-m treatment subplots using H-flumes fitted with FW-1 water level recorders (Brakensiek et al., 1979). The water level recorders were modified so that average water depth was electronically recorded at 5-min intervals beginning with rain onset and continuing for 1 h after rain cessation. Runoff rates were calculated from a single calibration equation, , developed from 12 randomly selected flumes as reported by Baumhardt et al. (1993b). The runoff rate was integrated with time and used to estimate cumulative infiltration depth (rain minus runoff). Soil water content of each subplot was measured monthly in duplicate in-row access tubes using neutron scattering beginning 0.15 m beneath the surface in 0.30-m depth intervals to a depth of 2.85 m. The neutron equipment (Model 503DR, Campbell Pacific Nuclear, Martinez, CA) was calibrated June 1988 in soil with water contents varying from 0.05 to 0.26 m3 m-3, according to the procedure described by Lascano et al. (1986). For the resulting calibration , standard error was 0.61% of the slope and 2.98% of the intercept values. General crop growth observations were made; however, only the cotton lint yields estimated from hand samples collected along duplicate paired 2-m-long rows (8 m total sample length) will be reported.


   Results and discussion
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
 NOTES
 Results and discussion
Summary and conclusions
 REFERENCES
 
The soil water balance for the CCC and TWC production systems was quantified in the simplified form

where the difference in measured precipitation, P, and runoff, R, is taken to be equal to the sum of the measured change in soil water, S, and the crop transpiration and soil water evaporation, ET, with all terms expressed in mm. Contributions to the soil water balance from surface water run-on were prevented with soil berms, while ground water contributions are not included, because the water table depth exceeds 30 m. Water loss due to drainage beyond 3 m was not included because the soil water contents (0.15–0.20 m3 m-3) at depths > 2.0 m would support negligible unit gradient unsaturated flow based on corresponding unsaturated hydraulic conductivities of 10-12 m s-1 to 10-15 m s-1 (Baumhardt et al., 1995). Comparisons of the soil water balance were divided into seasons for growing cotton (summer), May to October, or wheat (fallow), November to April.

Precipitation, Runoff, and Infiltration
Measured P quantifies the only water source of our soil water balance. The long-term (1931–1995) average precipitation listed by month in Table 1 indicates that rain in May and June is adequate to establish a cotton crop. Cumulative annual rain exceeded the long-term record in 1992 and 1995. Those years contained months (May–June 1992; Sept. 1995) with noticeably higher than average rain amounts that resulted in measured runoff. Because spring (May–June) rain totals were well below average, except in 1992, cotton establishment during our study depended on surface soil water. Precipitation during September and October is critical to cover crop (wheat) establishment for the TWC system. Below-average September–October rainfall occurred during the study and delayed wheat crop establishment except in 1995.


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  		Table 1 Mean monthly precipitation for 1931 to 1995 from nearby (20 km) Brownfield, TX (long-term mean), and for 1992 to 1995 at Wellman, TX{dagger}

 
Measured R quantifies, by difference, the tillage and residue treatment effects on infiltration and detention of precipitation on the soil water balance. As an example, measured precipitation and runoff from bare (CCC) or residue-protected (TWC) soil during one 1992 storm show the value of intercepting raindrop impact (Fig. 1) . Total rain during a 6-h period was 55 mm; however, more than 30 mm of rain fell in less than 30 min, which is typical of the intense, short-duration storms of this region (Frederick et al., 1977). In this example, runoff from CCC soil was 37 mm, or about 67% of the rain, compared with 5 mm from soil protected by TWC residues. The residues increase infiltration by retarding runoff, as described by Baumhardt et al. (1993b), and by intercepting raindrop impact and maintaining higher soil surface hydraulic conductivity, as reported by Baumhardt and Lascano (1996). Compared with the CCC bare soil, runoff from soil with terminated wheat residue cover began later, thus increasing the opportunity time for infiltration. Generally, for all measured natural rain events, runoff decreased and infiltration increased in the TWC plots compared with the CCC plots, which increased the amount of water available for evaporation and crop use.



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  		Fig. 1 Rain and runoff on DOY 143, 1992. Rain for the event totaled 55 mm with a 30 minute period when the sustained rain intensity was 60 mm h-1. Runoff for the conventional tillage continuous cotton (CCC) was 37 mm, compared with 5 mm for the terminated wheat–cotton (TWC) residue plots

 
Measured rain and cumulative infiltration (rain minus runoff) for the years 1992 to 1995 are plotted in Fig. 2 . Rain and runoff data recorded during 1992 begin on DOY 136, when the water balance measurements were initiated. Rain amounts varied from a maximum of 575 mm during 1995 to a minimum of 242 mm during 1993, which covers a range from 110 mm above to about half of this area's long-term mean annual rain depth of 465 mm. Typically, runoff was measured during rain events that included multiple or single intense storms with rain depths exceeding 35 mm (data not shown). Most runoff events, totaling 8 for TWC and 17 for CCC during the 4-yr study, occurred in the months of May through July; however, some runoff was measured in September and October.



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  		Fig. 2 Cumulative annual precipitation and infiltration, calculated as precipitation minus runoff, for the conservation tillage terminated wheat–cotton (TWC) and conventional tillage continuous cotton (CCC) cropping systems. Error bars show the standard deviation of the mean precipitation minus runoff

 
Annual runoff from soil protected by TWC residues ranged from a maximum of 10 mm during 1992 to <2 mm during the rest of the study. The effective rain, or the ratio of infiltration amount to rain depth, was about 99% for TWC. Infiltration into CCC bare soil plots varied more than TWC plots, with increased runoff that averaged 46 mm and ranged from a minimum of 9 mm in 1994 to a 99 mm maximum in 1992. The effective rain for CCC was about 88% during the four study years. Infiltration with CCC relative to that with TWC was reduced by 89 mm in 1992 and 53 mm in 1995; both are significant at . Because runoff was reduced with TWC residues, the overall amount of precipitation available for residue and lint production was increased relative to the CCC system. The amount of water consumed to produce wheat residue for the TWC system was further analyzed by comparing it with the amount of water conserved by the runoff-controlling residues.

Water Use
Soil water evaporation and crop water use with CCC and TWC cropping systems during the combined fallow and growing seasons were taken as the sum of the soil water change and the annual precipitation minus runoff (Fig. 3) . Annual crop water use and evaporation with the CCC and TWC systems varied from a maximum of nearly 700 mm in 1992 to a minimum of <250 mm in 1993. While water use varied each year, annual differences in total water use between the TWC and CCC cropping systems varied <1 SD, except in 1995. Compared with the CCC cropping system, the combined fallow and growing season water use and evaporation was increased 145 mm overall during this study by the TWC cropping system through reduced runoff. Even with increased water use to grow wheat residue during fallow for cover in the TWC system, the mean annual water use by the TWC cropping system was not significantly different from the CCC system during 1992 through 1994. For both cropping systems, most water use occurred in response to the high evaporative demand during the May to October summer growing season (80 and 76% of the water use by CCC and TWC, respectively). The difference in May to October water use by cotton with TWC during 1995 was significantly greater than for the same period with CCC and resulted in the only significant difference in annual water use.



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  		Fig. 3 Annual water use by conventional tillage continuous cotton (CCC) and conservation tillage terminated wheat–cotton (TWC) cropping systems, with error bars showing the combined standard deviation of runoff and soil water use. Shading within the histograms shows water use partitioned into growing (fill) and fallow (open) periods. For TWC, the fallow period represents water use for wheat growth

 
In addition to increased soil water due to increased rain infiltration, TWC residues further improved environmental conditions during cotton seedling establishment compared with CCC. For example, standing TWC wheat residues protected seedlings from wind driven rain in 1992 that injured CCC cotton. In this case, the growing season was too short to replant cotton and sorghum was replanted as a catch-crop. The overall cropping system water use was similar in 1992 for both summer crops: 590 mm for sorghum (failed CCC cotton) and 616 mm for the surviving TWC cotton. Crop establishment is the primary and overriding concern in evaluating the adaptability of any cropping system and TWC residues offer seedling cotton protection during establishment when seed zone soil water is sufficient for establishment.

Alternatively, the condition that most often prevents dryland crop establishment in semiarid regions is the lack of sufficient soil water at seeding depth when planting. Successful establishment of cotton was not achieved using the TWC cropping system in 1993 and 1994 or the CCC cropping system during 1993, because of dry surface soil conditions. The corresponding summer water use of 203 and 224 mm for TWC during 1993 and 1994, and 211 mm for CCC plots during 1993 was attributed primarily to water evaporation from the soil. Summer water use during 1994 by the CCC cropping system was 305 mm. Cotton was successfully established in both TWC and CCC cropping systems during 1995. The resulting cotton water use in 1995 for the TWC system increased about 110 mm more than for the CCC system, with about half of the water (48 mm) obtained from increased infiltration. These data show that the presence of residues increases the amount of water used by summer crops; however, in our study early crop growth conditions and soil water content at planting were critical to crop establishment and governed subsequent water use.

Water use during the intervening fallow period between summer crops, shown in Fig. 3, compares the CCC cropping system bare soil water evaporation with evaporation and transpiration from the TWC growing wheat crop for 1992 through 1995. As with the summer crops, surface soil water content at planting was critical for establishment and growth of the wheat crop. Depending on the surface soil water content, wheat usually emerged at 10 d to as many as 25 d after planting, which affected fallow water use by the TWC cropping system. During this study, annual fallow-period water use in the TWC cropping system varied from 5 to 44 mm more than with the CCC cropping system, resulting in an average increase of 25 mm water use due to wheat transpiration in the TWC system. The average precipitation during this period was 129 mm; thus, wheat in the TWC cropping system used most of the fallow-period precipitation, whereas 25 mm of water was stored in the CCC bare soil. Under the conditions of our test, the overall fallow-period water use with TWC was not significantly different from CCC, but the reduced soil water content was typically in the surface seed zone, thus making cotton crop establishment problematic.

Yield
Measured cotton lint yields reported in Table 2 were obtained in years of precipitation extremes that ranged from less than the 90th percentile to greater than the 15th percentile during crop establishment and growth periods. Total lint production in this study was 798 kg ha-1 for the CCC system and 994 kg ha-1 using the TWC system, or an overall average annual lint yield of about 200 kg ha-1 for the CCC and 250 kg ha-1 for the TWC systems. The greatest yield difference between these systems occurred in 1992, when May rain totaled 148 mm, well above either the 67 mm average or 75th percentile depth of 95 mm. In addition to adequate rain for crop establishment, the soil profile available water content supported good crop growth and yield in 1992. Below-average (25th percentile) rain depth during May and June of 1993 and 1994 in the absence of adequate available soil water prevented cotton establishment and growth for TWC, but CCC only failed in 1993. Direct, nonzero lint yield comparisons could be made only during 1995, when TWC increased cotton lint yield 76 kg ha-1 relative to the CCC system, but this difference was not significant . Similar results from related studies at this location indicated a nonsignificant overall mean lint yield increase of almost 20% with the TWC compared with CCC cropping system (Keeling and Lascano, 1987; Keeling et al., 1988; Keeling et al., 1989b).


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  		Table 2 Cotton lint yield and water use efficiency of conventional continuous cotton (CCC) compared with terminated wheat–cotton (TWC). While lint yield of the TWC was greater than CCC during 1995, the difference was not significant (P = 0.95). Offsetting crop failures in 1992 and 1994 obscure treatment comparisons, but water use efficiency of CCC exceeded TWC

 
The ratio of harvested lint (kg ha-1) to measured ET (mm) is reported as water use efficiency (WUE; kg ha-1 mm-1) in Table 2. Under the dryland conditions of our test, the WUE for CCC cotton was 1.66 to 1.51 kg ha-1 mm-1, compared with smaller WUE values of 1.02 and 1.22 kg ha-1 mm-1 with TWC. Other reported WUE values for CCC type production systems range from a similar 1.36 kg ha-1 mm-1 for near dryland conditions and no post-plant irrigation (Howell et al., 1984) to >2 kg ha-1 mm-1 for cotton grown with supplemental irrigation (Jordan, 1983). The low WUE under dryland production reflects the more severe growing conditions; however, expected water conservation with TWC residues failed to increase overall WUE. In contrast, Lascano et al. (1994) reported WUE of 2.6 kg ha-1 mm-1 for irrigated TWC cotton, because less soil water was lost to evaporation. In our study, the early vegetative growth of cotton was initially protected by the wheat residue, but the crop did not achieve a corresponding increase in boll formation (boll-set) and maturation due to late season water stress as observed during 1992.

Because cotton crop failures occurred during two of the four growing seasons with either above- or below-average rain, offsetting yield benefits were identified for both cropping systems. For the TWC cropping system, seedling cotton was protected by residues during above average (>90th percentile) wind-driven spring rain, resulting in superior crop establishment. Cotton seedling protection from blowing soil by TWC residue management is another common benefit of this cropping system. Overall cotton lint yield with TWC exceeded CCC; however, when spring rain was less than the 15th percentile, cotton crop establishment was superior with the CCC system, because soil water had not been consumed to grow wheat residues.

Our results show that the TWC cropping system used fallow precipitation to produce wheat for residue and actually increased cotton production risk by reducing the amount of water available to establish and grow cotton. No such cotton establishment and production problems were reported from a 2-yr study by Keeling et al. (1989a), because above-average spring rain (120% of the 75-yr average for May–June) enabled crop establishment that was followed by above-average summer (122% of the 75-yr average for July–August) and fall (134% of the 75-yr average for September–October) rain. The critical factor for adapting crop production systems for use in semiarid drylands is the preservation of soil water for primary crop establishment during years with below-average rain. Similar conclusions on the limitations of green fallow systems were reported in west-central Kansas (Schlegel and Havlin, 1997) and eastern Colorado (Vigil and Nielsen, 1998).


   Summary and conclusions
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
 NOTES
 Results and discussion
 Summary and conclusions
REFERENCES
 
Our results show that TWC residue reduced water lost as runoff by increasing infiltration, thus increasing effective rain from 89% for CCC to 99% for TWC cropping system. The overall fallow-period water use with TWC was not significantly different from CCC, and annual differences in total water use between the TWC and CCC cropping systems were not significant. Cumulative lint production in the CCC system was 798 kg ha-1 and 994 kg ha-1 using the TWC system, but the WUE for CCC cotton was greater than with TWC. Because soil water had been consumed to grow wheat residues in the TWC system, cotton establishment was problematic. Spring rains were insufficient to replenish the surface soil water and establish cotton in either CCC or TWC cropping systems during 1993 and in TWC during 1994.

Successfully adapted dryland production systems minimize crop risks such as seedling establishment failure. The TWC residues are beneficial in limiting seedling establishment risk from damaging rain; however, the option to replant the primary or a suitable secondary crop also neutralizes the crop injury risk. In semiarid regions and under dryland conditions, stored soil water offsets the common crop establishment risk due to inadequate rain, but growing wheat for residue during fallow draws on this risk-controlling soil water. Crop establishment risk with TWC has otherwise been controlled under irrigated conditions by timely applications of water (Keeling et al., 1989a). Because no significant gains in water storage or cotton lint yield were observed under dryland conditions with TWC compared with CCC, assuming greater crop establishment risk with TWC cotton production is not recommended in the Texas South Plains.National Climatic Data Center 1998


   ACKNOWLEDGMENTS
 
Mr. Burkey Slaughter is gratefully acknowledged for his sustained assistance in the overall crop production and field plot maintenance of this study. We are also grateful to the Monsanto Agricultural Company that funded, in part, the initial years of this research.


   NOTES
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
 NOTES
Results and discussion
 Summary and conclusions
 REFERENCES
 
1 The mention of trade or manufacturer names is made for information only and does not imply an endorsement, recommendation, or exclusion by USDA-ARS. Mention of a pesticide does not constitute a recommendation for use nor does it imply registration under FIFRA as amended. Back

Received for publication January 7, 1999.
   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
 NOTES
 Results and discussion
 Summary and conclusions
 REFERENCES
 




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