B - 1651 Salt Tolerance of TDOC Z TA245.7 B873 NO.1651 5E1?‘ It“? . @xhw,._;%_r.w....€..+. .,.- . riivrnz.’ . .. 510:1. .2?! s55; . i»: .44}; ‘anal. 51:3. . .3. 2.... :1: .. .. 9.... > , t ...&.:...... . .i,..b_..mzfixn...r .. 1...? 2; ....~., . y... The Texas Agricultural Experiment Station - Charles J. Arntzen, Director ~ The Texas A&M University System - College Station, Texas [Blank Page in ' is Salt Tolerance of Guayule (Parthenium argentatum) by S. Miyamoto J. Davis |_. Madridl lProfessor, former research technician, and graduate assistant, respectively, Texas A&M University Agricultural Research Center at El Paso, 1380 A&M Circle, El Paso, Texas 79927. Cover design by Fiox A. Pike, commercial artist, Department ofAgricultural Communications, The Texas Agricultural Experiment Station; uayule drawing by Karen Glenn, art director, Texas Engineering Experiment Station. Contents q Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 Tolerance at Different Stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2 Germination Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1.4 Emergence Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3 Seedling Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 5 Establishment Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 6 Regrowth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 9 Overall Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 12 implication to Cultivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 13 Direct Seeding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 13 Establishment by Transplants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 13 Clipping Harvest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 14 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 14 Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 15 Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 17 xd/ ‘O Summary Because of the strategic and industrial importance of natural rubber, there has been renewed interest in cultivating guayule (Parthenium argentatum). This study was conducted to determine salt tolerance at different stages of growth, mainly for evaluating ' agronomic potential of guayule in saline areas. Re- sponses to salinity were evaluated by a series of greenhouse experiments and a 5-year field plot test established on Bluepoint loamy sand (Typic Torripsa- ment), using cultivar 593 and various USDA selections. Guayule seed (NaOCl treated) germinated well in highly saline solutions (up to 23 dS m"), but emer- gence and survival of guayule seedlings were reduced significantly even at salinity of irrigation water as low as 1 dS m“. Guayule hypocotyl and seedlings were highly susceptible to salt damage induced through roots or seedling leaves. Guayule establishment by direct seeding using existing furrow methods would be difficult in saline areas. The tolerance of guayule to salts improved signifi- cantly after the seedling stage. Nursery plants, grown in seedling trays for 10 weeks in a greenhouse and transplanted in the spring, achieved 95 percent survival when irrigated with 4.5 dS m" water. Growth rates of transplants during the first year were reduced - severely by increasing salinity, but shrub yields after two years of growth were reduced by only 15 percent when irrigated with 4.5 dS m" water and 51 percent when irrigated with 7.0 dS m" water. Clipping of shrubs after 2 years caused 16, 27, and 39 percent mortality (averaged over the cultivars) when irrigated with 0.9, 4.5, and 7.0 dS m" waters, respectively. Mortality rates were especially high in selections N576 and 12229. Shrubs that had survived clipping grew well for the following two years with minimal irrigation (72 mm plus 52 mm rainfall for the two years). Shrub yields, rubber contents, and rubber yields under minimal irrigation were not significantly affected by the saline treatment. Regrowth from the second clipping, under frequent irrigation, was re- duced significantly by the saline treatment, for ex- ample, 27 and 36 percent shrub yield reductions at irrigation water salinity of 4.5 and 7.0 dS m", respectively. The corresponding reductions in rubber yields were 9 and 27 percent respectively. Salt stress generally increased rubber contents, but did not compensate for the reduction in shrub yields. Cultivar differences in shrub yields or rubber contents were statistically significant, but were less than 18 and 13 percent, respectively. Overall, selections 11591 and 11619 produced the largest shrub and rubber yields. The maximum shrub and rubber yields attained with the tested selections were 9.6 Mg ha" and 490 kg ha" per year from clipping harvest, respectively. Guayule has the potential of becoming an agro- nomic crop in saline areas, but improvements in seedling vigor, rubber contents, and water utilization efficiency are essential. Salt tolerance of established guayule is higher than alfalfa and almost as tolerant as Pima and Upland cotton. However, tolerance at the seedling stage is lower than carrots, one of the most salt-sensitive crops currently grown in the Southwest. Shrub mortality may also become a problem with some selections following clipping, especially when soil salinity exceeds about 5 dS m“. Introduction Guayule (Parthenium argentatum Gray) is a desert shrub native to the Chihuahuan Desert of northeastern Mexico and west Texas. Native guayule was utilized as early as 1900 for limited production of rubber " (McGinnies andHaase 1975). Cultivation of irrigated guayule began in 1916 in Arizona and was expanded considerably in the southwestern United States during World War ll for emergency rubber supplies. Shortly after the.war, its production in the United States was discontinued partly because of the development of synthetic rubber. Recently, however, there has been renewed interest in cultivating guayule. Natural rubber is a commodity .Q of strategic and industrial importance, and the demand is expected to increase worldwide (National Academy of Science 1977). Most synthetic rubber evidently does not have sufficient elasticity, resiliency, and low-heat buildup characteristics for today’s high per- formance requirements (Cornforth et al. 1980). ln addition to rubber, resin and wax contained in guayule plants are being assessed as by-products of economic value (Schloman 1988; Palu et al. 1983). The potential guayule production area in the United States includes Texas, New Mexico, Arizona, and California. With the exception of the Lower Rio Grande Valley and Winter Garden areas of Texas, irrigation is considered necessary for guayule cultivation. Irriga- tion waters in the southwestern United States usually contain dissolved salts in excess of 800 mg L-l. ln the Trans-Pecos, one of the potential guayule production areas in Texas, salinity of irrigation water ranges from 2000 to 6000 mg L", and the A potential for salt problems is high with most crops (Miyamoto et al. 1984a). War-time research indicated that established guayuie could tolerate considerable salinity (Retzer and Mogen 1946). Guayule plants which had been grown in saline soils actually had higher rubber contents, although the contents were not high enough to compensate for the reduction in shrub yields. A sand culture experiment involving guayuie transplants, however, showed a 40 percent reduction in dry shrub weights when the transplants were grown for 12 weeks with a NaCl solution having the electrical conductivity (EC) of 4.0 dS m" (Wadleigh and Gauch 1944). This study also indicated that guayuie plants were sensitive to Mg. These data suggest that guayuie plants are only moderately tolerant to salinity, and that the tolerance could vary depending on the type of salts and the stages of growth. ln 1982, a new round of saline tolerance studies was initiated mainly to determine the agronomic potential of guayuie in saline areas. This bulletin is a consolidated summary of the research. Tolerance at Different Stages Germination Stage Guayule is currently propagated exclusively by seed, yet little information is available concerning salt effects on seed germination (the emergence of root radicle). ln general, salts are known to reduce germi- nation through increasing osmotic stress and/or by causing specific ion or toxic effects (Bernstein 1974). The osmotic effect may reduce the rate of germination and , if high enough, the final germination percentage. Specific ion effects, usually caused by Na, Cl, and occasionally Mg, may partially be alleviated by in- creasing the concentration of other ion species such as Ca and S04 (LaHye and Epstein 1969). However, it is unknown how guayuie seed might respond to salt stress. Two separate experiments were conducted to evaluate salt effects on seed germination. ln the first experiment, four guayuie selections (USDA 11604, 11633, 11646, A48118) and one cultivar (593) devel- oped during the Emergency Rubber Project were collected from an experimental plot in El Paso, cleaned, and separated through floatation in acetone. The portion which sank in acetone was soaked, as suggested by Naqvi and Hanson (1980), in a 0.5 percent NaOCl solution (Clorox) for 2 hours and rinsed with distilled water. Fifty seed lots were placed in petri dishes containing various saline solutions (25 ml each) and a bed of sterilized cotton fiber. The saline solutions had electrical conductivity (EC) read- ings of 0.9 to 22 dS m“ and a Na/Ca ratio of 3, a typical ratio observed in saline well waters of the middle Rio Grande Basin. As an additional treatment, MgClz was added in place of CaClz up to 60 me L“. Also in a separate treatment the sodium adsorption ratio (SAR) was increased from 21 to 41 while main- taining the same anion composition and total salinity. The petri dishes were placed in an incubator (diurnal temperature 19° to 22° C), and germinated seed counted periodically in a split plot design (selections as subplot) with five replicates. The seed was con- sidered germinated when the length of the radicle exceeded twice the seed length. Seed germination began in 3 days and was com- pleted mostly within 1 week. Germination counts made on the 12th day are shown in Figure 1. The percent germination in distilled water ranged from 50 to 85 percent, and some of the low germination may have been caused by poor seed quality. Significant salt effects did not appear until solution salinity increased to approximately 15 dS m" (or 200 me L“) in selections 11604, 11633, and A48118; 22 dS m" (or 300 me L") in selection 11646 and cultivar 593. Increasing Mg concentrations from 0 to 30 to 60 me L“ while maintaining the same total salinity did not affect germination. Increasing the SAR of the incubat- ing solution from 26 to 41 did not cause a significant reduction in germination. The percent of germination differed significantly among the tested cultivars. 100 SELECTION 80- 11646 p- GERMINATION, % I SEmaln I SEaub 0 t T Q 5 1O 15 2O 25 I I ec or SOLUTION, dsm" Figure 1. Seed germination of guayuie selections as related to the electrical conductivity (EC) of saline solutions at a diurnal temperature regime of 19° to 22°C. SE main, the standard error of the experiment for the saline treatments; SE sub, the standard error of cultivar. g However, when the germination data were normalized by the germination in deionized water, the cultivar effect diminished. The second germination experiment was conducted in the same manner as the first, except that three vegetable crops (which are known for establishment difficulties) were included for comparison: carrot (Daucus carota L. cv. lmperator 58), chile pepper (Capsicum annum. L. cv. New Mexico 6-4) and tomato (I_ycopersicon esculentum M. cv. Rutgers). For guayule, cultivar 593 was used. Saline solutions (Table 1) having somewhat higher concentrations than those used in the first experiment were added to petri dishes, and seed lots (50 each) were incubated under two diurnal temperature regimes; 17°-26° C and 22°-32° C. Germination counts were made periodically for 3 weeks. Guayule seed germination began in 3 days and was completed mostly within 1 week. Vegetable seed placed in distilled water also started germinating in 4 days and completed germination within 6 days, except for chile pepper which took 8 days. The seed incu- bated in a saline solution with 12 dS m" or higher took several more days to germinate. The germination counts made at 3 weeks (Figure 2) indicate that guayule seed germinated better than tomato or carrot seed in the saline solutions. Guayule seed (cv. 593) 4'\ germinated better in this experiment than in the first experiment, perhaps because of superior seed quality. lt is apparent that guayule seed can germinate as well as conventional vegetable crops in saline solutions. 10o fsEmain 5Q . _ 8°_ ISEsub z 9 l- <. E so- - E c: Ill u 5 4°" OGUAYULE - a 5 ACARROT "i 2O oromrro 5 XPEPPER o l V, I l I I I o -j 1o 2o so EC OF SOLUTION, asm" Emergence Stage Field reports indicate that it is extremely difficult to obtain good stands of guayule by direct seeding (Tingey and Clifford 1946; Tingey 1952). Guayule seedlings either do not emerge or die after emergence. Seedling emergence apparently decreases rapidly with increasing seeding depth. Naqvi and Hanson (1980), for example, observed a reduction in emer- gence from 81 to 32 percent when seeding depth was increased from the surface to 12 mm in greenhouse experiments. Emergence also decreases with de- creasing seed size (Naqvi and Hanson 1980). Guayule seed, the size of a sand particle, produces a hypocotyl lacking vigor. Salt stress may compound emergence problems, but no quantitative data are currently available. A greenhouse experiment was subsequently con- ducted to observe effects of salinity on seedling emergence of guayule. Bluepoint fine loamy sand (calcareous, mixed, thermic Typic Torripsament) was placed in plastic pots (13 cm in diameter) to a depth of 11 cm. Guayule seed (bulk collection and cultivar 593) was placed 50 per pot, 5 mm deep, and the seeded pots were surface-irrigated once a week using 17 mm of various saline solutions (Table 2). Seedling emergence was monitored for 20 days in a greenhouse at a diurnal regime of 19° to 29° C using a split plot design with five replicates. Three pots per treatment were sectioned at different depths 2 weeks after seeding, and salinity of the saturation extract and soil water contents determined by the methods of the U.S. Salinity Laboratory (1954). Seedlings of both the bulk collection and cultivar 593 began to appear 5 to 6 days after the first irrigation, and emergence was completed in 2 weeks (Figure 3). Thereafter, the stand began to decline in both the bulk collection seed and cultivar 593. Stands decreased with increasing salinity, and only a few seedlings survived at irrigation water salinity of 4.5 dS m" or greater. Soil water contents at 0-11 mm depth one day after irrigation averaged 0.14 kg kg“ and those immediately before irrigation 0.06 kg kg" or about0.1 MPa in soil water suction. Soil salinity measured 2 weeks after seeding (or immediately before the third irrigation) showed high salt accumulation at 0-5 mm depth (Figure 4), presumably due to salt deposition during water evaporation. The seed germination study mentioned earlier indi- cated that guayule seed germinates within 3 to 5 days when solution salinity is less than about 15 dS m". Soil salinity readings obtained immediately before irrigation (Figure 4) were not high enough to inhibit seed germination. Salinity levels shortly after irrigation are presumably lower, thus most seed must have germinated. Upon germination, guayule root radicles usually extend several cm below the seeded zone '\qure 2. Seed germination of four crop species as related , electrical conductivity (EC) of saline solutions at a diurnal temperature regime of 22° to 32° C; SE, the standard error of the experiment. 6° BULK EC within one week. Soil salinity at such a depth (Figure 4) was, however, low. d, " A hypothesis was then sought to explain low emer- gence of guayule when irrigated with saline waters. ' Since the highest salt accumulation had occurred at the soil surface (Figure 4), it was hypothesized that - emergence was reduced due to mortality of hypocotyls _ when pushing through the salted-soil surface. Under ¢ ~ this hypothesis, emergence would have little rela- tionship to the ability of seed to germinate in high - saline solutions, but rather to the ability of hypocotyls to withstand high salinity. An emergence experiment was conducted in green- house pots to test this hypothesis using guayule and, for comparison, three vegetable crops mentioned " T ' earlier (carrots, chile, and tomato). Seed lots (50 each) CV 593 were placed 3 mrn deep, and the potted soils were " surfaced-irrigated first with distilled water. At the first sign of seedling emergence (3, 4, 5, and 6 days for " guayule, tomato, carrot, and pepper, respectively), a 3 mrn layer of salted-loamy sand was placed over — emerging seedlings. The salted-sand had saturation extract salinity readings of 1 1 , 16, 32, 40, and 46 dS m". - (These readings are comparable to those observed in the top 3 mm soil layer when irrigated with waters of 0.8 to 7.2 dS m"). The pots were subirrigated with tap water until the salted-layer became wet at 4.5 to 6 day intervals. Emergence through the salted-layer was then recorded. w The results of this experiment revealed a striking difference in emergence among the crops tested (Figure 5). Guayule had the lowest emergence and STAND count, x STAND COUNT, % :- .° i TIME, days Figure .3. Seedling stand counts of guayule (bulk seed collection and cv. 593) grown in greenhouse pots surface- irrigated weekly with saline solutions. 100 I sEmaln I $Esub I _1 ' EXTRACT SALINITY, dSm TOMATOE 6Q 50- i- 0 5 10 15 20 25 .. o . l l l l l 1 l 1 l l m O e Z Li,’ eo— ~ _ m PEPPER m _ E CARROT LU E 40“ .. D E >< GUAYULE _ g 2o_ _ I i I I . 0 10 20 30 4O 5O W EC OF SALTED LAYER, as"? Figure 4. Salinity of the soil saturation extract measured 2 We?“ an?’ Seedlng a? d/ffefe"? depths 0f Rolled sQi/S Figure 5. Seedling emergence of four crop species through \I¢ which had been surface-irrigated with various saline a 3 mm Myer of sa/ted_/oamy sand p/aced on ememing solutions. seedy-figs fiomato the highest, in direct contrast to the germina- ion data shown in Figure 2. Since the layer of salted- sand was applied after germination of the seed, the reduction in emergence observed must be attributed to a post-germination problem, presumably hypocotyl mortality. lt appears that guayule hypocotyls are exceptionally sensitive to salinity. Q Seedling Stage The effect of salts on seedling growth and mortality rate is an important concern during the seedling stage of most crops. Crop seedlings are vulnerable to salt damage, not necessarily because salt tolerance at this stage is lower than at later stages, but because the roots are short and present in the soil surface where soluble salts usually accumulate (Bernstein 1974). Guayule seedlings remain small (less than 2 cm tall with acotyledon length of 2 to 3 mm) for a period of 1 to 2 weeks after emergence. According to various field reports, seedling mortality is high during this period, yet the role of salinity is not known. Three greenhouse experiments were performed for evaluating salt effects on seedling mortality, using the same materials as the previous emergence experi- ments; cv 593, Bluepoint fine loamy sand, and the three vegetable crop species. Seed was planted in 4I~pots and placed in a greenhouse where diurnal ."emperatures were regulated between 23° to 36° C. When the first true leaf emerged (10, 12, 15, and 17 days after seeding to guayule, tomato, carrot, and 10°‘ j 22-32°c f,- -- '-’ Z ——— 24 - 40°C l / / -. / XX >- ROOT EXPOSED / 7y a‘? 80 - / / - - o GAUYULE o l- — A CARROT / / - a‘ o TOMATO // / / t- soa x PEPPER // _ o: / / O . _ E 0 _ _ E 4o _l D _ l- m. LU an 2o_ _ as 0 s 1o 15 2o 2s EC OF SOLUTION, dsir?‘ ‘igure 6. Seedling mortality of four crop species when their root systems were exposed for 15 days to various saline soil solutions under ambient temperature regimes of 22° - 32° C (solid lines) and of 24° -40° C (dotted lines). pepper, respectively), one set of pots was transferred to a greenhouse compartment with a diurnal tempera- ture regime of 22° and 32° C. Seedling roots, leaves, and stems were then separately exposed to different levels of salinity for 15 days. Seedling root exposure to salinity was achieved by subirrigation with the saline solutions given in Table 1 every 4 to 6 days. Seedling leaf exposure to salinity was achieved by spraying saline solutions (Table 1) onto the seedling leaves until completely wet. The pots with sprayed plants were subirrigated with tap water. Seedling stem contact with high salinity was achieved by placing salted-loamy sand to a depth of approximately 3 mm around the seedling stems, then subirrigating with water of low salinity until the salted-sand layer bacame wet. Desiccated seedlings were counted 15 days after the treatment of roots or stems, and 6 and 9 days after the first and the second spraying of seedling leaves. When seedling roots were exposed to salinity, guayule exhibited the highest mortality, followed by carrot and chile pepper (Figure 6). Mortality increased greatly with increasing ambient temperatures. When seedling leaves were sprayed with saline solutions, guayule again exhibited the highest mortality among the crops tested, and mortality generally decreased with elevating temperatures (Figure 7). increasing temperature resulted in lower relative humidity, which might have reduced salt absorption as discussed by Moser (1975) and Grattan et al. (1981). When seedling stems were exposed to high saline solutions (equiva- 1oo- I—22-a2°c — I—-—24 - 40's one SPRAY / ssl SEEDLING MORTALITY, 96 O 1O 2O 3O sc OF SOLUTION, ass?‘ Figure 7. Seedling mortality of four crop species when seedling /eaves were sprayed with various saline solutions under ambient temperature regimes of 22°-32°C (solid lines) and of 24° -40° C (dotted lines). Table 1. Composition of saline solutions used for the second seed germination experiment and seedling mortality experiments. Water EC TDS SAR Na Ca Mg HCO3 Cl S04 No. dS m" me L" - - - - - - - - - - - - - — - - - - - - - - - -me L“ - - - - - - - - - - - - - - - - - — - - — — — — - - 1 0.9 9 5 6.4 1.9 0.7 2.4 4.7‘! 1.9 2 12 150 19 99 33 18 2.4 117 3O 3 18 225 24 148 49 27 2.4 192 3O 4 23 300 28 198 66 36 2.4 267 30 5 32 450 34 297 99 54 2.4 418 3O No. 1: municipal water supply, city of El Paso. No. 2-5: ion composition similar to typical saline groundwater of the middle Rio Grande lent to salinity of seawater), mortality increased only by 5 to 20 percent in guayule, and by 10 percent in carrot. A further examination revealed that mortality was confined to small seedlings whose leaves were in contact with the salted-sand. lt appears that the stems of seedlings are very tolerant to salinity. The above experiments indicate that seedling mor- tality is associated largely with root or leaf but not stem exposure to the salts accumulated at the soil surface. According to the emergence experiments mentioned earlier, seedling emergence is also con- trolled by the salts accumulated at the soil surface. It should then be possible to increase plant stands through water application which minimizes salt accu- mulation at the soil surface. To examine this possibility, the third greenhouse experiment was conducted in a manner similar to the first seedling emergence exper- iment described earlier. Seed of the bulk collection and cultivar 593 were placed 5 mm deep and irrigated in three different ways: (1) surface-irrigated every_2 days at a rate of 0.88 cm per application, (2) surface- irrigated every 7 days at a rate of 1.7 cm, and (3) subirrigated every 2 days by placing the pots in a shallow pan containing the designated saline solu- tions. The water application rates given above were the amount required to provide a leaching fraction of 30 percent. Stand counts were taken periodically for 3O days. Soil samples were also collected from the top 1 cm and analyzed for electrical conductivity of the saturation extract. The results indicated significantly higher plant stands with high frequency surface water application (Figure 8). (The results from cv. 593 were similar, thus they are omitted). The worst stand was obtained under the subirrigated condition. The salinity of the saturation extract of the soil samples collected from the top 1 cm was the lowest under every 2 days surface irrigation, followed by weekly surface irriga- tion, and every 2 days subirrigation (dashed lines in Figure 8). Establishment Stage Since guayule establishment by direct seeding is unreliable and seed is currently scarce and costly, guayule is established in the field mostly by trans- plants. Bare-root transplants were once used, but recently transplants have been grown in nursery trays or other forms of seedling containers or car- tridges. Several field reports from Arizona and Cali- fornia indicate high rates of survival when such transplants were irrigated (Bucks et al. 1983). One report from Pecos, however, indicated poor establish- ment when transplants were irrigated with saline waters having EC of 5 dS m" (personal communi- cation with Dr. J. Moore, TAES Pecos Station). It is however, uncertain if this was caused by high salinity BULK COLLECTION O SURFACE IRRIG., EVERY 2 DAYS A SURFACE IRRIG., WEEKLY 6o_ X SUBIRRIGATED, EVERY 2 DAYS "18 ,.-—-—X STAND COUNT, % sc OF IRRIG. WATER, dsm" Figure 8. Stands of guayule seedlings measured 30 days after seeding as affected by water application methods and salinity of irrigation solutions. d ¢ ‘d or by other reasons. The following study was con- ducted to evaluate salt effects on the survival rate and growth of guayule transplant. Field plots (unit plot size of 6 x 7 m established on Bluepoint loamy sand) was used to evaluate the effect of saline waters on transplant survival and growth. Six USDA selections (11591, 11605, 11619, 11646, 12229, and N576), one hybrid developed in California (4265XF), and cultivar 593 were evaluated. Seedlings were grown in a greenhouse for 10 weeks in nursery trays having an individual seedling cavity size of 2.5 x 2.5 cm square at the top, and tapered to a depth of 5 cm. Seedlings, about 4 cm tall, having 6 to 8 secondary leaves and a firm root-ball, were transplanted on April 23, 1982 into the field plots bedded as shown in Figure 9. Prior to transplanting, the plots had received 3O cm each of four simulated irrigation waters having salinity of 0.9, 2.4, 4.6, and 7.2 dS m" (solutions 1 through 4 and 6 of Table 2). Salinity of these solutions was slightly higher than those used in the greenhouse experiments, because salinity of tap water which was used as stock water had increased. The water num- bered 6 was provided to evaluate Mg effects. Seed- lings were planted 30 cm apart along the rows in a split plot with salinity as the main plot and cultivars as subplots in four replicates using a total of 80 plants per cultivar per treatment. After planting, the simulated irrigation waters men- tioned above were applied with a gated pipe.to the center dip of the bed (Figure 9) to pack soils around seedling root balls and to minimize salt accumulation in the beds. Until the end ot May, irrigation waters were applied weekly at 2.05 cm per application or 4.1 cm on the basis of wet ground surface area, which is slightly less than the potential evaporation rate of 4.6 cm/week estimated by the Penman combination method (Penman 1963). In June, irrigation was re- duced to twice a month using the same rate per application. During July and August, the plots were irrigated through conventional furrows twice a month at 4.1 cm per application. lrrigation during 1983 was made at 6.2 cm per application when 70 percent of l<————-150 cM-————% Figure 9. The cross-sectional sketch of the crop bed used for the guayule transplant experiment. the available water in the 60 cm rootzone was de- pleted. A neutron probe was used to measure soil water storage. The total amounts of irrigation waters applied for 2 years were 169, 159, 142, and 101 cm for waters having salinity of 0.9, 2.4, 4.6 and 7.2 dS m“, respectively. Transplanting experiments were repeat- ed in June 1983 with irrigation twice a week until the end of July. The rainfall for the 2-year period amounted to 27 cm. Transplant mortality and plant height were monitor- ed periodically. Toward the end of the first growing season (19 weeks after planting), crown volumes (assuming an oval sphere) were estimated from height and crown diameter. All shrubs were harvested in February 1984 by clipping at 5 to 7.5 cm above the root crown. Dry weight was determined after defolia- tion, and rubber and resin contents measured by petroleum ether and acetone extraction methods, respectively (Tipton and Gregg 1982). Leaves were analyzed for Na, Ca, and Mg concentrations with an atomic absorption unit after 20 percent HCl extraction, Table 2. Composition of irrigation solutions used for emergence as well as field plot tests. Water EC TDS SAR Na Ca Mg H603 CI S04 No. dS m" me L“ - - - - - - - - - - - - - - - -me |_-‘ - - - - - - - - - - - - - - - - - - - - - - - - - - - 1 0.9 9 5 6.4 1.9 0.7 2.4 4.7 1.9 2 212 25 8 16 7.7 1.0 2.4 17 5 3 4.5 50 1 1 33 11.0 6.0 2.4 27 20 4 7.0 82 14 53 19.0 10.6 2.4 46 34 5 8.2 100 16 66 22.0 12.0 2,4 57 40 6* 2.3 25 8 , 12 3.0 10.0 2.4 17 5 *This water was used only for the field plot experiment. and Cl by the AgNOa titration method following 0.2 N HNOa extraction (Chapman and Pratt 1961). Soil samples were collected periodically at a depth incre- ment of 30 cm and analyzed for salinity of the saturation extract. Transplant mortality in the spring planting continued for about 12 weeks, and thereafter only a few died. Mortality increased with increasing salinity of irrigation water from 4.6 to 7.2 dS m“ (Table 3). The correspon- ding salinity of the saturation extract in the top 30 cm during 4O days after transplanting was 3.2 and 4.8 dS m“ in the saturation extract or 11.7 and 17.6 dS m” in soil solution at a mean soil water content of 0.11 kg kg“, respectively. ln the summer planting, mortality increased greatly, while soil salinity was essentially equal to that of the spring transplanting (Table 3). The daily maximum temperature during the first 4 weeks after the spring planting averaged 26°C as compared to 37°C after the summer planting. The rainfall after the spring and the summer plantings was comparable, 11 and 18 mm, respectively, for the first 5 weeks. The average plant heights of the eight selections showed an increase of a few cm during the first 4 weeks after planting irrespective of the saline treat- ments (Figure 10). Thereafter, a significant diffference in plant height appeared among the saline treatments. Salinity of the saturation extract in the top 60 cm during the period of July through September, the peak growing period, averaged 1.1, 3.1 and 5.2 dS m“ in the saturation extract (or 2.7, 7.5 and 12.7 dS m" in soil solution at a mean soil water content of 0.09 kg kg“) when irrigated with waters of 0.9, 4.6 and 7.2 dS m", respectively. Plant heights measured PLANT HEIGHT, cm l o 4 a 12 16 2o T|ME,weeks Figure 10. Plant heights of guayule transplanted in April and grown with various saline waters. 12 weeks after the summer planting were about 1/3 of the heights obtained after the spring planting. Plant heights measured at the end of the first growing season (19 weeks after planting) averaged 24, 19 and 14 cm, when irrigated with waters of 0.9, 4.6 and 7.2 dS m", respectively (Table 4). The cor- responding crown volumes averaged 6,300, 3,700 Table 3. Transplant mortality of guayule selections measured 12 weeks after spring (April 23) and summer (June 9) transplanting in loamy sand irrigated at three levels of salinity. Spring Transplant Summer Transplant EC of lrrig. Water 0.9 , 4.6 7.2 0.9 » 4.6 7.2 EC of Sat. Extract 0.9 3.2 4.8 1.0 3:3 4.9 EC of Soil Solution’ 1.8 6.4 9.6 2.0 6.6 9.8 \ , .............................. 4265XF 0a“ 0a 6a 14a 28a 67a 1 1591 2a 0a 10a 20a 25a 85a 12229 7a 8a 1 1 a 1 8a 37a 88a 593 2a 0a 20a 10a 57b 84a 1 1619 2a 9a 20a - - - 11605 2a 5a 32b - - - N576 5a 9a 35b t- - - Average ' 3 5 21 16 37 81 ‘ Electrical conductivity of saturation extract made from soil samples from 0 to 30 cm depth. 2 Electrical conductivity of soil solution at a mean soil water content estimated as (SW/ MS)°'88 ECe where SW the saturation water content, MS the mean soil water content of the field soil and 0.88 the increase in EC per unit increase in salt concentrations. ° Numbers in columns followed by the same letter are not significantly different at a 5 percent level by the DMR test used at each salt level. f\ Table 4. Plant height and individual crown volumes of guayule selections measured at the end of the first growing season 19 weeks after the spring planting. Plant Height Crown Volume EC of Water 0.8 4.6 7.2 0.8 4.6 7.2 A EC of Sat. Extract‘ 1.2 3.3 5.2 1.2 3.3 5.2 EC of Soil Solution 2.7 7.5 12.7 2.7 7.5 12.7 .................................. N576 26a“ 21 a 17a 7.9a 4.8a 2.8a 12229 25a 22a 15ab 6.8a 4.3a 1 .7b 11591 25a 22a 14b 6.7ab 4.5a 1.6b 11605 25a 21ab 13b 6.9a 4.4a 1.3b 11619 23a 18b 14b 6.0b 3.1b 1.6b 11646 23a 19b 14b 6.0b 3.9a 1.5b 4265XF 23ab 17b 13bc . 5.6bc 2.9b 1.2b 593 20b 16b 11c 4.4c 2.7b 0.9b Average 24 19 14 6.3 3.7 1.6 ‘ Electrical conductivity of saturation extract made from soil samples from 0 to 60 cm depth. 2 Numbers in column followed by the same letter are not significantly different at a 5 percent level. and 1,600 cm“ per plant, or 41 and 75 percent _ ' ' ' r\ reduction when salinity of irrigation water increased 70") from 0.9 to 4.6 and 7.2 dS m", respectively (Table 4). 50.0- I Shrubs in the lowest saline treatment grew to the Ca extent of leaving no space between them along the 30.0- row. Selection N576 produced the largest crown 2° o__ volume and cultivar 593 the smallest. ' Shrub, rubber, and resin yield data obtained after 2 two years are presented in the next section along F» 1o,o— é I with regrowth data. Likewise, the quantities of water m‘ W used to produce unit quantities of.shrub, rubber, or g I; M9 I resin are discussed in the next section. ‘z 5.0- . Varietal differences in leaf Na, Ca, and Mg concen- g g____; trations (expressed on the basis of dry leaf matter) i- 3'0‘ were small, mostly less than 15 percent, and statisti- E 23.. cally insignificant. Only the average concentration of o the eight selections of cultivars are shown in Figure g 11. Calcium concentrations were very high, and de- o 1-0- creased significantly with increasing salinity of irri- z, ' gation waters. Leaf Cl concentrations were also rela- Q tively highYranging from 7 to 10 g kg“ and increased u. 0'5" linearly with Cl concentrations in irrigation waters. j Re A N“ growth 0.2 4 ________--O i G - - - (o) SD uayule establishment by direct seeding is currently '5 unreliable, and establishment by transplanting is 9-1 i I T costly. Repeated harvests of regrowth from clipped . 0 2 » 4 6 plants seem to be ideal (Garrot and Flay 1983). EC QF |RR|GAT|QN WATER, d5m-1 '\ However, little is known about salt effects on regrowth or yields of rubber from clipping. The following field study was conducted t0 evaluate salt effects on Figure 11. Leaf ion concentrations of 2-year-old guayule as regrowth and rubber production from clipped plants. re/afed l0 Salinity 0f iffigafiv" Wafer- The experimental plots used were the same as those used for the establishment experiment described in the previous section, but because of reduced research funding only half of the original plots were used (or up to 40 plants per cultivar per treatment). The first clipping was made at 5 to 7.5 cm above the root crown in February 1984 after 2 years of growth. The clipped plants were grown for 2 years (1984 and 1985), under limited irrigation and for an additional one year (1986) under intensive irrigation (Table 5). Irrigation in 1982 and 1983 was made (April through mid September) when 70 percent of the available soil moisture in the top 60 cm had depleted, and in 1986, March through mid September at 60 percent depletion. lrrigations in 1984 and 1985 were applied in April and again in August of each year. Plots were fertilized twice a year at 50 kg N ha“ using ammonium sulfate. Shrub stand counts were taken in the spring and at the end of each growing season. Soil salinity was measured three times per season, using the saturation extract of soil samples collected at a 3O cm interval to a depth of 90 cm. Harvested shrubs (defoliated top portion) were analyzed for dry weight, and rubber and resin contents by the methods described in the pre- vious section. Results of soil saturation extract analyses (Table 6) indicate that soil salinity did not change greatly during the regrowth period when irrigated with waters of comparatively low salinity (0.9 and 2.2 dS m"). At higher salinity in irrigation waters, soil salinity readings increased considerably during the regrowth period. However, salinity of soil solutions, estimated by an equation in a footnote of Table 3, was greater during the 1984-85 seasons than during the_~.1986 season, because of lower soil moisture contents. Clipping caused substantial shrub mortality (Table 7). Mortality rates ranged from 5 to 6O percent and were affected significantly by the saline treatments as well as by cultivar. Selections 11229 and N576 regis- tered mortality less than 20 percent, except at the highest salt level. All mortality had occurred after the first clipping, and the shrubs simply did not show regrowth. The shrubs which had regrowth survived for the rest of the test period, including the period of severe water stress during the 1984-85 seasons. Shrub yields (average of seven selections and one cultivar) decreased significantly with increasing salinity (Table 8). An exception was the second harvest following the 1984-85 season where shrubs were grown with minimal irrigation. High water stress reduced shrub growth, especially in the plots irrigated with low salt water. The shrub yields listed were computed based on the average dry weight of the shrubs harvested from the area of complete stand Table 5. Harvesting sequence and the amount of various saline waters applied. Salinity of First two Next 2 years Additional 1 year irrigation years regrowth regrowth water (1982, 1983) (1984, 1985) (1986) dS m“ irrigation Rain irrigation Rain Irrigation Rain ________________________________________________________________________________ 0.8 169 27 7O 46 121 19 2.4 159 27 70 46 105 19 4.6 142 27 70 46 74 19 7.2 101 a 27 70 46 74 19 Table 6. Salinity of the soil saturation extract (ECe) and the estimated salinity of soil solutions (ECS) at a mean soil water content* in O-60 cm depth. Salinity of The second Regrowth Regrowth irrigation year (1983) 1984-1985 1986 water ECQ ECs Ece ECS ECe E65 ......................... ._ .dS m‘ 0.8 1 .6 3.9 1 .9 5.9 2.0 4.4 2.2 2.9 6.9 3.5 11.0 3.8 8.3 4.5 5.2 12.4 6.2 19.5 7.7 16.9 7.0 6.0 14.3 6.7 21.1 8.9 19.6 *Mean soil water contents of 1983, 1984-85 and 1986 seasons were 0.095, 0.07, and 0.10 kg kg“, respectively. w wk $1 i l /'\ Table 7. Mortality of shrubs after clipping harvest of 2-year-old shrubs. Salinity of irrig. water 0.9 2.2 4.5 7.0 Salinity of sat. ext. 1.6 2.9 5.2 6.0 Salinity of soil soc. 3.9 6.9 12.4 14.3 Avg. »% Mortality .................................................................................. ..°/o ................................................................................ .. N576 20 38 61 59 45a 1 1229 37 38 4O 37 38a 4265XF 17 22 35 40 29b 11646 1O 2O 16 53 25bc 11619 15 , 25 11 29 20c 593 14 21 15 25 19c 1 1605 1 1 15 2O 28 18c 1 1591 5 15 15 2O 14c Average 16a 24b 27b 36c 26 LSDmain : LSDSUb z 14, gubfleven : times 43,800 plants per ha, a theoretical plant popula- tion for the planting spacing used. The actual yields in the two low salt treatments were considerably smaller than the listed value, because of shrub Pwnortality, and can be computed by multiplying by the percent of stands. The actual yields from the two high salt treatments were greater than the estimate based on the proportional reduction caused by stand losses by as much as 3O percent, because of the increases in the size of the shrubs grown next to the dead shrubs. Shrub yield differences among the selection were statistically significant, but the magnitude of the dif- ference was mostly small, for example less than 18 percent except for selection 4265XF and at the highest salt level (Appendix I). Selection N576 produced the largest shrub yield in the first two years, but suffered high mortality after clipping, along with selection 12229. The actual yields from these selections were much smaller than listed values. Overall, selection 11591 gave the largest yield, and cultivar 593 the smallest yield (Appendix I). Rubber contents increased with increasing salt stress during the 1982-83 and the 1986 seasons, but the magnitude of the increases was fairly small; 8 g kg" (or 13 percent of the control) and 7 g kg" (12 percent), respectively (Table 8). The effect of the saline treatments on rubber content was significant at 5 and 1O percent levels in 1982-83 and 1986 harvests, -respectively. Rubber contents during the 1982-83 season were highest at the lowest level of salinity. This may have been caused by a longer period of "Wvater stress, since the shrub in the plots were the argest. Rubber contents were also affected signifi- cantly by cultivar, but the magnitude of the difference was rather small, at most 1O g kg“ (Appendix I). Selection N576 had the highest rubber contents in 11 the first two harvests, and selections 11619 and 12229 in the third harvest. Resin contents were highest at the lowest salt level and often decreased with increasing salinity. However, the saline treatment was statistically not a significant factor even at the 1O percent level in all of the three harvests. Resin contents were influenced highly sig- nificantly by selection. Selection N576 and hybrid 4265XF had the highest resin content, and cultivar 593 the lowest in all of the three harvests (Appendix I). Rubber yields were highly significantly affected by the saline treatment in the first harvest, and at a 5 percent level in the third harvest. In the second harvest, salt effects were significant only at the 1O percent level. The magnitude of yield reduction when irrigated with water of 4.5 dS m" was 13 percent in the first harvest and about 2O percent in the subse- quent harvests (Table 8). The greater reduction ob- served in the second and the third harvest was probably due to the increase in soil salinity (Table 6). Rubber yields were affected highly significantly by cultivar. In the first harvest, selection N576 produced the largest yield (Appendix l), but this selection as well as selection 12229 suffered high mortality after clipping (Table 7). Selections 11591 was among the top rubber producers in all of the three harvests with minimal mortality. Selection 11619 did not rank high in the first harvest, but was among the top producers in regrowth harvests. Cultivar 593 produced the least quantity of rubber in all three harvests. The amount of water used to produce 1 kg of dry shrub ranged from 2.0 to 2.6 m3 (or 2000 to 2600 tons of water to produce 1 ton of dry shrub) in the first harvest (Table 8). The water use, however, declined to 1.5 to 2.1 m3 per kg of shrub and 22 to 38 m3 per kg of rubber in the subsequent harvests (Table 8). Table 8. Shrub yields, rubber contents, resin contents, rubber yields, and water use efficiency averaged over the eight guayule selections. EC of irrig. water (dS m") 0.9 2.2 4.5 7.0 DRY SHRUB (Mg ha") 1982-88** 9.8a" 8.6ab 8.85 4.98 1984-85 8.4 8.2 5.4 5.4 1988* 8.6a 7.2ab 8.25 5.55 RUBBER CONTENT (g kg") 1982-88* 81a 62a 65ab 895 1984-85 82 78 78 78 1988 55 58 84 82 RESIN CONTENT (g kg") 71982-88 88 77 78 81 1984-85 88 8o 78 88 1988 108 97 84 89 RUBBER YIELD (kg ha“) 1982-88** 820a 580a 540a 8405 1984-85 520 470a 410 410 1988* 490a 420ab 4005 8405 WATER USED/SHRUB (m3 kg") 1982-88 2.0 2.1 2.0 2.8 1984-85 1.8 1.9 2.1 2.1 1988 1.8 1.7 1.5 1.8 WATER USED/RUBBER (m3 kg") 1982-88 88 85 81 88 1984-85 22 25 28 28 1988 29 80 28 28 **, *: significant at the 1 and 5 percent levels, respectively. ‘ Numbers followed by the same letter in row are not significantly different at a 5 percent level. Overall Assessment The single most striking characteristic of guayule identified by this program is the large differences in salt tolerance at different stages of growth. Most crops do show stage differences in salt tolerance, but not to the extent observed here. Guayule was most susceptible to salts at the emer- gence to seedling stage. In fact, guayule was more susceptible to salts than carrots. Carrots are one of the most difficult crops to establish in saline areas, and stand failures are common when furrow irrigated with water of 1 dS m" or more (Miyamoto et al. 1984a). Low saline tolerance may also be a reason why native guayule stands are not reported on saline soils. Conversely, extensive emergence of volunteer seedlings are reported in field plantings after rainfall. The reason for high susceptability of guayule hypocotyls and seedlings is not known. Microscopic observations show that guayule leaves are covered with trichomes and readily absorb water, whereas seedling leaves of many crops have a waxy surface which repels water. This difference in wettability may partly explain why guayule seedlings die so easily when broughtinto contact with saline waters. 12 Guayule becomes less susceptible to salts after the seedling stage, but not abruptly. At the end of the first season after transplanting, plant size (measured as crown volume) was still reduced by 41 and 75 percent when irrigated with waters of 4.6 and 7.2 dS m", respectively. (The mean salinity of the saturation extract in 0 to 60 cm depth was 4.3 and 5.6 dS m", respectively.) Wadleigh and Gauch (1944) reported a 4O percent reduction in top dry matter when trans- plants of an unspecified selection were grown in sand culture for 14 weeks with a NaCl-nutrient solution having EC of approximately 4.0 dS m". Our data coincide with theirs. Growth responses of guayule after seedling transplanting are comparable to those of most vegetable crops. Growth differences among the saline treatments during the second growing season decreased; for example, only a 15 percent reduction in shrub dry weight at salinity of irrigation water of 4.6 dS m“. Overcrowding of stands when irrigated with the low salt water may have partly contributed to reducing the ‘.1 shrub yield differences. However, it appeared that guayule became tolerant to salts as the plants became firmly established. Differences in shrub yield among the saline treatments decreased further during the w iv "\ regrowth phase. Established guayule is almost as salt tolerant as Pima and Acala cotton grown in the Southwest (Longenecker 1973). The reason why guayule becomes tolerant to salts after the seedling stage is not known, but several possibilities can be suggested. First, the development of an extensive root system may supply sufficient water to overcome high osmotic stress. Second, the mature root system may deter Na uptake or store Na in the roots. Leaf analysis of established guayule shows exceptionally low concentrations of Na (Figure 11). According to the data of Wadleigh and Gauch (1944), Na ions cause greater growth reduction than Ca at the same osmotic pressure. Sodium secretion from mature leaves is another possibility. Another unexpected finding was that guayule re- quires large quantities of water to produce biomass. In the present study, the total water use (irrigation plus rainfall) was up to 196 cm for the first two years and 140 cm for the last one year. Drainage losses were kept minimal by applying water less than field capacity. Shrub yields increased roughly in proportion to increasing irrigation. A separate study (Miyamoto et al. 1984b) and the work performed at Yuma, Arizona (Bucks et al. 1984) demonstrated that this linear relationship exists for up to 3 cm of water application for the first two years. This water consumption rate cannot be considered low, and is comparable to alfalfa, one of the highest water-consuming crops grown in the Southwest. The amount of water used to produce 1 kg of dry shrub (top portion only) per ha ranged from 2.0 to 2.6 m3 in the first harvest, which is about twice the value for alfalfa given by Hanson and Samis (1979). The amount of water used to produce shrub tops was reduced by about one-third in the regrowth harvest, as the root system had already been established. Guayule shrubs can tolerate drought, but they are not efficient in water use. Implication To Cultivation F\ Direct Seeding Guayule establishment by direct seeding has been difficult due to lack of seedling vigor. This study indicates that salinity compounds establishment diffi- culties. Salinity of water used for direct seeding establishment must be as low as possible. In addition, water must be applied in such a way as to minimize salt accumulation at the soil surface. The results shown in Figure 8 illustrate this point. Trickle or high frequency sprinkler should be preferred over furrow methods for establishing guayule by direct seeding. ln fact, Bucks et al. (1983) reported 65 percent emer- gence and 34 percent seedling survival after 2 months when sprinkler-irrigated with water of 1.4 dS m" for 8 days and twice a week thereafter in loamy sand in Yuma, Arizona. Field reports using furrow methods indicate frequent failures. Tingey (1952) in California, for example, reported plant stands less than 1O percent of the sown seed under furrow irrigation. Salinity of the water used was not specified, but salinity of most irrigation water in that region rarely exceeds 1 dS m". We obtained a 30 percent initial stand when furrow-irrigated twice a day for 35 days with water of ‘ 0.8 dS m“, and the stand later declined to 10 percent, similar to the results of Tingey (1952). When water of "4.5 dS m" was used, no seedlings survived. Stand counts observed in these field tests are considerably lower than those observed in the greenhouse, pre- ’\ sumably because of higher water evaporation rates and other stress factors present in the fields. Surface seeding with some sort of anti-evaporants may improve the success rates of guayule establishment. 13 Above all, improvements in seedling vigor must be made if guayule is to be established by direct seeding without costly modification of water application methods. Establishment by Transplants Transplanting is the most reliable method currently available for establishing guayule. However, several precautions should be taken. Spring or fall is un- doubtedly preferred to summer for transplanting (Table 2). Quality and size of the transplants are also im- portant. Salinity of the water does not need to be as low as that for direct seeding, but the rate of transplant growth can be reduced if salinity of water exceeds1 to 2 dS m" (Figure 10). lf reduced rates of transplant growth are acceptable, and salt accumulation in crops is minimized, water having salinity up to about 4.5 dS m" can be used without risking significant transplant losses (Table 2). Off-centered planting or double row planting as used in our experiment are preferred, especially when water of high salinity is used for irrigation. Sprinkler irrigation would be an alternative to furrow methods for transplant establish- ment. Salt damage from sprinkling of saline water, although many exceptions exist, becomes severe in most crops when salinity of irrigation water exceeds about 4 dS m“ and sprinkled during day hours (Moore and Murphy 1979). Since guayule is sensitive to foliar absorbed salt damage (Figure 7), salt damage to guayule seedlings can occur even at low salinity. Clipping Harvest Guayule establishment by direct seeding is currently unreliable, and establishment by transplanting is costly. Clipping harvests seem to be an alternative, but shrub mortality can be a problem. The extent of mortality observed here after clipping was greater than those reported in Arizona (Garrot and Ray 1983). Most mortality occured in the spring, and the shrubs had been water-stressed before clipping. Mortality appeared to have been associated with characteristics of selections and salinity (Table 7). Maas et al. (1984) also reported mortality rate of 36 percent when shrubs grown in 12 dS m“ treatment for two years were clipped. In their experiment, shrub mortality continued and by the fourth year, most plants irrigated with 9 and 12 dS m“ died. Mortality problems can be minimized by selecting cultivars which have low rates of mortality and/or by controlling soil salinity below about 5 dS m". At present, selections 11591 and 11619 may be good choices. Replacing dead shrubs with new transplants is an option, but may be imprac- tical in low value crops like guayule. The frequency of a clipping would depend largely upon the yield levels desired, availability and quality of irrigation water, and, to some extent, row and plant spacing and cultivars. lf high yields are the principal objective, yearly clipping with frequent irrigation on close- spaced planting would be necessary. Some of the earlier research in California (Hunter and Kelley 1946; Tingey 1952; Veihmeyer and Hin- dickson 1961) indicated that water stress increased rubber contents as well as rubber yields. This study and those reported earlier (Miyamoto et al. 1984b; Buck et al. 1984) also show that stressing guayule increases rubber contents, but not to the extent of offsetting the reduction in shrub yields. Likewise, salt stress was reported to increase rubber contents (Retzer and Mogen 1946). This study confirmed this finding under frequent irrigation. However, the in- crease did not offset reduction in shrub yields. lf high yields per acre are the primary concern, guayule must be grown with low water stress and low salt stress. Acknowledgments This project was initially supported in part by a grant from the Latex Commission and later by the Binational Agricultural Research and Development (BARD) fund. At the initiation of this project, guayule materials were obtained from Dr. Tipton at the TAMU ‘l4 Research Center at El Paso, Dr. Whitworth at New Mexico State University, and Dr. Naqvi at the University of California, Riverside. We also acknowledge the contribution of K. Piela, B. Sullivan, and C. Enriquez who assisted this program. Bernstein, L. 1974. Crop growth and salinity. In: Drainage for Agriculture, J.V. Schilfgaarde (ed.), Agron. Mono- graph. No. 17. Amer. Soc. Agron., Madison, p. 39-54. Bucks, D. A., Dierig, D. A., Chandra, G. R., Backhaus, R. A., Roth, R. L., and Alcorn, S. M. 1983. Progress in direct seeding of guayule. In: Summaries of Guayule Rubber Society. 4th AnnualConf, Riverside, p. 14. Bucks, D. A., Nakayama, F. S., and French, O. F. 1984. Water management for guayule rubber production. Trans. Amer. Soc. Agric. Eng. 2711763-1770. ‘ P\ Chapman, H., and Pratt, P. 1961. Methods of analysis for soils, plants and waters. Univ. of Calif., Riverside. Cornforth, G. C., Lacewell, R. D., Collins, G. S., Whitson, R. E., and Hardin, D. C. 1980. Guayule-economic implica- tions of production in the southwestern United States. Tex. Agric. Exp. Stn., MP-1466, Texas A&M University, College Station. Garrot, D. J., and Ray, D. T. 1983. Regrowth in guayule in response to clipping: a final report. In: Summaries of Guayule Rubber Society. 4th Annual Conf., Riverside, p. 18. Grattan, S., Maas, E. and Gata, G. 1981. Foliar uptake and injury from saline aerosol. J. Environ. Qual. 10:406. ~"\ Hanson, E. G., and Sammis, T. W. 1979. Crop production functions for alfalfa, cotton, corn and grain sorghum. In: Proc. Inter, Amer. Conf. on Salinity and Water Management Technology, S. Miyamoto (ed.), Texas A&M Agric. Res. Ctr., El Paso, p. 117-136. Hunter, A. S., and Kelley, O. J. 1946. The growth and rubber contents of guayule as affected by variations in soil moistixe stresses. J. Am. Soc. Agron. 38:118-134. LaHye. P.. anc Epstein, E. 1969. Salt tolerance by plants. Science 1661295-298. Longenecker, D. E. 1973. The influence of soil salinity upon fruiting and shedding, boll characteristics, fiber quality, and yields of two cotton species. Soil Sci. 115:294-302. Maas, E. V., Donovan, T., and Francois, L. E. 1984. Salt tolerance of guayule. In: Guayule Rubber Society, 5th Annual Conf., Riverside, p. 79. McGinnies, W. G., and Haase, E. G. 1975. Guayule: A rubber producing shrub for arid and semi-arid regions. Univ. of Arizona, Office of Arid Lands Studies, Paper No. 7, Tucson. Miyamoto, S., Moore, J., and Stichler, C. 1984a. An overview of saline water irrigation in far west Texas. In: Proc. lrrig. & Drainage Specialty Conf., ASCE, J. Reppogle (ed.), Flagstaff, p. 222. “Miyamoto, S., Piela, K., and Davis, J. 1984b. Water use, growth and rubber yields of four guayule selections ,.-\ as related to irrigation regimes. lrrig. Sci. 5:95-103. 15 Literature Cited Moore, J., and Murphy, J. M. 1979. Sprinkler irrigation with saline water. In: Proc. Inter Amer. Conf. on Salinity and Water Management Technology. S. Miyamoto (ed.), Texas A&M Univ. Agric. Res. Ctr., El Paso, p. 213-221. Moser, B. 1975. Airborne sea salt: Techniques for experi- mentation and effects on vegetation. In: Cooling Tower Environmental Proc., P. J. Hanna, Sr., (ed.), College Park, MD 4-6, March 1974, ERDA Tech. lnfor. Ctr., Oak Ridge, pp. 353-369. Naqvi, H. H., and Hanson, G. P. 1980. Recent advances in guayule seed germination procedures. Crop Sci. 20:501-504. National Academy of Science. 1977. Guayule: An alternative source of natural rubber. Washington. Palu, S. E., Garrot, Jr., D. J., and Day, P. T. 1983. Comparative study of guayule waxes and jojoba wax. In: Summaries of Guayule Rubber Society 4th Annual Conf., River- side, p. 57 Penman, H. L. 1963. Vegetation and hydrology. Tech. Commun. 53. Commonw. Bur. Soils. Harpenden, England, p. 125. Retzer, J. L., and Mogen, C. A. 1946. The salt tolerance of guayule. J. Amer. Soc. Agron. 38:728-742. Schloman, W. W. 1988. The utilization and economic impact of by-products derived from guayule. In: Summaries of Guayule Rubber Society 6th Annual Conf., p. 40. Tingey, D. C., and Clifford, E. D. 1946. Comparative yields of rubber from seeding guayule directly in the field and transplanting nursery stock. J. Am. Soc. Agron. 38:1068-1072. Tingey, D. C. 1952. Effect of spacing, irrigation, and fertili- zation on rubber production in guayule sown directly in the field. Agron. J. 44:293-302. Tipton, J., and Gregg, E. 1982. Variation in rubber concen- tration of native Texas guayule. Hort Sci. 17:742-744. U. S. Salinity Laboratory Staff. 1954. Diagnosis and improve- ment of saline and alkali soils, L. A. Richards (ed.). Agric. Hdbk. 60 USDA. Veihmeyer, F. J., and Hendrickson, A. H. 1961. Responses of a plant to soil moisture changes as shown by guayule. Hilgardia 30:621-637. Wadleigh, C. H., and Gauch, H. G. 1944. The influence of high concentrations of sodium sulfate, sodium chloride, calcium chloride and magnesium chloride on the growth of guayule in sand culture. Soil Sci. 58:399-403. - Q i 1 V, 11 L, “H ,... [Blank Page in Orignfl V .1: ‘i Appendix I Soil salinity, shrub yield, resin contents, and rubber yields ol guayule selections and a cultivar 1982-83 1984-85 1986 SALINITY STATUS* ................................................................ .. dS m" ........................................................................................ .. ECi* 0.9 2.2 4.5 7.0 0.9 2.2 4.5 7.0 0.9 2.2 4.7 7.0 ECe 1.6 2.9 5.2 6.0 1.9 3.5 6.2 6.7 2.0 3.8 7.7 8.9 ECs 3.9 6.9 12.4 14.3 5.9 11.0 19.2 21.1 4.4 8.3 16.9 19.6 SHRUB YIELDS ...................................................................... .. Mg kg-‘ ...................................................................................... .. N576 10.6a 9.7a 9.9a 6.9a 5.7bc 4.60 (4.4)bc (4.9)ab 8.9a 6.6ab (5.2)b (6.1 )a 11591 117a 98a 98a 53ab 77ab 76a 67a 58ab 97a 77ab 65ab 57a 11619 9.9ab 8.1 b0 8.5 6.1 a 6.7abc 7.4a 5.6abc 6.1 ab 9.4a 8.9a 6.9ab 6.6a 12229 9.9ab 8.9ab 8.1a 5.3ab 7.7ab 8.6a 5.7abc 6.6a 9.5a 7.5ab 6.2ab 5.1 a 11646 9.9ab 8.9ab 8.8a 4.3b 5.20 5.2bc 4.9abc (4.9)ab 5.7b 5.6b 5.7ab (5.6)a 11605 10.0ab 9.7a 8.7a 4.1 b 5.50 4.30 5.7abc 5.2ab 9.5a 6.0b 5.6ab 5.0a 593 8.7 b0 6.80 6.5b 2.60 4.60 4.9bc 4.00 4.30 7.8ab 5.2b 5.2b 4.6a 4265XF 7.60 6.50 6.3b 4.5ab 8.3a 6.8ab 6.3ab 5.1 ab 8.8a 9.3a 8.2a 5.2a Ave. 9.8 8.6 8.3 4.9 6.4 6.2 5.4 5.4 8.6 7.2 6.2 5.5 RUBBERCONTENTS .......................................................... ugkg“ ............................................................................................ H N576 73a 73a 77a 84a 90a 85a 91a 680 43d 53b0 67ab 68ab 11591 530 57b0 63b 64bc 75b 75ab 74bc 73ab0 510d 58ab 70a 72a 11619 540 540 56b 600 90a 73ab 74bc 70b0 63ab 59ab 66ab 69ab 12229 58bc 60b 57b 74ab 85ab 74ab 75b0 83ab 72a 58ab 64ab 62bc 11646 63b 65b 61b 66b0 77ab 74ab 610 79abc 58bc 65a 56b 530 11605 66b 65b 67ab 69b0 84ab 77ab 84ab 84a 53bcd 55abc 63ab 72a 593 5800 61b 71a 72b 72b 68b 78b 84a 510d 65a 67ab 62bc 4265XF 60b 63b 64b 66b0 84ab 81ab 74b0 72abc 520d 470 58b 40d Ave. 61 62 65 69 82 76 76 76 55 58 64 62 RESWJCONTENTS ................................................................ ..gkg-‘ .......................................................................................... U N576 113a 85a 95a 104a 102a 87a 89a 102ab 117ab 112a 100a 96b 11591 82bc 74abc 81b0 77b0d 810 78a 730 860d 96bc 83bc 93ab 83bc 11619 82bc 75ab0 720d 720d 800d 79a 78bc 81d 900 91abc 86ab 83bc 12229 93b 81ab 80bc 83bc 94ab 84a 86ab 850d 108ab0 112a 85ab 82bc 11646 90b 81ab 84b 82bc 89b0 86a 89a 93bc 105ab0 102ab 89ab 94b 11605 82bc 72b0 80bc 78b0d 86b0 85a 740 820d 99b0 83bc 72b0 77b0 593 730 640 65d 68d 66d 66b 660 67e 860 790 620 610 4265XF 86b 80ab 720d 87b 90b0 75ab 710 109a 123a 111a 89ab 135a Ave. 88 77 78 81 86 80 78 88 103 97 84 89 RUBBER YIELDS .................................................................. .. kg ha-‘ .......................................................................................... .. N576 770a 710b0 760a 580a 51 Oabcd 390bc 400a 330b 3800 350ab 350a 410a 1 1591 620b0 560bc 620b 340b 580ab0 570ab 500a 420ab 49Ob0 450ab 460a 410a 1 1619 530b0d 4400d 480bcd 370b 600abc 540ab 410a 430ab 590ab 530a 460a 460a 1 2229 570bcd 530b0d 4600d 390b 650ab 640a 430a 550a 680a 440ab 400a 320ab 1 1646 620b0 580ab 540b0 280bc 380cd 400bc 300a 390ab 3300 360ab 320a 300ab 1 1605 660ab 630ab 580b0 280bc 460bcd 3300 480a 440ab 500b0 330b 350a 360ab 593 500cd 410d 4600d 1900 330d 3300 310a 360ab 4000 340b 350a 290ab 4265XF 460d 410d 400d 300b0 700a 550ab 470a 370ab 460b0 440ab 480a 210b Ave. 590 530 540 340 530 470 410 410 480 41 0 400 350 The numbers in parentheses are less credible than others due to high shrub mortality. *ECi = salinity of irrigation waters; ECe = salinity of the soil extract; ECs = salinity of soil solutions. 17 Appendix ll A conversion table tor selected units Category SI or Metric Units To Convert to __ Multiply by v ti» Area ha acre 2.47 Depth of irrigation m inch 39 cm lnch 0.4 Plant population ha" plant/ acre 0.405 Rubber, resin g kg" % 0.10 Salinity dS m" mmho/cm 1.00 ppm 735 Soil water content kg kg" % by wt. 100 Soil water suction MPa bars 10 Temperature C F 9/5 x C + 32 Volume m3 gallons 264 ft° 35.3 Water use m3 kg“ gal/lb 120 Yield mg ha" lb/acre 892 tons/acre 2.24 - vii 18 [Blank Page in angina Bulletin] % n5‘? v Mention of a trademark or a proprietary product does not constitute a guarantee or a warranty of the product by The Texas Agr‘tu Experiment Station and does not imply its approval to the exclusion of other products that also may be suitable. All programs and information of The Texas Agricultural Experiment Station are available to everyone without regard to race, color, religi n v . age, handicap, or national origin. é 1M—1-90