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© 2005 Plant Management Network. Risk Management in North Texas Soybean: J. J. Heitholt, J. B. Farr, and R. L. Sutton, Texas Agricultural Experiment Station, Texas A&M, Dallas 75252 Corresponding author: J. J. Heitholt. j-heitholt@tamu.edu Heitholt, J. J., Farr, J. B., and Sutton, R. L. 2005. Risk management in north Texas soybean: Mid-March soybean plantings uncertain; maturity group IV cultivars reliable. Online. Crop Management doi:10.1094/CM-2005-0329-01-RS. Abstract The popularity of early (March and April) soybean plantings using maturity groups (MG) 3.9 to 5.1 has become widespread among commercial growers in north Texas due to the adverse impact of hot and dry weather in July and August. The efficacy of April planting is well documented, but there is less consensus on whether March planting is worth the risks associated with potentially cold, wet weather at planting. Likewise, it is not clear whether cultivars maturing earlier than MG 3.9 or later than MG 5.1 would be competitive under March plantings. In 2002 and 2003, we grew 20 soybean cultivars ranging from MG 0.8 to MG 6.1 on low-yielding sites with poor surface drainage and clay soil textures in the northern Texas Blacklands at Prosper, Texas (33.2°N). Four planting dates ranged from mid-March to mid-May and July drought was severe both years. Plant stands from March planting dates were lower than April planting dates. In 2002, the 15 March planting date (12 bu/acre) was out-yielded by later planting dates (16 to 23 bu/acre). In 2003, the 1 April (16 bu/acre) planting out-yielded the other three plantings (11 bu/acre). Although yield was affected by planting date-by-cultivar interactions, MG IV cultivars were generally higher than other MGs regardless of planting date. Early-maturing cultivars planted in March were visibly shorter than the same cultivars planted later. In the 14 March 2003 planting only, fungicide-treated seed resulted in a 3 bu/acre yield increase above the untreated seed. Our results support two ideas. First, mid-March planting dates in this region can often be less competitive than April planting dates if stand loss and poor seedling growth associated with wet (2002) or cold (2003) weather occurs. Second, cultivars from MG 3.7 to 5.1 are likely to be the most competitive cultivars across a wide range of planting dates when grown on heavy clay soils in north Texas. Introduction Numerous planting dates are used for soybean in north Texas ranging from February to July. The rationale for planting early is to position reproductive growth with the potential for early-season rainfall and cooler temperatures during May and June (4,10,11). Alternatively, planting later (May) usually results in better conditions to establish stands, but increases production risk by synchronizing reproductive growth stages with the period of time during the growing season with the greatest risk of hot, dry weather. Although late plantings have a high yield potential if favorable weather occurs, typical weather patterns do not favor this practice in north Texas. Bowers (4) thoroughly tested the comparison of April versus May plantings in north Texas with 12 cultivars ranging from MG III to MG VII and reported yields were greatest in April plantings. Furthermore, MG III and MG IV cultivars out-yielded later-maturing cultivars in four of six environments. Since the Bowers (4) report, an increasing number of commercial soybean producers in north Texas have begun to plant soybean in March, although yield trials validating this planting strategy are not available. This relatively new planting date dilemma raises at least two additional concerns. The first concern is the issue of using MG II and MG III cultivars in this region. Results with MG II and III in southern latitudes have been encouraging in some cases (4,5) and discouraging in others (3,16). Similarly, but in a more northern region, Steele and Grabau (20) planted MG II cultivars (but no MG III cultivars) in April, May, and June and found no early-planting advantage. Since there are few data comparing cultivars earlier than MG 3.8 versus the traditional MG 3.9 to MG 5.1 cultivars for southern latitudes, this issue should be revisited. Second, when planting in March, it is unclear whether fungicide-treated seed should be used. Because of the treatment’s low cost and the risks involved in not using it, use of treated seed is often advocated. However, more field tests are needed in this geographical region to quantify fungicide-seed-treatment effects. Several studies have exhibited planting date-by-maturity group interactions. In Nebraska, Elmore (7) reported that a determinate cultivar yielded higher when planted in late-May or early June as compared to five indeterminate cultivars that yielded better when planted in early or late May. Nevertheless, cultivar yield rankings, especially when only the five indeterminate cultivars were considered, were rather consistent across the three planting dates. Likewise, in Ohio, late planting reduced the yield of both an indeterminate and a determinate MG III cultivar similarly (2). In Kentucky, six cultivars (MG 00 to MG IV) were planted from late April to late June (15). The MG IV cultivars out-yielded the MG II and III cultivars when planted early, but the yield differential was reduced for June planting dates. In Wisconsin, a cultivar-by-planting date interaction was found with early May plantings out-yielding late May plantings and with one cultivar exhibiting a greater response than two others (17). Bowers (4) also addressed this issue and found statistically significant cultivar-by-planting date interactions but, in general, April plantings substantially out-yielded May plantings across all 12 cultivars. The objectives of this research were (i) to extend the findings of Bowers (4) by characterizing the yield response of MG 0 to MG VI cultivars planted in March versus later plantings on a heavy clay soil in north Texas, and (ii) to quantify the effects of a seed treatment on plant stand and yield of soybean when planted from March to May. Two-Year Study at Low-Yielding North Texas Sites On 15 March, 13 April, 1 May, and 15 May 2002 and on 14 March, 1 April, 17 April, and 1 May 2003, seed from soybean cultivars ranging in maturity from MG 0.8 to 6.1 were inoculated with Cell-Tech 2000 (Nitragin, Inc.) and planted at 200,000 seeds per acre in 2002 but at 150,000 (MG IV and greater) to 200,000 (MG III and lower) seeds per acre in 2003 at Prosper, Texas (33.2°N, 96.8°W). Seed were drilled into a flat seedbed using a 14-inch row spacing. Plots were 8 rows (9.3 ft) wide and 15 feet long. Seventeen cultivars were tested in 2002 and 18 in 2003. In 2002, seed of one cultivar and four cultivars in 2003 were treated with a commercial fungicide containing captan, PCNB, thiabendazole, and metalaxyl (Gustafson, Inc., McKinney, TX) and compared to untreated seed of the same four cultivars. Plots were end-trimmed to 10 ft prior to harvest of the center four rows. Mechanical harvests were performed within a week that specific planting date-by-cultivar combinations matured (8) in order to mimic “real-world” harvests. Soil type was a Houston Black clay with pH 8.2. Soybean had no apparent nutrient deficiency. The preceding crop was wheat that was harvested in June of the previous year and the field was fallowed until soybean planting. Stand density (10 June 2002 and 29 June 2003) and date of growth stage R8 (8) were recorded. Weeds were controlled with a preplant incorporation of pendimethalin (2002) or preemergence metolachlor (2003) followed by a postemergence, one-time application of a mixture of sethoxydim and fomesafen in both years. Weather. Weather data was typical for this region of north Texas (Table 1). Excessive rain was a problem during March 2002 but was essentially absent during July and August. In 2003, the only useful rains occurred in June. Temperatures were also typical, reaching high levels that undoubtedly inhibited both vegetative and reproductive growth in both seasons. Table 1. Monthly averages for temperature and monthly totals for rain data for Prosper, Texas in 2002 and 2003. Long-term averages are presented in the three right columns.
x Rain data collected from McKinney, TX and temperature from Dallas, TX in 2003 because the Prosper hardware failed from mid-April to October 2003. y March temperatures only cover days postplanting (15 March 2002 and 14 March 2003). z Some low temperatures reached were 29°F, 32°F, and 43°F at 7, 11, and 19 days after the 15 March planting in 2002 and 44°F, 39°F, 27°F, and 30°F at 1, 9, 16, and 26 days after planting the 14 March planting, respectively, in 2003. Experimental design, data preparation, and statistical analysis. A randomized complete design with a split-plot arrangement was used. Planting dates were the main plots and cultivars were the subplots and four replicates were used each year. The date that a cultivar reached growth stage R8 in each planting date was plotted against the decimal MG value provided by the seed company (Table 2). Eight curves (and their equations) generated by these plots were then used to adjust each cultivar’s company-defined decimal MG to a corrected MG that more closely represented its actual phenotype in this environment (Table 2). In this paper, we use Arabic numerals with one digit after the decimal to describe specific maturity where known, but we use Roman numerals when referring to a general MG. Table 2. Cultivars used in the planting date study with company-defined maturity and calculated maturity from the eight environments. PD represents planting date.
For both years, statistical analysis indicated significant planting date and cultivar effects on yield and plant stand (P < 0.01 for both effects in both years). Additionally, the planting date-by-variety interaction effects were significant on yield but not plant stand. However, interaction effects on yield were primarily due to changes in the magnitude of differences between cultivars at a given planting date and rarely due to cross-over changes. For example, plots of yield as a function of MG (not shown) indicated curvilinear trends with a peak in the MG 3.5 to 5.1 range yet the trend lines were relatively parallel with an absence of cross-over type interaction. The one exception was the trend line for yield from the 15 May 2002 planting that formed a plateau from the lowest MG cultivars (MG 0.8) to about MG 4.0 and declined rapidly at values above MG 4.0. Thus, this line crossed the other three trend lines. Since cross-over type interactions were conspicuous for only one out of eight plantings, we chose to include in our presentation, the means averaged across planting dates and cultivars along with the primary presentation of interaction means normally dictated when interactions are found. Plant stand. Heavy rains following planting in March 2002 (Table 1) reduced stands compared to stands established at later plantings (Table 3). In 2003, cold temperatures (27°F) that occurred 16 days after planting compromised plant stands of the early planting (Table 4). Stands for the 1 April planting were adequate, but low rainfall in April and May reduced stands of the last two plantings. Table 3. Number of plants (1,000/acre basis) on 10 June of soybean plots from 17 varieties (plus one treated variety) planted on four different dates in the spring of 2002 at Prosper, Texas.
x One batch of Garst D399 seed was treated w/ Rival + Allegiance courtesy of Gustafson. y Hutcheson seed used for 15 March was of such poor quality, a substitute batch of seed was obtained for subsequent planting dates. Table 4. Number of plants on 29 June of soybean plots from 18 varieties (plus four treated varieties) planted on four different dates in the spring of 2003 at Prosper, Texas.
x One batch of Stine 2789. Garst D399, Pioneer 94B54, and DP 5110S seed was treated w/ Rival + Allegiance courtesy of Gustafson. y Hutcheson seed used for 14 March and 17 April was of such poor quality, a substitute batch of seed was obtained for subsequent planting dates. In both years, there were differences in plant stand among cultivars across and within planting dates, especially in the March planting dates. For example, two cultivars that differed consistently in plant stand following the March planting dates were DP4690RR and Garst D399. Averaged across years, March planted DP4690RR produced 101,000 plants per acre whereas Garst D399 (untreated) produced only 55,000 plants per acre. At this time, however, we cannot separate the two possible causes of this cultivar difference, differences in the seed production environment or physiological/genetic differences. There was no increase in plant stand for Garst D399 (fungicide treated) versus Garst D399 (untreated) for any of the plantings in 2002 and for the 14 March 2003 planting. However, there were differences, albeit inconsistent, in plant stand between fungicide-treated and untreated seed for the last three planting dates in 2003 (P < 0.05). Averaged across the four cultivars receiving fungicide, treated seed reduced plant stand for the 1 April 2003 planting (120 versus 130 plants per acre) but increased stand in the 17 April planting (103 versus 93 plants per acre) and the 1 May planting (105 versus 85 plants per acre). In Wisconsin, metalaxyl seed treatment had no influence on soybean plant stand (9). Because cultivar effects on plant stand were relatively strong and fungicide effects were inconsistent in the present study, it appears that seed quality played a more important role in plant stand than seed treatment. Planting Dates and Yield Yields were greater when soybean was planted 13 April 2002, 1 May 2002, and 1 April 2003 as compared to other planting dates (Tables 5 and 6). For the four planting dates within a given year, plant stand appeared to be related to yield (r ≥ 0.98) in some cultivar-year combinations (Garst D160RR in 2002, Pioneer 94B54 in 2002, and AG4702 in 2003). For most cultivars, however, no statistical link was found between yield and plant stand for the four planting dates. Our results suggest that mid-March, but not necessarily late March, is too early to plant soybean in this region because these planting dates were the lowest yielding. However, our interpretation may be overly conservative because these cultivars were planted flat on a heavy clay soil and subjected to post-planting cool temperatures or heavy rains which greatly compromised seedling growth and stands. In contrast, our 2003 and 2004 variety performance trials with MG IV and early MG V cultivars located at Bardwell, Texas (32.3°N, 96.7°W), produced yields that averaged 27 bu/acre (2003) and 35 bu/acre (2004), with planting dates of 27 March 2003 and 26 March 2004 (13,14), respectively, suggesting that late March plantings have success potential. Table 5. Yield of 17 soybean varieties planted on four planting dates at Prosper, TX in 2002. Yields are corrected to 13% moisture.
x One batch of Garst D399 seed was treated with Rival plus Allegiance courtesy of Gustafson. y Hutcheson seed used for 15 March was of such poor quality; a substitute batch of seed was obtained for subsequent planting dates. z Values within the Planting Date Average row followed by the same letter are not significantly different (P > 0.05). Table 6. Yield of 18 soybean varieties planted on four planting dates at Prosper, TX in 2003. Yields are corrected to 13% moisture.
x One batch of Stine 2789, Garst D399, Pioneer 94B54, and DP 5110S seed was treated w/ Rival + Allegiance courtesy of Gustafson. y Hutcheson seed used for 14 March and 17 April was of such poor quality, a substitute batch of seed was obtained for subsequent planting dates. Hutcheson was not included in the average and LSD calculations. The differences between years prevent us from declaring a narrow planting date window as optimal for our region. However, the yield results of the present study agree with others (3,4,10,12,19) that found planting in April or as close to April as possible would increase the chances of higher yields in this region with a 33°N latitude. This finding may not necessarily apply to regions north of Dallas, TX or to irrigated fields. In Arkansas (at 35°N), Ahkter and Sneller (1) did not find April planting dates to yield greater than June plantings when 27 MG IV genotypes were tested under irrigation. Fungicide Seed Treatment and Subsequent Yield Use of treated seed had no effect on yield in any of the four planting dates in 2002 nor did it affect yield of the last three plantings in 2002. However, treated seed increased mean yield (P < 0.05) of the four cultivars tested when the 14 March planting was considered (13.2 versus 10.3 bu/acre). Ironically, seed treatment did not affect plant stand for this planting date suggesting that the yield increase was achieved by some other avenue. This result provides good evidence that seed treatment may reduce risk from March plantings although the mechanisms need to be elucidated. Maturity Groups and Yield Significant interactions between planting date and cultivar were found in both years. In 2002, however, yields of MG IV cultivars were generally higher than other maturities for each planting date except for the 15 May planting when MG 0.8 to MG 4.7 cultivars out-yielded the later-maturing cultivars (Table 5). A similar result was found in 2003, when yield of MG 3.7 to MG 4.7 cultivars (both within and averaged across planting dates) out-yielded both earlier and later-maturing cultivars (Table 6). Averaged across dates and years, cultivars from MG 2.3 to 3.3 had yields (11.7 bu/acre) similar to the yield of cultivars with relative maturity greater than MG 5.5 (i.e., Hutcheson, AG5501RR, and Croplan YRC56) (13.1 bu/acre). The lower yield of the MG 2.3 to MG 3.3 cultivars was likely related to their smaller vegetative size (based on visual observation) especially in plants resulting from March planting. At later planting dates, plants from MG 2.3 to MG 3. cultivars were visibly taller than plants from the March planting and this was associated with their relative competitiveness on those later planting dates. The low yield of MG V cultivars likely resulted because fruiting occurred during the extreme drought in July and August whereas the earlier maturing types fruited during late June. Additional factors that might have led to the reduced yield of the MG V cultivars, especially in the 15 May 2002 planting, include excessive plant stand. In this case, our 2002 seeding rate of 200,000 seeds per acre was likely too high and resulted in stands of 162 to 202 plants per acre for three of the MG V cultivars. Normally, this plant density is not a problem but in our study, leaf area index of these late-planted MG V cultivars was visibly greater than earlier maturing cultivars and these MG V cultivars were clearly more susceptible to water stress. Consequently, it is likely that the combination of a slightly excessive plant stand and robust canopies exacerbated the extent of water stress and yield loss in these MG V cultivars compared to the earlier maturing types planted 15 May 2002. When planted on 1 May in both years, however, yield of MG V cultivars were somewhat competitive with MG IV cultivars suggesting that they may have partly escaped the heat and water stress that plants from the 15 May 2002 planting experienced. Two Kentucky studies (6,15) found early-maturing cultivars did not provide a yield advantage in late plantings in Kentucky (38°N); however, a third Kentucky study found that isolines (cv. Clark) with a delayed-flowering phenotype had a yield disadvantage compared to earlier flowering isolines when planted late (18). Optimal Maturity Group for Selected Planting Dates Eight curves (similar to Fig. 1) plotting yield as a function of corrected MG provided a peak for each planting date (Table 7). In most cases, a useful and definitive MG peak could not be specified and a plot of the optimal MG as a function of planting date did not result in a significant relationship (figure not shown). Although these results do not support a “spread-out-harvest” strategy of planting MG III and MG IV cultivars in April and planting MG V cultivars in May, our data does not rule out the strategy either. The cultivars most widely planted across all planting dates in this region are from MG IV. However, from 1999 to 2003 at this location, we obtained yields of 40 bu/acre or greater only once and that was with a mid-May planting date and an MG V cultivar that produced seed in September 2001 when temperatures were cool and moisture plentiful.
Table 7. Soybean Maturity Groups that yielded 95% of maximum using curves generated by plotting yield versus Maturity Group as represented in Figure 1.
* na = the MG range for 95% of maximum yield was too wide (greater than 1.0 MG) to declare an optimal MG. Summary Mid-March plantings did not prove successful in these two years, although as stated earlier, we have observed consistent “on-farm success” of late March plantings at latitudes just 1° south of the our site and some success to the north. In one of the two March plantings, fungicide-treated seed resulted in a 3-bu/acre yield increase. Yields resulting from mid-April and early May planting dates did not clearly separate themselves in this two-year test. Nevertheless, it is generally agreed that waiting until mid-May (without reason) to plant soybean in this region is less successful than planting in April. Maturity Group IV cultivars exhibited the best yield consistency across planting dates which is consistent with the fact that cultivar choices for commercial acreage in north Texas are mostly MG IV. Acknowledgment We thank the Texas Soybean Board for funding the project and to Jennifer Riggs (Gustafson, Inc.) for treating the seed. We also thank Robert Alexander, Wayne Davenport, Richard Drye, Faraz Haghighi, Matt Short, and Jeff Stowers for technical support and Nitragin, Inc. for supplying inoculant. We offer special thanks to Travis Miller for reviewing the manuscript and to the commercial companies that provided seed. Literature Cited 1. Akhter, M., and Sneller, C. H. 1996. Yield and yield components of early maturing soybean genotypes in the mid-south. Crop Sci. 36:877-882. 2. Beurelein, J. E. 1988. Yield of indeterminate and determinate semidwarf soybean for several planting dates, row spacings, and seeding rates. J. Prod. Agric. 1:300-303. 3. Boquet, D. J. 1998. Yield and risk utilizing short-season soybean production in the mid-southern USA. Crop. Sci. 38:1004-1011. 4. Bowers, G. R. 1995. An early soybean production system for drought avoidance. J. Prod. Agric. 8:112-119. 6. Egli, D. B., and Bruening, W. P. 2000. Potential of early-maturing soybean cultivars in late plantings. Agron. J. 92:532-537. 7. Elmore, R. W. 1990. Soybean cultivar response to tillage systems and planting date. Agron. J. 82:69-73. 8. Fehr, W. R., and Caviness, C. E. Stages of soybean development. 1977, Spec. Rep. 80. Iowa State Univ., Ames, IA. 9. Guy, S. O., Oplinger, E. S., and Grau, C. R. 1989. Soybean cultivar response to metalaxyl applied in furrow and as a seed treatment. Agron. J. 81:529-532. 10. Heatherly, L. G. 1999. Early soybean production system (ESPS). Pages 103-118 in: Soybean production in the midsouth. L. G. Heatherly and H. F. Hodges, eds. CRC Press, Boca Raton, FL. 11. Heatherly, L. G, and Bowers, G. R. 1998. Early soybean production system handbook. 6009-091998-11000. United Soybean Board, St. Louis, MO 12. Heatherly, L. G., and Spurlock, S. R. 2001. Economics of fall tillage for early and conventional soybean plantings in the midsouthern USA. Agron. J. 93:511-516. 13. Heitholt, J. J., Farr, J. B., and Sutton, R. L. 2003. Northeast Texas soybean variety trial. Texas Agric. Exp. Station, Texas A&M Univ., Dallas. 14. Heitholt, J. J., and Sutton, R. L. 2004. Northeast Texas soybean variety trial. Texas Agric. Exp. Station, Texas A&M Univ., Dallas. 15. Kane, M. V., Steele, C. C., and Grabau, L. J. 1997. Early-maturing soybean cropping system: I. Yield responses to planting date. Agron. J. 89:454-458. 16. Logan, J., Mueller, M. A., and Graves, C. R. 1998. A comparison of early and recommended soybean production systems in Tennessee. J. Prod. Agric. 11:319-325. 17. Pedersen, P., and Lauer, J. G. 2003. Soybean agronomic response to management systems in the upper Midwest. Agron. J. 95:1146-1151. 18. Pfeiffer, T. W., and Harris, L. C. 1990. Soybean yield in delayed plantings as affected by alleles increasing vegetative weight. Field Crops Res. 23:93-101. 19. Popp, M. P., Keisling, T. C., McNew, R. W., Oliver, L. R., Dillon, C. R., and Wallace, D. M. 2002. Planting date, cultivar, and tillage system effects on dryland soybean production. Agron. J. 94:81-88. 20. Steele, C. C., and Grabau, L. J. 1997. Planting dates for early-maturing soybean cultivars. Agron. J. 89:449-453. |
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