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© 2008 Plant Management Network.
Accepted for publication 29 February 2008. Published 1 July 2008.

Texas Gulf Coast Soybean Yield Affected by Soybean Variety and Planting Date

W. J. Grichar, Texas AgriLife Research, Beeville 78102;
J. D. Janak, Texas AgriLife Extension Service, Victoria 77904; and
P. McGuill, Texas AgriLife Extension Service, Wharton 77488

Corresponding author: W. J. Grichar. w-grichar@tamu.edu

Grichar, W. J., Janak, J. D., and McGuill, P. 2008. Texas Gulf Coast soybean yield affected by soybean variety and planting date. Online. Crop Management doi:10.1094/CM-2008-0701-02-RS.

Abstract

Soybeans (Glycine max) are planted along the upper Texas Gulf Coast from mid-March through May to try to take advantage of early season spring and summer rains and also to complete harvest before hurricane season and fall rains become a problem. These plantings are with maturity groups (MG) IV and V and are mainly grown under nonirrigated conditions. Under normal rainfall conditions (rainfall in April, May, and early June), this study shows that a late March or early April planting date provided the highest yield although a May plant date can result in yields of greater than 50 bu/acre if rainfall is received at the proper times. However, when planting was delayed, there was a greater risk of detrimental late-season effects from drought and southern green stink bug (Nezara viridula) or the brown stink bud (Euschistus heros). In 2004 and 2005, at both locations, soybeans planted at the early plant date took longer to reach physiological maturity than the later plant dates. Generally, the earlier the plant date, the greater number of days from planting till harvest.

Introduction

Soybeans (Glycine max) are grown along the upper Texas Gulf Coast and this area has become the largest soybean production area in the state. Most soybeans in this area are planted from mid-March through May and are categorized as early soybean production system plantings (ESPS). Production components such as planting date and variety can be manipulated to counter the effects of various environmental factors on soybean development and yield (4,6,9). Growers plant soybeans early in the season to increase the likelihood that the plants complete the flowering stages prior to the onset of high temperatures that often occur in July and August. Early planted soybeans also will tend to complete the critical flowering, seed set, and seed filling (8,10) during the late spring and early summer when precipitation is more common in this area than later in the growing season. Moisture and temperature stress during early reproductive stages can reduce soybean yield by reducing the number of pod, seeds, and seed mass (1,3). Both determinate and indeterminate soybean cultivars have reduced growth rates under drought stress but resume normal growth rates when the stress is removed (3,12). This may be an important growth attribute to consider if producers expect considerable soil moisture deficits due to short, intermittent droughts during the growing season (12).

The objectives of this research were to identify the components of soybean production encompassing variety and planting date that could increase soybean yield along the upper Texas Gulf Coast. This information will aid producers in adapting planting practices that will improve soybean yield and reduce the chance of yield reductions.

Plantings Along the Texas Gulf Coast

Field experiments were conducted in 2003 [one location, Victoria Co. (28.4°N, 96.5°W)] and 2004 through 2005 at two different locations [Wharton Co. (29.2°N, 96.3°W) and Victoria Co. (28.4°N, 96.5°W)] in the Texas soybean production area along the upper Texas Gulf Coast. These two areas are separated about 90 miles apart (east to west). Soil type at the Wharton Co. location was a Lake Charles Clay with a pH of 7.2 while the Victoria Co. locations were a Houston black clay with a pH range of 7.4 to 7.7. Fertilizer was applied by the grower as needed according to Texas Cooperative Extension recommendations for soybean. Generally, the test areas received 40 to 60 lb/acre of phosphorus with no nitrogen or potassium. Plots were maintained weed-free throughout the growing season using a premix of S-metolachlor plus metribuzin (Boundary, Syngenta Crop Protection, Greensboro, NC) applied preemergence at the rate of 1 qt/acre. Grass and broadleaf weed escapes were controlled with postemergence applications of clethodim (Select, Valent USA Corp., Walnut Creek, CA) at 12.5 oz/acre and acifluorfen (Blazer, BASF Corp., Research Triangle Park, NC) at 1.5 pt/acre, respectively. Postemergence herbicide applications included Agridex (Helena Chemical Co., Memphis, TN) at the rate of 0.25% v/v. The number of postemergence herbicide applications varied from year to year depending on weed emergence problems.

Soybean seed was planted with a vacuum planter (Monosem ATI Inc., Lenoxa, KS) to provide a uniform seeding rate of 10 seed/ft (138,000 seeds/acre) on a pair of rows with 38-inch centers. Three planting dates, approximately two to three weeks apart, were used each year with the first date around 15 March depending on weather conditions. Planting dates in Victoria Co. in 2003 were 21 March, 2 April, and 17 April. In 2004 planting dates in Wharton Co. were 24 March, 21 April, and 6 May while at the Victoria Co. location planting dates were 22 March, 19 April, and 6 May. These dates were spread out due to above normal rainfall which was received during the normal March to April planting window and prevented entry into fields. Planting dates in 2005 in Wharton Co. were 15 March, 29 March, and 12 April while in Victoria Co. the planting dates were 30 March, 12 April, and 27 April. Soybean plantings were delayed at the Victoria Co. location due to heavy rainfall in early to mid-March. Harvesting was accomplished mechanically with a small plot combine and plot yields adjusted to 12% moisture.

Experimental Design and Data Analysis

The treatment design was a factorial arrangement using a randomized complete block design with a planting date and soybean varieties as factors. Treatments were replicated three times with soybean variety plot size two rows (38-inch centers) by 30-ft long. An analysis of variance was performed using the ANOVA procedure for SAS (SAS Institute Inc., Cary, NC) to evaluate the significance of planting date and soybean variety on soybean yield and time from planting until harvest. The Fishers Protected LSD at the 0.05 level of probability was used for separation of mean differences. Since environmental conditions were different at each location and soybean cultivars varied from year-to-year, data are presented separately by location and years.

Rainfall

Rainfall amounts were variable for the both areas (Table 1). Rainfall in 2003 can be characterized as below average for March through May but above-average rainfall for the remainder of the growing season. In 2004 above-average rainfall was received at both locations for all months except March, July, and August which were drier than normal. Rainfall in 2005 was below normal for both areas. In Wharton Co., only September produced above-average rainfall while in Victoria Co., March and July produced above-average rainfall (Table 1). The above normal rainfall in September came too late to be of any help during the 2005 growing season.

Table 1. Monthly rainfall at the study locations.

Soybean Variety Response to Planting Date

2003. For all varieties, except DP 4933 (MG IV) and HBK 5123, soybean yield increased as planting date was delayed from 21 March to 17 April. At the late March and early April planting date, DP 5110S (MG V) and HBK 5101 (MG V) were among the highest yielding soybean varieties; however, both of these varieties produced lower yields at the first harvest when compared with the later harvests (Table 2). The benefits of the Early Season Production System (ESPS) and the use of ESPS as a late-season drought avoidance system (4,6) were negated by early-season drought. With the soybean varieties, DP 5110S and HBK 4920, the April 2 planting date produced the highest yields while with HBK 5123, the March 21 and April 17 plant dates produced higher yields than the early April plant date. The later planted soybeans were able to take advantage of the normal to above-average rainfall in June and July while the 21 March planting was inhibited by below-average rainfall during April and May (Table 1).

Table 2. Yield response of soybean varieties to planting dates in Victoria
Co., 2003.

2004. Soybean yields were above normal (authors' personal observations) due to the good moisture conditions coupled with moderate summer temperatures (data not shown). Generally yields were highest in Wharton Co. with the April planting date for most varieties, regardless of MG (Table 3). However, AG 4902 and DP 4724 produced higher yields at the May planting date than the other planting dates while Garst 5012 (MG V), Garst 5212 (MG V), HBK 4992 (MG IV), HBK 5101, HBK 5123, and NK 452 (Group V) produced the best yields at the March planting date.

Table 3. Yield response of soybean varieties to planting dates at two locations in 2004.

At the Victoria Co. location, all varieties except Garst 5212, HBK 5101, and HBK 5123 produced lower yields at the March planting date compared with the other planting dates while yields from HBK 5101 were consistent across all planting dates (Table 3). Grichar (5) reported that in years of adequate moisture during the April through June growing period along the Texas Gulf Coast, soybean yields were greatly enhanced with the mid-April planting date compared with March planting dates. At the March planting date, only HBK 5101 and HBK 5123 produced over 37 bu/acre. At the mid-April planting date, DK 51-51 (MG V) yielded over 50 bu/acre while at the early May planting date, AG 4902, DK 51-51, and HBK 4992 yielded over 50 bu/acre.

With HBK 5212, the April planting date produced higher yields than the other planting dates, while no difference in yield between the mid-April and early-May planting dates were noted with DK 51-51, DP 4724, DP 4933, DP 5110S, HBK 5101, HBK 5123, and NK 452. For several soybean varieties (AG 4902, DK 4651, Garst 5012, and HBK 4992), the May planting produced the highest yield (Table 3).

The excellent yields for all varieties with the May planting can be attributed to the above-average rainfall during the early part of the growing season (Table 1). This late planting occurred in a year with above-average rainfall and fruiting occurred when soil moisture was adequate for both MG. Although below-average rainfall was received in July and August, there was sufficient sub-soil moisture to maintain the soybean plant during the reproductive stage. In previous research across the southern US, the planting of early-maturing cultivars was shown to be less important under conditions of more plentiful rainfall (1,4,11).

2005. At the Wharton Co. location, soybean yields were less than 30 bu/acre across all planting dates and soybean varieties (Table 4) due to below-average rainfall for April through August (Table 1). Drought stress during seed formation and development in soybean is mainly responsible for reduced seed yield (13). Generally, delaying the planting date did not affect soybean yield. Only AG 4903, DP 5414, and Garst 5012 resulted in an increase in yield when planting date was delayed from mid-March until mid-April. Croplan 48491 and Garst 4999 produced higher yields at the late March planting dates than the other two dates.

Table 4. Yield response of soybean varieties to planting dates at two locations in 2005.

At the Victoria Co. location, the March planting date consistently resulted in higher yields across all varieties than mid- or late-April planting date (Table 4). At the March planting date, only Garst 5012 (MG V) and UA 4805 (MG IV) produced yields over 20 bu/acre while HBK 5123 and HBK 5894 yielded less than 5 bu/acre. Some varieties did produce comparable yields between March and mid-April planting dates while other varieties did not produce any yield at the mid-April planting date. No yield was obtained with any varieties at the late-April planting. The lack of yield with soybean varieties at the latter two planting dates can be attributed to lack of rainfall during the growing season and also a heavy infestation of the southern green stink bug (Nezara viridula) and the brown stink bug (Euchistus heros) (2,7). Ashley and Ethridge (1) reported that lack of moisture had more of an effect on soybean yield when drought occurred from flowering to physiological maturity compared with the emergence to flowering period. Temperatures were typical for both areas with high 90’s (°F) and low 100’s for July and August (data not shown). The high temperatures undoubtedly also inhibited both vegetative and reproductive growth during the season (9).

Heatherly (6) reported that yield differences between MG IV and V cultivars were not different under nonirrigated conditions when planted in April near Stoneville, MS. He also reported that in 16 May to 1 June plantings, yields from MG V, VI, and VII cultivars were not different but all exceeded the yield of MG IV cultivars. Under limited rainfall conditions in 2005, our results were similar and yields varied between soybean varieties but not between MG IV and V when planted in late April.

Plant Date to Harvest Interval

Accurate harvest dates were not obtained in 2003 but were obtained in 2004 and 2005. Generally, the later the planting date, the lower number of days from planting until harvest.

2004. At both locations, soybeans planted at the early plant date took longer to reach physiological maturity than the later plant dates (Table 5). At Wharton Co., the late March planting date resulted in the longest time interval from planting until harvest with a time interval of 124 to 145 days. DP 5110S and Garst 5212 took 145 days until harvest while DG 3484 took 124 days from planting until harvest (Table 5). At the April 21 planting, no difference in number of days from planting until harvest was noted with any soybean variety except Garst 5212 which was not harvested. At the early May planting date, only HBK 5123 took over 140 days from planting until harvest, with no difference in the other soybean varieties.

Table 5. Days from planting to harvest at two locations in 2004.

At the Victoria Co. location, all soybean varieties took at least 147 days from planting until harvest with the March planting. At the mid-April planting, all soybean varieties took 119 to 133 days from planting until harvest. At the early May planting, Garst 5212 took 131 days from planting until harvest while AG 4902, DK 4651, and DP 4724 took only 109 days from planting until harvest.

2005. Harvest results in 2005 were variable at both locations and varied among soybean varieties (Table 6). At the Wharton Co. location, when planted on 15 March, HBK 5123 and HBK 5894 took 160 days while DP 5414 took 147 days from planting until harvest. At the late March planting, AG 4902 took 161 days, while HBK 5123 and HBK 5894 took 146 days. AG 4801, DP 4690, Garst 4612, Garst 4999, and Pioneer 94M90 took only 118 days from planting until harvest. At the mid-April planting, AG 4902, DP 51110S, and HBK 5894 took 147 days while AG 4801 and HBK 5123 took only 119 days.

Table 6. Days from planting to harvest at two locations in 2005.

At the Victoria Co. location, when planted 30 March, DP 5414, Stine S5502, and SG 5151 took at least 132 from planting until harvest (Table 6). Many varieties took 111 days. At the mid-April planting date, AG 5301, DP 5110S, and Stine S5502 took over 130 days from planting until harvest while AG 4902, AG 4801, and Croplan RC4655 took 104 days or less.

Heatherly (7) reported that near Stoneville, MS, cultivars planted before 16 April took an average 5 days longer to reach R1 (beginning bloom) than did cultivars planted after 16 April to 1 May. When cultivars were planted from May through June, the number of days to R1 decreased as planting date was delayed. Heatherly (7) concluded that the reproductive period of later-maturing cultivars would occur later in the season when stored soil moisture has been reduced, probability of rainfall is lower, and air temperatures are higher.

Summary

Under normal rainfall patterns, using a MG IV and V soybean, a late March to mid-April plant date provided the best timing to optimize soybean yield regardless of variety or MG for soybeans planted along the Texas Gulf Coast with a 28 to 29°N latitude. Planting soybeans in May can produce acceptable yields in abnormal growing seasons with sufficient late-season rains, but growers should base their planting decisions on long-term average precipitation trends for this area. In contrast, Heitholt et al., (9) reported that a mid-March planting date was not desirable for north Texas (33°N latitude) due to stand loss and poor seedling growth associated with cold and wet weather conditions. They did conclude however, that waiting until mid-May to plant soybeans in that region was less successful than planting in April. Bowers (4) also reported on similar work in North Texas and found that, in general, April plantings outyielded May plantings across all twelve cultivars. The use of MG V cultivars resulted in fruiting during hot, dry conditions normally found in July and August while the early maturing types fruited during June when soil moisture was adequate and temperatures were not as severe.

Literature Cited

1. Ashley, D. A., and Ethridge, W. J. 1978. Irrigation effect on vegetative and reproductive development of three soybean cultivars. Agron. J. 70:467-471.

2. Baur, M. E., Boethel, D. J., Boyd, M. L., Bowers, G. R., Way, M. O., Heatherly, L. G., Raab, J., and Ashlock, L. 2000. Arthropod populations in early soybean production systems in the midsouth. Environ. Entomol. 29:312-328.

3. Beurlein, 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.

4. Bowers, G. R. 1995. An early soybean production system for drought avoidance. J. Prod. Agric. 8:112-119.

5. Grichar, W. J. 2007. Planting date, cultivar, and seeding rate effects on soybean production along the Texas Gulf Coast. Online. Crop Management doi:10.1094/CM-2007-1101-01-RS.

6. Heatherly, L. G. 1996. Yield and germinability of seed from irrigated and nonirrigated early- and late-planted MG IV and V soybean. Crop Sci. 36:1000-1006.

7. Heatherly, L. G. 2005. Soybean development in the midsouthern USA related to date of planting and maturity classification. Online. Crop Management doi:10.1094/CM-2005-0421-01-RS.

8. Heatherly, L. G. 2005. Midsouthern USA soybean yield affected by maturity group and planting date. Online. Crop Management doi:10.1094/CM-2005-0418-01-RS.

9. 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.

10. Kane, M. V., Steele, C. C., and Grabau, L. J. 1997. Early-maturing soybean cropping systems: I. yield responses to planting dates. Agron. J. 89:454-458.

11. Mayhew, W. L., and Caviness, C. E. 1994. Seed quality and yield of early-planted, short-season soybean genotypes. Agron. J. 86:16-19.

12. 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.

13. Reicosky, D. C., and Heatherly, L. G. 1990. Soybean. Pages 639-674 in: Irrigation of Agricultural Crops. B. A. Stewart and D. R. Nelson, ed. Agron. Monogr. 30. ASA-CSSA-SSSA, Madison, WI.