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CROP ECOLOGY, PRODUCTION & MANAGEMENT

Grain Yield and Yield Components of Doublecropped Winter Wheat as Affected by Wheat and Previous Soybean Production Practices

^a Clemson Univ., Pee Dee Research and Education Center, 2200 Pocket Road, Florence, SC 29506
^b USDA-ARS, Coastal Plains Soil, Water, and Plant Research Center, 2611 W. Lucas St., Florence, SC 29501

* Corresponding author (jfrdrck{at}clemson.edu)

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Development and grain yield of doublecropped winter wheat (Triticum aestivum L.) are influenced by the production practices used to produce the wheat crop and potentially by those used to produce the previous crop. This 2-yr field study was conducted on a Goldsboro loamy sand (fine-loamy, siliceous, thermic Aquic Kandiudult) to determine whether production practices used in the spring to produce the previous soybean [Glycine max (L.) Merr.] crop affect wheat grain yield and yield component responses to fall production practices. Treatments were deep tillage the previous spring prior to planting soybean using row widths of 19 or 76 cm, deep tillage in the fall prior to wheat planting, deep tillage in both the spring and fall, and no deep tillage for wheat planted with and without surface tillage. Fall deep tillage was the only treatment that consistently increased grain yield and all of the yield components; increasing grain yield, fertile head number per square meter, kernel number per head, and individual kernel weight by an average of 27, 11, 10, and 3%, respectively, over all other treatments. Grain yield and kernel number per square meter responses to fall deep tillage were greatest with no spring deep tillage, with no surface tillage, or when the previous soybean was grown using 76-cm-row widths. Grain yield, fertile head number per square meter, and kernel weight were all higher without surface tillage than with surface tillage. Results from this study show that production practices used to produce the previous soybean crop, such as row width and spring deep tillage, can have a significant effect on the grain yield and yield component responses of wheat to fall production practices.

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
WINTER WHEAT can be an important source of plant residues in no-surface-tillage systems on the southeastern Coastal Plain, especially when doublecropped with soybean, a crop that leaves few residues after seed harvest. Few studies have identified the optimum set of production practices needed to produce winter wheat in this region with no surface tillage. With conventional practices centered on disking, annual deep tillage is recommended for Coastal Plain soils that contain a tillage pan, a naturally occurring hardpan layer (E soil horizon), or both (Busscher et al., 1986; NeSmith et al., 1987, Martin et al., 1979). Fracturing these compacted layers promotes faster and deeper root growth into the subsoil where leached nutrients and additional water can be found. Drought stress generally develops slowly during the wheat growing season, with the most severe drought stress occurring during the grain-filling period (Frederick and Camberato, 1994, 1995a, 1995b). Therefore, deep tillage effects should last well into the grain-filling period of winter wheat.

Although deep tilling is usually necessary, little is known about the optimum time to deep till for winter wheat produced on the Coastal Plain, especially for wheat grown with no surface tillage. If controlled traffic is used during the growing season, deep tilling once prior to wheat planting is usually sufficient for optimum soybean yields when soybean is interseeded into winter wheat (Khalilian et al., 1991). However, the optimum time to deep till may depend on the specific management practices used to produce the crop. For example, Frederick et al. (1998) found deep tillage done prior to planting both wheat and soybean resulted in the highest doublecropped soybean yield when the soybean was planted with no surface tillage and 19-cm-row widths. In contrast, they found the timing of deep tillage had little effect when the soil was disked and the soybean was planted with 76-cm-row widths. Surface residues increase water infiltration and soil water availability (Langdale et al., 1992) and, therefore, may reduce the need for deep tillage for most crops. However, for winter wheat, deep tillage appears to be more important when no surface tillage is used, compared with disking (Frederick and Bauer, 1996). Additional factors that could affect wheat yield and yield component responses to deep tillage include whether the previous summer crop was deep tilled and the amount of soil fracturing by the deep tillage implement used.

How wheat is produced affects grain yield by increasing or decreasing the number of fertile heads per square meter, the number of kernels per head, and/or individual kernel weight. The number of fertile heads per square meter and number of kernels per head determine the number of kernels per square meter, a parameter that is often closely associated with grain yield (Frederick and Bauer, 1999). With respect to responses to management practices, an increase in one wheat yield component is often compensated for by a reduction in a subsequently formed yield component (Frederick and Marshall, 1985; Frederick and Camberato, 1995a). Therefore, examining the components of wheat grain yield can determine whether a treatment had no effect at all on the crop or whether a positive increase in one component was compensated for by a reduction in another component. If compensation occurs, researchers may be able to devise improved production strategies that will prevent the reduction in the compensatory yield component.

The development and final grain yield of doublecropped winter wheat may depend on both the production practices used to produce the wheat crop and those used to produce the previous soybean crop. Understanding whether these production effects occur or not, and the magnitude of their impact on wheat yield, will aid in the development of new wheat cropping systems for the Coastal Plain region. The objectives of this study were (i) to determine how wheat production practices and those practices used to produce the previous soybean crop affect winter wheat grain yield and yield components and (ii) to identify which yield component(s) has the greatest effect on winter wheat grain yield over the different treatments examined.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Site Description and Cultural Practices
Soft red winter wheat (Northrup King cv. Coker 9134)¹ was grown following doublecropped soybean on a Goldsboro loamy sand (fine-loamy, siliceous, thermic Aquic Kandiudult) soil in 1995 and 1996 at the Pee Dee Research and Education Center located near Florence, SC. Northrup King Coker 9134 was selected for this study because of its high grain yield potential, high straw yield, and good disease and insect resistance (Graham et al., 1999). The experimental site was the same, and the same treatments were applied to each plot in both years. Wheat was also grown on these plots in 1994 using the same surface and deep tillage treatments as described below for the 1995 and 1996 wheat crops. Data from 1994 were not include in this study's analysis since 1994 was the first year of the study and no treatments had been imposed on the previous soybean crop.

Cultural practices used to produce the previous soybean crop in 1994, 1995, and 1996 have been described in detail (Frederick et al., 1998). For the wheat crop, phosphorus and potassium fertilizers and lime were broadcast applied each year to all plots in the fall before planting at rates based upon soil test results. The no-surface-tillage plots were sprayed before planting with glyphosate [N-(phosphonomethyl)glycine] at a rate of 1.12 kg a.i. ha^-1. Wheat seeds were planted on 20 and 21 November 1994 and 1995, respectively, with a John Deere 750 grain drill. Seventy-three seeds per meter of crop row were planted in rows spaced 0.19 m apart oriented in a north-south direction. Each plot was 16 rows wide and 15.2 m long.

Ammonium nitrate was broadcast onto all plots immediately after wheat planting at a rate of 34 kg N ha^-1 with a 3-m-wide Gandy fertilizer spreader (Gandy Co., Owatonna, MN). Ammonium nitrate was also applied at a rate of 56 kg N ha^-1 to all plots at Feekes Growth Stage 5.0 (stem erect growth stage; Large, 1954).

Treatments Applied
Treatments were all combinations of surface tillage (disked or no surface tillage), spring deep tillage (deep tilled or no deep tillage prior to planting the previous soybean crop), row width culture of previous soybean crop (production practices used with row widths of 76 or 19 cm), and fall deep tillage (deep tillage or no deep tillage prior to wheat planting). Each treatment was replicated four times. The same level of surface tillage was used to produce both the soybean and wheat crops. Plots assigned to be disked were disked twice to a depth of 18 cm before planting. After disking in the spring, the soybean plots having the 19-cm-row width assigned to be deep tilled were deep tilled to a depth of 41 cm (top of B soil horizon) with a four-shanked ParaTill (Bigham Brothers, Inc., Lubbock, TX). A four-shanked Kelly (Kelly Mfg. Co., Tifton, GA) in-row subsoiling unit mounted in front of a four-row planter was used to deep till to a depth of 41 cm the appropriate soybean plots having the 76-cm-row width. Shanks were mounted as opposed pairs and spaced 71 cm apart on the ParaTill and spaced 76 cm apart on the Kelly subsoiling unit. Both deep tillage devices were equipped with a serrated cutting coulter mounted in front of each shank. The same ParaTill and depth settings were also used for the fall deep tillage treatment.

Parameters Evaluated
At harvest maturity (kernel hard stage), a 1-m-long section of crop row was hand-harvested from each of the six center rows of each plot to determine wheat grain yield and yield components. In both years, the number of fertile (grain bearing) heads was counted after sample harvest, and the grain from each sample was threshed, cleaned, dried at 75°C for 2 d, and weighed. Individual kernel weight was determined by counting, drying, and weighing 200 kernels from each sample. Kernel number per head and kernel number per square meter were calculated from the head number, grain yield, and individual kernel weight data. Apparent harvest index (harvest index measured at harvest maturity) was calculated by dividing the grain yield of each sample by the biological yield (total aboveground dry weight). Grain yield data were converted to a 130 g kg^-1 water basis. Yield and yield component responses to fall deep tillage in 1995 have previously been reported (Frederick and Bauer, 1996).

Rainfall data were collected during the growing season at a weather station located about 200 m from the experimental field. The rate of rainfall accumulation was generally above normal until about day 70 of the year in 1995 and below normal thereafter (Fig. 1). Rate of rainfall accumulation was near to above normal until about day 90 in 1996 and below normal for most of the remainder of the growing season (except for 5.3 cm of rain which occurred on Day 121). Growing degree days were calculated by averaging the daily maximum and minimum air temperatures. A maximum threshold of 30°C was used for the daily high temperature and a minimum threshold of 0°C was used for the daily lows. A base temperature of 0°C was used for degree day calculations. Growing degree day accumulation was less in 1996 than in 1995, especially during the grain filling period (Fig. 1).

View larger version (20K): [in this window] [in a new window]   Fig. 1. Cumulative rainfall and cumulative growing degree days (CGDD) for the 1995 and 1996 spring growing seasons. X symbols indicate normal cumulative rainfall and growing degree days, based on monthly 30-yr averages (1951–1980). Arrows indicate average date of 100% inflorescence emergence (Feekes growth stage 10.5; Large, 1954) over all treatments in 1995 and 1996.

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
The combined statistical analysis of data over years is shown in Table 1. Only the fall deep tillage and year effects were consistently significant over all of the variables measured. Averaged over all treatments, grain yield, apparent harvest index, kernel number per head, individual kernel weight, and kernel number per square meter were 36, 62, 56, 27, and 7% higher in 1995 than in 1996, respectively (data not shown). In contrast, average head number per square meter was 32% lower in 1995. There were few year x treatment interaction effects, with the exception of the year x surface tillage interaction that was significant for four of the six variables (Table 1). When significant, each variable was higher with no surface tillage than with disking in 1995, but lower with no surface tillage in 1996 (data not shown).

Averaged over the other treatments, wheat grain yields were increased 28% by fall deep tillage but increased only 11% by spring deep tillage, compared with no deep tillage. Grain yields averaged 3220 kg ha^-1 with fall deep tillage and 3018 kg ha^-1 with spring deep tillage. The greater response and higher average yield with fall deep tillage suggest that some soil recompaction occurred during the summer months, even though controlled traffic was used. The magnitude of the response to fall deep tillage depended on whether or not the plots were deep tilled in the spring. For example, fall deep tillage increased grain yields an average of 20% when the plots were also deep tilled in the spring, but were increased an average of 34% when the plots were not spring deep tilled. The plots receiving no deep tillage in the fall nor spring had the lowest average yield (2300 kg ha^-1), whereas the plots deep tilled in both the fall and spring had the highest average yield (3300 kg ha^-1). However, the additional 145 kg ha^-1 obtained by deep tilling in both the fall and spring, compared with deep tilling in the fall alone, probably would not pay for the cost of the spring deep tillage operation.

The row width used to plant the previous soybean crop also had an effect on the wheat yield response to fall deep tillage. When the 76-cm-row width was used to produce the previous soybean crop, the response to fall deep tillage was relatively large (29%) even if the soil was deep tilled the previous spring (Table 2). In contrast, for the 19-cm-row width system, fall deep tillage increased average wheat yield by only 13% when the plots were deep tilled the previous spring. When deep tilled in the spring but not the fall, grain yields averaged 2550 and 2951 kg ha^-1 for the wheat grown following soybean planted with the 76- and 19-cm-row widths, respectively. These row-width differences were probably due to the type of devices used to deep till the soil prior to soybean planting in the spring. With the 76-cm soybean row width system, the soil was in-row subsoiled for the plots receiving deep tillage. These devices generally fracture only a small portion of the soil profile, primarily near the subsoiler shanks (Busscher et al., 1999). Therefore, much of the soil probably was not fractured when the 76-cm-row width was used to plant the previous soybean crop, thus accounting for the relatively large wheat yield increase that resulted from fall deep tillage. In contrast, with the 19-cm soybean row width system, the soil was deep tilled with a Paratill which loosens almost all the soil located between the tillage shanks (Busscher et al., 1999). If minimal soil compaction occurred during the summer months, there would have been less response to fall deep tillage with the 19-cm soybean row width system (deep tillage with Paratill) than with the 76-cm soybean row width system (in-row subsoiled), as was found.

There were few treatment effects on apparent harvest index (Table 2). Apparent harvest indices were usually higher with fall deep tillage than with no fall deep tillage. Surface tillage influenced the apparent harvest index response to spring deep tillage. Average apparent harvest indices were 10% higher with spring deep tillage than with no deep tillage when the soil was disked, but 5% less with deep tillage when the wheat was planted with no surface tillage.

Components of Grain Yield
Average fertile head number per square meter was 4% higher with no surface tillage than with disking (Table 3). This response was unexpected because plant densities are usually less with no surface tillage than with disking (Frederick and Bauer, 1996), which may result in fewer heads per square meter at maturity. Average increases in fertile head number due to deep tillage were about 10% for both the fall only and spring only deep tillage treatments. Higher head numbers per square meter were generally found when the plots were deep tilled both in the fall and spring (504 heads), compared with either time alone (about 470 heads). The most benefit from deep tilling both times occurred for the wheat grown with no surface tillage and the wheat following soybean grown with the 76-cm-row width.

Fall deep tillage also had the greatest effect on individual kernel weight (Tables 1 and 3). Fall deep tillage increased wheat kernel weight an average of 3%, with surface tillage and spring deep tillage affecting the magnitude of the response. When disked, individual kernel weight was increased an average of 2% by fall deep tillage but increased an average of 6% with no surface tillage. When the soil was deep tilled the previous spring, there was little change in kernel weight with fall deep tillage. However, when the soil was not deep tilled in the spring, fall deep tillage increased individual kernel weight an average of 6%. This response indicates spring deep tillage can have an effect well into the growing season of the subsequent wheat crop.

Fertile head number per square meter and kernel number per head determine the number of kernels per square meter, which is usually closely associated with wheat grain yield (Frederick and Bauer, 1999). Treatment main effects on kernel number per square meter (Tables 1 and 3) were similar to those found for grain yield. Wheat kernel number per square meter was 5% higher when the 19-cm soybean row width was used than when the 76-cm soybean row width was used. As for grain yield, kernel number per square meter was 5% higher for no surface tillage than for disking. Spring deep tillage increased kernel number per square meter an average of 11%, whereas fall deep tillage increased kernel number an average of 23%. Kernel number per square meter averaged 11 470 with fall deep tillage and 10 930 with spring deep tillage. These results support the grain-yield responses showing the benefits from fall deep tillage are greater than those from deep tillage the previous spring. Unlike grain yield, there was no treatment interaction effects on kernel number per square meter (Table 1).

Over all treatments, the number of fertile heads per square meter had a greater effect on wheat grain yield than the number of kernels per head in 1995, but these two yield components had about the same effect in 1996 (Fig. 2). The close association between head number per square meter and grain yield suggest that a good plant stand and managing for a high fertile tiller number per plant are important for obtaining high winter wheat yields on the Coastal Plain. Grain yield was most closely associated with the number of kernels per square meter (Fig. 2). In contrast, there was little association between wheat grain yield and individual kernel weight (Fig. 2). Frederick and Bauer (1999) proposed that grain-yield improvement for wheat grown on the Coastal Plain has been the result of breeders selecting for a higher kernel number per square meter, rather than heavier kernels. They concluded that selection for heavier wheat kernels in this region is limited by the warm and dry weather conditions that frequently occur during grain fill and by the desire to avoid extending the duration of grain fill because of the loss in doublecropped soybean yield that would occur due to the delay in soybean planting. The close association we found between kernel number per square meter and grain yield, and lack of association between grain yield and kernel weight, support their hypotheses about yield improvement in winter wheat.

View larger version (35K): [in this window] [in a new window]   Fig. 2. Winter wheat grain yield as a function of fertile head number per square meter, kernel number per head, kernel number per square meter, and individual kernel weight in 1995 and 1996. Regression equations shown are those derived by linear regression analysis. Each value is a plot mean.

Fall deep tillage had the greatest effect of any treatment on the components of yield and was the only treatment that had a positive effect on all of the yield components. Planting with no surface tillage also had a positive effect on the number of fertile heads per square meter and individual kernel weight, but had no effect on kernel number per head. In no case did we find one yield component reduced in response to an increase in a previously determined yield component, as has frequently been reported to occur in wheat (Frederick and Marshall, 1985; Frederick and Camberato, 1995a). This would indicate that higher wheat yields on the Coastal Plain can be obtained by using production practices that result in little to no yield component compensation.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
South Carolina Agric. Exp. Stn. Technical Contribution no. 4570.

¹ Mention of trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by Clemson University and the USDA-ARS or does not imply its approval to the exclusion of other products or vendors that may be also be suitable.

Received for publication March 1, 2000.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 

• Busscher, W.J., P.J. Bauer, and J.R. Frederick. 1999. Soil strength for varying soil type and deep tillage in a Coastal Plain field with hardpans. p. 17–22. In J.E. Hook (ed.) Proc. 22nd Annu. Southern. Conserv. Tillage Conf. for Sustainable Agric., Tifton, GA.
• Busscher, W.J., R.E. Sojka, and C.W. Doty. 1986. Residual effects of tillage on Coastal Plain soil strength. Soil Sci. 141:144–148.
• Frederick, J.R., and P.J. Bauer. 1996. Winter wheat responses to surface and deep tillage on the Southeastern Coastal Plain. Agron. J. 88:829–833.[Abstract/Free Full Text]
• Frederick, J.R. and P.J. Bauer. 1999. Physiological and numerical components of wheat yield. p. 45–84. In E.H. Satorre and G.A. Slafer (ed.) Wheat—Ecology and physiology of yield determination. Food Products Press, New York, NY.
• Frederick, J.R. and J.J. Camberato. 1994. Leaf CO₂-exchange rate and associated leaf traits of winter wheat grown with various spring fertilization rates. Crop Sci. 34:432–439.[Abstract/Free Full Text]
• Frederick, J.R., and J.J. Camberato. 1995a. Water and nitrogen effects on winter wheat in the southeastern Coastal Plain: I. Grain yield and kernel traits. Agron. J. 87:521–526.[Abstract/Free Full Text]
• Frederick, J.R., and J.J. Camberato. 1995b. Water and nitrogen effects on winter wheat in the southeastern Coastal Plain: II. Physiological responses. Agron. J. 87:527–533.[Abstract/Free Full Text]
• Frederick, J.R., and H.G. Marshall. 1985. Grain yield and yield components of soft red winter wheat as affected by management practices. Agron. J. 77:495–499.[Abstract/Free Full Text]
• Frederick, J.R., P.J. Bauer, W.J. Busscher, and G.S. McCutcheon. 1998. Tillage management for doublecropped soybean grown in narrow and wide row width culture. Crop Sci. 38:755–762.[Abstract/Free Full Text]
• Graham, W.D., R.J. Gambrell, and C.W. Myers. 1999. Performance of small grain varieties in South Carolina—1999. S.C. Agric. Exp. Stn. Circ. 175.
• Khalilian, A., C.E. Hood, J.H. Palmer, T.H. Garner, and G.R. Bathke. 1991. Soil compaction and crop response to wheat/soybean interseeding. Trans. ASAE 34:2299–2303.
• Langdale, G.W., W.C. Mills, and A.W. Thomas. 1992. Use of conservation tillage to retard erosion effects of large storms. J. Soil Water Conserv. 47:257–260.
• Large, E.C. 1954. Growth stages in cereals: Illustrations of the Feekes scale. Plant Pathol. 3:128–129.
• Martin, C.K., D.K. Cassel, and E.J. Kamprath. 1979. Irrigation and tillage effects on soybean yield in a Coastal Plain soil. Agron. J. 71:592–594.[Abstract/Free Full Text]
• NeSmith, D.S., W.L. Hargrove, D.E. Radcliffe, E.W. Tollner, and H.H. Arioglu. 1987. Tillage and residue management effects on properties of an Ultisol and double-cropped soybean production. Agron. J. 79:570–576.[Abstract/Free Full Text]

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Frederick, J. R. Articles by Busscher, W. J. Search for Related Content PubMed Articles by Frederick, J. R. Articles by Busscher, W. J. Agricola Articles by Frederick, J. R. Articles by Busscher, W. J. Related Collections Soybean Wheat Crop Systems