Open access peer-reviewed chapter

Cover-Crop Management Influences Residue Biomass and Subsequent Weed Suppression in a Conservation Agriculture Corn and Cotton Rotation

Written By

Andrew J. Price, Edzard van Santen and Lina Sarunaite

Submitted: December 21st, 2015 Reviewed: May 6th, 2016 Published: November 9th, 2016

DOI: 10.5772/64132

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Abstract

The use of winter cover crops is an integral component of conservation systems in a corn and cotton conservation agriculture rotation. Field experiments were conducted from the autumn of 2003 through cash crop harvest in 2006 at three locations. The treatments were five cover-crop-planting timings each fall and four cover-crop termination timings each spring. Five crimson clover or cereal rye planting timings occurred: on the average first 0○C temperature date, 4 and 2 weeks prior and 4 and 2 weeks after the average 0○C temperature date. Termination dates were 1–4 weeks prior to the average optimum soil temperature date for the establishment of each cash crop. Results showed that biomass production by winter covers decreased with even a week’s delay in winter cover-crop seeding and resulted in a corresponding increase in summer annual weed biomass. More than 10 times difference in biomass produced by clover was observed when clover was planted on the earliest date and terminated on the last date compared to late planting and early termination, rye eight times. Correspondingly, weed biomass was 556 kg ha−1 in the treatment with least rye biomass, eight times higher compared to the treatment with greatest rye biomass.

Keywords

  • alternative weed control
  • conservation tillage
  • cover crops
  • crop rotation
  • weed biomass

1. Introduction

Resistance management has become the dominating weed science research and extension focus. In the Southeastern and Mid-South United States, questions concerning management of herbicide resistant Amaranthus species, horseweed (Conyza Canadensis L.), and Italian ryegrass (Lolium multiflorum Lam.), comprise the majority of Cooperative Extension Service (CES) calls in these regions. Conservation agriculture (CA) practices are especially threatened by the emergence and rapid spread of glyphosate-resistant Palmer amaranth (A. palmeri S. Wats.). Hundreds of thousands of CA hectares are at risk of being converted to higher-intensity tillage systems due to the inability to reliably control herbicide-resistant weeds in CA systems, especially dry land systems where soil applied herbicides risk non-activation [1]. Currently, the integration of high-residue cover-crop systems, inversion of the soil profile facilitating burial of the surface seedbank, and overlapping residual herbicides are increasingly being recommended by state CES throughout the Southeastern Coastal Plain and Mid-South Delta for herbicide-resistance management [13]. The CES in the Southeastern and Mid-South United States is also more frequently recommending tillage to enable increased pre-planting and pre-emergence herbicide use [35]. Between-row cultivation is also a proven method of controlling many troublesome and resistant weed species [4, 6]. However, conventional tillage practices decrease soil and water quality and may exclude producers from participating in government loan, insurance, and incentive programs designed to promote soil conservation stewardship. With the rapid spread of acetolactate synthase (ALS) and glyphosate-resistant Palmer amaranth, the hectares in CA could potentially decline further without the development of new, effective weed-control strategies [1].

In the 2012 Weed Science special issue “Herbicide Resistant Weeds”, authors describe the need to understand a diverse best management practices (BMPs), including “emphasizing cultural management techniques that suppress weeds by using crop competitiveness” and “using mechanical and biological management practices where appropriate” [7]. Specific examples among many BMPs include crop rotation and cover-crops mulches, respectively. Interest in utilizing high-residue cover crops as a weed management tool is continually increasing from both producers and conservation organizations such as the Soil and Water Conservation Society and USDA Natural Resource Conservation Service among others who both actively support conservation practices through outreach programs and fiscal incentives. This special issue manuscript also states that the appropriate time for cover-crop termination is complex and that the optimum planting and termination timing will be regional and often farm-specific, and concludes “the greatest challenge to the use of any cover crop is the added complexity associated with integration into existing cropping systems.”

To reduce the use of intensive tillage practices in integrated weed management systems for controlling problematic weeds, further evaluation of alternative control strategies is necessary. High-residue cover crops, which have been shown to provide early-season weed control, may be utilized in cotton along with other management tactics to suppress Amaranthus growth [818]. Although early-season weed control is possible with cover crops, season-long control has required the use of herbicides [14, 16, 1921]. In addition, the quantity of mulch needed to physically suppress weeds has been evaluated [22].

In the past, cover-crop termination has been facilitated utilizing pre-plant (PP) burndown herbicides before planting. The CES recommends terminating winter covers relatively early in the spring, due to concerns for excessive cover-crop biomass interfering with planting operations or excessive soil moisture depletion [23, 24]. However, planting into residue is commonplace (Figure 1) and it is well known that planting date affects subsequent residue cover [25].

Figure 1.

Cotton planted into cereal rye cover crop for weed suppression.

Cooperative extension service recommendations also generally recommend waiting approximately 2–4 weeks after desiccating cereal winter covers before planting cotton to avoid allelopathic effects [26, 27]. However, little research has been conducted evaluating how management of high-residue cover-crop biomass production in situ affects biomass amounts attained as well as weed and crop response. Thus, the objective of this research was to determine how cover-crop planting and termination timing influence subsequent residue and weed biomass and crop yield responses.

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2. Materials and methods

Field experiments were conducted at the Alabama Agricultural Experiment Station’s E.V. Smith Research Center at Shorter, AL, and Tennessee Valley Research and Extension Center at Belle Mina, AL, from autumn of 2003 through cash crop harvest in 2006. The experiment was also conducted at the University of Florida West Florida Education and Research Center at Jay, FL, from autumn of 2004 to cash crop harvest in 2006. The three locations were selected due to their relatively distant latitude positions and differing soil types, which, according to previous observations concerning forage biomass yield, would influence winter cover-crop growth. Latitude ranged from Belle Mina at 34.689595, E.V. Smith at 32.427626 to Jay, FL, at 30.777618. The soil types were Compass loamy sand (coarse-loamy, siliceous, subactive, thermic Plinthic Paleudults) at E.V. Smith, Decatur silty loam (fine, kaolinitic, thermic, Rhodic Paleudult) at Tennessee Valley, and a Dothan sandy loam (fine-loamy, siliceous, thermic Plinthic Kandiudults) at Jay.

The treatments were five cover-crop-planting timings each fall and four cover-crop termination timings each spring. The five crimson clover or cereal rye-planting timings occurred on the average 30 year first 0C temperature date, 4 and 2 weeks prior and 4 and 2 weeks after the average 30 year 0C temperature date. Termination dates were 1–4 weeks prior to the average 30-year optimum soil temperature date for the establishment of corn or cotton (Table 1 and 2). Termination dates were 4, 3, 2, and 1 week prior to the chosen date for corn and cotton establishment, which we based on the long-term average date of the minimum soil temperature ideal for corn (Zea mays L.) or cotton (Gossypium hirsutum L.) seeding as recommended by the Auburn University CES recommendations (Tables 1 and 2).

Belle Mina, AL Shorter, AL Jay, FL
2003/2004 2004/2005 2005/2006 2003/2004 2004/2005 2005/2006 2004/2005 2005/2006
Seeding dates
25-Sep 27-Sep 25-Sep 09-Oct 08-Oct 12-Oct 29-Oct 04-Nov
09-Oct 11-Oct 11-Oct 20-Oct 21-Oct 25-Oct 10-Nov 17-Nov
22-Oct 26-Oct 24-Oct 10-Nov 10-Nov 07-Nov 29-Nov 02-Dec
04-Nov 08-Nov 07-Nov 21-Nov 03-Dec 22-Nov 13-Dec 12-Dec
18-Nov 18-Nov 18-Nov 08-Dec 16-Dec 07-Dec 20-Dec 22-Dec
Termination dates
23-Feb 23-Feb 22-Feb 23-Feb 23-Feb 22-Feb 03-Feb 10-Feb
01-Mar 01-Mar 01-Mar 01-Mar 01-Mar 01-Mar 10-Feb 17-Feb
08-Mar 09-Mar 08-Mar 08-Mar 09-Mar 08-Mar 17-Feb 24-Feb
15-Mar 18-Mar 15-Mar 15-Mar 18-Mar 15-Mar 24-Feb 03-Mar

Table 1.

Crimson clover seeding and termination dates.

The experiment for each location was a randomized complete block design (r = 3) with a split-block restriction on randomization. This design was chosen for practical reasons because it enabled us to handle seeding and termination operations for the cover crop efficiently. We assigned cover-crop-planting dates (5) to horizontal and termination dates (4) to vertical strips. For each location x-year combination, therefore, we had three different sizes of experimental units (Steel and Torrie, 1987). The largest experimental unit (TD) equals one-quarter of the block size, the second largest (PD) equals one-fifth of the block size, and the smallest (PD × TD combinations) equals 1/20 of the block size. This design also led to three different sources of experimental errors catering to each experimental unit. Depending on location, the smallest experimental unit (henceforth called plot) was 4 m wide and 8 m long containing four rows of corn and cotton with a 1-m row spacing.

Belle Mina, AL Shorter, AL Jay, FL
2003/2004 2004/2005 2005/2006 2003/2004 2004/2005 2005/2006 2004/2005 2005/2006
Seeding dates
25-Sep 27-Sep 25-Sep 09-Oct 08-Oct 12-Oct 29-Oct 04-Nov
09-Oct 11-Oct 11-Oct 20-Oct 21-Oct 25-Oct 10-Nov 17-Nov
22-Oct 26-Oct 24-Oct 10-Nov 10-Nov 07-Nov 29-Nov 02-Dec
04-Nov 08-Nov 07-Nov 21-Nov 03-Dec 22-Nov 13-Dec 12-Dec
18-Nov 18-Nov 18-Nov 08-Dec 16-Dec 07-Dec 20-Dec 22-Dec
Termination dates
02-Apr 04-Apr 05-Apr 23-Mar 23-Mar 22-Mar 10-Mar 16-Mar
09-Apr 11-Apr 10-Apr 31-Mar 30-Mar 29-Mar 17-Mar 24-Mar
16-Apr 18-Apr 17-Apr 07-Apr 06-Apr 04-Apr 24-Mar 31-Mar
22-Apr 28-Apr 24-Apr 13-Apr 13-Apr 12-Apr 29-Mar 07-Apr

Table 2.

Cereal rye seeding and termination dates.

Winter cover crops included crimson clover (Trifolium incarnatum L.) cv. AU Robin preceding corn and cereal rye (Secale cereale L.) cv. Elbon preceding cotton. Both the phases of rotation were present on adjacent areas within the same field tier. Crimson clover and cereal rye were established with a no-till drill at a seeding rate of 28 and 100 kg ha−1, respectively, at the times described previously. In the spring, cover-crop biomass samples were collected immediately prior to termination by clipping all aboveground plant parts close to the soil surface from one randomly selected 0.25-m2 section in each plot. Plant material was dried at 60C for 72 h and weighed. Each plot was mechanically rolled/crimped at the timings described previously immediately prior to chemical termination, as described by Ashford and Reeves [28], to aid in cover-crop desiccation and the process leaves a uniform mat of residue on the soil surface. Clover was then sprayed with glyphosate (N-(phosphonomethyl) glycine) at 1.12 kg ae ha−1 plus 2,4-D amine (2,4-D-dimethylammonium) at 0.20 kg ai ha−1, while rye was terminated with glyphosate alone, utilizing a compressed CO2 backpack sprayer delivering 140 L ha−1 at 147 kPa.

Because the central Alabama and West Florida sites had a well-developed hardpan, the experimental areas were in-row subsoiled within the week prior to corn and cotton planting with a narrow-shank parabolic subsoiler equipped with pneumatic tires to close the subsoil channel (KMC, Tifton GA, USA). Corn hybrid cv. Dekalb 69-72RR and cotton cultivars DP 444 BG/RR, ST 5242 BR and DP555BRR were planted at Shorter, Belle Mina, and Jay Florida, respectively. Each cash crop was planted 1 week after the final termination date for winter cover crops at each location with a four-row planter equipped with row cleaners and double-disk openers (Great Plains Mfg., Inc. Salina, KS, USA).

At the corn eight-leaf or cotton four-leaf growth stage, all aboveground biomass for all weeds were harvested from two between the row randomly selected 0.25-m2 sections per plot and treated in a similar manner as to cover-crop samples described above. Immediately after weed sampling, glyphosate was applied at 1.12 kg ae ha−1. Plots were then kept weed-free until harvest utilizing Alabama CES-recommended herbicide applications. For the determination of corn grain yield, the two center rows of each plot were harvested with a plot combine, dried to constant moisture (150 g H2O kg−1), and weighed. Seed cotton yield was determined by machine harvesting the middle two rows of each plot with a spindle picker.

Data were analyzed separately for each location using generalized linear-mixed models methodology as implemented in SAS® PROC GLIMMIX. Year, planting date and termination date, and all their interactions were considered fixed effects. Interaction of reps with planting date and termination date was considered random effects. Interaction effects were considered to be important whenever the calculated P-value was less than 0.10. Treatment differences were calculated by Dunnett’s single degree-of-freedom contrasts.

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3. Results and discussion

3.1. Crimson clover cover-crop biomass

Climatic conditions encountered at the three locations resulted in large differences in biomass production. The maximum biomass production (5447 kg ha−1) was observed at Shorter, AL, when crimson clover was seeded 4 weeks prior to the average first 0C temperature and terminated 1 week prior to planting the corn cash crop (data not shown). The least biomass production (24 kg ha−1) was observed at Belle Mina, AL, when the clover was seeded at the last establishment date (4 weeks post 0C temperature) and terminated 1 week prior to corn planting (data not shown).

The most general model for this type of study is a classification model that treats seeding and termination dates as categorical variables resulting in a 5 by 4 factorial arrangement. The three-way interaction was significant (P = 0.051) only for the Bella Mina location (data not shown). The two-way interactions termination date by year was significant for the northern and southernmost locations only (P ≤ 0.001), whereas seeding date interacted significantly with years for all three locations (P < 0.0001). The seeding by termination date interaction was significant only for Belle Mina and Jay (P < 0.026). Main effects for seeding and termination dates were significant at all locations except for termination date at Shorter.

Cover crop seeding date Growing season
2003–2004 2004–2005 2005–2006
Clover biomass (kg ha−1)
Belle Mina, AL
−4 weeks 2861 1928 1904
−2 weeks 1435 2336 1753
Median date 604 945 757
+2 weeks 304 263 381
+4 weeks 76 121 85
SE 172
Dunnett’s P versus median-seeding date
−4 weeks <0.0001 <0.0001 <0.0001
−2 weeks <0.0001 <0.0001 <0.0001
+2 weeks <0.0001 0.009 0.265
+4 weeks <0.0001 0.001 0.010
Shorter, AL
−4 weeks 1808 4750 4511
−2 weeks 2135 3827 3935
Median date 1223 1061 1958
+2 weeks 1321 359 805
+4 weeks 914 414 425
SE 332
Dunnett’s P versus median-seeding date
−4 weeks 0.462 <0.0001 <0.0001
−2 weeks 0.117 <0.0001 <0.0001
+2 weeks 0.998 0.302 0.030
+4 weeks 0.884 0.373 0.002
Jay, FL
−4 weeks NA 601 2123
−2 weeks NA 468 979
Median date NA 230 465
+2 weeks NA 103 205
+4 weeks NA 90 132
SE 86
Dunnett’s P versus median-seeding date
−4 weeks NA 0.011 <0.0001
−2 weeks NA 0.164 <0.0001
+2 weeks NA 0.683 0.113
+4 weeks NA 0.605 0.026

Table 3.

Clover biomass (kg ha1) by location and year as influenced by cover-crop seeding date, which were based on the 30-year average day of first frost at each location. Further seeding dates were either 2 or 4 weeks prior (−) or later (+) than that date. Data are averaged over termination dates.

Crimson clover dry biomass yield was significantly reduced by the delay in seeding date at all locations and years (Table 3).

In 2003–2004 at Belle Mina, crimson clover planted 4 and 2 weeks prior to the average 0C date yielded 2257 and 831 kg ha−1 higher, respectively, than plots planted on the average 0C date (604 kg ha−1), and 2785 and 1359 kg ha−1 higher, respectively, than the latest planting date. Similar trends were observed in 2004–2005 and 2005–2006 except for one comparison. Belle Mina is the coldest of the three experiment locations with an average temperature of 10, 5.5, and 3.8C during November, December, and January, respectively. These observations indicate that it is very important to plant a legume cover crop such as crimson clover early enough to get sufficient growth before cooler temperatures reduce growing degree days. Less than 400 kg ha−1 of biomass was produced when crimson clover was seeded 2 weeks after the average 0C temperature at Belle Mina in any year. At Belle Mina in 2003–2004 and 2005–2006, clover biomass was maximized by waiting until 1 week prior to planting to terminate the cover crop gaining an additional 521 and 195 kg ha−1, respectively, compared to terminating at the CES recommended 2 weeks prior to planting.

At Shorter, the variability in crimson clover biomass production among the years was very pronounced; biomass production was less in 2003 compared to 2004 and 2005. Significant reduction in crimson clover biomass production was observed with an advanced seeding date only in 2004 and 2005, as indicated by contrasts. If the seeding of crimson clover was delayed by 4 weeks compared to the earliest date, 3689 and 2553 kg ha−1 less biomass were produced in 2004 and 2005, respectively. No significant differences in crimson clover biomass production were, however, observed with early or delayed termination in 2004 and 2005 (Table 4).

Cover crop seeding date Growing season
2003–2004 2004–2005 2005–2006
Clover biomass (kg ha−1)
Belle Mina, AL
−1 week prior 1637 1015 1323
−2 week prior 1116 1364 1131
−3 week prior 832 1119 833
−4 week prior 639 977 617
SE 144
Dunnett’s P versus first termination date
−1 week prior <0.0001 0.991 <0.0001
−2 week prior 0.022 0.059 0.007
−3 week prior 0.550 0.729 0.431
Shorter, AL
−1 week prior 1860 2348 2827
−2 week prior 1315 2005 2385
−3 week prior 1691 1813 2389
−4 week prior 1054 2162 1706
SE 335
Dunnett’s P versus first termination date
−1 week prior 0.187 0.956 0.039
−2 week prior 0.891 0.972 0.310
−3 week prior 0.360 0.781 0.306
Jay, FL
−1 week prior NA 474 1144
−2 week prior NA 217 945
−3 week prior NA 201 588
−4 week prior NA 300 446
SE 77
Dunnett’s P versus first termination date
−1 week prior NA 0.264 <0.0001
−2 week prior NA 0.787 <0.0001
−3 week prior NA 0.687 0.426

Table 4.

Clover biomass (kg ha1) by location and year as influenced by cover-crop termination date, which were 4, 3, 2, and 1 week prior to corn planting. Termination dates were based on a 30-year average soil temperature. Data are averaged over seeding dates.

Dry biomass accumulation was maximized if crimson clover was allowed to grow until 1 week prior to corn planting compared in 2006.

At the southernmost location Jay, except the three-way interaction, all other main and interaction effects were significant for crimson clover biomass production. Significant differences among years were observed, with biomass production less in 2004–2005 compared to 2005–2006. In 2004–2005 and 2005–2006, the earliest planting date resulted in 601 and 2123, respectively. With every 2-week delay in seeding, the cover-crop biomass production was reduced by more than half in almost all comparisons (Table 3). Significantly high biomass was accumulated when crimson clover was terminated only a week or 2 prior to the corn planting in 2005–2006 compared with the earliest termination date (Table 4).

3.2. Weed biomass in corn

The three-way interaction (year by PD by KD) was not significant for any location. The interaction of termination date with year was significant for both Belle Mina and Shorter locations (P ≤ 0.04). Interactions of seeding date with year as well as with termination date were not significant (P ≥ 0.11). Years did not have a significant effect at any of the locations (P ≥ 0.12). The effect of termination date (P ≤ 0.05) and seeding date (P = 0.09) was significant at Belle Mina and Shorter only.

At Belle Mina, weed biomass was only 81 kg ha−1 in 2003/2004 growing season corresponding to crimson clover biomass of 2861 kg ha−1 when the cover crop was seeded 4 weeks prior to the average 0C temperature (data not shown). Weed biomass increased with delay in cover-crop seeding date indicating that a greater amount of crimson clover residue produced by earlier seeding dates suppressed early-season weed biomass production in corn. However, contrasts indicate no significant reduction in weed biomass if crimson clover was planted 4 or 2 weeks after the average 0C temperature. In the 2004–2005 growing season, weed biomass production was significantly reduced by seeding crimson clover 4 and 2 weeks prior to the average 0C temperature; again, the higher biomass production resulted in less weed biomass. No significant differences in weed biomass production were observed if crimson clover was seeded on the average 0C temperature or thereafter. In 2005/2006, seeding dates had no significant effect on weed biomass production. No significant effect of delayed termination on weed biomass production was observed in 2003–2004 and 2004/2005 growing seasons compared to the first termination date (4 weeks prior to average 0C temperature). However, in 2005/2006 growing season, a significant reduction in weed biomass was observed with only a week’s delay in crimson clover termination. This could be attributed to the increase in crimson clover biomass production with delayed termination, which in turn resulted in early season weed suppression.

At Shorter location, no significant increase or decrease in weed biomass production was observed with seeding of crimson clover earlier or later than the average 0C temperature date. However, weed biomass production in general increased with delay in crimson clover seeding date; in 2003/2004 and 2005/2006 growing seasons, weed biomass ranged from 16 to 28 kg ha−1 for the first two crimson clover seeding dates, whereas the final seeding date plots averaged nearly 109 kg ha−1 weed biomass during both the growing seasons. The effect of termination dates was pronounced only in 2005/2006; significantly less weed biomass was produced if the termination was delayed by even a week (data not shown).

At Jay location, our southernmost location, no definite trend in weed biomass production was observed with earlier seeding or termination of the crimson clover (data not shown). This could be due to rapid decomposition of residue due to warmer temperatures and higher rainfall at this location compared to the northern locations.

3.3. Corn grain yield

Corn grain yield was not affected by crimson clover seeding and termination dates at Belle Mina. Though no statistically significant differences were observed, plots with the earliest seeding of the crimson clover yielded numerically highest at this location. At both Shorter and Belle Mina, significant differences in corn grain yield were observed across years (Tables 5 and 6).

Cover crop seeding date Growing season
2003–2004 2004–2005 2005–2006
Corn grain yield (kg ha−1)
Belle Mina, AL
−4 weeks 10,471 9262 4646
−2 weeks 9474 8712 4686
Median date 9963 8684 5228
+2 weeks 10,054 8434 4607
+4 weeks 9344 8414 4831
SE 370
Dunnett’s P versus median-seeding date
−4 weeks 0.501 0.386 0.380
−2 weeks 0.534 1.000 0.445
+2 weeks 0.998 0.919 0.324
+4 weeks 0.326 0.897 0.702
Shorter, AL
−4 weeks 11,986 7631 5703
−2 weeks 11,701 7701 5709
Median date 12,429 7333 5629
+2 weeks 11,325 7363 5840
+4 weeks 11,533 7864 5296
SE 379
Dunnett’s P versus median-seeding date
−4 weeks 0.592 0.847 0.999
−2 weeks 0.175 0.731 0.999
+2 weeks 0.015 1.000 0.949
+4 weeks 0.065 0.431 0.792
Jay, FL
−4 weeks NA 5582 13520
−2 weeks NA 6259 14328
Median date NA 5236 12982
+2 weeks NA 6318 12083
+4 weeks NA 6432 12694
SE 945
Dunnett’s P versus median-seeding date
−4 weeks NA 0.972 0.878
−2 weeks NA 0.446 0.216
+2 weeks NA 0.397 0.560
+4 weeks NA 0.310 0.986

Table 5.

Corn grain yield (kg ha1) by location and year as influenced by cover-crop seeding date, which were based on the 30-year average day of first frost at each location. Further seeding dates were either 2 or 4 week prior (−) or later (+) than that date. Data are averaged over termination dates.

Grain yield decreased with the progression of the experiment. Weather conditions were different among the years, 2004 being a normal rainfall year whereas in 2005 majority of the rainfall was received in July at Belle Mina (6 in.) and Shorter (8.5 in.); 2006 was a drought year at both the locations throughout the summer. These differences in rainfall events can likely explain some of the yield differences observed among years at both the locations. Corn is most sensitive to water stress during silking or flowering, and pollination stages of growth and drought stress during this period can result in poor grain development and yield losses.

Cover crop seeding date Growing season
2003–2004 2004–2005 2005–2006
Corn grain yield (kg ha−1)
Belle Mina, AL
−1 week prior 9880 8389 4946
−2 week prior 9707 8392 5201
−3 week prior 10,117 9196 4842
−4 week prior 9741 8827 4209
SE 425
Dunnett’s P versus first termination date
−1 week prior 0.988 0.745 0.370
−2 week prior 1.000 0.748 0.155
−3 week prior 0.818 0.827 0.491
Shorter, AL
−1 week prior 10,916 7579 4382
−2 week prior 12,094 7424 5949
−3 week prior 12,453 8225 6933
−4 week prior 11,717 7085 5278
SE 500
Dunnett’s P versus first termination date
−1 week prior 0.482 0.797 0.392
−2 week prior 0.895 0.920 0.616
−3 week prior 0.547 0.209 0.037
Jay, FL
−1 week prior NA 5615 12,565
−2 week prior NA 5867 12,872
−3 week prior NA 6225 13,468
−4 week prior NA 6155 13,581
SE 784
Dunnett’s P versus first termination date
−1 week prior NA 0.926 0.673
−2 week prior NA 0.987 0.853
−3 week prior NA 1.000 0.999

Table 6.

Corn grain yield (kg ha1) by location and year as influenced by cover-crop termination date, which were 4, 3, 2, and 1 week prior to corn planting. Termination dates were based on 30-year average soil temperature. Data are averaged over seeding dates.

3.4. Cereal rye cover-crop biomass

When analyzed by location, the three-way interaction was not significant at Belle Mina. The interaction of experiment years with seeding date was significant. The main effect of seeding date, termination date, and year was also significant. In general, rye biomass production declined with every 2-week delay in seeding the cover crop (Table 7).

Cover crop seeding date Growing season
2003–2004 2004–2005 2005–2006
Rye biomass (kg ha−1)
Belle Mina, AL
−4 weeks 8878 5062 6396
−2 weeks 7852 5232 4078
Median date 6584 2863 2479
+2 weeks 4500 2149 3085
+4 weeks 2649 913 2066
SE 611
Dunnett’s P versus median-seeding date
−4 weeks 0.004 0.006 <0.0001
−2 weeks 0.200 0.003 0.070
+2 weeks 0.010 0.701 0.788
+4 weeks <0.0001 0.018 0.933
Shorter, AL
−4 weeks 5566 5331 6177
−2 weeks 5053 4893 6269
Median date 4344 2610 5372
+2 weeks 2779 518 2553
+4 weeks 1276 213 1370
SE 356
Dunnett’s P versus median-seeding date
−4 weeks 0.020 <0.0001 0.198
−2 weeks 0.298 <0.0001 0.128
+2 weeks 0.002 <0.0001 <0.0001
+4 weeks <0.0001 <0.0001 <0.0001
Jay, FL
−4 weeks NA 3605 5006
−2 weeks NA 2982 5341
Median date NA 2559 4695
+2 weeks NA 1687 3349
+4 weeks NA 1545 2706
SE 253
Dunnett’s P versus median-seeding date
−4 weeks NA 0.005 0.727
−2 weeks NA 0.480 0.142
+2 weeks NA 0.026 <0.0001
+4 weeks NA 0.007 <0.0001

Table 7.

Rye biomass (kg ha1) by location and year as influenced by cover-crop seeding date, which were based on the 30-year average day of first frost at each location. Further seeding dates were either 2 or 4 week prior (−) or later (+) than that date. Data are averaged over termination dates.

Delaying cereal rye planting 4 weeks significantly lowered the rye biomass yield in all the years. Biomass production was in general less at this location in 2003/2004 and 2004/2005 growing seasons. Earlier termination of rye also significantly reduced biomass. Biomass production in all the years was increased if rye was terminated a week or 2 prior to cotton planting (Table 7). However, no significant differences in biomass production were observed if rye was terminated 3 or 4 weeks prior to cotton planting.

At Shorter location, all the interactions and main effects were significant for rye biomass production. Delayed seeding of rye significantly reduced dry biomass accumulation (Table 7). In 2004–2005, no significant differences in rye dry biomass accumulation occurred if rye was seeded on the third seeding date or later. Significant planting and termination date interaction were also observed at this location. The maximum biomass production was 8523 kg ha−1 in year 2006 when rye was planted 2 weeks before the 0C temperature date and terminated a week prior to cash crop planting. The least biomass produced at Shorter was 140 kg ha−1 when covers were planted on the last planting date and terminated on the first planting date (data not shown).

At our southernmost location Jay, all two-way interactions and main effects were significant. Rye biomass production was better in year 2006 compared to year 2005. As observed at other two locations, delayed seeding or earlier termination reduced dry biomass accumulation by rye (data not shown). The maximum observed rye biomass at this location was 7468 kg ha−1 produced when rye was planted 4 weeks prior to the average 0C temperature and terminated 2 weeks before the seeding of cotton.

3.5. Weed biomass in cotton

Dry weights of weeds were more in cotton compared to corn at all site years due to the earlier sampling time in corn when fewer summer annual weeds had emerged. The cover-crop biomass observed at each location was reflected in the subsequent results observed for weed control. The three-way interaction was not significant at any of the locations. The interaction of year with seeding and termination date was significant at all the locations except at Jay. The seeding by termination date interaction was not significant at any location.

In general, there was an increase in weed biomass in cotton with earlier termination and late planting of the rye cover crop. At Belle Mina, numerically less weed dry biomass was observed corresponding to a high rye cover-crop residue (Table 8).

Cover crop seeding date Growing season
2003–2004 2004–2005 2005–2006
Belle Mina, AL
−4 weeks 31 133 214
−2 weeks 54 182 455
Median date 406 275 945
+2 weeks 250 297 368
+4 weeks 345 478 664
SE 102
Dunnett’s P versus median-seeding date
−4 weeks 0.010 0.601 <0.0001
−2 weeks 0.017 0.865 <0.0001
+2 weeks 0.519 0.999 <0.0001
+4 weeks 0.965 0.283 0.077
Shorter, AL
−4 weeks 316 289 62
−2 weeks 318 381 53
Median date 470 440 58
+2 weeks 474 467 81
+4 weeks 970 378 88
SE 101
Dunnett’s P versus median-seeding date
−4 weeks 0.425 0.438 1.000
−2 weeks 0.437 0.953 1.000
+2 weeks 1.000 0.997 0.998
+4 weeks <0.0001 0.944 0.996
Jay, FL
−4 weeks NA 48 53
−2 weeks NA 50 48
Median date NA 80 88
+2 weeks NA 53 85
+4 weeks NA 87 65
SE 14
Dunnett’s P versus median-seeding date
−4 weeks NA 0.338 0.259
−2 weeks NA 0.390 0.160
+2 weeks NA 0.495 1.000
+4 weeks NA 0.993 0.626

Table 8.

Weed dry biomass (kg ha1) in cotton by location and year as influenced by cover-crop seeding date, which were based on the 30-year average day of first frost at each location. Further seeding dates were either 2 or 4 week prior (−) or later (+) than that date. Data are averaged over termination dates.

Weed biomass averaged only 31 kg ha−1 corresponding to rye biomass of 8878 kg ha−1 in plots seeded with rye 4 weeks before the average 0C temperature in 2003. No significant differences in weed biomass production were observed in 2004 among different seeding dates. In 2005, weed biomass was maximum in plots seeded with rye on the median seeding date averaging 945 kg ha−1 and less in the later-seeded plots. This is likely due to less rye biomass (2479 kg ha−1) production in these plots. No significant differences in the weed biomass production were observed among the termination dates in 2003 and 2004 (data not shown). In 2005, however, the plots terminated on the final termination date had the least weed biomass.

At Shorter, no significant differences in weed biomass production were observed among seeding dates in 2004 and 2005 (Table 8). The maximum observed weed biomass was 970 kg ha−1 corresponding to rye biomass of 1276 kg ha−1 in 2005, when rye was seeded 4 weeks after 0C freeze. The effect of termination dates on weed biomass production was significant in 2003; weed biomass decreased with delay in rye cover-crop termination date (Table 9).

At Jay location, weed biomass production was less compared to other two locations. No differences in weed biomass production were observed among seeding dates at this location (Table 8). The delay in rye termination decreased weed biomass production. In 2004, however, plots terminated a week before cotton planting had more weed biomass than plots terminated 2 and 3 weeks prior to cotton planting (Table 9).

Cover crop seeding date Growing season
2003–2004 2004–2005 2005–2006
Belle Mina, AL
−1 week prior 287 201 272
−2 week prior 153 150 424
−3 week prior 165 397 755
−4 week prior 265 345 665
SE 116
Dunnett’s P versus first termination date
−1 week prior 0.998 0.678 0.035
−2 week prior 0.815 0.456 0.288
−3 week prior 0.858 0.975 0.890
Shorter, AL
−1 week prior 104 141 17
−2 week prior 341 389 74
−3 week prior 532 430 64
−4 week prior 1061 603 118
SE 24
Dunnett’s P versus first termination date
−1 week prior <0.0001 0.001 0.771
−2 week prior <0.0001 0.228 0.973
−3 week prior <0.0001 0.392 0.952
Jay, FL
−1 week prior NA 64 20
−2 week prior NA 51 51
−3 week prior NA 48 83
−4 week prior NA 91 118
SE 77
Dunnett’s P versus first termination date
−1 week prior NA 0.322 <0.0001
−2 week prior NA 0.070 0.001
−3 week prior NA 0.052 0.125

Table 9.

Weed dry biomass (kg ha1) in cotton by location and year as influenced by cover-crop termination date, which were 4, 3, 2, and 1 week prior to cotton planting. Termination dates were based on 30-year average soil temperature. Data are averaged over seeding dates.

The decrease in dry weed biomass with corresponding increase in rye biomass is in accordance with the previous studies. Teasdale [29] concluded that weed biomass production is correlated with the cover-crop biomass. Smeda and Weller [30] also reported an increase in residual weed suppression by no-till-rye residues when the time between cover-crop desiccation and crop planting was reduced, probably due to allelopathic effects.

3.6. Cotton seed lint yield

There were differences in cotton seed lint yield among the years likely due to weather conditions but cotton lint yield was not affected by the rye cover-crop seeding and termination dates at any site year (data not shown). Cotton seed lint yield averaged 3784 kg ha−1 in 2003, 4269 kg ha−1 in 2004 to 2252 kg ha−1 in 2005 at Belle Mina. At Shorter, the maximum seed cotton lint yield was obtained in the year 2004 averaging 4065 kg ha−1. At Jay, yield was less in 2005 but was comparable to other two locations in 2005. Thus, cover-crop biomass did not interfere with attaining yields, and it reflects current knowledge on residue management at planting.

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4. Conclusions

In this study, early planting of the cover crop with its later termination for subsequent corn and cotton plantings has increased cover-crop biomass accumulation compared to the late planting and early termination of the cover crop. Increased cover-crop biomass suppressed subsequent total weed dry biomass. These findings indicate that high-residue cover crops have predictable potential for suppressing early-season weeds in corn and cotton. If farmers are utilizing glyphosate-resistant corn-cotton rotation systems, these findings hold particular importance with current glyphosate-resistant weed-control issues. Because corn and cotton yields were not negatively impacted, we can conclude that high residue obtained by planting crimson clover or rye cover crops timely and terminating either a week or 2 prior to cash crop planting is feasible. Ideal management will result in maximum cover-crop biomass production and subsequent weed suppression.

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Written By

Andrew J. Price, Edzard van Santen and Lina Sarunaite

Submitted: December 21st, 2015 Reviewed: May 6th, 2016 Published: November 9th, 2016