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Published in Agron. J. 96:247-251 (2004).
© American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA

PRODUCTION PAPER

Integrating Herbicide-Resistant Corn Technology in a Kura Clover Living Mulch System

Richard P. Affeldta, Kenneth A. Albrecht*,b, Chris M. Boerboomb and Edward J. Buresb

a Dep. of Crop and Soil Sci., Oregon State Univ., 107 Crop Science Bldg., Corvallis, OR 97331
b Dep. of Agron., Univ. of Wisconsin–Madison, 1575 Linden Drive, Madison, WI 53706

* Corresponding author (kaalbrec{at}wisc.edu).

Received for publication April 10, 2003.

   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Previous research has shown that with adequate suppression, kura clover (Trifolium ambiguum M. Bieb.) can be managed as a living mulch in corn (Zea mays L.); however, significant yield loss was observed in some environments. This study evaluated two herbicide-resistant corn hybrids at three levels of kura clover living mulch suppression over multiple environments. In 1999 and 2000 near Arlington and in 2000 near Lancaster, WI, glyphosate [N-(phosphonomethyl)glycine]-resistant corn (Roundup Ready corn, RRC) and glufosinate [2-amino-4-(hydroxymethylphosphinyl) butanoic acid]-resistant corn (Liberty Link corn, LLC) hybrids were planted where kura clover had been (i) killed for monocrop corn, (ii) strongly suppressed with glyphosate and dicamba (3,6-dichloro-2-methoxybenzoic acid), or (iii) lightly suppressed with only glyphosate. Suppressed kura clover also had a 25-cm clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) plus dicamba-killed band into which corn was planted. Subsequent postemergence applications of glyphosate or glufosinate herbicide were made for each hybrid. Corn whole-plant yield ranged from 17.3 to 19.9 Mg ha–1, and grain yield ranged from 10.8 to 12.3 Mg ha–1. Yield of whole-plant and grain across both corn hybrids did not differ between monocrop corn and corn in strongly suppressed kura clover. Whole-plant yield of monocrop corn was 8 to 11% greater and grain yield 8 to 9% greater than in lightly suppressed kura clover, respectively. Both hybrids had similar corn whole-plant yield, but LLC grain yield was lower than that of RRC. Kura clover recovery in the season following corn production was similar among living mulch suppression treatments by mid-July. Herbicide-resistant corn technology allowed for consistent kura clover living mulch management with little or no whole-plant or grain yield loss.

Abbreviations: LLC, Liberty Link corn (glufosinate resistant) • RRC, Roundup Ready corn (glyphosate resistant)


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
USE OF CORN SILAGE to replace a portion of alfalfa (Medicago sativa L.) or other perennial legumes in rations has increased in the North-Central USA. Corn silage production requires less labor and machinery time and has more consistent feeding value than other harvested forages (Coors and Lauer, 2001). However, a limitation to corn silage and grain production on erodible soils is the potential for excessive soil loss. Alternative cropping systems that improve soil conservation are needed for mixed crop and livestock enterprises on highly erodible landscapes.

Living mulches are vegetative covers that are grown in association with cash crops (Paine and Harrison, 1993). Compared with tilled systems, living mulches can reduce soil erosion (Wall et al., 1991), suppress weeds (Enache and Ilnicki, 1990), and reduce insect pests (Litsinger and Moody, 1976). Also, when legumes are used as a living mulch, they can supply N to the main crop (Scott et al., 1987).

Corn production in living mulch and interseeded systems typically results in yield loss in the North-Central USA from competition for moisture and N (Kurtz et al., 1952; Pendleton et al., 1957). Fisher and Burrill (1993) and Zemenchik et al. (2000) also note that cool spring temperatures could reduce corn yields because of delayed planting or by giving a cool-season clover a competitive advantage over corn, a warm-season grass.

The key to the successful use of living mulches for corn production is controlling competition from the mulch crop. However, if the mulch suppression is excessive, it will not recover. Zemenchik et al. (2000) showed that corn could be grown in a kura clover living mulch when adequately suppressed by herbicide, without reduced corn whole-plant or grain yields. In this system, kura clover will recover to full production within 12 mo of corn harvest. However, corn performance in the living mulch was not consistent across environments. They concluded that close monitoring and control of kura clover competition is necessary to attain high yields and reduce risk of corn yield loss with early planting dates.

Pedersen et al. (1999) found that herbicide-resistant corn technology could be a powerful tool for controlling living mulch competition as needed under different growing conditions. Glyphosate- and glufosinate-resistant corn technologies provide increased flexibility by allowing a wide postemergence application window with no risk of corn damage, as well as excellent weed control (Hamill et al., 2000; Johnson et al., 2000).

This study was developed to assess the potential of using herbicide-resistant technology for consistent corn production in established kura clover to avoid significant corn whole-plant or grain yield loss. The objectives were to (i) compare the performance of two herbicide-resistant corn hybrids and their respective herbicides in the living mulch system and (ii) evaluate the recovery of kura clover in the year after corn production.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Field studies were conducted in 1999 and 2000 near Arlington (43°18' N, 89°21' W) and in 2000 near Lancaster, WI (42°50' N, 90°47' W). The 1999 experiment at the Arlington location was on a well-drained to moderately well-drained Plano silt-loam (fine-silty, mixed, mesic Typic Argiudoll) that was in an upland area with a capability class of I. In 2000, the experiment at Arlington was on a well- to moderately well-drained Huntsville silt loam (fine-silty, mixed, mesic Cumulic Hapludoll) that was in a low-lying area with a capability class of II because of potential for flood damage from water retention. At Lancaster, the soil was a moderately well-drained Rozetta silt loam (fine-silty, mixed, mesic Typic Hapludalf) with a capability class of III because of potential for erosion. All sites had an established stand of kura clover that was well nodulated and harvested regularly for two or more years before corn planting. The Lancaster site had ‘Rhizo’ kura clover; the Arlington sites had ‘Endura’ kura clover. Soil P, K, and pH levels were maintained as for alfalfa based on soil test recommendations for those locations (Kelling et al., 1991).

In all environments, kura clover was 10 to 20 cm tall 1 wk before planting and was clipped to a 5-cm height. This facilitated planting by reducing the aboveground biomass that the planter would have to cut through and allowed for better herbicide coverage in the suppression treatments. Nine samples of the clipped material were collected for yield, and subsamples were oven-dried at 60°C for 4 d to determine dry matter yield and N concentration.

Corn was no-till–sown into kura clover that was 6 to 10 cm tall on 11 May 1999 in Arlington and 5 May 2000 in Lancaster and Arlington. Two field corn hybrids, Dekalb brand DK493 RR (Roundup Ready) and Pioneer brand 36H75 (Liberty Link), with similar relative maturity (101 d) and average yield performance in southern Wisconsin, were utilized because of their herbicide resistance traits. At Lancaster, a four-row White model 6104 (White Manufacturing, Coldwater, OH) no-till planter was used to plant corn seeds 4 cm deep on a 0.76-m row spacing at 77000 seeds ha–1. At Arlington, a four-row Kinze model PT (Kinze Manufacturing, Williamsburg, IA) no-till planter was used to plant seeds as above, except at a rate of 78000 seeds ha–1. At both locations, macronutrients in the starter fertilizer (6–24–24) were applied with the planter and placed 5 cm to the side and 2 cm below the seed at a rate of 9.9, 7.7, and 14.4 kg ha–1 N, P, and K, respectively.

The experiment was arranged as a randomized complete block with four replications. Plot dimensions in 1999 at Arlington were 3.0 by 7.6 m and were 3.0 by 9.1 m in the other two environments. Each plot had four corn rows where one of the center rows was used for grain and the other for corn whole-plant yield and the outside two rows were border rows. Outside the experimental area, four corn rows were planted as border.

Two levels of living mulch suppression for each of the two corn hybrids were used to find the most effective chemical management strategy to suppress spring growth of kura clover. Monocrop corn for each hybrid was grown in killed kura clover for comparison with living mulch treatments. The six treatments included RRC or LLC planted into kura clover that was (i) killed for use as a monocrop corn control, (ii) strongly suppressed (glyphosate plus dicamba preplant), or (iii) lightly suppressed (glyphosate only preplant). The living mulch treatments had a 25-cm killed band over the corn row to aid corn establishment.

Rates and timing of herbicide applications are outlined in Table 1. Glyphosate was broadcast-applied for preplant suppression in all plots and for postemergence kura clover suppression and control of other weeds in RRC plots. Dicamba was broadcast before planting to kill kura clover in the monocrop corn plots and at a reduced rate in the strongly suppressed plots. Dicamba plus clopyralid was applied in 25-cm bands to kill a strip in all living mulch plots to provide spatial separation between the emerging corn and the recovering kura clover, based on previous research (Pedersen et al., 1999; Zemenchik et al., 2000). Glufosinate was applied for postemergence kura clover suppression and control of other weeds in LLC plots. All glufosinate applications included 3.35 kg ammonium sulfate ha–1.


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  		Table 1. Treatment description for corn hybrid and kura clover suppression for living mulch systems in 1999 and 2000 near Arlington and Lancaster, WI.

 
Postemergence applications of glyphosate or glufosinate herbicide were made to all treatments at the corn V3 to V5 stage (30 to 45 d after planting) when interrow kura clover regrowth in the lightly suppressed treatments reached a height of 15 cm. A second application was made if clover regrew to that height again before corn canopy closure. In 1999, the application was made 30 d after planting. The 2000 Lancaster location received hail that severely damaged the kura clover 15 d after planting corn but did not affect the corn because it had not emerged. The postemergence herbicide application of glyphosate or glufosinate was made 21 June 2000 (45 d after planting). In 2000 at Arlington, two postemergence herbicide applications were made because of vigorous kura clover growth. The first application was made on 4 June (30 d after planting); the second, 19 d later when clover regrowth again reached 15 cm. All treatments were sidedressed with 45 kg N ha–1 at the V3 to V5 stage (approximately 20 June) to prevent N from being a limiting resource in the system. This amount of N was based on previous research with corn in kura clover living mulch systems (Zemenchik et al., 2000).

Whole-plant corn (as for silage) at approximately 40% kernel milk line was hand-harvested to a 15-cm stubble height from the center 7.6 m of one randomly chosen row from the two center rows within each plot, except in 1999 at Arlington where 6.1 m of row was harvested. Harvested corn was mechanically chopped to a 3- to 5-cm particle size using commercial equipment. Subsamples of approximately 800 g of wet weight were collected by hand and oven-dried at 60°C to determine dry matter content for calculation of yield on a dry matter basis.

Corn grain yield was determined by hand-harvesting corn ears at physiological maturity from the remaining center row of the same length as above. Harvested ears were passed through a stationary small-plot corn sheller. Corn grain yields were adjusted to a moisture concentration of 155 g kg–1. Corn population within each plot was determined by counting the number of plants in portions of rows harvested for whole-plant and grain yield.

Kura clover biomass was measured in living mulch treatments at the time of whole-plant corn harvest to assess the relative vigor of the remaining kura clover stand. Living vegetation was hand-harvested from two 0.3- by 0.76-m quadrats in each plot (0.46 m2 plot–1). This vegetation was oven-dried at 60°C to determine yield on a dry matter basis. Kura clover yields from 1999 and 2000 living mulch treatments were also determined in the beginning of the 2000 and 2001 growing seasons, respectively, to assess the recovery of the kura clover mulch. Forage yield was measured by harvesting the center 0.76 m of the previous year's plots with a flail-type harvester that cut forage to a 7- to 8-cm stubble height. Subsamples of approximately 500 g were dried at 60°C to determine yield on a dry matter basis. The first harvest was taken in early June and the second harvest in mid-July.

Analysis of variance (ANOVA) procedures using the GLM procedure of SAS (SAS Inst., 1990) at the P = 0.05 level were used to test the effects of environment, treatment, and treatment x environment interaction for all responses measured. Separation of treatment means was accomplished using Fisher's protected LSD (P = 0.05). Single degree-of-freedom contrasts at the P = 0.05 significance level were used to compare RRC and LLC and were also used to compare the levels of kura clover suppression.


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Environment
Combined precipitation for April, May, and June was near or above the 30-yr mean in all three environments; thus, a deficit in soil moisture did not likely limit early-season corn development (Table 2). In 2000, total precipitation in May and June at Arlington was more than twice normal; this provided adequate moisture for the kura clover to recover from initial herbicide suppression and grow vigorously through the summer months. In this environment, two postemergence herbicide applications were necessary by 23 June to suppress the vigorous growth of the kura clover living mulch. Herbicide-resistant technology was especially useful in an environment requiring a wide postemergence application window, such as the 2000 Arlington experiment where the living mulch recovered quite vigorously after initial suppression.


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  		Table 2. Monthly precipitation and mean monthly temperatures for two test sites in Wisconsin.

 
The treatment x environment interaction was not significant for whole-plant yield, grain yield, or population; therefore, data were combined across the three environments. The greatest-yielding environment for both whole plant (19.4 Mg ha–1) and grain (12.4 Mg ha–1) was in 2000 at Arlington (data not shown); this can most likely be attributed to a warm period 3 wks after planting and adequate moisture throughout the season. The next greatest corn whole-plant yield of 18.7 Mg ha–1 was at Lancaster in 2000, followed by 17.9 Mg ha–1 at Arlington in 1999. Grain yields at Lancaster and in 1999 at Arlington were 11.1 and 11.5 Mg ha–1, respectively. There were periods of moisture stress in mid-July at the time of corn tasseling in both of these environments that probably contributed to reduced yields (Table 2). Preliminary work by Pedersen et al. (1999) suggested that herbicide-resistant corn hybrids and their associated postemergence herbicides could minimize the risk associated with corn production in a kura clover living mulch system. The lack of treatment x environment interactions (P = 0.91 for whole plant, P = 0.55 for grain) in these experiments indicates that the kura clover management strategies employing herbicide-resistant corn hybrids and their respective herbicides are consistent and reliable across environments with relatively cool springs (Arlington 2000) and minor midsummer water deficit (Arlington 1999 and Lancaster). Lack of kura clover suppression after corn emergence resulted in yield loss in some environments in earlier research (Zemenchik et al., 2000).

Corn Whole-Plant and Grain Yield
Corn whole-plant and grain yields were significantly affected by the different kura clover management strategies (Table 3). Corn whole-plant yield ranged from 17.3 to 19.9 Mg ha–1 and was greatest for RRC and LLC in monocrop and LLC in strongly suppressed kura clover. A single degree-of-freedom contrast for whole-plant yield of the two hybrids showed that there was no difference between RRC and LLC (P ≤ 0.05), despite the fact that a similar contrast for population showed that RRC had more plants per hectare than LLC (Table 3). Whole-plant yield in monocrop corn treatments did not differ from yield with strong suppression of living mulch. However, corn yields in monocrop and strong-suppression treatments were greater than in light-suppression treatments. This is consistent with Fisher and Burrill (1993), Cardina and Hartwig (1980), and Prine (1967), who found that early suppression of living mulch competition was essential to maintain corn yields. It also confirms the findings of both Zemenchik et al. (2000) and Pedersen et al. (1999), who reported that early-season competition from kura clover living mulch reduced grain and whole-plant yields.


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  		Table 3. Yield of corn whole plant and corn grain, and corn populations in corn–kura clover living mulch systems near Arlington and Lancaster, WI, in 1999 and 2000 with single degree-of-freedom contrasts.{dagger}

 
Corn grain yield ranged from 10.8 to 12.3 Mg ha–1 and was greatest in monocrop and strongly suppressed living mulch treatments for both hybrids (Table 3). Corn grain yield for monocrop treatments did not differ from strongly suppressed living mulch treatments, and both of these yielded more grain than corn grown in living mulch with light suppression. Corn grain yield responded similarly to level of suppression as whole-plant yield did, in that strong suppression early was necessary to protect yield.

A contrast of the two hybrids revealed that RRC yielded more grain than LLC, which can most likely be attributed to the population difference between the two corn hybrids noted earlier (Table 3). There was no interaction between postemergence herbicide treatments for grain yield in this experiment, but because of different modes of action, interactions might have been expected. Our observation was that glufosinate caused rapid desiccation of kura clover and weed foliage followed by normal clover regrowth. Kura clover treated with glyphosate stopped growing but remained green for at least a week, and regrowth was slow with small, distorted leaves for much of the remainder of the season. Since glyphosate is slowly metabolized in plants, it may result in some level of clover suppression through the entire growing season (Coupland, 1984; Sandberg et al., 1980).

Kura Clover Mulch and Recovery
Kura clover often has significant early-spring growth with the typical spring air and soil temperatures in the North-Central USA. In these experiments, harvest or grazing of the kura clover before no-till corn planting was possible. Average forage yield for all locations was approximately 0.9 Mg ha–1 (data not shown) of kura clover dry matter that was clipped and left on the experimental area. This represented a return of approximately 36 kg ha–1 N.

Kura clover yield in autumn following corn harvest was low, ranging from 0.5 to 0.8 Mg ha–1 (Table 4). Most of the kura clover foliage had senesced and decomposed shortly after corn tasseling as light availability diminished beneath the dense corn canopy. Contrasts revealed that lightly suppressed living mulch treatments had more post–corn harvest kura clover than strong suppression treatments, but there was no difference between RRC and LLC. It would not be practical to harvest this forage, but it could serve as a protein supplement to cattle grazing residue after grain harvest.


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  		Table 4. Yield of kura clover post corn harvest and recovery in the spring of the season following corn production from living mulch treatments near Arlington and Lancaster, WI, with single degree-of-freedom contrasts.

 
There was greater recovery of kura clover the spring following corn production from light suppression than for strong suppression treatments at first harvest in June, but light- and strong-suppression treatments did not differ at the second harvest in July (Table 4). There were virtually no weeds in the first harvest, and biomass yields ranged from 3.1 to 3.6 Mg ha–1 (Table 4). An adjacent area of nontreated kura clover that was harvested at the same time as the first-recovery harvest yielded 4.5 Mg ha–1. Second-recovery harvest yields ranged from 2.8 to 2.9 Mg ha–1. Visual ratings of the weed component of second harvest did not differ for light- and strong-suppression treatments, and it was estimated that weeds were 15% of the total biomass (data not shown). Adjacent areas of nontreated kura clover harvested at the same time as second harvest yielded 2.9 Mg ha–1. We estimated that the living mulch was fully recovered by this time, but no statistical comparison can be made.

Previous research using alfalfa as a living mulch indicates that alfalfa stands would need to be thinned to a density that might not be viable for forage production the year after corn (Eberlein et al., 1992). The kura clover recovery in this experiment supports the findings of Zemenchik et al. (2000) that kura clover will fully recover by mid-July the year following corn production, a function of its rhizomatous nature. These results demonstrate that herbicide-resistant technology provides adequate suppression of a kura clover living mulch for corn production and does not inflict long-term damage on the living mulch.


   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Previous research has shown that with adequate suppression, kura clover can be managed as a living much in corn with no corn whole-plant or grain yield loss. However, significant yield loss was observed in some environments. Using herbicide-resistant corn technology across three environments, we observed little or no loss of whole-plant or grain yield for RRC and LLC grown in a kura clover living mulch. Suppression of kura clover with glyphosate plus a low rate of dicamba before corn planting provided greater whole-plant and grain yields than preplant suppression with glyphosate alone. Lower corn whole-plant and grain yields in glyphosate-only preplant suppression treatments indicate that adequate early suppression of the living mulch is essential to prevent yield loss. Herbicide-resistant technology may prove especially useful in a cool and wet spring where a wide postemergence application window would be needed to allow slowly developing corn seedlings to establish. The kura clover mulch recovered to full production by the second harvest in mid-July the year following corn production. Glyphosate and glufosinate do not seem to inflict long-term damage on the kura clover living mulch, indicating excellent potential for a long-term no-till corn and forage rotation.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Research was partially funded by Hatch Project no. 5168.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 




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