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Agronomy Journal 93:308-313 (2001)
© 2001 American Society of Agronomy

SOIL AND CROP MANAGEMENT

Interseeding Cover Crops into Soybean and Subsequent Corn Yields

W.Dean Hivelya and William J. Coxb

a Dep. of Nat. Resources, Cornell Univ., Ithaca, NY 14853
b Dep. of Crop and Soil Sci., Cornell Univ., Ithaca, NY 14853

Corresponding author (wjc3{at}cornell.edu)


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
Organic producers in the northeastern USA have difficulty establishing cover crops after soybean [Glycine Max (L.) Merr.] harvest. We interseeded species into soybean on an organic farm without livestock to identify cover crops that do not interfere with soybean harvest, provide significant ground cover, and increase subsequent corn (Zea mays L.) yields. Foenugreek (Trigonella foenum-graceum L.), rye (Secale cereale L.), wheat (Triticum aestivum L.), strawberry clover (Trifolium fragiferum L.), and Austrian winter pea (Dolichos lignosus L.) did not meet establishment and height requirements at the time of harvest. White clover (Trifolium repens L.), red clover (Trifolium pratense L.), barrel medic (Medicago lupulina L.), alfalfa (Medicago sativa L.), annual ryegrass (Lolium multiflorum L.), and creeping red fescue (Festuca rubra L.) met these requirements and generally provided >30% ground cover. Interseeded grasses provided the most biomass (0.5–1.1 Mg ha-1) at spring plowdown. Interseeded legumes did not establish well in 1996–1997 and produced only 0.1 to 0.2 Mg ha-1 biomass in 1997. Corn yielded more following Dutch white clover (7.2 Mg ha-1) and medium red clover (6.7 Mg ha-1) than following no cover (5.7 Mg ha-1) in 1996 but yielded the same in 1997 (5.7, 6.3, and 6.2 Mg ha-1, respectively). Corn yielded less following annual ryegrass (5.3 Mg ha-1) and creeping red fescue (5.1 Mg ha-1) than following no cover in 1997. More research is needed to identify conditions that would reduce the risk of poor establishment of interseeded legumes or reduced corn yields following interseeded grasses.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
ORGANIC GROWERS typically rely on mechanical tillage systems for weed control and cover crops for erosion control and as a supplemental N source (Batte et al., 1993). Soil erosion is greatest from row-cropped fields, especially following soybean because of its low residue production and rapid decomposition (Van Doren et al., 1984). In the northeastern USA, organic producers typically harvest soybeans in mid-October, which can make it difficult to establish cover crops after harvest because of the short growing season (Johnson et al., 1998). Interseeding cover crops into soybean may result in more rapid and reliable establishment of cover crops in organic soybean fields in the northeastern USA.

Interseeding red clover into small grains is a common practice in the northeastern USA (Singer and Cox, 1998) and can provide up to 85 kg N ha-1 to the subsequent corn crop (Vyn et al., 1999). Interseeding grass or legume species into corn during the last cultivation, however, is not a common practice despite successful establishment of these cover crops in New York (Scott et al., 1987). Interseeding rye or oat (Avena fatua L.) into soybean in August resulted in successful establishment of both species as cover crops in Iowa (Johnson et al., 1998). Interseeded rye, however, reduced the yield of the subsequent corn crop. Other studies have also shown that a rye cover crop may reduce subsequent corn yields because of allelopathic effects (Raimbault et al., 1990; Kessavalou and Walters, 1997) or N immobilization under low N conditions (Ebelhar et al., 1984; Blevins et al., 1990; Karlen and Doran, 1991). Organic farms often have fields with low N conditions, especially in the absence of livestock on the farm (Lockeretz, 1997), so rye may not be the best cover crop for organic systems. Unfortunately, most other cover crops that are planted after fall harvest do not establish well in northern latitudes (Johnson et al., 1998).

Sales of organic products have increased 20% annually in the USA since 1989, and this has resulted in a significant increase in the number of farmers that employ organic practices (Duram, 1998). A major obstacle to successful management of organic cropping systems is the lack of university research and outreach on organic practices (Duram, 1999). A major concern of organic producers in the northeastern USA is successful establishment of cover crops in harvested soybean fields. We compared 11 cover crops interseeded into soybean during the last cultivation with no cover crop or with rye seeded after harvest on an organic farm with no livestock in central New York. The objective of this study was to identify interseeded cover crops that did not interfere with soybean harvest, provided a minimum of 30% ground cover in the fall and spring, and produced significant spring biomass N to increase the yield of the subsequent corn crop.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
Field experiments were established on a certified organic farm in central New York (42°25' N, 76°35' W) in 1995 and 1996. Soil test values, taken in the fall of both years, indicated an average pH of 6.8 and medium levels of P (3 mg kg-1) and K (35 mg kg-1) using Morgan's solution (pH of 4.8) as described by Lathwell and Peech (1965). The first corn phase of an alfalfa–corn–soybean–corn–wheat rotation preceded soybean in both years of the study, so different fields were used each year. Soil type was a Lansing silt loam (fine-loamy, mixed, mesic Glossoboric Hapludalf) with a 3 to 8% slope, or moderate erosion potential.

The cooperating farmer moldboard-plowed and disked the fields and planted `Vinton 81', a late Group I food-grade soybean variety, with a 6-row corn planter in late May of 1995 and 1996. Seeding rate was about 500000 seeds ha-1 at 0.76-m row spacing. Two passes of a rotary hoe and two field cultivator operations provided weed control. Cover crop treatments were hand-sown into soybean in designated plots, 4.6 m (6 rows) wide by 6 m long, during the second cultivation in mid-July. Large-seeded species (rye, wheat, Austrian winter pea, and foenugreek) were broadcast at seeding rates of about 100 kg ha-1, and all plots were then cultivated by the participating farmer. Immediately after cultivation, small-seeded species (Dutch white clover, medium red clover, strawberry clover, alfalfa, barrel medic, annual ryegrass, and creeping red fescue) were broadcast at seeding rates of about 15 kg ha-1. The experimental area was then cultipacked with a two-row interrow cultipacker. Soybean yields were measured by harvesting the two center rows of each plot with a small-plot combine in mid-October of both years. Immediately after soybean harvest, rye was hand-seeded at a rate of about 135 kg ha-1 and lightly raked with a pitchfork. A no cover crop treatment was also included. The experimental design was a randomized complete block with four replications.

Cover crop residue and biomass were measured using a 0.25 m2 (33 by 76 cm) rectangular frame placed randomly within the second and fifth interrows of each plot. Measurements were taken at three dates in 1995–1996: immediately before soybean harvest in October (fall), in December after fall growth had ceased (winter), and immediately before spring plowing in May (spring). A 0.3-m snow depth prevented December sampling in 1996, so measurements were taken on only two dates (fall and spring) in 1996–1997.

Average height of interseeded cover crops was recorded at the fall sampling date. Height was measured from the plane of the rectangular frame, which was 8 cm above the inrow soil surface or the height of the lowest cluster of pods on the soybean plants. At all sampling dates, percent ground cover was measured, excluding crop residue and weeds, using the beaded string method (Sloneker and Moldenhauer, 1977). The string ran diagonally across the interrow, and 240 beads per plot were counted. The sampled interrow area represented two-thirds of the distance between soybean rows, so interrow percent ground cover was multiplied by two-thirds to obtain the whole-field percent ground cover presented in this manuscript. Cover crop establishment in the row area was generally negligible.

Cover crop biomass was also measured at all sampling dates. All cover crop biomass within the rectangular frame was clipped, dried, and weighed. Nitrogen concentrations of cover crop tissue were also determined at the spring sampling date using total Kjeldahl N procedures. To measure NO3–N at the spring sampling date, five 30-cm soil cores were taken from each plot and combined and analyzed colorimetrically with an autoanalyzer (Keeney and Nelson, 1982).

Following spring plowdown of the cover crops, Pioneer Brand `3790' hybrid corn was planted in the previous soybean experimental area with a 6-row corn planter in late May of 1996 and 1997 at 0.76-m row spacing. Two passes of a rotary hoe and two cultivator operations provided weed control. An organic starter fertilizer was also applied in a band at rates of 8, 10, and 8 kg ha-1 of N, P, and K, respectively, during corn planting in both years. The organic farm did not have livestock, so the farmer relied exclusively on previous legumes in the rotation (alfalfa and soybean) to provide N to the corn crop. Five soil cores from the upper 0.3-m soil depth were taken from each plot at the fifth leaf stage (V5) of corn growth (Ritchie et al., 1993) to determine soil NO3–N concentrations (Magdoff, 1991). At the corn silking stage, 10 ear leaves per plot were collected to determine total ear leaf N concentrations (Cerrato and Blackmer, 1991). Fifteen corn stalks per plot were collected at corn harvest to measure stalk NO3–N concentrations (Binford et al., 1990). Corn yield was measured by hand-harvesting the center two rows of each plot. A 10-ear subsample was used to determine shelling percentage and grain water. Grain yield was then adjusted to 155 g kg-1 water content.

Statistical analysis was performed with General Linear Models (GLM) procedures using the SAS statistical software package (SAS Inst., 1992). The Bartlett test on the combined analysis indicated that error terms were not homogeneous for spring ground cover, biomass, and biomass N. Consequently, a separate analysis for years is presented for these variables. The other measured variables had homogeneous error terms, so both separate and combined analyses were performed. The linear additive model for the combined analysis was:

where y is the variable to be analyzed, µ is the overall mean, Yi is the effect of the ith level of years (random), ßij is the effect of jth block on the ith year, Ck is the effect of the kth level of the cover crop treatment (fixed), YCik. is the year x cover crop treatment interaction, and {epsilon}ijk is the residual error term. Differences among treatment means were determined using Fisher's protected LSD test (P = 0.05), except for corn yield. A protected LSD value of P = 0.10 was used for corn yield to minimize the weighted average risk of Type I, II, and III errors (Carmer and Walker, 1988). Pearson correlation coefficients among treatment means were also determined for all measured variables using PROC Correlation (CORR) procedures.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSION
 REFERENCES
 
Cover Crop Establishment and Height at Soybean Harvest
Interseeded rye and wheat, which grew considerably between soybean leaf fall in late September and harvest in mid-October, averaged 4 to 16 cm taller compared with other interseeded cover crops at soybean harvest in 1995 (Table 1). Interseeded rye and wheat averaged 8 cm in height above the lowest soybean pods, which interfered with soybean harvest. Likewise, Austrian winter pea, which averaged 3 cm in height above the lowest pods, interfered with soybean harvest mainly because it wrapped around soybean due to its vining growth habit. Although interseeded rye, wheat, and Austrian winter pea did not affect soybean yields (data not shown), they were considered poorly adapted because they could stain soybean seed at harvest, resulting in unacceptable quality for the organic soybean market.


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  		Table 1. Species establishment, winterkill, and height above lowest soybean pods at soybean harvest of interseeded cover crops in 1995–1996 and 1996–1997

 
Strawberry clover met height requirements, exhibited limited fall growth, and provided >30% ground cover by early winter of 1995. Strawberry clover, however, winter-killed in 1995 and failed to establish in 1996 (Table 1). Consequently, strawberry clover was considered poorly adapted for interseeding into soybean. Likewise, foenugreek, which died shortly following germination in both years, was considered poorly adapted for interseeding into soybean. Dutch white clover, medium red clover, barrel medic, alfalfa, annual ryegrass, and creeping red fescue met establishment, height, and overwintering requirements and were considered potential interseedings into soybean. These species and other interseeded species did not affect soybean yields in 1995 (2.1 Mg ha-1) or 1996 (2.3 Mg ha-1). The data presented in the remainder of this manuscript will focus exclusively on these treatments.

Ground Cover, Biomass, and Biomass Nitrogen of Cover Crops
All interseeded cover crops produced >30% ground cover by soybean harvest in the fall of 1995 (Table 2). Annual ryegrass and alfalfa, which had the same amount of ground cover as that of medium red clover, produced more ground cover compared with creeping red fescue and barrel medic. Also, annual ryegrass produced the most biomass, and creeping red fescue produced the least biomass in the fall of 1995 (Table 2). Nevertheless, all interseeded cover crops produced sufficient ground cover to reduce potential soil erosion (Laflen and Moldenhauer, 1979) associated with the significant precipitation events in October and November of 1995 (25 cm). At spring plowdown in 1996, all interseeded cover crops, except for barrel medic, produced more ground cover than rye seeded after harvest, which produced 41% ground cover but only 0.1 Mg ha-1 biomass. Interestingly, creeping red fescue, which produced the least biomass in the fall of 1995, produced the most (along with interseeded rye) among interseeded cover crops by spring plowdown in 1996. Cover crop N concentrations ranged from about 20 to 45 g kg-1 at spring plowdown in 1996 (Table 2). Creeping red fescue and medium red clover accumulated >30 kg ha-1 biomass N, which exceeded the biomass N accumulation of other cover crops (Table 2). Nevertheless, the biomass N accumulation of these species is much less than that of legume cover crops in middle latitudes of the USA (Holderbaum et al., 1990; Blevins et al., 1990).


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  		Table 2. Percent ground cover, above ground biomass, tissue N, and biomass N of interseeded cover crops in 1995–1996 and 1996–1997

 
Precipitation was again abnormally high in the fall of 1996 (35 cm from Sept. through Nov.), which contributed to patchy establishment of the interseeded legumes (Table 1). Nevertheless, all interseeded legume cover crops provided 27 to 43% ground cover by soybean harvest in the fall of 1996, except for barrel medic (Table 2). In contrast, annual ryegrass and creeping red fescue, which are well adapted to wet soil conditions (Balasko et al., 1995), provided 68 to 78% ground cover. All interseeded cover crops, however, had less ground cover in the spring of 1997 than in the fall of 1996, except for creeping red fescue. November temperatures averaged only 4°C, 2.5°C below normal, which resulted in early winter dormancy and limited late fall growth of the cover crops. Rye seeded after harvest failed to establish and produced no ground cover, biomass, or biomass N in 1997. Also, the interseeded legume cover crops did not over-winter well and produced only 0.1 to 0.2 Mg ha-1 biomass and 2 to 6 kg ha-1 biomass N by spring plowdown (Table 2). In contrast, creeping red fescue (and interseeded rye) produced 1.0 Mg ha-1 biomass and about 20 kg ha-1 biomass N.

Rye, which was broadcast-seeded after a mid-October harvest of organic soybean in the northeastern USA, did not produce significant biomass in either year of the study. The use of a no-till drill instead of broadcast-seeding after soybean harvest may have improved the establishment and growth of rye although wet soil conditions would have prevented the use of a no-till drill in 1996. Also, interseeded grass cover crops adapted better than legume cover crops to the excessively wet fall soil conditions that occur in the northeastern USA. Organic producers, however, prefer to use legume cover crops because of the N contribution to the cropping system (Batte et al., 1993). In 1997, however, interseeded legume cover crops accumulated only 2 to 6 kg ha-1 biomass N.

Cover Crop Nitrogen Contribution and Corn Yields
When averaged across years, soil NO3–N concentrations in the upper 0.3-m soil depth at spring plowdown and at the V5 stage of corn growth did not differ among cover crop treatments (Table 3). Ear leaf N concentrations and stalk NO3–N concentrations of corn, however, had year x cover crop treatment interactions (Table 4). Corn following Dutch white clover and medium red clover cover crops had greater ear leaf N concentrations at silking in 1996 compared with corn following no cover crop or following rye seeded after harvest. Both cover crop treatments also had greater soil NO3–N concentrations at the V5 stage of corn growth compared with rye seeded after harvest in 1996. Nevertheless, only corn following medium red clover had stalk NO3–N concentrations >250 mg ha-1, the critical concentration for maximum corn yields as reported by Binford et al. (1990). In 1997, a year when interseeded legume cover crops accumulated only 2 to 6 kg ha-1 biomass N, ear leaf N concentrations did not differ among cover crop treatments. Corn following all cover crop treatments had stalk NO3–N concentrations <100 mg kg-1 in 1997. Such low stalk NO3–N concentrations indicates that, except for corn following medium red clover in 1996, interseeded legumes did not provide sufficient N to meet the corn N requirement.


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  		Table 3. Soil NO3–N concentrations at the 0.3-m soil depth in the spring and the 5th leaf (V5) stage of corn growth following different cover crops in 1996 and 1997

 

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  		Table 4. Corn ear leaf N, stalk NO3–N before harvest, and grain yield following different cover crops in 1996 and 1997

 
Corn yield also had a year x cover crop treatment interaction (Table 4). Corn following Dutch white clover and medium red clover yielded greater than corn following no cover crop or following rye seeded after harvest in 1996. In contrast, corn following interseeded grasses (including interseeded rye and wheat) yielded the same as corn following no cover crop or following rye seeded after harvest. Apparently, interseeded Dutch white clover and medium red clover provided additional soil N to increase corn yields in 1996, as indicated by greater soil NO3–N concentrations at the V5 stage and greater ear leaf N concentrations. Indeed, corn yields in 1996 had significant correlations with soil NO3–N concentrations at the V5 stage (r = 0.55) and with ear leaf N concentrations at silking (r = 0.44) (Table 5). Vyn et al. (1999) also reported positive correlations between soil NO3–N concentrations at the V5 stage and corn yields when unfertilized corn followed red clover, ryegrass, and oilseed radish (Raphanus sativus L.) interseeded into winter wheat or winter barley (Hordeum vulgare L.).


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  		Table 5. Correlation coefficients for measurements in 1995–1996 and 1996–1997 (n = 32)

 
Corn following interseeded legume cover crops yielded the same as that following no cover crop in 1997. Poor establishment and growth of interseeded legumes in 1996–1997 resulted in no additional N contribution to the subsequent corn crop, as indicated by similar ear leaf N concentrations and stalk NO3–N concentrations between interseeded legumes and no cover crop treatments. Interestingly, corn following interseeded annual ryegrass and creeping red fescue yielded less than that following no cover crop in 1997. In fact, corn following interseeded creeping red fescue yielded the least in both years of the study despite having the greatest biomass N at plowdown. Nonleguminous cover crops can immobilize N, especially under low N conditions, which can result in reduced yields of the subsequent corn crop (Karlen and Doran, 1991; Torbert et al., 1996; Vyn et al., 1999). Soil NO3–N concentrations at the V5 stage, however, did not differ among cover crop treatments. Consequently, N immobilization following decomposition of creeping red fescue may not have contributed to the reduced corn yields. Creeping red fescue can have an allelopathic effect on corn (Weston, 1996), which may have contributed to reduced corn yields following creeping red fescue in both years of the study.


   CONCLUSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
REFERENCES
 
We interseeded cover crops into organic soybean during the last cultivation to identify species that did not interfere with soybean harvest, provided a minimum of 30% ground cover in the fall and spring, and produced significant biomass N to increase yield of the subsequent corn crop. Interseeded rye, wheat, and Austrian winter pea grew above the lowest soybean pods and interferred with soybean harvest. Foenugreek did not establish and strawberry clover either did not establish or winter-killed. All five species were considered poorly adapted for interseeding into organic soybean. Dutch white clover, medium red clover, alfalfa, annual ryegrass, and creeping red fescue did not interfere with soybean harvest and provided more than 30% ground cover in the fall and spring (except for medium red clover in 1996–1997). Interseeded legumes, however, did not establish well in 1996–1997 and produced only 0.1 to 0.2 Mg ha-1 biomass. Interseeded annual ryegrass and creeping red fescue provided >75% ground cover and produced 0.5 to 1.1 Mg ha-1 biomass in both years. If erosion control is of prime importance, interseeding either grass species into organic soybean could reduce the erosion potential after soybean harvest in the northeastern USA.

In 1996, corn following interseeded medium red clover and Dutch white clover, which produced 25 to 30 kg ha-1 biomass N, had greater soil NO3–N concentrations at the V5 stage, ear leaf N concentrations, and yields compared with corn following no cover crop or rye seeded after harvest. In 1997, however, corn following interseeded legumes, which produced only 2 to 6 kg ha-1 biomass N, had similar soil NO3–N concentrations at the V5 stage, ear leaf N concentrations, and yields compared with corn following no cover crop. Corn following interseeded creeping red fescue yielded the least in both years. Also, corn following interseeded annual ryegrass yielded less than that following no cover crop in 1997. More research is needed to identify what environmental conditions or management practices would reduce the risk of poor establishment of interseeded legumes into soybean or reduced corn yields following interseeded creeping red fescue or annual ryegrass.

Received for publication April 3, 2000.
   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 




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