Published online 13 July 2005
Published in Agron J 97:1239-1244 (2005)
DOI: 10.2134/agronj2005.0052
© 2005 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Production Papers
Cover Crop Effects on Corn Yield Response to Nitrogen on an Irrigated Sandy Soil
Todd W. Andraski* and
Larry G. Bundy
Dep. of Soil Sci., 1525 Observatory Dr., Univ. of Wisconsin, Madison, WI 53706-1299
* Corresponding author (andraski{at}wisc.edu)
Received for publication February 14, 2005.
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ABSTRACT
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Nonlegume winter cover crops are extensively grown to control wind erosion in the Central Sands region of Wisconsin. Subsequent corn (Zea mays L.) yield benefits following winter cover crops can occur on these coarse-textured soils even though cover crop biomass and residual N recovery are minimal due to the limited time period for cover crop growth. A 3-yr study was conducted to determine cover crop species and management effects on subsequent corn grain yield responses to N fertilizer. Cover crops were planted in late summer following sweet corn harvest and included oat (Avena sativa L.), winter triticale (xTriticosecale), winter rye (Secale cereale L.) with and without the top growth removed, and fallow. Cover crop treatments were plowed in the spring, and corn was grown with six N fertilizer rates (0 to 280 kg ha–1). In 2 of 3 yr, economic optimum N rates (EONR) for corn were lower (32 ± 8 kg N ha–1), and corn grain yields at the EONR were higher (1.4 ± 0.3 Mg ha–1) where cover crops were grown compared with fallow. These results were similar following all cover crops, including winter-killed oat and rye with top growth removed, indicating that beneficial cover crop effects were primarily the result of a rotation effect rather than direct N contributions from the cover crop. The yield enhancement provided by cover crops probably offers the greatest practical benefit to growers since lowering N rates on these soils may increase the risk of N deficiency in years with high leaching potential.
Abbreviations: EONR, economic optimum nitrogen rate
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INTRODUCTION
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COVER CROP use in northern crop production areas is often limited by the relatively short growing season remaining after the primary crop is harvested. However, vegetable crops, such as sweet corn or potato (Solanum tuberosum L.), harvested in late summer provide a longer growth period for cover crops, and soil or nutrient conservation advantages could be derived under these conditions. Nonlegume cover crops, primarily winter rye, are frequently used during the overwinter period in the Central Sands region of Wisconsin to reduce wind erosion and potentially recover residual N from the soil or provide other benefits to subsequent crops. Previous work (Ditsch and Alley, 1991; Ditsch et al., 1993; Vaughan and Evanylo, 1998) showed that significant amounts of N can be accumulated by nonlegume cover crops, but most of this work was done in warmer climates. The majority of studies found in the literature report no subsequent corn yield benefit following a fall-planted rye cover crop compared with winter fallow, with a few studies reporting negative and positive yield increases (Wagger, 1989; Clark et al., 1997; Kessavalou and Walters, 1997; Vyn et al., 2000; Kuo and Jellum, 2002). Wisconsin research on an irrigated sandy soil showed that winter rye cover crops following sweet corn or potato accumulated very little residual N from the soil or crop residues (Bundy and Andraski, 2005). Results from this work showed that while subsequent whole-plant corn dry matter yields and N uptake were not significantly affected by the presence of a rye cover crop, corn grain yields at below-optimum N rates (0 and 112 kg ha–1) were significantly higher where the rye cover crop was grown.
Additional research is needed to determine if cover crop benefits to subsequent crops occur across a range of N fertilizer rates, especially at the rates recommended for optimum yield levels. Information is also needed to determine if cereal crops other than rye will produce similar benefits and to identify the key factors contributing to the beneficial cover crop effect. This information should assist growers to fully exploit the potential advantages of winter cover crops. The objectives of this study were to: (i) determine the relationship between cover crop benefits and N rate applied to the subsequent corn crop, (ii) determine the effects of cereal cover crop species on subsequent corn grain yield, and (iii) evaluate some cover crop management variables to obtain information about the mechanisms responsible for the cover crop effect.
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MATERIALS AND METHODS
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Research to accomplish project objectives was conducted from 2001 to 2003 at the University of Wisconsin Agricultural Research Station at Hancock (44°07' N, 89°32' W) on a sprinkler-irrigated Plainfield loamy sand soil (mixed, mesic Typic Udipsamment). Monthly average air temperature, precipitation, and irrigation amounts are shown in Table 1. A randomized complete block design in a split-plot arrangement with four replicates was used. In the study year, corn was grown following several winter cover crops (main-plot treatment) with a range of corn N fertilizer rates (subplot treatment).
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Table 1. Air temperature and precipitation for 2000 to 2003 compared with long-term averages (1961–1990), Hancock, WI.
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In the year preceding each study year, sweet corn was grown with 190 kg ha–1 of N fertilizer as NH4NO3 (split-sidedress), and the snapped, unhusked ears were harvested in mid-August. The field was disked before and after moldboard plowing following sweet corn harvest, and cover crop treatments were established in late August. Cover crops included fallow (no cover crop), oat, winter triticale, and winter rye. Seeding rates were 115 kg ha–1 for oat (cv. Gem) and 145 kg ha–1 for winter triticale (cv. Wolf River) and winter rye (cv. Spooner) in 18-cm rows. An additional treatment included rye with the top growth removed just before spring tillage to obtain information about whether the beneficial cover crop effect on this soil is mainly associated with the top growth or the root system of the rye. Oat and triticale were included to address the question of whether cover crop benefits similar to those found with rye will occur with other nonlegume crops. Freezing over winter will kill oat while winter triticale will survive to produce spring growth similar to winter rye. Cover crop yield was determined in mid-November for oat after the first killing frost and the following spring (early May) for triticale and rye by collecting aboveground tissue from a 1-m length of row from six locations within each replicate.
The entire field was moldboard-plowed, disked, and planted to corn in early May within 3 d of triticale and rye cover crop sampling. Corn (DK493 in 2001, DKC5073 in 2002, and P37R71 in 2003) was planted in 91-cm rows at an average density of 76 500 seeds ha–1, and starter fertilizer (6, 5, and 28 kg ha–1 of N, P, and K, respectively) was applied in a band 5 cm below and 5 cm laterally from the seed. Subplot treatments included N fertilizer as NH4NO3 split-sidedress applied at rates of 0 to 280 kg ha–1 in 56 kg ha–1 increments. Applications were banded on the soil surface about 20 cm from the corn row approximately 4 and 7 wk after planting, and each application consisted of one-half of the total N fertilizer rate. Individual subplot size was 7.6 m long and 3.7 m wide (four rows). Corn grain yields were determined by harvesting all ears from the middle two rows from each plot using a plot combine in late October or early November. Corn yields are reported at a grain H2O concentration of 155 g kg–1.
Cover crop tissue samples were dried at 60°C, weighed to determine dry matter content, ground to pass a 0.14-mm screen, and analyzed for total N and C using a Carlo Erba Model NA 1500 C and N analyzer (Carlo Erba, Milan, Italy). Soil samples were collected to a 0.9-m depth in 0.3-m increments from the fallow treatment following sweet corn harvest and from all cover crop treatments the following spring before tillage. Samples were dried at 33°C, ground to pass a 2-mm screen, and NO3–N was determined by automated analysis of 2 M KCl extracts (Bundy and Meisinger, 1994).
Data were subjected to an analysis of variance (PROC ANOVA) for the appropriate experimental design (SAS Inst., 1992). Significant treatment differences were evaluated using a protected least significant difference (LSD) test at the 0.05 probability level for main effect means and interactions. Economic optimum N rate (EONR) and grain yield at EONR were determined using regression analysis (PROC REG). The EONR reflects a fertilizer to corn price ratio calculated from prices of $0.55 kg–1 N fertilizer ($0.25/lb) and $98.44 Mg–1 corn grain ($2.50/bu).
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RESULTS AND DISCUSSION
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Cover Crop
Cover crop dry matter yields averaged 1.2 Mg ha–1 and varied considerably between years (Table 2). Yields ranged from 0.6 to 3.0 Mg ha–1 for oat, 0.2 to 1.9 Mg ha–1 for winter triticale, and 0.6 to 1.4 Mg ha–1 for winter rye. Bundy and Andraski (2005) reported winter rye cover crop yields ranged from 0.4 to 0.9 Mg ha–1 in a study conducted at this location from 1996 to 1998. These yield levels are similar to those reported in a review of winter nonlegume cover crop yields grown in the northern region of the USA (Snapp et al., 2005). Despite the shorter growing period for winter-killed oat, its yields were significantly higher than winter triticale and rye in 2001 and 2003. Yields of winter triticale and rye were similar in 2001 and 2002, but rye yields were significantly higher in 2003. The higher oat yield was likely the result of its rapid growth ability in late summer and fall when soil temperatures are warm. Conversely, winter triticale and rye utilize more energy for storing carbohydrates in the root system for winter survival, resulting in less aboveground biomass production during the fall season. For this study, winter triticale and rye biomass production were minimal following the overwinter period due to cool soil temperatures and a limited growth period before plowing and corn planting in early May.
Cover crop yield variation among years appears to be related to climatic conditions during the cover crop growing period. For example, oat yield (3.0 Mg ha–1) was much higher when September and October (2000) cumulative air temperatures were greater than the 30-yr average (Table 1). The higher triticale and rye yields in 2001 (average 1.7 Mg ha–1) was likely influenced by the above-average temperature in April. Cover crop N uptake and yield were strongly correlated (r = 0.97; p < 0.001), and N uptake ranged from 7 to 91 kg ha–1 for oat, 4 to 38 kg ha–1 for triticale, and 9 to 34 kg ha–1 for rye (Table 2). The C/N ratio of cover crops ranged from 15:1 to 38:1 (Table 2) and was inversely related to cover crop N concentration (r = –0.92; p < 0.001).
Soil profile (0–0.9 m) NO3–N contents were relatively low at the time of cover crop planting following sweet corn grown with 190 kg N ha–1, ranging from 27 to 44 kg ha–1 (Table 3). Soil profile NO3–N contents were 60 to 85% lower the following spring and were generally unaffected by cover crop treatment. There was no correlation between cover crop N uptake and the change in soil NO3–N content during the overwinter period for any year.
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Table 3. Soil profile (0–0.9 m) NO3–N contents at the time of winter cover crop planting (August) and in May of the study year before corn planting.
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Cover crop N uptake values in 2001 were greater than the overwinter decrease in soil NO3–N. This indicates some of the N supplied to the cover crop was mineralized from sweet corn residue and/or soil organic matter. Fairly rapid N mineralization of sweet corn residue seems probable considering the warm soil temperatures in late summer and early fall coupled with the relatively low C to N ratio (23:1) of the residue (Bundy and Andraski, 2005). Precipitation in September and October 2000 (104 mm) was below the long-term average (164 mm), potentially minimizing NO3 leaching of N mineralized from sweet corn residue. Above-average temperatures during the critical cover crop growth period, coupled with mineralized N from residue, likely caused the higher cover crop yields and N uptake. Data presented by Bundy and Andraski (2005) show a strong correlation between winter rye yield and N uptake (r = 0.98; p < 0.001), and these measurements were highest when September and October cumulative rainfall was below normal. In this region, cover crop yields, and resultant N recovery from soil and/or previous crop residues on sandy soils prone to high leaching losses of NO3, appear to be highly dependent on climatic conditions during critical growth periods in fall and early spring.
Cover Crop and Nitrogen Rate Effects on Corn Yield
The effect of cover crop and N rate on corn grain yield was significant in all 3 yr with the exception of cover crop in 2001 (Table 4). However, a significant cover crop x N rate interaction occurred in 2001 where corn yield was lowest following winter fallow and oat cover crop at the 0 kg N ha–1 rate (Table 5). In 2001, corn yield increased as N rate increased to more than 168 kg ha–1 and was similar among all cover crop treatments at N rates greater than 0 kg ha–1. In 2002, corn yields in the fallow treatment were significantly lower than most cover crop treatments (Table 6). Yields increased to the highest N rate (280 kg N ha–1) apparently due to fertilizer N loss via NO3 leaching. Total rainfall in June 2002 was 450% above the long-term average, and 240 mm of rainfall occurred within a 24-h period about 10 d following the first N application. In 2003, corn yields were significantly higher for all cover crop treatments compared with the fallow treatment (Table 7). Removal of winter rye top growth resulted in significantly lower corn yields only at the 0 kg N ha–1 rate and may be related to the low rye yield in 2003 (Table 2).
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Table 4. Analysis of variance summary for the effect of winter cover crop and corn N rate on corn grain yield, 2001 to 2003.
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It is interesting to note the lower corn yields at the 0 kg N ha–1 rate in the high rainfall/leaching year of 2002 compared with 2001 and 2003. This implies that significant N contributions from sources other than fertilizer can occur on this low organic matter, irrigated sandy soil. Using 15N-depleted NH4NO3, Bundy and Andraski (2005) reported total N uptake values of 34 to 71 kg ha–1 in sweet corn where no N fertilizer was applied and identified irrigation water, soil organic matter, and precipitation as potential N sources.
Corn yield response to N fertilizer rate for each cover crop treatment and year was further evaluated using quadratic regression models (Table 8; Fig. 1)
. Table 8 shows the EONR and yield at EONR determined from the regression model. In 2001, corn yield was higher following triticale, rye, and rye removed compared with fallow where no N was applied, but yields were similar as N rate increased (Table 5; Fig. 1). The declining yield benefit with increasing N rate suggests that N mineralization of these cover crop residues provided some N to the subsequent corn crop. The similar corn yields following oat and fallow indicate that N mineralized from winter-killed oat residue was leached before the subsequent corn crop could utilize this N. The above-normal rainfall in May 2001 (183 mm), compared with the long-term average of 83 mm, was conducive to high NO3 leaching losses of any N mineralized from the winter-killed oat residue. About one-half (98 mm) of May rainfall occurred the week before winter triticale and rye was plowed under. Interestingly, the EONR for corn ranged from 192 to 201 kg N ha–1 following all cover crops compared with 223 kg N ha–1 for the fallow treatment (Table 8). This decrease in the EONR for corn following cover crops compared with fallow ranged from 22 to 31 kg N ha–1 (Table 9). However, corn yields at the EONR among cover crops were not significantly different (Table 5), resulting in no yield benefit following cover crops (Table 9).
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Table 8. Regression models for the relationship between corn N rate and corn grain yield, economic optimum N rate (EONR), and yield at EONR following several winter cover crops, 2001 to 2003.
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Fig. 1. Relationship between N rate and corn grain yield following several winter cover crops, 2001 to 2003. Response curves (lines) were generated from regression models shown in Table 8.
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Table 9. Decrease in economic optimum N rate (EONR) and yield increase at EONR for corn following several cover crops compared with fallow, 2001 to 2003.
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As previously discussed, corn yields in 2002 increased to the highest N rate applied for all cover crop treatments, likely due to fertilizer N losses via NO3 leaching (Tables 6 and 8). This resulted in no reduction of the EONR for corn following cover crops (Table 9). Corn yield at the 280 kg N ha–1 rate averaged 12.54 Mg ha–1 following cover crops compared with 10.96 Mg ha–1 following fallow, resulting in an average yield benefit of 1.58 Mg ha–1 following cover crops (Tables 8 and 9). The corn yield benefit following cover crops in 2002 was similar at all N rates, implying no direct N contribution from cover crops (Fig. 1). Corn yield may have responded to fertilizer N rates greater than 280 kg ha–1, potentially influencing EONR differences among cover crop treatments. However, the 280 kg N ha–1 rate was likely near the EONR considering the high corn yields achieved at this rate.
In 2003, corn yield at the 0 kg N ha–1 rate was highest following rye, intermediate following oat and triticale, and lowest in the fallow and rye top-growth-removed treatments (Table 7; Fig. 1). Corn yield benefits following oat, triticale, and rye removed were similar to corn following rye where N fertilizer was applied, indicating corn can utilize fertilizer N more efficiently following cover crops. Corn yield at the EONR averaged 13.22 Mg ha–1 following cover crops compared with 11.91 Mg ha–1 following winter fallow, resulting in an average corn yield benefit of 1.31 Mg ha–1 following cover crops (Table 9). Similar to 2001, the EONR for corn following cover crops was an average of 36 kg N ha–1 lower than following winter fallow (Table 9). The EONR ranged from 217 to 234 kg N ha–1 following cover crops compared with 262 kg N ha–1 following winter fallow (Table 8). Unlike 2001, the lower EONR values in 2003 do not appear to be the result of a direct N contribution of N from cover crop residues since corn yield benefits following cover crops were still evident at N rates at or above the EONR (Fig. 1).
Rotation benefits of cover crops to the subsequent corn crop appear to be slightly greater than from soybean (Glycine max L.) on this soil. Applying the corn to N fertilizer price ratios used in this work to data from a study by Bundy et al. (1993), corn yield benefits following soybean occurred in 2 of 4 yr and averaged 0.74 ± 0.32 Mg ha–1. A reduction in the EONR also occurred in 2 of 4 yr and averaged 21 ± 9 kg N ha–1. More recently, Bundy and Andraski (2005) report that corn yield benefits associated with a previous potato crop are similar to benefits following a winter rye cover crop, and these yield benefits were even greater following potato–winter rye cover crop in most years. Corn yields following potato were an average of 0.83 and 1.74 Mg ha–1 higher without and with a cover crop, respectively, compared with corn following sweet corn without a winter cover crop. Whether a corn yield benefit following potato would have occurred at the EONR in their study is not known since N fertilizer was applied at one-half of the recommended rate to minimize the dilution of N-labeled fertilizer applied the previous year.
The C to N ratios reported for sweet corn, potato, soybean, and green cereal crop residues range between 15:1 and 40:1 (Green and Blackmer, 1995; Ranells and Wagger, 1997; Bundy and Andraski, 2005). Residue decomposition and N mineralization rates are relatively rapid for these crops (Broder and Wagner, 1988; Honeycutt and Potaro, 1990; Alva et al., 2002). Of the total N contained in these crop residues (
25 to 40 kg N ha–1), N released from the readily mineralizable organic N fraction is likely lost via NO3 leaching before utilization by subsequent crops on irrigated sandy soils. In general, N supplied by the previous crop appears to have a minimal effect on the subsequent corn yield benefit observed on this soil.
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SUMMARY
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Winter cover crop dry matter yield averaged 1.16 ± 0.86 Mg ha–1 and was significantly higher for winter-killed oat compared with winter triticale and winter rye in 2 of 3 yr. Cover crop yield and N uptake was strongly correlated, and N uptake values averaged 24 ± 28 kg ha–1. Cover crop yields and N uptake from soil and/or previous crop residues were highly dependent on climatic conditions during critical growth periods in fall and early spring.
Subsequent corn grain yields were significantly higher in 2 of 3 yr where cover crops were grown and were similar following winter-killed oat, winter triticale, and winter rye with and without the top growth removed. The EONR was an average of 32 kg N ha–1 lower for corn following cover crops compared with corn following winter fallow in 2001 and 2003. In 2001, yield benefits following cover crops diminished with increasing N rates, but in 2003, yield benefits following cover crops did not diminish as N rate increased. Similar to 2003, corn yields in 2002 were significantly higher following cover crops compared with winter fallow at all N rates, but EONR was the same for all treatments due to N fertilizer losses via leaching. Collectively, these results suggest that the lower EONR values and higher corn yields were not mainly due to direct N contributions from the cover crop but rather to non-N-related factors (rotation effect) possibly including processes allowing more efficient utilization of plant available N.
The reduction in EONR and the corn yield benefits following cover crops were similar for winter-killed oat, winter triticale, and winter rye with and without top growth removed. The lack of significant grain yield differences between the rye cover crop with and without the top growth removed suggests that any beneficial cover crop effect is mainly associated with the presence of a cover crop in the crop sequence rather than the top growth.
In addition to the general benefit of providing wind erosion control on sandy soils, results from this study show that fall-planted cover crops such as oat, winter triticale, and winter rye can provide significant yield benefits to the subsequent corn crop at slightly lower N fertilizer rates (20 kg ha–1) in some years. The yield enhancement provided by cover crops probably offers the greatest practical benefit to growers since lowering N rates on these soils may increase the risk of N deficiency in years with high leaching potential.
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ACKNOWLEDGMENTS
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The authors are grateful to Julie Studnicka for technical assistance and the staff at the Hancock Research Station.
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NOTES
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Research supported by the Wisconsin Fertilizer Research Program, the Univ. of Wisconsin Nonpoint Pollution and Demonstration Project, and the College of Agric. and Life Sci., Univ. of Wisconsin-Madison.
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REFERENCES
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ABSTRACT
INTRODUCTION
