TECHNICAL ARTICLE
Cover Crop Effects on Crop Yields and Soil Organic Carbon Content Kenneth R. Olson,1 Stephen A. Ebelhar,2 and James M. Lang3
Abstract: An 8-year cover crop study was conducted in southern Illinois to evaluate the effects of conservation tillage systems on corn and soybean yields and for the maintenance and restoration of soil organic carbon (SOC) and soil productivity of previously eroded soils. In 2001, the no-till (NT), chisel plow, and moldboard plow (MP) treatment plots, which were replicated six times in a Latin square design, were split (with cover crop and without) on sloping, moderately well-drained, moderately eroded soil. The average corn and average soybean yields were similar for NT, chisel plow, and MP systems with and without cover crops. By 2009, the tillage zone, subsoil, and rooting zone of all treatments had similar SOC on a volume basis for the cover crop treatments as for the same tillage treatment without a cover crop. However, using the baseline 2000 SOC contents only, the NT with cover crops maintained most of the SOC levels in the topsoil and subsoil during the 8-year study, when the sediment was high in SOC and retained in the upland landscape by soil conservation practices, including border and filter strips and sod waterways adjacent to the plots, with and without cover crops. Soil carbon creation retention in the upland landscape was greatest for the MP treatments when sediments were retained by the soil conservation practices, which should reduce soil erosion and sediment rich in SOC being transported by overland flow into water and the eventual release of methane and carbon dioxide to the atmosphere. Key words: Organic carbon, soil erosion, soil loss, tillage, no-till. (Soil Sci 2010;175: 89Y98)
C
over crops are grown to protect the soil from erosion and nutrient loss by either leaching or runoff (Reeves, 1994). Cover crops have been shown to reduce off-site sediment transport (Mutchler and McDowell, 1990; Langdale et al., 1991; Decker et al., 1994; Dabney, 1998; Delgado, 1998). Cover crops can increase nutrient use efficiencies (Lal et al., 1991; Lal, 1997; Delgado, 1998; Shipley et al., 1992). Sainju and Singh (2008) examined the influence of cover crops and N fertilization rate in no-till (NT) strip-tilled and chisel-tilled Georgia soils. They found N storage in tilled and non-tilled soils can be increased using a legume or a cover crop. The severity of erosion can be reduced by maintaining crop residue on the soil surface (Dickey et al., 1985; Alberts and Neibling, 1994). At planting, with chisel plowing residue, cover is 30% and much higher with NT because of a lack of, or minimum, soil disturbance (Lal et al., 1994). Lueschen et al. 1 Department of Natural Resources and Environmental Sciences, S-224 Turner Hall, University of Illinois, Urbana, IL 61801. Dr. Kenneth Olson is corresponding author. E-mail:
[email protected] 2 Department of Crop Sciences, Dixon Springs Agricultural Center, Simpson, IL. 3 Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana, IL. Received December 1, 2009. Accepted for publication December 8, 2009. Copyright * 2010 by Lippincott Williams & Wilkins, Inc. ISSN: 0038-075X DOI: 10.1097/SS.0b013e3181cf7959
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(1991), for a corn-soybean rotation in Minnesota, observed 69% to 82%, 49%, and 10% of soybean residue cover on the soil surface after corn planting in NT, chisel plow (CP), and moldboard plow (MP) system plots, respectively. Generally, conservation tillage resulted in an increase in crop yield compared with that of an MP system. Lawrence et al. (1994) showed in a 4-year study in a semiarid environment in Australia that NT had a higher crop yield than did reduced-till fallow or conventional-till fallow. A positive linear response between yields of corn and soybean and amount of residue applied to an NT system was observed by Wilhelm et al. (1986). Lueschen et al. (1991), in a corn-soybean rotation in Minnesota, found an increase of 6.30 Mg haj1 in yield of the NT system greater than the MP system in a dry year. Kapusta et al. (1996) studied the effects of tillage systems for 20 years and found equal corn yield in NT, reduced till, and conventional tillage despite the lower plant population in NT. Tillage effects on crop yields were not profound in the early years of the tillage study (Kitur et al., 1994a; Olson et. al., 2004). In these studies, Olson et al. (2004) evaluated the effects of conservation tillage systems such as NT and CP on corn and soybean yields and for the maintenance and restoration of soil productivity of previously eroded soils. Evaluations of yield response of these conservation tillage systems over time are needed to assess returning this land to crop production. Crop yields for 14 years seem to show improved long-term productivity of NT compared with that of the MP and CP systems. However, the erosion rates of the CP and MP were higher than the tolerable soil loss standards, and the soil organic carbon (SOC) levels (Olson et al., 2005) were declining in all tillage treatments. Decline of SOC in agricultural systems and increased awareness of its importance to global C budgets have accelerated evaluations of land management impacts on soil C dynamics and storage (Lal, 1999). Land use practices that may affect SOC sequestration are a switch to NT (Omonode et al., 2006), greater cropping frequency (Bremer et al., 1994; Campbell et al., 1995), and the application of organic amendments such as manure (Sommerfeldt et al., 1988) and cover crops (Lal et al., 1995). Fronning et al. (2008) found that the winter rye cover crop did not significantly affect total SOC compared with untreated and did not overcome C losses associated with harvesting corn stover for cellulose-based biofuel production. The impact of tillage and cover crops on SOC sequestration (net increase) or loss has been the focus of many studies because these management techniques contribute to atmospheric C loss or sequestration. The SOC sequestration or retention has been shown to retain more SOC with decreasing soil disturbance or enhanced crop rotation diversity. In 67 long-term agricultural experiments from around the world, West and Post (2002) summarized that SOC stock can be increased by either rotation enhancement or residue input and composting of residues. Pikul et al. (2008) showed in a South Dakota study that the potential to sequester C was very limited under rotated corn and not possible under continuous corn grain. Continuous corn grain required additional tillage operations, and as a result, lost more SOC than www.soilsci.com
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rotated crops. The greater crop diversity in the corn-soybean rotation contributes to SOC retention, where residue return approximately equals the loss of SOC. Change in frequency and intensity of tillage practices alters the bulk density and soil organic matter in the soil profile. Mann (1986) reported that the reduction in SOC content (by volume) of soils having an initial content of between 20 and 50 g kgj1 was 20% less after cultivation, which was most pronounced during the first 20 years of cultivation. In addition, changes in SOC storage were more variable in the upper 15 cm of soil than in the upper 30 cm. Kitur et al. (1994b) and Hussain et al. (1999) evaluated the effects of MP, CP, and NT on SOC content (by weight) and found that the content was lowest for MP and highest for NT. The treatment differences in SOC were attributed to the effects of incorporation of most plant residues below the 0- to 5-cm layer in the MP and CP treatments. Effects of tillage on SOC content were not significant in the 5- to 15-cm layer. Ismail et al. (1994) observed a decrease in SOC (by volume) in the 0- to 30-cm silt loam layer of soil during the first 5 years, no change in the next 5 years, and an increase in SOC in the last 10 years in both NT and MP in comparison with sod plots. The SOC was higher in NT than in MP. Hunt et al. (1996) and Angers and Giroux (1996) found that NT systems increased SOC content (by weight) compared with MP and CP systems in the top 5-cm layer of soils with a range of soil textures, including loamy sand, silt loam, and silty clay loam. Corn and soybean were grown in southern Illinois on the sloping and eroding plot area on a yearly rotation system (Olson et al., 2005). The surface layer of MP had significantly lower SOC after 12 years compared with CP and NT. All treatments reduced the long-term SOC content of the tillage zone, subsoil, and rooting zone when compared with the baseline 1989 SOC values taken from the sod plot area before tillage treatment applications. The CP and MP systems lost more SOC than the NT system. In an attempt to further reduce soil erosion rates and in an attempt to sequester or maintain SOC, cover crops were introduced in 2001. The objectives of the modified 8-year study were to evaluate the effects of cover crops on (i) corn and soybean yields of tillage systems NT, CP, and MP; (ii) the maintenance and restoration of SOC and soil productivity of previously eroded soils in southern Illinois; and (iii) the retention of SOC in the upland landscape with the use of conservation practices including border and filter strips and sod waterways.
MATERIALS AND METHODS A tillage and cover crop experiment was started in 2001 at the Dixon Springs Agricultural Research Center in southern Illinois. The soil at the study site was a moderately eroded phase of Grantsburg silt loam (fine-silty, mixed, mesic Typic Fragiudalfs) (Soil Survey Staff, 1999), with an average depth of 64 to 75 cm to a root-restricting fragipan. The area with an average slope of 6% had been in a tillage experiment for 13 years before the start of this experiment. Three tillage treatments (NT, CP, and MP) were split plot (with and without cover crops) in 2001. Starting with soybean in 2002, soybean and corn were grown in alternate years. The experimental design was two complete Latin squares and each square having three rows and three columns (Cochran and Cox, 1957) that allowed for randomization of the tillage treatments (NT, CP, and MP) both by row (block) and by column. This replication was used to control random variability in both directions. Each tillage treatment was randomized six times in 18 plots with a size of 9 m 12 m, and the plots were then split with and without cover crops to become 4.5 m 12 m. Within the plots the columns were separated with
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6-m buffer strips of no-till corn or soybean. There was a 60-m-wide filter strip between the plot area and the 100-m sod waterway. The implements used in each tillage system and depth of tillage were as follows: NT (John Deere No-Till planter with wavy coulters), CP (straight-shanked chisel plowed to 15 cm with diskings to 5 cm), and MP (moldboard plowed to 15 cm with diskings to 5 cm). In the spring of each year, the MP and CP plots were moldboard and chisel plowed followed by 2 diskings and planting. In odd years, corn was planted at the seeding rate of 64,000 seeds haj1 with fertilizers of 218 kg haj1 N, 55 haj1 P, and 232 kg haj1 K. In even years, soybeans were planted at 432,000 seeds haj1 with no fertilizer. Chemical weed control practices were used during the study. The percentage surface residue was determined after planting by the line-transect method (Hill et al., 1989). The soil loss rates were determined using USLE (Walker and Pope, 1983) and RUSLE 2. Plant population for the center 0.001 ha of each plot was determined by counting at 25 days after planting. The crop yield and plant population data from 2002 to 2009 were collected as part of this cover crop study.
Field and Laboratory Methods Soil samples were collected in August 2000 (the year before the cover crops were established), in August 2003, July 2007, and June 2009 at depths of 0 to 5, 5 to 15, 15 to 30, 30 to 45, 45 to 60, and 60 to 75 cm for SOC determination. The sampling depth was limited because of the presence of a rootrestricting fragipan at the 64- to 75-cm depth. Previous soil sampling found only trace amounts of SOC present below the 75-cm depth, probably from previous grass roots penetrating the fragipan along the prism faces. Four soil cores, one from near each of the four corners of the plot (1.5 m from adjacent, above or below plot, and 1.5 m from buffer or border strip), were obtained for each depth and composited by crumbling and mixing. The samples were air-dried and pulverized to pass through a 2-mm sieve before analysis. The SOC was determined after removal of undecomposed plant residue using the WalkleyBlack procedure (Soil Survey Staff, 1984). Field moist core bulk density was determined (Soil Survey Staff, 1984) using a Model 2000 soil core sampler manufactured by Soil Moisture Equipment Corp.
Statistical Methods Statistical analyses for all parameters were performed using the procedures from Statistical Analysis System computer software (SAS Institute, 2002). Analysis of variance and least square means of selected variables (in the case of crop yield) were performed by General Linear Model procedures. A least significant difference procedure was used at the P = 0.05 level to determine if there were significant SOC differences between cover crop treatments on each of the three tillage treatments for the same date and depth and for SOC differences from 2000 to 2009 for each tillage treatment with and without cover.
RESULTS AND DISCUSSION The NT system maintained a significantly higher amount of residue on the soil surface as compared with that of the CP and MP systems at planting during each selected year (Table 1). Crop residue on the soil surface was higher with corn as previous crop compared with that of soybean because of higher residue production from corn and lower rate of decomposition of corn residue (Lueschen et al., 1991) than soybean residue. On Grantsburg soil with 5% to 7% slopes, the estimated annual soil * 2010 Lippincott Williams & Wilkins
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Cover Crop Effects on Crops and Soil
TABLE 1. Effects of Cover Crops on Tillage Treatment Residues After Planting and Soil Loss at Dixon Springs Soil Loss†
Residue Present From Previous Crop (% cover) 2004 Tillage NT NT CP CP MP MP
Cover Y N Y N Y N
2005
2006
SOC
- - - - -Mt haj1 Yearj1 - - - - -
2007
- - - - - - - - - - - - - - - - - - - - - - - - - - - Cover Crop Effect by Tillage Treatment - - - - - - - - - - - - - - - - - - - - - - - - 95a* 92a 29a 23a 14a 9a
88a 85a 24a 18a 10a 5a
95a 90a 30a 24a 12a 8a
84a 78a 25a 21a 15a 10a
6.2a 8.1a 18.6a 22.4a 24.3a 30.1a
0.10a 0.13a 0.30a 0.37a 0.40a 0.50a
*For each year, means within the same column, same tillage, but with different cover followed by the same letter are not significantly different at the 0.05 probability level. † Soil loss is calculated by Universal Soil Loss Equation and RUSLE2. SOC content in the sediment is equal to the SOC content of the topsoil. CP: chisel plow; MP: moldboard plow; NT: no-till; SOC: soil organic carbon.
loss (Table 1), calculated using USLE and RUSLE 2, was 8.1, 22.4, and 30.1 Mg haj1 with the NT, CP, and MP systems without cover crops and 6.2, 18.6, and 24.3 Mg haj1 with cover crops, respectively (Walker and Pope, 1983). The higher percentage of crop residue (Table 1) on the soil surface with the NT system protected the soil from erosion, keeping it below the tolerance level of 8.4 Mg haj1 yearj1 (Walker and Pope, 1983). On the other hand, rill erosion was observed with the MP and CP systems with and without cover crops caused in part by less residue on soil surface compared with that of the NT system with or without cover crop. The amount of SOC removed per year from the plots by soil erosion is provided by tillage treatment with and without cover crops.
From 2002 to 2009, each tillage treatment (NT, CP, and MP) with and without cover crops had statistically similar 4-year corn and 4-year soybean populations (Table 2). Rainfall data (30-year average growing season rainfall by month for the southeastern Illinois) and 2002Y2009 growing seasons are shown in Table 3. The 30-year average cumulative rainfall during April to September in southeastern Illinois was 61.7 cm. During the study, three of the years (2004, 2007, and 2008) could be characterized as dry years, with a growing season rainfall of 38.3, 44.4, and 45.8 cm, respectively. In 2004, the driest year, the soybean yields were zero not harvested for all treatments (Table 4) because all plant-available water above the 64- to 75-cm-deep fragipan was extracted from
TABLE 2. Soybean and Corn Population With and Without Cover Crops at Dixon Springs, Illinois, Tillage Plots 2002
2004
2006
2008
4-Year Averages
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Soybean - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Tillage NT NT CP CP MP MP
Cover Crop Y N Y N Y N
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Pt haj1 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 298,000a+ 293,000a 380,000a 393,000a 403,000a 420,000a 2003*
253,000a 240,000a 233,000a 228,000a 245,000a 255,000a 2005
330,000a 320,000a 400,000a 363,000a 415,000a 388,000a
290,000a 310,000a 398,000a 390,000a 333,000a 360,000a
293,000a 290,000a 353,000a 342,000a 350,000a 355,000a
2007
2009
4-Year Averages
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Corn - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Tillage NT NT CP CP MP MP
Cover Crop Y N Y N Y N
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Pt haj1 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 61,000a+ 59,500a 60,000a 61,300a 61,000a 60,000a
72,000a 70,500a 76,000a 76,000a 68,000a 69,500a
66,000a 68,800a 67,500a 68,000a 66,000a 68,300a
68,600a 65,000a 65,800a 65,500a 67,600a 64,000a
66,900a 66,000a 67,300a 67,700a 65,700a 65,500a
+Values with and without cover crops in the same tillage treatment and year followed by the same letter are not significantly different at the 0.05 probability level. *The corn was replanted 3 times with the rows from the last 2 plants being close together. All of the plots had to be thinned to 60,000 pt/ha in year 2003. CP: chisel plow; MP: moldboard plow; NT: no-till.
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TABLE 3. Rainfall Data During the Growing Seasons From 2002 to 2009 at Dixon Springs in Southern Illinois - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Rainfall, cm - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Year
April
May
June
July
August
September
Growing Season
2002 2003 2004 2005 2006 2007 2008 2009 2002Y2009 Average 30-Year average
19.0 12.4 6.5 10.0 7.5 8.2 11.6 12.9 11.0 11.9
24.7 32.2 13.5 4.7 10.2 7.3 6.6 20.0 14.9 12.9
3.1 11.9 5.4 6.5 7.0 7.1 5.8 9.9 7.1 10.3
5.1 4.0 8.1 10.8 21.3 9.9 11.6 34.7 13.1 9.4
7.2 13.5 4.8 18.2 7.7 4.5 7.0 9.4 9.0 9.0
18.8 12.6 0.0 6.8 21.3 7.4 3.2 13.2 10.4 8.2
77.9 86.6 38.3 57.0 75.0 44.4 45.8 100.1 65.6 61.7
all treatments including the NT system before any significant grain development. The 8-year average rainfall for the April through September period was 65.6 cm, which is slightly higher than the 61.7 cm 30-year average (Table 2). Years 2003 and 2009 were considered wet years. Soybean yields (Table 4) for 2002, 2006, and the 3-year averages were significantly higher for CP without cover crops than with cover crops. However, the 3-year average soybean yields for NT and MP treatments with and without cover were not significantly different. The corn yields for all tillage treatments with and without cover were not significantly different. The SOC contents of the Grantsburg (fine-silty, mixed, mesic Oxyaquic Fragiudalfs) of the tillage plots are provided in Table 5. To establish the baseline SOC values for the plot area,
measurements were taken in the fall of 2000 from the proposed split plot area while still in the three different treatments (NT, CP, and MP) before the application of the cover crop treatment. Using the proposed experimental design (complete Latin square with two squares), the 2000 SOC values shown in Table 5 by treatment represent the mean values of the proposed locations of the six NT, six CP, and six MP plots after 12 years of a previous tillage study (Olson et al., 2005). Before the establishment of the cover crops in 2001, the NT and CP SOC levels were significantly higher than the MP treatments (Olson et al., 2005). The SOC was initially determined by volume (kilograms per layer) for the 0- to 5-, 5- to 15-, 15- to 30-, 30- to 45-, 45- to 60-, and 60- to 75-cm layers. These SOC values were reported in Table 5, column 3. The SOC of the combined layers (0Y75 cm)
TABLE 4. Soybean and Corn Yields of Tillage Plots With and Without Cover Crops at Dixon Springs, Illinois 2002
2004
2006
2008
3-Harvest Year Averages
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Soybean - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Tillage NT NT CP CP MP MP
Cover Crop Y N Y N Y N
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Mg haj1 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2.24a+ 2.37a 1.78a 2.07b 1.98a 1.98a
0a# 0a# 0a# 0a# 0a# 0a#
2.90a 3.17a 2.84a 3.37b 3.30a 3.10a
3.10a 2.84a 2.90a 2.84a 3.04a 3.04a
2.74a 2.79a 2.51a 2.76b 2.77a 2.71a
2003
2005
2007
2009
4-Year Averages
- - -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Corn - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Tillage NT NT CP CP MP MP
Cover Crop Y N Y N Y N
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Mg haj1 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 6.86a+ 6.67a 7.13a 7.33a 8.45a 7.72a
11.40a 11.44a 11.63a 11.86a 12.04a 11.42a
6.20a 6.46a 6.73a 6.80a 6.73a 7.33a
12.33a 13.13a 12.64a 13.61a 13.97a 14.03a
9.10a 9.41a 9.54a 9.85a 10.30a 10.00a
+Values with and without cover crop in the same tillage treatment and year followed by the same letter are not significantly different at the 0.05 probability level. #Not harvested in 2004 because of drought conditions and lack of sufficient grain development to justify harvesting. CP: chisel plow; MP: moldboard plow; NT: no-till.
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TABLE 5. Effects After 8 Years of Tillage and Cover Crops on the Volumetric SOC Content of the Grantsburg Soil August 2000 Treatment Without cover crops NT
With cover crops NT
NT cover crop effects
Without cover crops CP
With cover crops CP
CP cover crop effects
Without cover crops MP
Depth, cm
August 2003
July 2007
June 2009
Tillage and Cover Crop Effect Year 2000Y2009
- - - - - - - - - - - - - - - - - - - - - - kg Layer1 or Layer Thickness 1 m 1 m - - - - - - - - - - - - - - - - - - - - -
0Y5 5Y15 15Y30 30Y45 45Y60 60Y75 0Y75 (all)
1.21 1.47 0.97 0.46 0.33 0.26 4.70
0Y5 5Y15 15Y30 30Y45 45Y60 60Y75 0Y75 (all) 0Y5 5Y15 15Y30 30Y45 45Y60 60Y75 0Y75 (all)
1.21 1.47 0.97 0.46 0.33 0.26 4.70 0.00NS 0.00NS 0.00NS 0.00NS 0.00NS 0.00NS 0.00NS
0Y5 5Y15 15Y30 30Y45 45Y60 60Y75 0Y75 (all)
1.07 1.43 0.96 0.32 0.39 0.20 4.37
0Y5 5Y15 15Y30 30Y45 45Y60 60Y75 0Y75 (all) 0Y5 5Y15 15Y30 30Y45 45Y60 60Y75 0Y75 (all)
1.07 1.43 0.96 0.32 0.39 0.20 4.37 0.00NS 0.00NS 0.00NS 0.00NS 0.00NS 0.00NS 0.00NS
0Y5 5Y15 15Y30 30Y45 45Y60 60Y75 0Y75 (all)
0.76 1.23 0.92 0.45 0.26 0.15 3.77
1.53 1.44 0.95 0.44 0.20 0.20 4.76
1.16 1.33 0.94 0.46 0.25 0.23 4.37
1.19 1.33 1.03 0.49 0.28 0.21 4.53
j0.02NS j0.14NS +0.06NS +0.03NS j0.05NS j0.05NS j0.17NS
1.66 1.36 1.04 0.44 0.30 0.21 5.01 +0.13NS j0.08NS +0.09NS 0.00NS +0.10NS +0.01NS +0.25NS
1.21 1.44 0.95 0.50 0.34 0.26 4.70 +0.05NS +0.11NS +0.01NS +0.04NS +0.09NS +0.03NS +0.33NS
1.16 1.29 1.18 0.45 0.28 0.23 4.59 j0.03NS +0.04NS +0.15* j0.04NS 0.00NS +0.02NS +0.06NS
j0.05NS j0.18* +0.21* j0.01NS j0.05NS j0.03NS j0.11NS
1.03 1.48 1.00 0.44 0.29 0.29 4.53
0.74 1.07 0.83 0.38 0.37 0.27 3.66
0.69 1.08 0.81 0.43 0.36 0.31 3.68
j0.38* j0.35* j0.15NS +0.11NS j0.03NS +0.11NS j0.69*
1.04 1.49 1.01 0.57 0.31 0.27 4.69 +0.01NS +0.01NS +0.01NS +0.13* +0.02NS j0.02NS +0.16NS
0.75 1.24 0.81 0.44 0.31 0.23 3.98 +0.01NS +0.17* j0.02NS +0.06NS j0.06NS j0.04NS +0.32NS
0.72 1.33 0.83 0.40 0.32 0.25 3.85 +0.03NS +0.25* +0.02NS j0.03NS j0.04NS j0.06NS +0.17NS
j0.35* j0.10NS j0.13NS +0.08NS j0.07NS +0.05NS j0.52*
0.66 1.22 0.96 0.40 0.37 0.26 3.87
0.65 1.07 0.66 0.44 0.36 0.33 3.51
0.62 1.11 0.91 0.40 0.31 0.27 3.62
j0.14* j0.12* j0.01NS j0.05NS +0.05NS +0.12NS j0.15NS
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TABLE 5. (Continued) August 2000 Treatment With cover crops MP
MP cover crop effects
Depth, cm 0Y5 5Y15 15Y30 30Y45 45Y60 60Y75 0Y75 (all) 0Y5 15Y30 5Y15 30Y45 45Y60 60Y75 0Y75 (all)
August 2003
July 2007
June 2009
Tillage and Cover Crop Effect Year 2000Y2009
- - - - - - - - - - - - - - - - - - - - - - kg Layer1 or Layer Thickness 1 m 1 m - - - - - - - - - - - - - - - - - - - - 0.76 1.23 0.92 0.45 0.26 0.15 3.77 0.00NS 0.00NS 0.00NS 0.00NS 0.00NS 0.00NS 0.00NS
0.66 1.44 0.91 0.40 0.34 0.27 4.02 0.00NS +0.22* j0.05NS 0.00NS j0.03NS +0.01NS +0.15NS
0.67 1.14 0.68 0.45 0.40 0.34 3.68 +0.02NS +0.02NS +0.07NS +0.01NS +0.04NS j0.01NS +0.16NS
0.61 1.09 0.90 0.38 0.32 0.34 3.64 j0.01NS j0.12NS j0.01NS j0.02NS +0.01NS +0.07NS +0.02NS
j0.15* j0.14* j0.02NS j0.07NS +0.06NS +0.19* j0.13NS
*Means of six replications are significantly different at P = 0.05. CP: chisel plow; MP: moldboard plow; NT: no-till; SOC: soil organic carbon.
of MP treatment was significantly lower (3.77 kg layerj1) than those of the NT (4.70 kg layerj1) and CP (4.37 kg layerj1) treatments (Olson et al., 2005) in the year before cover crop establishment in 2000. Table 5 includes the SOC content (by volume) for the upper six soil layers of the cover crop experiment in years 2003, 2007, and 2009. Significant difference in SOC occurred between NT with and without cover crops for the 15- to 30-cm layer as well as CP without cover crops for the 5- to 15-cm layer (Table 5, column 6). By July 2009, the cover crop effect for NT resulted in the SOC being statistically similar for all other layers (Table 5, column 6) when compared with that of NT plots without cover crops. The CP and MP treatments with cover crops did not result in any significant differences between cover crop treatments. It should be noted that for the NT treatment with and without cover crops, the SOC on a volume basis for the 0- to 75-cm layer remained statistically the same (declined 0.11 and 0.17 kg layerj1, respectively) (Table 5, column 7) after 8 years of the cover crop experiment. This suggests that SOC losses from water erosion and some disturbance or mixing during NT planting, aeration, nitrogen injection disturbance in corn years and mineralization were almost equal to the SOC gain from the cover crop treatment. However, the 5- to 15-cm layer of NT with cover crop was significantly lower in SOC, but this was offset by significantly higher SOC in the 15- to 30-cm layer. The NT system with cover crops did maintain SOC levels in the 0- to 75-cm layer but did not sequester (increase) any SOC levels over time (when compared with baseline SOC levels in 2000). For the CP treatment with the cover crops, any gain in SOC in the 0- to 75-cm layer was offset by SOC loss resulting from years of tillage and erosion. The CP treatment SOC declined significantly (0.69 kg layerj1) without cover crops and with cover crops (0.52 kg layerj1) as a result of significant SOC losses in the surface layers. By 2009, the MP with cover crops had a statistically insignificant decline, 0.13 kg layerj1, in SOC level for the 0- to 75-cm layer as a result of significant SOC declines in the surface
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layers. For the MP treatments, cover crops helped reduce the rate of SOC loss as a result of tillage (aeration) associated with corn and soybean production and soil erosion but was not able to maintain the 2000 baseline SOC levels from before the cover crop treatments were applied. The SOC content data by volume are summarized in Table 6 for all treatments for the potential tillage zone (0Y15 cm), the subsoil layer (15Y75 cm), and the root zone (0Y75 cm). By 2009, the SOC of the CP treatment with and without cover crops also showed significant SOC content loss in tillage and rooting zones when compared with 2000 baseline values (Table 6, column 7). The differences over time in SOC between treatments in the tillage zones were attributed to the effects of management on erosion, disturbance, aeration, mineralization, and residue incorporation. The SOC content of the MP tillage zone (0Y15 cm) with and without cover crops also declined, but the results were not significantly different from the 2000 baseline levels for the rooting zone (0Y75 cm). The NT treatments with and without cover crops had no significant changes for the tillage, subsoil, or rooting zones. The SOC contents in the rooting zone (Table 6, column 8) decreased 4%, 16%, and 4% in the NT, CP, and MP systems without cover crops when 2009 values were compared with the 2000 baseline levels. With the addition of cover crops to all treatments, the SOC reductions were less (2%, 12%, and 3%, respectively). Eight years of cover crops were not effective in restoring SOC to higher than 2000 baseline levels. The SOC values (Table 6, column 6) were expressed on a Mt haj1 layerj1 basis to make it easier for the reader to compare this experiment with other research results. The cover crop treatment effects for each tillage treatment (NT, CP, and MP systems) show the effects of 8 years of tillage and cover crops had in 2009 on the input SOC rate change for the NT, CP, and MP systems: þ0.6 Mt haj1 layer Y1, +1.7 Mt haj1 layer Y1, and +0.2 Mt haj1 layer Y1, respectively. These insignificant gains in SOC by 2009 for the cover crop treatment in each tillage system did not result in any SOC sequestration or gains when compared with the 2000 baseline SOC values of the same treatment. The * 2010 Lippincott Williams & Wilkins
Copyright @ 2010 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
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Copyright @ 2010 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. 19.9 17.8 37.7 0.0NS 0.0NS 0.0NS
19.9 17.8 37.7
25.0 18.7 43.7 0.0NS 0.0NS 0.0NS
25.0 18.7 43.7
26.8 20.2 47.0 0.0NS 0.0NS 0.0NS
26.8 20.2 47.0
21.0 19.2 40.2 +2.2* j0.7NS +1.5NS
18.8 19.9 38.7
25.3 21.6 46.9 +0.3NS +2.9* +3.2NS
25.1 20.2 45.3
30.2 19.9 50.1 +0.5NS +2.0NS +2.5NS
29.7 17.9 47.6
18.1 18.7 36.8 +0.9NS +0.8NS +1.7NS
17.2 17.9 35.1
21.8 17.9 39.8 +3.3* +2.2* +5.5*
18.1 16.8 36.6
26.5 20.5 47.0 +1.6NS +1.7NS +3.3NS
24.9 18.8 43.7
Mt haj1 Layerj1 1 m 1 m
Means of six replications are significantly different at P = 0.05. CP: chisel plow; MP: moldboard plow; NT: no-till; SOC: soil organic carbon.
MP cover crop effects
0Y15 15Y75 0Y75 (all) 0Y15 15Y75 0Y75 (all)
0Y15 15Y75 0Y75 (all)
0j15 15j75 0j75 (all) 0j15 15j75 0j75 (all)
0Y15 15Y75 0Y75 (all)
0Y15 15Y75 0Y75 (all) 0Y15 15Y75 0Y75 (all)
June 2009
17.0 19.4 36.4 j0.3NS +0.5NS +0.2NS
17.3 18.9 36.2
20.5 18.0 38.5 +2.8* j1.1NS +1.7NS
17.7 19.1 36.8
24.5 21.0 45.9 j0.7NS +1.3NS +0.6NS
25.2 20.1 45.3
Tillage Effect With or Without Cover Crop SOC Loss or Gain
j2.9* +1.6NS j1.3NS
j2.6* +1.1NS j1.5NS
j4.5* j0.7NS j5.2*
j7.3* +0.4NS j6.9*
j2.3NS +1.2NS j1.1NS
j1.6NS j0.1NS j1.7NS
Mt haj1 Layerj1 1 m 1 m
j15 +9 j3
j13 +6 j4
j18 j4 j12
j29 +2 j16
j9 +5 j2
j6 0 j4
%
j0.32 +0.18 j0.14
j0.29 +0.12 j0.17
j0.50 j0.08 j0.58
j0.81 +0.04 j0.77
j0.25 +0.13 j0.12
j0.18 j0.01 j0.19
Mt haj1 Layerj1 Yearj1 1 m 1 m
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2000Y2009 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Volume 175, Number 2, February 2010
With cover crops MP
Without cover crops MP
CP cover crop effects
With cover crops CP
Without cover crops CP
NT cover crop effects
With cover crops NT
0Y15 15Y75 0Y75 (all)
Depth, cm
July 2007
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Without cover crops NT
Treatment (Six Replications)
August 2003
- - - - - - - - - - - - - - - - - - - - SOC Content - - - - - - - - - - - - - - - - - - -
August 2000
TABLE 6. Effects After 8 Years of Tillage and Cover Crops on the Volumetric SOC Content of the Grantsburg Soil
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TABLE 7. Effects After 8 Years of Cover Crops, Tillage, and Sediment Retention on the Volumetric SOC Content Retained on the Upland Landscape (on the Plots, in the Sediment Trapped in the Border and Filter Strips or Sod Waterway)
Treatment Cover Depth, (Six Replications) Crops cm NT NT CP CP MP MP
N Y N Y N Y
0Y75 0Y75 0Y75 0Y75 0Y75 0Y75
Tillage Effect With or SOC Stored on Upland Without Cover Crop SOC SOC Deposited as Sediment and Landscape as a Result Loss in Root Zone Retained in Border and Filter and Sod of Tillage, Cover Crops, 2000Y2009 Waterway (50% Sediment Delivery Ratio) and Sediment Retained - - - - - - - - - - - - - - - - - - - - - - - - - - Mt haj1 Layerj1 Yearj1 100 m 100 m - - - - - - - - - - - - - - - - - - - - - j0.19 j0.12 j0.77 j0.58 j0.17 j0.14
0.07 0.05 0.19 0.15 0.25 0.20
j0.12 j0.07 j0.58 j0.43 +0.08 +0.06
CP: chisel plow; MP: moldboard plow; NT: no-till; SOC: soil organic carbon.
tillage effects reported in Table 6, column 9, suggest that SOC levels in the rooting zone of the NT, CP, and MP systems without cover crops are declining at the rates of j0.19 Mt haj1 layer Y1 yearj1, j0.77 Mt haj1 layer Y1 yearj1, and j0.17 Mt haj1 layer Y1 yearj1, respectively. However, cover crop treatment for each tillage system in Table 6, column 9, did not completely offset the SOC losses from tillage in NT, CP, and MP systems, being reduced to j0.12 Mt haj1 layer j1 yearj1, j0.58 Mt haj1 layer j1 yearj1, and j0.14 Mt haj1 layer j1 yearj1, respectively. Only the NT system with cover crops and without cover crops maintained most of the 2000 baseline SOC level on the plots. The effects of 8 years of tillage, cover crops, and sediment collection on the volumetric SOC content (Mt haj1 layer j1 yearj1 or layer thickness 100 m 100 m) retained on the upland landscape (on the plots or in the sediment captured in the 7-m border, 35-m filter strips, and 100-m sod waterways) are shown in Table 7. Kreznor et al. (1990) found that the average sediment delivery ratio (SDR) for cropland in the loess-covered landscapes of Iowa and Illinois watersheds is approximately 0.50. The use of the soil and water conservation practices on the plots most likely resulted in significantly more than 50% of the sediment and SOC being retained on the upland landscape (including the plot area, border strip, filter strip, and sod waterway); however, we decided to use the established average cropland SDR of 50%. The calculations in Table 7 assume that this loess-covered plot area has an SDR of 50%, with the SOC remaining attached to the sediment. The sediment is retained by the soil conservation practices (primarily in the border and filter strips and sod waterways). Any SOC dissolved in runoff water and not attached to sediment could be delivered to the stream. The mass of the dissolved SOC is probably rather small when compared with the amount of SOC attached to sediment particles. However, if and when this dissolved SOC gets in the stream, it will most likely be quickly returned from the water to the atmosphere as either methane gas or carbon dioxide. The data (Table 7) suggest that the SOC stored on the upland landscape includes both the SOC stored or retained on the tillage and cover crop plots and the sediment retained in the border and filter strips and sod waterway. The sediment high in SOC is on the footslope and toeslope and between the plots on a sideslope and stream. Only MP treatments without and with cover crops plus sediments high in SOC did retain more (0.08 and 0.06 Mt haj1 layerj1 yearj1, respectively) SOC on the upland landscape. The NT and CP systems with cover crops did
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not maintain or increase SOC over time even with the SOC carbon credit for sediments retained in the entire upland landscape (j0.07 and j0.43 Mt haj1 layerj1 yearj1, respectively). The addition of sediment had the greatest effect on MP system because it had the greatest soil loss and sediment, rich in SOC, deposition in the border and filter strips and the sod waterways. It appears from the sediment buildup on the footslope soils (border strip, filter strip, and in sod waterway) during the past 8 years that sediment is being retained on upland landscape and not going into a stream. The addition of cover crops increased the amount of soil and SOC retained in the plots in all tillage treatments and reduced the amount transported to the border and filter strips and sod waterway. In summary, the NT system, with and without cover crop treatment, maintained higher levels of SOC in the root zone than did the CP and MP systems. Loss of SOC could make the tilled soil (CP and MP) more vulnerable to water erosion because of a reduction in slaking resistance. The SOC levels in the tillage zone, the subsoil, and the entire root zone (expressed on a volume basis) of the plots decreased insignificantly by 2009 under the NT, CP, and MP systems with and without cover crops. The CP system significantly decreased SOC levels in the tilled zone and the root zone. By 2009, the cover crop treatments had little effect on SOC levels of tillage zone, subsoil, and rooting zone of all tillage treatments. No SOC sequestration (net increase) occurred over time for any of the tillage treatments with cover crops when compared with baseline values (2000) before application of the cover crops. To determine whether SOC sequestration has occurred, it is important that researchers establish the baseline SOC levels before any treatment applications and use those values, rather than ones from the last year of experiment to determine SOC loss or gain. The NT treatment with cover crops did maintain more SOC than the CP and MP tillage systems, with SOC gain from cover crops almost equal to any loss from any disturbance or mixing during planting, nitrogen injection in corn years, and erosion during corn and soybean production. All tillage treatments (NT, CP, and MP) did lose sediment rich in SOC from the plot areas, but half of this sediment was retained on the upland landscape by soil conservation practices. The MP treatments with and without cover crops did retain SOC on the landscape when the retained sediment in the border and filter strips is added to the SOC retained in the soils of the plot areas, which should reduce sediment, rich in SOC, from being transported to streams and eventually released to the atmosphere as methane or carbon dioxide. * 2010 Lippincott Williams & Wilkins
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CONCLUSIONS Based on 8 years of crop yield measurements (4 years corn and 4 years soybean) for three tillage systems with and without cover crops, cover crops did not affect plant populations or crop yields. However, all three tillage systems with cover crops had statistically similar SOC levels with the same tillage system without a cover crop. No soil carbon sequestration (net increase) occurred over time for any of the tillage treatments with cover crops when compared with 2000 SOC levels for each treatment. The NT system seems to have resulted in reduced soil erosion and maintained more SOC than that in the MP and CP systems with or without a cover crop. However, on an upland landscape basis, the MP system with and without cover crops was the only tillage system to retain more SOC on the upland landscape as a result of more sediment rich in SOC being retained in the border and filter strips and sod waterways. Apparently, more humus is created in the MP system as a result of better mixing of plant residues into the soil by tillage each year and as a result of the more SOC-rich sediment being captured in the border and filter strips and sod waterway. This sediment, rich in SOC, seems to be retained for many years on the upland landscape as a result of the conservation practices and not immediately transported to the streams and returned as methane or carbon dioxide to the atmosphere. The results of this study should be applicable to similar root-restricting, sloping, and moderately eroded soils in Illinois, Indiana, Missouri, and Kentucky. ACKNOWLEDGMENT Published with the approval of the Director of the Office of Research at the University of Illinois, Urbana, Illinois. This study was funded as part of Regional Research Project 367 and in cooperation with North Central Regional Project NC-1017 (Soil Carbon Sequestration).
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