typically required after rolling to plant a cash crop into the desiccated cover crop residue. A common method to enhance the cover crop termination is a ...
EFFECTS OF RECURRENT ROLLING/CRIMPING OPERATIONS ON COVER CROP TERMINATION, SOIL MOISTURE, AND SOIL STRENGTH FOR CONSERVATION ORGANIC SYSTEMS T. S. Kornecki, F. J. Arriaga, A J. Price, K. S. Balkcom
ABSTRACT. Rolling/crimping technology has been utilized to mechanically terminate cover crops in conservation agriculture. In the southeastern United States, to eliminate competition for valuable soil moisture, three weeks are typically required after rolling to plant a cash crop into the desiccated cover crop residue. A common method to enhance the cover crop termination is a supplemental application of herbicides such as glyphosate. However, synthetic herbicides cannot be used in organic production, thus additional rolling operations might speed the desiccation process. On the other hand, recurrent rolling/crimping operations could cause additional soil compaction, which could be detrimental for water infiltration and crop root development. The objectives of this experiment were to determine the effectiveness of a singlestage roller with straight bars and a new two-stage roller in terminating either rye (Secale cereale L.) or a mixture of rye, crimson clover (Trifolium incarnatum L.), and hairy vetch (Vicia villosa L.) with repeated rolling operations, and the effect of repeated rolling on volumetric soil water content and soil strength. Cover crop termination dates were selected three weeks before planting date recommendations for vegetables in the northern Alabama region. In three growing seasons (2007, 2008, 2009), three weeks after rolling, both roller designs effectively terminated rye > 90%, which is above the recommended rye termination rate to plant a cash crop. No difference in termination rates were observed between two rollers. Rolling two or three times did not cause additional soil compaction, and rolled residue reduced soil strength compared to standing cover crops due to an improved termination rate and associated moisture conservation. Soil volumetric moisture content (VMC) after repeated rolling operations was significantly higher compared with standing rye and mixture covers. In the mixture, hairy vetch was actively growing two weeks after rolling even after three rolling operations, most likely due to too early growth stage for hairy vetch. Repeated rolling can be beneficial for faster mechanical termination of cover crops such as rye and crimson clover, but may not be adequate for mixtures that include hairy vetch. Keywords. Cover crops, Roller/crimper, Soil strength, Conservation systems.
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over crops are a crucial part of conservation agriculture, but they need to be managed appropriately to optimize their benefits (Brady and Weil, 1999). Previous research has identified cover crop benefits, including increased water infiltration, reduced runoff, reduced soil erosion, and reduced soil compaction (Kern and Johnson, 1993; Reeves, 1994; Raper et al., 2000a; Raper et al., 2000b). Flattening and crimping cereal cover crops by mechanical rollers/crimpers originated in Brazil to successfully terminate cover crops
Submitted for review in March 2013 as manuscript number PM 10186; approved for publication by the Power & Machinery Division of ASABE in July 2013. The use of trade names or company names does not imply endorsement by the USDA-Agricultural Research Service. The USDA is an equal opportunity provider and employer. The authors are Ted S. Kornecki, ASABE Member, Agricultural Engineer, Andrew J. Price, Weed Scientist, and Kipling S. Balkcom, Research Agronomist, USDA-ARS, National Soil Dynamics Laboratory, 411 South Donahue Drive, Auburn, Alabama; and Francisco J. Arriaga, Soil Scientist, University of Wisconsin, Department of Soil Science, Madison, Wisconsin. Corresponding author: Ted S. Kornecki, USDAARS, National Soil Dynamics Laboratory, 411 South Donahue Dr., Auburn AL 36832; phone: 334-887-8596; e-mail: ted.kornecki@ ars.usda.gov.
without herbicides (Derpsch et al., 1991), and this technology is now receiving significant interest within the United States. Mechanical termination of cover crops using a roller/crimper usually requires waiting at least three weeks before planting a cash crop into rolled residue (Ashford and Reeves, 2003; Kornecki et al., 2006). Many agricultural extension services recommended termination of the cover crop at least two weeks before planting, since this period is needed to prevent the cover crop from competing for soil moisture and nutrients (Hargrove and Frye, 1987). Ashford and Reeves (2003) indicated that when rolling was conducted at the appropriate plant growth stage (i.e., soft dough, Zadoks growth stage 85, Zadoks et al., 1974), the roller was equally effective versus chemical herbicides at terminating the cover crop (94%) and that rye termination rates above 90% were sufficient to begin planting of cash crop due to accelerated rye senescence. To speed up termination, producers utilize herbicides as a supplement to rolling. Decreasing the time between cover crop rolling and planting of a cash crop is especially important in vegetable production as vegetables need to be planted earlier in the spring to keep optimum planting dates for a particular region. However, in organic
Applied Engineering in Agriculture Vol. 29(6): 841-850
2013 American Society of Agricultural and Biological Engineers ISSN 0883-8542 DOI 10.13031/aea.29.10186
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vegetable production, synthetic herbicides cannot be used. Because of this restriction, several rolling applications over the same cover crop may be required to increase cover crop termination rate (Kornecki, 2012). There is a concern that additional soil compaction may occur which could be detrimental to water infiltration and cash crop root development. No research has been conducted regarding repeated rolling/crimping effects on soil compaction. There is very limited information regarding effects of the roller/crimper on soil compaction. Raper et al., (2004) compared three different pressures exerted by the crimping bar (due to the roller’s weight increase) of a small 1.1 m wide straight-bar roller to measure soil indentations on two soil types in Auburn, Alabama (Vaiden silty clay and Hiwassee clay). Their experiment was conducted on soils during high VMC (21.1% to 26.8%) and caused indentations of 12 and 6 mm, for 1.02 and 0.61 MPa average pressures, respectively. These results, however, did not provide any information related to soil compaction caused by rolling; also these results were obtained for very small experimental rollers in wet conditions which did not provide a firm soil surface necessary to obtain an effective crimping. To answer questions associated with soil compaction due to recurrent rolling, a replicated field experiment was conducted in Cullman, Alabama to evaluate the effects of recurrent rolling/crimping events on the termination rate of a single cover crop and a mixture of three cover crops, soil moisture content, and soil strength during the 2007, 2008, and 2009 growing seasons. The objectives of this study were: (1) determine the effectiveness of a roller with straight bars, and a two-stage roller in terminating a single cover crop (rye), and a mixture (rye, crimson clover and hairy vetch) after one, two, and three rolling passes; (2) determine the effect of recurrent rolling operations on volumetric moisture content (VMC) during the cover crop termination period; and (3) determine the effect of two and three rolling passes on soil strength and corresponding gravimetric soil moisture content (GMC) before and after application of the rolling treatments.
MATERIALS AND METHODS The experiment was established on a Hartsells fine sandy loam soil (Fine-loamy, siliceous, sub-active, thermic Typic Hapludults). In the fall of 2006, 2007, and 2008, two different winter cover crops were established: (1) Cereal
rye (seeding rate of 95 kg ha-1) and (2) a cover crop mixture (rye rate 53 kg ha-1, crimson clover and hairy vetch both 21 kg ha-1). These cover crops were drill seeded using a TyeTM grain no-till drill (AGCO, Duluth, Ga.) with 17 cm row spacing, and were planted 5 October, 10 October, and 15 October in 2006, 2007, and 2008, respectively. To optimize rye growth, ammonium nitrate (34-0-0) was broadcast onto the cover crop at a rate of 50 kg ha-1 N in early March. The day before rolling/crimping, cover crop height and biomass were determined from each plot. Height was measured at 10 randomly chosen locations throughout the plot using a custom-made scale rod and then averaged. For the mixture, the height for each of three plants was measured individually and then averaged. The biomass was collected from two different 0.25 m2 areas in each plot. The collected rye biomass was oven dried for 72 h at 55°C using an electric oven (Model No. SC-350 from Grieve Corporation, Round Lake, Ill.). Rolling treatments were applied 23 April 2007, 30 April 2008, and 12 May 2009 when rye was in the early milk growth stage (Zadoks growth stage 73, Zadoks et al., 1974), which is a desirable growth stage for rye termination (Nelson et al., 1995). Each recurrent rolling treatment (rolling twice and three times) was applied every other day from the previous rolling application. Cover crops were rolled parallel to the rows of the drilled winter cover crops. Rye and mixture injury, based on visual desiccation, were estimated on a scale of 0 (no injury symptoms) to 100 for complete plant death (Frans et al., 1986), and was evaluated at one, two, and three weeks after rolling. The speed of 6.4 km h-1 was chosen to match speeds commonly used in field chemical applications. Each plot was 6.1 m long and 1.8 m wide. The 1.8 m wide rollers utilized in the experiment were: a straight-bar roller (fig. 1a) and two-stage roller (fig. 1b). The straight bar roller is the original roller/crimper design adopted from Brazil. To make this roller more effective, its weight needed to be increased by adding water to the roller’s drum. The major problem with this roller was the excessive vibration generated with increasing operating speed. Because of the vibration problem, a new two-stage roller crimper concept was developed. The new roller significantly reduces vibration while maintaining or exceeding the crimping effectiveness compared with the original roller. This patented roller/crimper (Kornecki, 2011) is comprised of a primary smooth drum and a secondary springloaded crimping drum isolated from the primary smooth drum, so vibrations are not transferred to the roller’s frame
Figure 1. Equipment used in the experiment: (a) Straight bar roller/crimper, (b) Two-stage roller/crimper, (c) Tractor-mounted penetrometer.
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and tractor. Crimping force can be adjusted by presetting two compression springs located on each side of the roller. The two-stage roller has an advantage over the original straight bar roller due to the easy and fast adjusting of the crimping force without the need of filling the drum with water to manipulate roller’s weight. Before the rolling/crimping operation, soil strength was measured by a mobile soil cone index penetrometer (Raper et al., 1999) depicted in figure 1c. Soil strength as cone index and corresponding gravimetric soil moisture content (GMC) measurements were repeated after the completion of three rolling/crimping operations, to determine recurrent rolling effects on soil strength. Soil cone index and GMC data were obtained at least three weeks after rolling but not longer than 1 month after the last rolling application. The reason was that dealing with real weather and the associated soil conditions (wet soil after rain) it was impossible to keep three weeks after rolling as a scheduled target to obtain soil strength data and sampling of the soil to obtain the gravimetric moisture content. Stainless steel cone tips with the base area of 129 mm2 were utilized in the experiment (ASAE Standards, 2004b). Cone index data were obtained according to procedures described in ASAE standard EP542 (ASAE Standards, 2004a). Soil strength measurements were obtained from each plot (two per plot) from a non-trafficked area using five stainless rods with cone tips spaced 19 cm apart providing measurements on 76 cm wide strips up to 45 cm depth. Soil samples were obtained using a soil probe to a depth of 30 cm to determine the associated GMC. Three soil samples were taken at each plot. Then each sample was divided equally for two depths, 0 to 15 cm and 15 to 30 cm. Three samples from each depth were combined to make a composite sample. Factorial treatments were arranged in a randomized complete block design
Plot Number 101
R+4+A Roller Type Rolling Treatment Cover Crop
1.8m
(RCBD) with four blocks (replications). Treatments were randomized within each block (fig. 2). Additionally, volumetric moisture content was measured the day of rolling and after the first, second, and third week using a portable TDR moisture meter (Spectrum Technologies, Plainfield, Ill.). The sensor was equipped with 12 cm long rods and was inserted vertically into the soil surface. This rod length was selected to measure soil volumetric moisture content at a shallow depth, which should be similar to the available soil moisture for germination of the cash crop seeds planted into the residue cover. Five readings were taken close to the middle of each plot at marked locations spaced about 1.0 m apart. Percentages of cover crop termination rates were transformed using an arcsine square-root transformation method (Steel and Torie, 1980), but this transformation did not result in a change in the analysis of variance (ANOVA), thus, non-transformed means are presented. Analysis of variance (ANOVA) was performed on rye biomass, height, termination rates, VMC, soil strength and gravimetric moisture content using SAS GLM procedure (SAS, 2009). Rolling treatments were considered fixed effects and years were considered random effects. Treatment means were separated by the Fisher’s protected LSD test at the 0.10 probability level. Where interactions between treatments and years occurred, data were presented separately; otherwise, data were combined. Also, to determine a difference between two specific CI value treatment means, a preplanned single degree of freedom contrast procedure as described in Steel and Torrie (1980) was performed to detect these differences at the 10% (α=0.10) probability level (table 1).
BLOCK 1
BLOCK 2
BLOCK 3
BLOCK 4
101
R+4+A
201
M+2+B
301
M+3+B
401
R+3+A
102
M+3+A
202
R+2+A
302
M+4+A
402
R+3+B
103
R+2+B
203
R+3+B
303
M+2+A
403
R+2+B
104
R+3+B
204
M+1
304
R+4+B
404
R+2+A
105
R+2+A
205
R+1
305
M+3+A
405
R+1
106
M+2+B
206
M+4+B
306
R+4+A
406
M+1
107
M+2+A
207
M+4+A
307
M+1
407
M+4+A
108
M+4+B
208
R+3+A
308
R+3+B
408
R+4+A
109
M+4+A
209
M+2+A
309
R+2+A
409
R+4+B
110
R+4+B
210
M+3+B
310
R+2+B
410
M+4+B
111
M+1
211
M+3+A
311
M+4+B
411
M+2+A
112
M+3+B
212
R+2+B
312
R+3+A
412
M+2+B
113
R+1
213
R+4+B
313
M+2+B
413
M+3+A
114
R+3+A
214
R+4+A
314
R+1
414
M+3+B
6.1m
2.7m
Cover Crop R = RYE M = Mixture NOTE: Mixture consists of Rye + Clover + Vetch
Rolling Treatment 1. Not Rolled 2. Rolled 1 time 3. Rolled 2 times 4. Rolled 3 times
Roller Type A. Straight-Bar Roller B. Two-Stage Roller Rolling Speed: 6.4 km h¯
1
Figure 2. Experimental layout for factorial design with four blocks (replications). Factor I: cover crop, factor II: roller type, and factor III: rolling treatment. In each block there are 14 treatments randomly assigned to each plot within each block.
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Table 1. Preplanned single degree of freedom contrast comparisons for rolling treatments during 2007-2009 growing seasons. Contrast Treatment Comparisons Rye cover vs. Single rye cover crop vs. cover crop mixture: mixture (rye, crimson clover and hairy vetch) Straight bar roller vs. Straight bar roller at 6.4 km h-1 vs. two-stage two stage roller/crimper roller/crimper at 6.4 km h-1 Non-rolled vs. Standing cover crop (non-rolled) vs. cover rolled 1 time crop rolled once Non-rolled vs. Standing cover crop (non-rolled) vs. cover rolled two times crop rolled twice Non-rolled vs. Standing cover crop (non-rolled) vs. cover rolled three times crop rolled three times Rolled one time vs. Cover crops rolled once vs. cover crop rolled rolled two times twice Rolled one time vs. Cover crops rolled once vs. cover crop rolled rolled three times three times Rolled two times vs. Cover crops rolled twice vs. cover crops rolled three times rolled three times
RESULTS HEIGHT AND BIOMASS FOR RYE AND MIXTURE There were significant differences (P-value
