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Strip-tillage and Cover Crop Systems

Contents

 Fuel and Energy Savings
 Integrating Conservation Tillage with Cover Crop
 Weed Management in Conservation Tillage Systems
 Strip-Tillage Systems for Vegetable Production
 References Cited

	Strip-tillage and Cover Crop Systems for Vegetable Production
		John M. Luna and Tim O'Brien Department of Horticulture Oregon State University Corvallis, OR 97331
Increasing concerns for soil, water, and air quality, as well as concerns for declining soil productivity, necessitate the development of farming systems which integrate the mutual goals of profitability and environmental quality. Soil erosion of farmland from wind and water degrades soil quality and contributes to surface water and atmospheric contamination. Leaching of nitrates through the soil profile during winter rains has been identified as a source of non-point source contamination of groundwater in many agricultural areas of the United States. Conservation tillage systems and cover crops offer the potential to ameliorate many of the environmental concerns associated with agricultural practices, while improving soil productivity and economic profitability. An operational definition of conservation tillage used by the Natural Resources Conservation Service states that conservation tillage is "any tillage system that leaves greater than 30 percent residue remaining on the soil surface after planting" (Galloway et al., 1981). Several approaches to conservation tillage have been used growers, including: chisel plow, strip-till (Fig. 1), ridge-till, stubble-mulch-till, and no-till.
Figure 1. A Northwest Tiller is used to till 6" wide strips into a killed cover crop mulch prior to planting sweet corn. Tillage has been shown to be major factor in the loss of soil carbon (the major component of soil organic matter), which leads to decreased productivity. In a northern Alabama study, Edwards et al. (1992) compared conventional tillage, including moldboard plowing, with conservation tillage in which there was only a light disking once a year. Crop rotations were corn-wheat-corn-wheat and corn-wheat-

soybean-wheat, in which the winter wheat was not harvested but used as a cover crop. Organic matter contents in the soil after 10 years of the corn-wheat-corn-soybean rotations are shown in Fig. 2 as a function of depth for the conventional and minimum tillage treatments. The light disking used one a year to prepare for seeding with a conventional drill helped move some of the crop residue down into the 2-4-inch layer of the soil. According to Edwards et al., in the 10-year study the conservation tillage treatments accumulated organic matter at a rate of about 1,700 lbs/acre/year faster than the conventional tillage treatments. Although long-term effects of continued cultivation on soil organic matter have been frequently observed, there has been little direct measurement of soil carbon dioxide loss from soil following tillage. In a Minnesota study evaluating the effects of various fall tillage practices following a wheat harvest, Reicosky and Lindstrom (1993) used a portable infrared gas analyzer to measure carbon dioxide flux. Their results (Table 1) shows that rough-plowed land that did not receive secondary tillage lost
		2.5 2 1.5 1 0.5 0
				1		3	5	7
					Soil Depth (inches)
Figure 2. Residual soil organic matter after 10 years of corn-wheat-soybeans- wheat rotation at Crossville, Al (data from Edwards et al., -1992) more than one ton of carbon dioxide within 55 hours following plowing, and more than 4 tons of CO2 within 19 days after tillage. This was compared to 196 lbs of CO2in the non-tilled treatments 55 hours after the tillage occurred and 1,628 lbs of COnineteen days after tillage. Secondary tillage following plowing and other minimum tillage2

Table 1. Effect of all tillage practices on short-term carbon dioxide flux from the soil into the atmosphere. Data from Reicosky et al., 1993. practices clearly reduced loss of carbon dioxide compared to plowing only. This accelerated loss of soil carbon following tillage is related to changes in soil porosity as well as increased rates of microbial decomposition of organic matter. While tillage can have a beneficial effect of loosening soil compaction, killing unwanted vegetation, and aerating the soil, spring planting schedules frequently require soil preparation under excessively wet soil conditions in the Willamette Valley. Tillage under wet conditions can have severely detrimental effects to soil structure and can accelerate soil compaction problems. Fuel and Energy Savings Reducing tillage can also produce economic savings from fewer mechanical operations, with savings in labor, fuel and machinery. (Frye and Phillips, 1981). For example, in Western Oregon vegetable production systems, 5-8 separate tillage operations are commonly used to prepare a seedbed for vegetable planting. Cost estimates vary among different implements and soil conditions, but have been estimated to cost $8-15 per tillage pass per acre. Integrating Conservation Tillage with Cover Crop Cover crops have been used extensively in both annual and perennial crop production systems to accomplish multiple goals. Cover crops are defined as crops that are grown not for immediate economic gain through harvest but for their abilities to protect and improve soil quality rather than direct economic gain (Lal et al., 1991). Reviews of the advantages of utilizing cover crops have been provided by Luna, 1993; Shennan, 1992; and Bugg, 1992. Specific benefits include: increased soil fertility (Doran and Smith, 1991; Nova, 1995), decreased soil erosion (Meisinger et. al., 1991), increased nitrogen scavenging (Jackson et al., 1993), suppression of weeds (physically or chemically) (Barnes and Putnam, 1983), suppression of symphylan (Scutigerella immmaculata ) (Datta, 1996), suppression of nematodes (Ingham 1993), increased habitat for beneficial insects (Clark et. al. 1993), and decreased off-farm energy usage (Ess et al., 1994). Utilization of cover crops can also produce deleterious effects, including: delay of planting time associated with excess soil moisture (Luna, 1993), increased nitrogen immobilization (Wyland et al., 1995), increased insect pest and weed incidence (Bugg, 1991; Nova, 1995), and increased production costs (Allison and Ott, 1987).

Weed Management in Conservation Tillage Systems Integrating cover crops into conservation tillage systems as weed management tools have been shown to provide weed control comparable to herbicides in some situations (Crutchfield et al., 1985; Smeda and Putnam, 1988; Teasdale and Mohler, 1992; Purvis et al., 1985; Johnson et al., 1993). Research in this area has focused on exploiting competitive characteristics of living cover crop species for water, nutrients, and sunlight and, after the cover crop is killed, the ability of the dead cover crop mulch to suppress weeds (Putnam, 1990; Barker and Bhowmik, 1994; Masiunas et al., 1995; Teasdale, 1993). Cereal cover crop residues suppress weeds by modifying the light, temperature, moisture, and chemical environment of germinating seeds (Putnam, 1986 and Teasdale et al., 1991). Teasdale and Mohler (1992) noted that microclimatic changes caused by legume cover crops, namely alterations of temperature and light intensity, inhibit weed seed germination. Considerable research in the past decade has focused on the allelopathic effects of cover crops in conservation tillage systems. Allelopathy is defined by Zimdahl (1993) as a form of plant interference that occurs when one plant, through living or decaying tissue, releases a chemical inhibitor which interferes with the growth of another plant. The use of allelopathic mulches has been a common research theme in the development of integrated weed management strategies (Barnes and Putnam, 1983; Putnam and DeFrank, 1983; Overland, 1966; Leather, 1988). In Barnes and Putnam's (1983) study of cereal rye (Secale cereale , c.v.= 'Wheeler' and 'MSU-13') residues, the biomass of three summer annual weeds (Chenopodium album L., Digitaria sanguinalis L., and Ambrosia artemisiifolia L.) were significantly decreased when grown in the presence of rye cover crop residue. Chemical and physical effects of mulches have been difficult to distinguish in studies of allelopathy. Barnes and Putnam (1983) attempted to distinguish these effects by using poplar excelsior wood shavings (an inert material) to mimic physical mulch effects. Echinochloa crusgalli L. and Amaranthus retroflexus L. growth was significantly suppressed under rye residues when compared to the excelsior. In a greenhouse study, Barnes and Putnam (1986) reported that rye (Secale cereale , c.v.= 'Wheeler') residues in a simulated no-till environment reduced emergence of Panicum miliaceum L. by35% when compared to a wood shaving control mulch. Duration of weed suppressiveness provided by decomposing cover crop residue is an important consideration in developing weed management strategies. In the first year of a North Carolina study, Hinen and Worsham (1990) reported that rye (Secale cereale ) residues alone provided adequate weed control. In the secondyear of study, however, supplemental herbicide applications were required to maintain adequate weed control. Although decomposing plant residues can negatively impact weeds, negative impacts on subsequent cash crops have also been reported (Putnam et al., 1983). Barnes and Putnam (1986), report that rye (Secale cereale,  c.v.= 'Wheeler') residues reduced the emergence of lettuce (Lactuca sativa ) by 58% when compared to a wood shaving control mulch. In a recent Oregon study, Nova (1995) noted the possible allelopathic suppression of broccoli (Brassica oleracea var. italica ) by an oat (Avena sativa L., c.v.= 'Monida') cover crop.

Strip-Tillage Systems for Vegetable Production In Western Oregon, a participatory on-farm research project has been focused on developing and evaluating mixtures of cereal and legume cover crops for vegetable production since 1992 (Luna and McGrath, 1995). The most recent focus of this project has been on developing strip-tillage systems for vegetable production which utilize winter annual cover crops as killed mulches. Cover crop mulches have been shown to: conserve habitat for beneficial, predacious ground beetles and spiders, enhancing biological control reduce soil erosion from water and wind increase water infiltration rates and reduce surface water evaporation from soil suppress weeds Although some success has been shown in no-till vegetable production, because of the typically wet and cool soil conditions of the Willamette Valley during the spring planting season, a strip-tillage approach was chosen. In a Virginia study, Morse and Seward (1986) report that a no-till broccoli (Brassica oleracea var.italica ) and cabbage (Brassica oleracea var. capitata ) production system produced yields equal to or greater than conventionally grown broccoli and cabbage. Crops were transplanted into chemically suppressed mulches of hairy vetch, Austrian winter pea, and cereal rye. Results indicated that crops grown in the leguminous mulches yielded higher and grew more vigorously due to increased nitrogen mineralization, however all three cover crop species were conducive to broccoli and cabbage growth.
Figure 3. Strip tillage and cover crop mulch system for vegetable production. Hoyt (1984) reported that in a North Carolina study tomato and broccoli response to legume residues in strip till production systems were consistently greater than conventionally grown plots. Hoyt notes that if the summer cash crop is planted late enough for good spring growth of winter legumes, these residues will also provide soil coverage and ultimately increase the total amount of nitrogen recycled in the system. In our studies, conducted in the Willamette Valley of western Oregon,two types of rotary strip-rototillers, a Northwest Tiller[!]and a Multivator[!], were used to till narrow strips (6-8" wide) in a killed cover crop mulch (see Fig. 1).

	Several experiments have been conducted at both research station and on- farm sites, involving sweet corn, squash, and broccoli. Specific details of these experiments can be obtained from the authors, but yields are summarized in Table 2. In some experiments, strip-till and conventional tillage produced comparable yields, however in some situations the crop yield was reduced in the strip-tillage treatments. In the experiment at the Dickman Farm in 1996, the strips were tilled into wheat stubble left from a 1995 wheat harvest. There was considerable rainfall and cool weather after planting, which could have contributed to seed rot and poor emergence. Nitrogen immobilization by the carbonaceous wheat residue may also have occurred, contributing to poor corn growth. Table 2. Summary of crop yields in strip-till vegetable production systems in Western Oregon, 1993-96.
		Clearly strip-tillage systems show promise for vegetable production, with comparable yields demonstrated in several trials. However, integrating cover crops and strip tillage into a system will require better knowledge of ecological processes occurring within the soil. A new strip tillage machine is being planned that will include a subsoiling shank in front of the tillers to alleviate soil compaction. In most of the experiments reported here, the planting of the vegetable crop occurred immediately after the strips were tilled. A 7-10 day waiting period may be required following cover crop incorporation to allow for soil nitrogen to become more available. More knowledge is needed of insect and pathogen pests attacking the germinating seedlings.

References Cited Allison, J.R. and S.L. Ott. 1987. Economics of using legumes as a nitrogen source in conservation tillage systems. p.145-151. In J.F. Power (ed.). The role of legumes in conservation tillage systems. Soil and Water Conserv. Soc. Amer., Ankeny, IA. Barker, A.V. and P.C. Bhowmik. 1994. Use of crop residues for weed control in vegetable crops. Proc. Northeastern Weed Sci. Soc. 48:92-93. Barnes, J. and A.R. Putnam. 1986. Evidence for allelopathy by residues and aqueous extracts of rye (Secale cereale ). Weed Science. 34:384-390. Barnes, J.P. and A.R. Putnam. 1983. Rye residues contribute weed suppression in no- tillage cropping systems. J. Chem. Ecol. 9:1045-1057. Bugg, R. 1991. Cover crops and control of arthropod pests of agriculture. p. 157-163 In W.L Hargrove (ed.) Cover crops for clean water. Soil and Water Conserv. Soc. Amer. Ankeny, Iowa. Bugg, R. 1992. Using cover crops to manage arthropods on truck farms. HortScience 27:741-744. Clark, M.S., J.M. Luna, N.D. Stone, and R.R. Youngman. 1993. Habitat preferences of generalist predators in reduced-tillage corn. J. of Entomol. Sci. 28:404-416. Crutchfield, D.A., G.A. Wicks, and O.C. Burnside. 1985. Effect of winter wheat (Triticum aestivum ) straw mulch level on weed control. Weed Science. 34:110-114. Datta, B. 1996. Multiple pest suppression with cover crops in strawberry. M.S. Thesis. Oregon State University, Corvallis, OR. Doran, J.W. and M.S. Smith. 1991. Role of cover crops in nitrogen cycling. p. 85-90 In W.L. Hargrove (ed.) Cover crops for clean water. Soil and Water Conserv. Soc. Amer. Ankeny, Iowa. Edwards, J.H., C.W. Wood, D.L. Thurlow, and M.E. Ruf. 1992. Tillage and crop rotation effects on fertility status of a Hapludult soil. Soil Science Soc. Amer. J. 56:1577- 1582. Ess, D.R., D.H. Vaughan, J.M. Luna, and P.G. Sullivan. 1994. Energy and economic savings from the use of legume cover crops in Virginia corn production. Am. J. Alt. Ag. 9:178-185. Frye, W.W. and S.H. Phillips. 1981. How to grow crops with less energy. p. 17-18 In cutting energy costs (The 1980 Yearbook of Agriculture). J.Hayes (ed.) U.S. Dept. of Agric., Washington, D.C. Galloway, H.M., D.R. Griffith, and J.V. Mannering. 1981. Adaptability of various tillage- planting systems to Indiana soils. Coop. Exten. Serv. Bull. AY210. Purdue Univ., West Lafayette, IN. Hinen, J.A. and A.D. Worsham. 1990. Evaluation of rye varieties for weed suppression in no-till corn. p. 22-25. In J.P. Mueller and M.G. Wagger, (eds) Conservation tillage for agriculture in the 1990's. Spec. Bull. 90-1 N.C. State Univ., Raleigh. Hoyt, G.D. 1984. The effect of cover crops on strip-till vegetable and tobacco production. Soil Sci. Soc. of North Carolina Proc. 27: 10-20. Ingham, R. 1993. Report to the Oregon Potato Commission. Dept. of Botany and Plant Pathology, Oregon State University, Corvallis, OR. Jackson, L., L. Wyland, J. Klein, R. Smith, W. Chaney, and S. Koike. 1993. Winter cover crops can decrease soil nitrate, leaching potential. Calif. Agric. 47:12-15. Johnson, G.A. M.S. Defelice, and Z.R. Helsel. 1993. Cover crop management and weed control in corn. Weed Technol. 7:425-430. Lal, R., E. Regnier, D.J. Eckert, W.M. Edwards, and R. Hammond. 1991. Expectations of cover crops for sustainable agriculture. pps. 1-11. In W.L Hargrove (ed.). 1991. Cover crops for clean water. Soil and Water Conservation Soc., Ankeny, IA. Leather, G.R. 1983. Weed control using allelopathic crop plants. J. of Chem. Ecol. 9:983-989.

Luna, J. 1993. Multiple impacts of cover crops in farming systems. Proc. Oregon Hort. Soc. 84:198-201. Luna J.M., and D.G. McGrath. 1996. Evaluation of winter annual cover crops for western Oregon vegetable production systems. Proc. Oregon Hort. Soc. 87:100- 104. Masiunas, J.B., L.A. Weston, and S.C. Weller. 1995. The impact of rye cover crops on weed populations in a tomato cropping system. Weed Science. 43:318-323. Meisinger, J.J., W.L. Hargrove, R.L. Mikkelsen, J.R. Williams, and V.W. Benson. 1991. Effectof cover crops on groundwater quality. Pages 57-68 In W.L. Hargrove (ed.) Cover crops for clean water. Soil and Water Conserv. Soc. Ankeny, Iowa. Morse, R.D. and D.L. Seward. 1986. No-tillage production of broccoli and cabbage. Appl. Agric. Res. 1:96-99. Nova, S. 1995. Impact of cover crops on weed abundance and nitrogen contribution in Broccoli, Brassica oleracea var. italica, production systems in the Maritime Pacific Northwest. M.S. Thesis, Department of Horticuture, Oregon State University, Corvallis, OR. 97 p. Overland, L. 1966. The role of allelopathic substances in the "smother crop" barley. Amer. J. Bot. 53:423-432. Purvis, C.E., R.S. Jessop, and J.V. Lovett. 1985. Selective regulation of germination and growth of annual weeds by crop residues. Weed Res. 25:415-421. Putnam, A.R. 1986. Allelopathy: Can it be managed to benefit Horticulture? HortScience. 21:411-413. Putnam, A.R. 1990. Vegetable weed control with minimal herbicide inputs. HortScience 25:165-169. Putnam, A.R. and J. Defrank. 1983. Use of phytotoxic plant residues of selective weed control. Crop Prot. 2:173-181. Putnam, A.R., J. Defrank, and J.P. Barnes. 1983. Exploitation of allelopathy for weed control in annual and perennial cropping systems. J. of Chem. Ecol. 9:1001-1010. Reicosky, D.C. and M.J. Lindstrom. 1993. Fall tillage method: Effect of short-term carbon dioxide flux from soil. Agron. J. 85:1237-1243. Shennan, C. 1992. Cover crops, nitrogen cycling, and soil properties in semi-irrigated vegetable production systems. HortScience 27:749-754. Smeda, R.J., and A.R. Putnam. 1988. Cover crop suppression of weeds and influence on strawberry yields. HortScience 23:132-134. Teasdale, J.R. 1993. Interaction of light, soil moisture, and temperature with weed suppression by hairy vetch residue. Weed Sci. 41:46-51. Teasdale, J.R. and C. Mohler. 1992. Weed suppression by residue from hairy vetch and rye cover crops. Proc. First Int. Weed Control Congress. 2:516-518. Teasdale, J.R., C.E. Beste, and W.E. Potts. 1991. Response of weeds to tillage and cover crop. Weed Sci. 39:195-199. Wyland, L.J., L.E. Jackson, and K.F. Schulbach. 1995. Soil-plant nitrogen dynamics following incorporation of a mature rye cover crop in a lettuce production system. J. of Agric. Sci. 124:17-25. Zimdahl, R.1993. Fundamentals of weed science. Academic Press, Inc., New York. 450 pps.