Crop Residue and Plant Health: Research Overview and Implications for No-Till

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Reprinted from 1999 Columbia Basin Agricultural Research Annual Report. Spec. Rpt. 999, pp. 81-84, 1999 Oregon State University in cooperation with USDA-Agricultural Research Service, Pendleton, OR

CROP RESIDUE AND PLANT HEALTH: RESEARCH OVERVIEW AND IMPLICATIONS FOR NO-TILL

Stewart Wuest and Katherine Skirvin

Introduction eliminated altogether. The amount of sand, clay, and organic matter in a soil can Over the past four decades, influence the toxicity of residues (Patrick researchers have examined the effects of and Toussoun, 1965; Purvis and Jones, crop residue on the growth of plants. 1990). Results have been mixed and sometimes controversial. This article summarizes those Growth impairments relate to findings and draws conclusions for our local germination, emergence, growth rates, or cropping systems. tillering. Often the responses are very specific, for example, no effect on Residues have been shown to germination but a definite effect on shoot damage wheat and other crops in both growth (Mason-Sedun, 1986). A recently laboratory and greenhouse studies (Elliot et completed greenhouse study reported that al., 1978; Patrick and Toussoun, 1965). wheat seedling height was reduced by 20 Toxic effects can be simulated by simple percent 20 d after planting when 3-mo-old water extractions and also by more elaborate wheat residues were placed about an inch incubations and extractions of residue below the seed (Stewart Wuest, unpublished (Cochran et al.,1977; Kimber 1973; Lodhi data, 1998) (Fig. 1). There was also a delay et al., 1987; Martin et al., 1990; Mason- in the developmental rate of the seedlings Sedun et al., 1986). Toxic substances, from whose roots grew into fresh wheat residue. simple acetic acid (vinegar) to hormones, sometimes originate with microbial activity The effects of residue on plant health but can also be present under sterile are very complex. Dozens of substances conditions (Kimber, 1967; Purvis, 1990). have been extracted from fresh residues and This discussion will not distinguish between shown to inhibit growth of plants in the chemical toxic effects of residue and those laboratory. These substances can either of pathogens stimulated by the presence of stimulate or inhibit microbial growth in the residue. soil, including microbes that are wheat pathogens. In the laboratory, residues have Only recent, unweathered residues also been shown to make roots vulnerable to produce a toxic effect. Researchers have root infection and affect pathogen activity found that when kept dry, residue loses its (Patrick and Toussoun, 1965). phytotoxic potential in a year or less (Kimber 1967; Mason-Sedun et al., 1986; In field studies it becomes more Purvis and Jones, 1990). When fresh difficult to demonstrate that buried residues residues become moist and start to decay, reduce crop vigor or crop yield, but this is the length of time residue has negative not surprising given the complex nature of effects on plant growth ranges from a few the interactions among residues, soil, weeks to several months. After this initial microbes, and plants. Residue from period of negative impact, some residues different cultivars of wheat as well as have shown a yield-enhancing effect. If a differences in the age of the residue, the layer of soil separates residue from plants, moisture conditions while it aged, and soil the toxic effects are usually diminished or type produce varying amounts of toxicity. 81 There are other crop-health problems that possible to avoid problems with germination may be caused by the presence of residue in and prevent growing roots from the seed bed: disease, light interference, encountering toxins. difficulty in seed placement, and immobilization of nutrients (Elliott et al., Fresh residues left on the surface of 1981; Wilkins et al., 1988). Understanding the soil remain a concern. Should these be why certain plants in a crop stand are less pushed away from the seed row, or is an vigorous or more prone to diseases becomes inch or so of soil above the seed enough to very challenging. absorb and detoxify any leachates from the wet residues above the seed? There may be Given the number of questions about other reasons to clear residue from the seed the role of residue in plant health, it might row when planting fall wheat. Research at seem difficult to learn how to manage Pendleton has demonstrated that standing residues in a way that both protects soil stubble can reduce light penetration into the productivity and maximizes crop seed row enough to reduce seedling vigor production. There are, however, some and tillering of winter wheat (Wilkins et al., useful conclusions we can draw from what 1988). Whether this results in a reduction in we know about the potential toxicity of yield will depend on circumstances later in residues. the growing season.

Conclusions The risks and benefits of not disturbing standing stubble and residue on Residue toxicity is only likely to the soil surface need to be weighed. In cause problems in fall-seeded crops because many areas of the United States, standing this is when we have large quantities of stubble catches blowing snow and makes an unweathered residues. In the Columbia important contribution to soil water. This Basin there is little moisture to start may not be an important factor in much of decomposition of residues between summer the Pacific Northwest. On the other hand, harvest and fall planting. Annual spring ultra-low disturbance seeding systems have cropping systems should not encounter been credited with a reduction in weed much, if any, phytotoxicity of residue populations. If low disturbance systems that because the residue has been well leached help control weed populations can be and partially decomposed. Disease problems developed for the Pacific Northwest, the found in annual winter wheat cropping weed control benefits might outweigh the systems may be due to toxins, as well as shading or phytotoxic effects of surface pathogens found in unweathered residues. residue over the seed row. Standing stubble These residues are often plowed under the may also be part of a profitable solution in surface where they are intercepted by the areas where blowing soil degrades soil roots. productivity and damages seedling wheat.

There are both advantages and Loss of soil moisture by evaporation disadvantages to fall no-till systems is another factor whose importance will vary regarding the potential phytotoxic properties in different areas. In the no-till spring of fresh residues. No-till presents the cropping systems in Alberta, Canada, heavy, opportunity to plant into ground with no wet, cold soils are a major problem. In buried residue. As long as seeding contrast, here in the Pacific Northwest, equipment does not bury residue and keeps leaving residue near the seed row to reduce it from contacting the seed, it should be

82 evaporation is an advantage when we plant Lodhi, M.A.K., R. Bilal, and K.A. Malik. fall crops into our light, dry soils. 1987. Allelopathy in agroecosystems: wheat phytotoxicity and its possible roles in crop For a cropping system as a whole, rotation. J of Chemical Ecology 13:1881– crop residue benefits soil productivity and 1891. erosion control; we would be shortsighted to view it only as a liability. Our knowledge of Martin, V.L., E.L. McCoy, and W.A. Dick. the potential toxic effects of residue should 1990. Allelopathy of crop residues allow us to maximize the benefits of surface influences corn seed germination and early residue cover produced in no-till and avoid growth. Agron J 82:555–560. the hazards to plant health in fall-seeded systems. Mason-Sedun, W., R.S. Jessop, and J.V. Lovett. 1986. Differential phytotoxicity References among species and cultivars of the genus Brassica to wheat. I. Laboratory and field Cochran, V.L., L.F. Elliott, and R.I. screening of species. Plant Soil 93:3–16. Papendick. 1977. The production of phytotoxins from surface crop residues. Soil Patrick, Z.A., and T.A. Toussoun. 1965. Sci. Soc. Am. J. 41:903–908. Plant residues and organic amendments in relation to biological control. p. 440–459. Elliott, L.F., V.L. Cochran, and R.I. In: K.F. Baker and C.W. Snyder (eds) Papendick. 1981. Wheat residue and Ecology of soil-borne pathogens. U C Press, nitrogen placement effects on wheat growth Berkeley, CA. in the greenhouse. Soil Science 131:48–52. Purvis, C.E. 1990. Differential response of Elliott, L.F., T.M. McCalla, and A. Waiss, wheat to retained crop stubbles. I. Effect of Jr. 1978. Phytotoxicity associated with stubble type and degree of decomposition. residue management. p. 131–146. In: W.R. Aust J Agric Res 41:225–242. Oschwald (ed) Crop residue management systems. American Society of Agronomy, Purvis, C.E., and G.P.D. Jones. 1990. Madison WI. Differential response of wheat to retained crop stubbles. II. Other factors influencing Kimber, R.W.L. 1967. Phytotoxicity from allelopathic potential; intraspecific variation, plant residues. I. The influence of rotted soil type and stubble quantity. Aust J Agric wheat straw on seedling growth. Aust J Res 41:243–251. Agric Res 18:361–374. Wilkins, D.E., B.L. Klepper, and P.E. Kimber, R.W.L. 1973. Phytotoxicity from Rasmussen. 1988. Management of grain plant residues. II. The effect of time of stubble for conservation-tillage systems. rotting of straw from some grasses and Soil and Tillage Research 12:25–35. legumes on the growth of wheat seedlings. Plant Soil 38:347–361.

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5 Plastic residue 1 inch below seed

3 Wheat residue 1 inch below seed 2

1 Seedling height(cm)

0 5 10 15 20 25 Days after planting

Figure 1. Height of winter wheat (Madsen) seedlings with roots growing through fresh wheat or plastic residues placed 1 in. below the seed. Pendleton, OR 1998.