Tillage and Allelopathic Aspects of the CornâSoybean Rotation Effect

Chapter 14

Tillage and Allelopathic Aspects of the Corn—Soybean Rotation Effect

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I. C. Anderson and R. M . Cruse Department of Agronomy, Iowa State University, Agronomy Hall, Ames, IA 50011

Growth of young corn plants is reduced if their roots grow through a band of corn residue, but if the band is above the seed there is little toxicity. Water extract of residue or of decomposing residue in soil inhibit growth of corn seedlings, but if the extracts are filtered through a column of soil they have little toxicity. Under field conditions these residues have little effect on corn growth. The living roots of corn produce other types of water soluble chemicals which are more persistent in the soil. They are produced during the summer and decompose the following spring. Soybean growing in the field produces three chloroform soluble chemicals that stimulate corn seedling growth. Evidence suggests that corn leaves something in the soil that reduces grain yield of following corn and that soybean leaves something in the soil, in addition to avaiilable N, that increases yield of corn. Crop growth and yield is determined by numerous environmental and genetic factors. Many of these factors interact, resulting in a very complex biological system. The biological complexity of this system is exemplified by crop growth and production response to crop or plant sequences. Many studies have reported the effect of previously grown crop plants on crop growth and yield (7). Others have addressed weed effects on crop yield, particularly as the weeds may influence crop performance beyond that of strict competition for resources (2). The impact of the previous plant species on plant growth is well documented, yet the factor(s) causing the response often remains unknown. Crops grown in rotation often result in higher yields than crops grown in monoculture (3). Even with high fertility rates, the yield response favors the rotation. This has been termed the rotation effect. Studies have attempted to identify nonplant factors such as soil physical conditions (4), diseases (5), insects

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14. ANDERSON & CRUSE

Tillage & Allelopathic Aspects of Rotation Effect

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(6), and fertility (7) as causal agents. Generally, these factors fail to adequately explain the production differences between monoculture and rotations. The rotation effect, while partially caused by nonplant factors, is related to biological and/or chemical interactions between plant species. This biological interaction, allelopathy, may have significant implications with regards to crop management practices. In the United States, conservation tillage systems are gaining popularity. On many highly erodible soils, continuous corn with no-till management is the only continuous row crop production system allowed due to soil conservation requirements. Continuous corn has repeatedly resulted in lower yields than corn in rotation, but why this occurs is largely unknown. Allelopathic interactions from the previous year's corn crop is highly suspected. Many concerns have been expressed about the allelopathic impact of corn residue on the succeeding corn crop with conservation tillage systems. Tillage and Allelopathic Relationships Various corn residue management factors may affect allelopathic responses of the new corn crop. Residue age, or previous weathering history, and placement of the residue with respect to the seed seem quite important. In a greenhouse study, placing fresh (unweathered) corn residues at the corn planting depth resulted in dramatic (45%) root growth reductions compared to no residue application or residue placement above the seed (8). Placement of fresh residue 5 cm below the seed likewise resulted in significant root growth reductions compared to placement above the seed. In this study soil temperature and water content were common for all treatments. Dry shoot weights at 49 days after planting were similarly affected. In this same study, residue weathering, i.e., comparing effects of residue which remained on the soil surface over winter to that which was collected directly after harvest, was also significant. The greatest differences between residue effects occurred for those residues placed at or below the seed. Unweathered residue resulted in 69% of the root growth which occurred with weathered residue. Weathered residue resulted in 92% of the root growth which occurred without residue additions. No statistically significant differences between residue weathering effects were observed when residues were placed above the seed. This study identifies three potentially important management considerations: 1) corn residue can have significant allelopathic activity on corn; 2) weathering residues seem to reduce their allelopathic activity; and 3) residues placed above the seed planting depth have less allelopathic activity than those placed at or slightly below the planted seed. Tillage systems which leave residues on or near the soil surface, from the allelopathic perspective, seem to be more favored than those which incorporate residues. Some allelochemicals are water soluble. Thus surface placement of residues, as occurs with no-till, could result in rainfall "extraction" from these residues and movement with water through soil to the planted seed position. Various soilresidue extract interactions could occur, and thus influence the ultimate effect of this extract on corn seedlings. Yakle and Cruse (9) tested this "hypothetical"

In Allelopathy; Dakshini, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.


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ALLELOPATHY: ORGANISMS, PROCESSES, AND APPLICATIONS

situation in a laboratory study in which corn residues were incubated for 0, 15, or 30 days in soil. The residue/soil mixture was then extracted with tap water and either used to germinate corn seeds (for a 7 day period) or leached through 5 cm columns of soil before being used to germinate corn seeds. After 7 days, dry root and shoot weight of the seedlings were determined. Corn residue extract, soil extract, and tap water were compared. Generally, residue incubation in soil reduced the alleochemical activity (as determined by seedling growth), with activity inversely related to length of incubation time. Also, leaching the extract through soil reduced the effect of the extract on corn seedling root weight and shoot weight. These treatments did not have a significant effect on percent germination. Garcia and Anderson (10) sampled soils during the growing season from a field of continuous corn with three tillage practices consisting of no-tillage, spring disc, and fall moldboard plowing; depths of sampling were 5, 10, and 20 cm, respectively. These are approximate depths that tillages incorporated the residue. The control consisted of a fallow soil stored at 5°C. For water extraction, each soil sample was placed in a bottomless 0.5 L bottle. Drainage from the soil passed through an XAD-4 resin ion exchange column and was blown back to the soil surface for continuoous aerobic extraction for two days. Chemicals removed from the resin were used to wet germination paper for either corn or cress seed growth tests. At the May 1 soil sampling (Table 1) plots receiving all three tillage treatments contained chemicals that reduced seedling growth as compared to extracts of fallow soil. Table 1.

Growth of corn seedlings as affected by water extracts of soil samples collected during the growing season of second year corn with three tillage treatments (growth as a percentage of extracts from a fallow soil)

Tillage Treatment

Soils sampled on around the first day of each month Oct May Sept Aug June July

No-till Disc Plow

76 88 80

93 100 89

124 112 103

103 97 101

89 74 75

84 88 78

Toxicity also was present at the June 1 sampling, but by July the extracts were stimulatory as is common in decomposing residues (11). During the August and September samplings toxicity reappeared in the soil. The two types of bioassay gave similar results. The toxicity developing after July indicates that roots of living plants, and not the dead crop residue, produce the substances in the soil that were inhibitory to corn and cress seedling growth. Soil samples to a depth of 20 cm had as much or more inhibitory effect as soils from the top 5 cm which also indicates root involvement. The three soil tillage treatments had little effect on the disappearance of toxicity, the appearance of the stimulatory amount of activity, and the reappearance of toxicity later in the summer. In related studies, toxicity





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developed in soil of corn fields with the soil covered by plastic sheets during the growing season. These studies suggest the following. Leaching of allelochemicals from surface residue through soil is possible, although not likely to occur in sufficient quantities to cause early germination-growth problems. Chemicals leached from the residue into the soil more than a few days prior to corn planting will likely undergo transformation or breakdown processes in the soil reducing their inhibitory nature. Weathering of residues over winter will reduce allelopathic impacts of residue leachate in the spring. The greatest potential for allelopathy from corn residues seem to be from incorporation of corn residue shortly before corn planting. No-till management again seems favorable with regard to managing allelopathy from corn residues. The impact that corn residue allelochemicals has on corn yield has not yet been convincingly determined. Allelopathic Aspects of the Rotation Effect Throughout the middle western corn and soybean belt of the United States, corn grown following soybean yields greater than corn following corn with nitrogen fertilizer adequate for maximum yield. Results of a seven year study in Illinois showed a 17% greater yield of corn following soybean than corn following corn (12). The results in Table 2, from Schrader and Voss (13) in Iowa, illustrate the effects of soybean or meadow on corn yield vs. corn following corn. The magnitude of the rotation effect varies from year to year. During a droughthy and hot season of 1988 many farmers in southeastern Iowa reported corn after soybean yielded twice that of corn after corn. In contrast, corn after corn yielded greater than after soybean in 1989 due to corn essentially dying in late August of 1988 and thereby not using late August rainfall, whereas soybean recovered and used this moisture. The 1989 season also was dry and the extra stored soil moisture under corn was beneficial. In the deep soils of the midwest, crops of corn and soybean extract similar amounts of water. Table 2 indicates that at the highest rate of N corn partially remains influenced by the previous legume for two years.

1

Table 2.

Grain yield of corn (tonnes ha ) in monoculture and in rotations with soybean or Corn-Corn-Oat-Meadow from a long term study in Iowa

N fert. kg ha"

Continuous corn

Cornsoybean

1st year CCOM

2nd year CCOM

0 54 108 162

2.45 4.60 5.65 5.90

5.20 5.90 6.40 6.50

6.60 6.40 6.60 6.45

4.75 5.75 6.00 6.20

1



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It is difficult to determine if the rotation effect is due to toxicity left by the corn crop or if the soybean crop leaves a stimulatory effect. One method of determining if corn leaves something inhibitory to the following corn crop is to use continuous corn and determine if some hybrids leave a greater inhibitor effect than do other hybrids. Hicks and Peterson (14) in Minnesota, during a two year study, grew five hybrids in rotation and reported that hybrids varied slightly in how much inhibitory effect they leave. Dave Sundberg and I.C. Anderson (personal communication) in Iowa, grew six hybrids in all 36 possible combinations as previous and current hybrids during a four year study. Some of the results are reported in Table 3. A l l hybrids yielded less if grown following corn. All corn hybrids presumably left toxicity in the soil but Hybrid 4 left the greatest amount. Farmers frequently report that growing the same hybrid after itself appears to have a negative effect. In our study there was not a greater negative effect of a hybrid following itself. Note the magnitude of the rotation effect when Hybrid 3 followed soybeans. Table 3.

Grain yields of six corn hybrids grown with each of the six as previous corn crop (tonnes ha" ) 1

Previous hybrid 1 2 3 4 5 6 Soybean

Current Hybrid 4 5

1

2

3

7.5 8.3 8.3 7.2 8.5 7.5

8.4 8.7 8.3 7.7 8.5 9.0

-

-

8.9 8.4 8.9 8.3 8.7 8.7 9.7

6

Mean

9.6 9.7 9.2 9.0 9.4 9.6

8.1 8.6 8.3 7.6 8.5 8.5

9.1 9.0 9.2 9.0 8.8 8.7

8.6 8.8 8.7 8.1 8.7 8.7

-

-

-

-

Sarobol (15) at Iowa studied the effects of varying maturity and date of planting of both previous soybean and previous corn on the yield of the following corn crop (Table 4). In 1983 and 1984 five corn treatments were established: a very early hybrid planted May 15, an adapted hybrid planted May 15, June 30 and July 30, and a very late hybrid planted May 15. The five soybean treatments were similar in principle to that of corn. A control treatment of oat also was used. After the crops in each corn and soybean treatment matured or were killed by a frost, the grain was harvested and the crop residues were either left on the ground or removed. At the end of the fall the field was moldboard plowed to prevent any effects in the spring of variable surface residues on soil temperature and soil drying. In the spring the whole field was planted to a mid-season hybrid. Nitrogen fertilizer at a rate of 225 kg/ha' was applied before planting and an extra 55 kg/ha" applied before the last cultivation. The grain yield of corn following corn was less than corn following soybean. For corn following corn the least yield was from the corn following the very late hybrid. The next lowest yield was corn 1

1




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following the adapted hybrid planted May 15. Both of these treatments produced considerably more growth than those of the other three previous corn treatments. The least amounts of corn growth in 1983 and 1984 were by the 30 July planted adapted hybrid and 15 May planted early hybrid which matured about 5 weeks earlier than the adapted hybrid planted 15 May. The yield of corn following soybean was considerably greater than corn following corn, although the variation among previous soybean treatments was less

Table 4.

Effect of previous crop, its maturity, and date of planting on grain yield of corn grown the following year

Previous Crop (1983 and 1984) Type Corn Corn Corn Corn Corn Oat Soybean Soybean Soybean Soybean Soybean

Maturity Early Adapted Adapted Adapted Late

Planted 15 May 15 May 30 June 30 July 15 May

-

-

Early Adapted Adapted Adapted Late

15 May 15 May 30 June 30 July 15 May

1

Grain Yield (tonnes ha ) 1984 9.02 8.10 8.94 8.77 7.22 8.59 9.55 9.71 9.23 9.14 9.47

1985 7.71 7.70 7.63 8.61 7.42 8.07 8.40 9.59 8.65 9.29 8.69

Mean 8.37 7.90 8.29 8.69 7.32 8.33 8.98 9.65 8.94 9.22 9.08

than that with the previous corn treatments. The greatest yield of corn was following the adapted soybean cultivar planted 15 May and one of the least yields following the early soybean cultivar. The rotation effect between corn following the adapted soybean cultivar planted 15 May and the adapted corn hybrid planted 15 May was 21%. About 25% of this effects was an inhibitory effect of corn and 75 % a stimulatory effect due to soybean compared with oat. The mean effect of either removing or leaving previous crop residue had no effect on subsequent corn yield. Other studies (Crookson, 1982) showed similar results. These results agree with those reported in Table 1 by Garcia and Anderson (10) who proposed that allelochemicals from corn were being released by roots of the living corn plants into the soil. Neither the possible inhibitory effect of previous corn crop or possible stimulatory effect of the previous soybean crop (rotation effect) were due to the previous crop residues. Kalantari (17) and Nelson (18) extracted soil from soybean fields after harvest with chloroform to test for stimulatory chemicals in the soil. The chloroform extract was taken to dryness, dissolved in isopropanol, and applied to a D E A E sephadex column and eluted with isopropanol. Fractions were collected and bioassayed with the corn seedling assay (Kalantari), and by a Lemna minor assay



190


(Nelson). The results of a typical corn seedling assay is presented in Table 5. Stimulatory chemicals were found in Fraction 2, a slight inhibitory effect in Fraction 4, and a stimulatory peak in Fraction 12. The top of the column retained triacontanol that was stimulatory in the corn seedling assay. We made no attempt to identify the other two stimulatory chemicals. Chloroform extract of soybean straw showed activity in Fraction 2 but not in Fraction 12. Incubation of soybean straw with fallow soil for up to three weeks did not produce any activity in Fraction 12. Reis and Houtz (19) and Einhellig (20) added alfalfa meal to soil growing corn and other crops and reported a greater yield where alfalfa meal had been added than could be obtained with the highest rates of nitrogen fertilizer. They suggested that the response was due to triacontanol which could be isolated from alfalfa meal. Triacontanol, under certain prescribed conditions, stimulates plant growth.

Table 5. Corn seedling growth with column fractionated chloroform extracts of soybean soil (growth as a percentage of a water control) Source of sample 2 Soybean field Soybean residue Fallow soil

123 108 95

Column fraction 12 4 102 89 97

148 109 112

top 139

Conclusions 1.

2.

3.

4.

5.

Crop residue on soil surfaces slows the warming and drying of soil in the spring and that may have a negative effect on crop yield in cool temperate regions. If seedling roots of corn grow directly into a soil area with concentrated corn residue, growth of corn plants are decreased. Incorporation of corn stover by spring tillage could leave spots of concentrated residue in the soil. Water extracts of corn residue are toxic to corn seedling growth. Residue which has been weathered in the field had less effect. Water extracts of corn residue incorporated and incubated in soil were inhibitory to seedling growth. If these extracts, and those of residue itself were passed through a soil column toxicity was decreased. Therefore, chemicals released from corn residue in the soil have only a small effect on corn seedling growth. The least toxic effect of corn residue would be if no-tillage were used. Evidence indicates that the living roots of corn plants begin producing chemicals in the soil at about the anthesis stage of growth. These chemicals, or effects, accumulate and remain in the soil through the winter and are





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degraded during the following spring. The degraded products appear to be slightly stimulatory to corn seedling growth. The chemicals from the living plant root are relatively long lived in the soil and probably are different from those released from corn residue. 6. The toxicity, or inhibitory effect, left in the soil by a previous crop of corn decreases the yield of corn the following year compared to following a crop of oat. Corn hybrids vary in the amount of toxicity left. Very early maturing hybrids have less toxicity to corn the following year than do adapted, or very late maturing hybrids. 7. The effects of either removing corn residue or plowing it under after harvest in the fall have similar effect on the yield of the following corn crop; this again indicates that corn stover residue does not contribute to the cornsoybean rotation effect. 8. Compared with a previous crop of oat, soybean leaves a substance in the soil that increases grain yield of corn. Soybean crop residue, either removed after harvest or left in the soil, does not effect the yield of the following corn crop. Adding soybean residue to corn fields in the fall does not overcome the toxicity left in the soil by corn residues. 9. Chloroform extracts of soil from soybean fields, after harvest in the fall, contain chemicals that stimulate the growth of corn seedlings. One of these chemicals is triacontanol. Triacontanol may contribute to, but probably has no major role for, the stimulatory aspect of soybeans in the rotation with corn. 10. The total rotation effect frequently is a 10-20% increase in corn yield following soybeans compared to corn following corn. It appears that both the toxicity left in the soil by corn and the stimulatory effect left by soybean contributes to the rotation effect. If our studies about 25% of the rotation effect was due to reduction by previous corn and 75 % due to an increase from soybean. Literature Cited 1. Bullock, D. G.Crit. Rev. in Plant Sci. 1992, 11, 309-326. 2. Aldrich, R. J. In Allelochemicals: Role in Agriculture, Forestry, and Ecology. G . R. Waller, Ed. ACS Symposium Series 330; American Chemical Society: Washington, D C . 1987, pp. 300-312. 3. Russelle, M . P.; Hesterman, O. B.; Schaeffer, C . C . ; Heichel, G . H . In The Role of Legumes in Conservation Tillage Systems. J. J. Power, Ed. Soil Conservation Society. Washington, D C . 1984. 4. Harris, R. F . ; Chesters, G . ; Allen, O. N.Adv. Agron. 1986, 18, 107. 5. Curl, E . A.Bot. Rev. 1963, 29, 413. 6. Ware, G . W. Complete Guide to Pest Control with and without Chemicals. Thomson: Fresno, C A . 1980. 7. Kurtz, L . T . ; Boone, L . V . ; Peck, T. R.; Hoeft, R. G. In Nitrogen in Crop Production. R. D. Hauck, Ed. American Society of Agronomy. Washington, DC. 1984. 8. Yakle, G. A . ; Cruse, R. M.Canadian J. of Plant Sci. 1983, 62, 871-877.



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9. Yakle, G . A . ; Cruse, R. M.Soil Sci. Soc. Am. J. 1984, 48, 1143-1146. 10. Garcia, A . G . ; Anderson, I. C.Philipp. J. Crop Sci. 1984, 9, 61-64. 11. Einhellig, F. A . ; Leather, G . R.; Hobbs, L . L.J. Chem. Ecol. 1985, 11, 6572. 12. Odell, R. T . ; Walker, W. M.; Boone, L . V . ; Oldham, M . G . The Morrow Plots - A Century of Learning, Illinois Agric. Exp. Stn. Bull. 775. 1982. 13. Shrader, W. D; Voss, R. O. Crops and Soils, 1980, 32, 8-11. 14. Hicks, D. R.; Peterson, R. H.Annual Corn and Sorghum Res. Conf. 1981, 36, 89-93. 15. Sarobol, E . Ph.D. Dissertation, Iowa State University, Ames, IA, 1986. 16. Crookson, R. K. Plant Growth Regulatory Soc. Proc., 1982. 9, 137-143. 17. Kalantari, I. Ph.D. Dissertation, Iowa State University, Ames, IA, 1981. 18. Nelson, L . S . M . S . Thesis, Iowa State University, Ames, IA, 1985. 19. Reis, S.; Houtz, R.Hortic. Sci. 1983, 18, 654-662. 20. Einhellig, F . A . In Bioregulation for Pest Control, P. A . Heldin, Ed. ACS Symposium Series 276, American Chemical Society, Washington, D C . 1985, 109-130. RECEIVED July 29, 1994


Tillage and Allelopathic Aspects of the CornâSoybean Rotation Effect

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Tillage and Allelopathic Aspects of the CornâSoybean Rotation Effect