Weed population dynamics in wheat as affected by ...

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Crop Protection 24 (2005) 864–869 www.elsevier.com/locate/cropro

Weed population dynamics in wheat as affected by Astragalus sinicus L. (Chinese milk vetch) under reduced tillage K.B.D.P. Samarajeewaa, Takatsugu Horiuchib,, Shinya Obab a

Faculty of Agriculture, Sabaragamuwa University of Sri Lanka, P.O. Box 02, Belihul-oya, Sri Lanka Laboratory of Crop Production, Faculty of Applied Biological Sciences, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan

b

Received 22 November 2004; received in revised form 20 December 2004; accepted 7 January 2005

Abstract An understanding of the weed population dynamics under reduced tillage systems is essential in order to achieve successful weed control without using herbicides under a sustainable soil management system. A switch from conventional to conservational tillage alters the weed species composition and temporal pattern of emergence of weeds. A two-season experiment was conducted in 2000/ 2001 and 2001/2002 winters to determine the effect of Astragalus sinicus L. as a cover crop in wheat under minimum tillage (MT) and no-tillage (NT) as compared to conventional tillage (CT) on a clay loam soil. In both seasons, total weed biomass was greater in the no-tillage system and the continuous cultivation significantly reduced all the major weed species. Row seeding of A. sinicus resulted in lower weed biomass than broadcasting. Repeated cultivation affected wheat until the heading stage irrespective of the tillage or presence of the cover crop but the effect on ripening stage was not significant. Although, NT resulted in the lowest yield under the given conditions, successive cultivation of wheat with the incorporation of the cover crop did not affect the wheat yield significantly. An increase in the prevalence of weeds was observed as the degree of tillage was reduced but successive cultivation reduced the overall biomass significantly. The results showed the significance of a row seeded cover crop with wheat under MT in order to achieve comparable yield with CT. r 2005 Elsevier Ltd. All rights reserved. Keywords: Cover crop; Weed control; Minimum tillage; No-tillage

1. Introduction Use of conservation management production (e.g. reduced tillage, cover crops) systems has become more popular in recent years due to economics of crop production and regulatory mandates concerning environmental issues (Locke et al., 2002). This economically and ecologically sound management system has been gaining popularity, in many areas of the world in recent years (Swanton and Weise, 1991). A great deal of evidence has shown that conservational tillage systems can be more productive than conventional tillage

Corresponding author. Tel./fax: +81 58 293 2846.

E-mail address: horifi[email protected] (T. Horiuchi). 0261-2194/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2005.01.018

systems as a result of improved soil quality and water use efficiency (Halford et al., 2001). Weed control is often identified as the limiting factor in the adoption of conservational tillage crop production systems (Koskinen and McWhorter, 1986). However, the removal of tillage from crop production not only eliminates an important method of weed control, but also alters the environment where weeds and herbicides interact (Buhler, 1992). Systems with little of no tillage may increase the potential for the growth of certain weed species due to weed seed accumulation at or near the soil surface (Wruckle and Arnold, 1985). The soil tillage system affects weed flora. Changes in tillage have a significant effect on weed control and the weed population (Bilalis et al., 2003). A switch from conventional to conservational tillage systems will alter

ARTICLE IN PRESS K.B.D.P. Samarajeewa et al. / Crop Protection 24 (2005) 864–869

the species composition, total amount and temporal pattern of emergence of weeds, and thus result in a modified weed-crop relationship that is not normally observed in conventional tillage systems (Buhler, 1995). Several studies have documented that conservational tillage increased the density of perennial weeds, some annual grasses, and volunteer crops (Derksen et al., 1993), but, reported that changes in weed communities were influenced more by location and year than by tillage systems. They suggested weed community changes were fluctuated and were dependent on environment, location, and timing of management practices (Swanton et al., 1999). The composition of weed flora can be influenced by N management (Banks et al., 1976) but other studies concluded that factors other than N rate may have a greater influence on the composition of weed flora (Anderson and Milberg, 1996). These factors may include crop rotation impact on weed flora (Swanton and Weise, 1991). Several studies have examined the effect of crop rotation on weed flora (Anderson and Milberg, 1996). Very few studies, however, have considered the effect of cover crops on the composition of the weed flora under reduced tillage systems. Cover crops may suppress weeds by competing for water, light, and nutrients (Barnes and Putnam, 1983), and some cover crop species have demonstrated allelopathic properties that inhibit weed establishment and growth (Leather, 1983). The influence of cover crops on weed populations however is often inconsistent (Moore et al., 1994). To develop an effective integrated weed management system under reduced tillage systems, it is important to determine the population dynamics of weeds in the presence of cover crops. Astragalus sinicus L. (Chinese milk vetch or renge-sou), a winter-growing green manure legume, has been widely used in rice fields to fertilize the soil in Japan and China since the plant forms a symbiotic relationship with soil bacteria, forms

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root nodules and fixes nitrogen in the nodules (Murooka et al., 1993). The objective of this study was to determine the influence of tillage systems and the presence of an A. sinicus cover crop on the population dynamics of annual weeds and yield in wheat grown continuously on a clay loam soil.

2. Materials and methods Field experiments were conducted during winters 2000/2001 and 2001/2002 at the experimental field of the Faculty of Applied Biological Sciences, Gifu University on a clay loam soil (pH; 5.95, Total N; 0.175%, Total C; 1.994%, available P; 20.13 mg 100 g–1, available K; 9.87 mg 100 g–1, available Ca; 3.1 mg 100 g–1, available Mg; 2.1 mg 100 g–1). Before this experiment, the plots were under conventional tillage rice for 5 years followed by one-year notillage soybean. Climatic data during the two previous cropping seasons are shown in Fig. 1. Treatments in the successive years included three tillage systems (conventional, minimum and no-tillage) with two seeding methods of the cover crop (Table 1). Conventional tillage (CT) plots were mouldboard plowed to a depth of 15 cm before sowing. In the minimum tilled plots (MT),

Table 1 Summary of treatments Treatment

Tillage

Cover crop establishment

Tl T2 T3 T4 T5

Conventional Minimum Minimum No No

No cover crop Broadcasting Row seeding Broadcasting Row seeding

Fig. 1. Monthly mean air temperatures (vertical bars) and rainfall (m–m) during the growing seasons at Gifu, Japan.

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the blade was adjusted to disturb only the top 5 cm layer and in the no-till plots soil disturbance was limited to a 4 cm wide band created by the planting operation. Wheat (Triticum aestivum L.) var. Norin 61gou was row seeded on November 13th and 15th in the consecutive seasons at the rate of 120 kg ha–1 with 20 cm row spacing and Chinese milk vetch var. Gifu selection was seeded at the rate of 40 kg ha–1 either by broadcasting or row seeding (20 cm row spacing) in the reduced tillage plots. The experimental design was a randomized complete block design with three replicates. Plot size was 7 5 m2. The seeding depth of wheat was 1.5 cm on average. NPK (8:8:8) fertilizer was applied at the rate of 30 kg ha–1 before planting each year for all plots and NPK (13:13:13) was broadcast on to all plots at the rate of 150 kg ha–1 at stem erect growth stage. Before establishing the experiments, soil samples (0–15 cm) were randomly collected, mixed, air-dried and crushed to pass a 2 mm sieve. Representative samples were taken for laboratory analysis. The samples were analyzed for pH (1:2 soil:water ratio), total N and total C using CN analyzer (Sumigraph model NC-800, Shimadzu Corporation, Japan). Available K, Ca and Mg were analyzed by Polarized Zeeman Atomic Absorption spectrophotometer (Hitachi Corporation, Japan). Available P was determined by colorimetry according to Murphy and Riley (1962). Chlorophyll content was determined by Chlorophyll meter model SPAD-502 (Minolta Co., Ltd., Japan). Three SPAD meter readings were taken on each fully expanded leaf (inter-venal areas) at monthly intervals. Mean plant length was measured at monthly intervals. Four 0.25 m2 quadrats were randomly placed within each plot for destructive harvests. Samples were taken to determine Astragalus biomass on 17 January, 18 March, 21 May 2001; 15 January, 19 March, 20 May 2002. Three destructive harvests during the wheatgrowing season were made to determine the weed biomass (15 January, 20 March, 19 May 2000; 17 January, 21 March, 22 May 2001). Weeds and cover crop were identified, grouped into species and oven dried to a constant weight at 70 1C in a forced air drier, after which they were weighed and their biomass recorded. Wheat plants were harvested at maturity each year (June 13, 2001 and June 15, 2002) by combining 1.5 m of the center 5 rows within each treatment and seed yields were adjusted 14.5% moisture. Wheat populations at grain harvest were determined by counting and recording the number of plants harvested within each plot. Spikes were threshed and sub samples were used to determine the yield components. All data were subjected to analysis of variance and means were separated by Duncan’s multiple range test at the 5% probability level.

3. Results and discussion 3.1. Plant height In the 2000/2001 season, no significant differences were found in plant height in the early stages of growth irrespective of the treatments up to heading stage but differences became significant at the ripening stage (Table 2). No till treatments (T4 and T5) showed significantly lowest plant height. No significant differences were recorded for any treatment on plant height. In the 2001/2002 season, plant height was significantly reduced at the heading stage compared to the previous season in each treatment although under an almost similar pattern of weather and cultural practices. No significant reduction was found at the ripening stage compared to the previous season. Continuous cultivation of crops resulted significant reduction of the plant height at the heading stage but no significant differences were found at the ripening stage. 3.2. SPAD value In the 2000/2001 season, SPAD value was unaffected by the given treatments at the maximum tillering stage (Table 3). At the heading stage highest and lowest values were observed in T1 and T4, T5 treatments, respectively. But the T2 showed significantly higher value than T3. At the ripening stage, the values were not significantly different. No differences were found at the ripening stage. In the 2001/2002 season, the significantly highest value was observed in T1 at the max tillering stage, but the differences were not clear in the establishment methods used under reduced tillage. At the heading stage, the lowest SPAD value was observed in T4 and T5. The seeding method did not affect the SPAD value of wheat at heading stage. However, these differences

Table 2 Influence of different tillage systems and cover crop on plant height of wheat in two seasons Treatment

Heading stage 2000/2001

Tl T2 T3 T4 T5

35.3 36.4 36.8 38.3 36.9

Ripening stage 2001/2002 *

28.3b 25.4ab* 28.2b* 27.9b* 23.3a*

2000/2001

2001/2002

85.6c 80.3c 79.1b 70.2a 70.0a

79.6b 73.2ab 74.0ab 66.4ab 63.1a

Values within columns followed by the same letter are not significantly different and values between the columns in the same category followed by an asterisk are significantly different according to the Duncans (po0.05) test.


were decreased at the ripening stage. Continuous cultivation under same tillage practice significantly reduced the value in the second consecutive year except in T1 and T2.

3.3. Weed suppression The densities of each weed species in the weedy controls were affected by tillage systems, method of establishment of the cover crop and the year (Table 4).

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Galium spurium L. (False cleavers) was the dominant weed species in 2000/2001 and 2001/2002. In both years, it emerged throughout the entire growing seasons. Biomass of all the species concerned was significantly lower in CT plots and higher in NT plots in each harvest. G. spurium biomass was significantly increased in the second observed season in NT plots although the method of establishment of the cover crop had not affected treatments except at 6MAP in 2001/2002. In the early stage of growth, T2 plots did not show any significant differences from control plots but the

Table 3 SPAD value as affected by tillage and cover crop in two seasons Treatment

Tl T2 T3 T4 T5

Max tillering

Heading

Ripening

2000/2001

2001/2002

2000/2001

2001/2002

2000/2001

2001/2002

33.7 32.4 32.6 33.6 33.4

30.1d* 27.5bc* 28.1c* 26.2ab* 25.8a*

34.8d 30.2c 26.2b 22.3a 21.3a

30.0c* 25.3b* 26.3b 20.1a 20.2a

25.6 24.4 24.5 19.2 19.3

28.3* 21.1* 25.3 19.6 18.3

Values within columns followed by the same letter are not significantly different and values between the columns in the same category followed by an asterisk are significantly different according to Duncan’s (po0.05) test.

Table 4 Weed emergence as affected by tillage systems and cover crop in two seasons Weed species

Treatment

Weed dry biomass (gm–2) 2MAP

4MAP

2000/2001

2001/2002

2000/2001

2001/2002

2000/2001

2001/2002

6MAP

Galium spurium

T1 T2 T3 T4 T5

g/m2 2.0a 10.5b 4.4ab 30.1c 22.9c

3.1a 18.5b 8.2a 21.4b* 11.2ab*

5.8a 18.8b 13.7a 34.0b 35.0b

9.3a 29.8d 17.8b 23.0c* 22.3c*

5.6a 26.1b 25.5b 44.9bc 47.8c

10.2a 41.0b 50.2b 31.8ab 26.lab*

Cerastium glomeratum

T1 T2 T3 T4 T5

0.3a 2.6a 0.8a 34.3b 28.0b

0.4a 5.0a 0.6a 23.3b 21.1b

0.5a 7.7a 1.4a 45.2c 28.1b

2.1a* 4.1a 2.5a* 62.0b* 65.4b*

2.1a 9.9a 2.1a 54.4b 37.9b

6.8a 16.6ab 5.0a 41.2b 29.3ab

Alopecurus acqualis

T1 T2 T3 T4 T5

0.8a 0.5a 0.6a 17.7b 17.1b

2.5ab 0.4a 1.2a 5.4ab 9.5b

3.6a 0.6a 3.1a 16.8b 17.7b

10.9b 3.7a* 4.7a* 30.2c* 33.3c*

15.1 11.7 7.2 15.2 15.3

9.4 8.8 5.3 12.7 13.8

T1 T2 T3 T4 T5

5.3a 8.2 9.1bc 11.4c 14.3d

7.5a 9.5ab 10.2b 13.2c 12.1bc

10.3a 12.3b 15.2c 18.5d 19.8d

9.6a 10.2a 16.5b 22.3c* 18.2b

13.3a 19.6c 17.2b 19.3c 20.4c

15.2a 15.6a* 21.2b* 21.3b 23.0b*

Others

Values within columns followed by the same letter are not significantly different and values between the columns in the same category followed by an asterisk are significantly different according to Duncan’s (po0.05) test.


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Table 5 Total weed biomass as affected by tillage systems and cover crop in two seasons Treatments

2MAP

4MAP

6MAP

2000/2001

2001/2002

2000/2001

2001/2002

2000/2001

2001/2002

T1 T2 T3 T4 T5

8.51a 22.0a 15.11a 86.81b 101.9b

11.5a 24.0b 10.1a 38.4c 26.4b

20.46a 45.92c 32.6a 114.2e 94.5c

25.4a 37.6b 25.1a 115.2c 134.5d

36.2a 67.4b 52.1ab 127.6c 121.5c

41.4a 49.1ab 44.0a 85.8c 61.8b

Tillage (T) Seeding (S) TS

Level of significance 0.01 0.01 ns 0.01 ns ns

0.01 0.05 ns

0.01 ns 0.01

0.01 ns ns

0.01 ns ns

Values within columns followed by the same letter are not significantly different according to Duncan’s (po0.05) test.

differences increased throughout the season. In the early season observations, the dry biomass of G. spurium was significantly increased in NT plots. Cerastium glomeratum (sticky chick weed) and Alopecurus aequalis (short-awned foxtail) responded to the given treatments in an almost equal manner except at the later stage of growth. Weed biomass showed no difference between CT and MT at all stages of growth. Biomass of these species was significantly increased in 2001/2002 season at 4MAP. As a whole, other minor species showed mixed responses but NT plots showed significantly higher weed biomass while CT the lowest. Ngouajio et al. (2003) found weed species richness was the greatest in the early growing season and was affected by cover crop. Their weed populations were similar in all the management systems concerned in the first year but there was better weed suppression in the organic, integrated systems than in conventional. However, the number of weed species in the no-till system decreased with the no-till system. Torresen and Skuterud (2002) observed a shift in weed composition with the tillage system and they recorded more winter annual, biennial and perennial weed species with reduced tillage systems. Hald (1999) and Van Elsen (2000) reported greater species richness in organic farming systems compared to conventional systems. Buhler et al. (1994) monitored perennial weed populations after 14 years of varying tillage and crop rotation (continuous corn vs. corn–soybean). Grass weed species such as Seteria viridis L. (green foxtail) and Hordeum jubatum L. (foxtail barley) were observed with more frequency in no-tillage than in conventional tillage (Wruckle and Arnold, 1985). The effect of tillage and wheat in rotation with other crops resulted in greater weed populations in no-tillage regardless of the rotation (Blackshaw et al., 1994). Bryson and Hanks (2001) observed over a fiveyear period of reduced tillage cotton and soybean a general increase in perennial weeds, especially woody

species and vines. Swanton et al. (1999) did not observe consistent relationships between weed density and tillage system but found differences in composition of weed populations between conventional and no-tillage systems. Total weed biomass was significantly increased when the intensity of the tillage was reduced (Table 5). At the first harvest (2MAP), total dry biomass was fluctuated from 8.51 gm–2 (CT) and 101.9 gm–2 (NT) confirming that the presence of cover crop has not been able to reduce the weed biomass at the early stage of growth. Under NT total weed dry biomass was significantly reduced in the second season with row seeding resulting in significantly lower biomass than broadcasting.

3.4. Wheat yield Yield varied with tillage system, method of establishment of cover crop and year (Table 6).Wheat grain yield was significantly affected in both years but the yield reduction in the second season was not significant. The lowest yield was observed in NT plots. MT with cover crop showed no significant difference from the CT plots in the second consecutive year. The grain yield reduction caused by row seeding of the cover crop was 55% and 34.2% in the two consecutive years in MT plots, respectively. Kernal weight was affected significantly by reduced tillage in the first year and the differences were clearly evident in the second consecutive season. Number of heads per square metre and number of kernels per head were significantly affected by the treatments. From the yield components, the number of heads per square meter was not significantly different between Tl and T2. The yield components were not significantly affected by the method of establishment of Chinese milk vetch. In another study, Swanton et al. (2002) concluded that although weed densities under


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Table 6 Yield and yield components of wheat as affected by tillage and cover crop in two seasons No of heads (m–2)

No of kernels per head

Kernal weight (mg)

Harvest index

Grain yield (gm–2)

2000/2001

2001/2002

2000/2001

2001/2002

2000/2001

2001/2002

2000/2001

2001/2002

2000/2001

2001/2002

T1 T2 T3 T4 T5

355.0c 346.0c 170.3a 173.6a 202.b

344.0b 340.0b 166.6a 169.6a 133.3a

36.6b 26.7a 31.6ab 27.3a 30.0a

39.3b 37.8b 28.6a 30.1a 26.6a

24.1b 21.8a 21.4a 21.3a 21.7a

25.9c 25.6b 22.4b 20.8a 20.8a

0.56 0.55 0.54 0.55 0.55

0.54 0.55 0.54 0.54 0.55

313.0d 200.1c 110.1ab 98.7a 129.9b

308.6c 291.8c 100.2b 99.3b 70.1a

Tillage (T) Seeding (S) TS

Level of significance 0.01 0.01 0.01 0.01 0.01 0.01

0.01 0.01 ns

0.01 ns ns

0.01 ns ns

0.01 ns ns

ns ns ns

ns ns ns

ns ns 0.01

0.01 0.01 0.01

Treatment

Values within columns followed by the same letter are not significantly different according to Duncan’s test (po0.05).

different tillage treatments varied among years in corn and soybean, this variability did not affect crop yield. In summary, weed densities varied with tillage treatment. Weed densities were greater in the no tillage treatment when compared with conventional and minimum tillage treatments. But the second consecutive season significantly reduced the biomass of all dominant species under no tillage. The wheat yield was not significantly affected by the reduced weed biomass. Row seeding resulted in significantly lower weed biomass. References Anderson, T.N., Milberg, P., 1996. Weed performance in crop rotations with and without leys and at different nitrogen levels. Ann. Appl. Biol. 128, 505–518. Banks, P.A., Santlemann, P.W., Tucker, B.B., 1976. Influence of longterm soil fertility treatments on weed species in winter wheat. Agron. J. 68, 825–827. Barnes, J.P., Putnam, A.R., 1983. Rye residues contribute weed suppression in no-tillage cropping systems. J. Chem. Ecol. 9, 1045–1057. Bilalis, D., Siridas, N., Economou, G., Vakali, C., 2003. Effect of different levels of wheat straw soil surface coverage on weed flora in Vicia faba crops. J. Agron. Crop Sci. 189, 233–241. Blackshaw, R.E., Larney, F.O., Lindwall, C.W., Kozub, G.C., 1994. Crop rotation and tillage effects on weed populations on the semiarid Canadian prairies. Weed Technol. 8, 231–237. Bryson, C.T., Hanks, J.E., 2001. Weed shifts in deep hollow watershed, leflore county, MS. In: Rebich, R.A., Knight, S.S. (Eds.), The Mississippi Delta Management Systems Evaluation Areas Project, 1995–1999. Mississippi Agricultural and Forestry Experimental Station Information Bulletin, vol. 377, pp. 86–90. Buhler, D.D., 1992. Population dynamics and control of annual weeds in corn (Zea mays) as influenced by tillage systems. Weed Sci. 40, 241–248. Buhler, D.D., 1995. Influence of tillage systems on weed population dynamics and management in corn and soybean in the central USA. Crop Sci. 35, 1247–1258. Buhler, D.D., Stoltenberg, D.E., Becker, R.L., Gunsolus, J.L., 1994. Perennial weed populations after 14 years of variable tillage and cropping practices. Weed Sci. 42, 205–209.

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