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Published online 5 June 2006
Published in Agron J 98:1023-1029 (2006)
DOI: 10.2134/agronj2005.0289
© 2006 American Society of Agronomy
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Tillage

Tillage System Effects on Competition between Barley and Sterile Oat

K. Dhimaa,*, I. Vasilakogloub, A. Lithourgidisc, S. Papadopouloud and I. Eleftherohorinose

a Agron. Lab., Technol. & Educ. Inst. of Thessaloniki, 541 01 Thessaloniki, Greece
b Weed Science Lab, Technol. & Educ. Inst. of Larissa, 411 10 Larissa, Greece
c Agron. Dep., Univ. Farm, Aristotle Univ. of Thessaloniki, 570 01 Thermi, Greece
d Entomol. Lab., Technol. & Educ. Inst. of Thessaloniki, 541 01 Thessaloniki, Greece
e Agron. Lab. Aristotle Univ. of Thessaloniki, 541 24 Thessaloniki, Greece

* Corresponding author (dimas{at}cp.teithe.gr)

Received for publication October 17, 2005.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
The short-term effect of three tillage systems [minimum (MT), reduced (RT), and conventional (CT)] on growth and yield components of two six-row barley (Hordeum vulgare L. cv. ‘Athinaida’ and ‘Plaisant’) in presence or absence of sterile oat (Avena sterilis L.) was studied in northern Greece during the 2003–2004 (Yr 1) and 2004–2005 (Yr 2) growing seasons. Sterile oat was controlled using a postemergence (POST) application of imazamethabenz {(±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-4(and 5)-methylbenzoic acid (3:2)} at the early tillering stage of barley. The competitive ability of both barley cultivars against sterile oat was similar. Sterile oat total fresh weight and stem number were less in CT compared to those in RT and MT in Yr 1, a wet growing season, but were greater in Yr 2, a dry growing season. Barley grain yield was greatest and not affected by tillage in Yr 1 whereas in Yr 2, overall yield was lower and MT reduced grain yield by 14% compared to yield in RT and CT treatments. Furthermore, averaged across tillage system and barley cultivar, total weight, ear number, and grain yield of barley grown with sterile oat interference was lower by 10 to 33%, 16 to 45%, and 20 to 38%, respectively, to that of barley grown where sterile oat was controlled. These results indicate that both barley cultivars had satisfactory competitive ability against sterile oat and minimum or reduced tillage systems could be viable as short-term alternative management systems for barley production.

Abbreviations: CT, conventional tillage • MT, minimum tillage • POST, postemergence • RT, reduced tillage • WAT, weeks after tillering


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
CONVENTIONAL TILLAGE, including moldboard plow, tandem harrow disc, and cultivator, is the common tillage practice in Greece for seedbed preparation and weed control before the planting of winter cereals. The conventional tillage system depletes soil moisture and organic matter (Campbell, 1978; Halvorson et al., 2002). Conversely, conservation tillage, including no-tillage, minimum, and reduced tillage, have been shown to increase soil organic matter and improve soil structure and production efficiency (Choudhary et al., 1997; Logan et al., 1991; Uri, 1999). In addition, CT has been adopted in many North America cropping areas to reduce soil erosion, nitrate leaching, and subsoil compaction. Conservation tillage reduces the number of trips across a field and recently has been used in some Greek areas where winter cereals are grown to reduce production cost (Lithourgidis et al., 2005).

Tillage systems, in most cases, have limited impact on grain yield of barley, wheat (Triticum aestivum L.), and corn (Zea mays L.) (Beyaert et al., 2002; Cantero-Martinez et al., 2003; Halvorson et al., 2002; Latta and O'Leary, 2003; Legere et al., 1997; Lithourgidis et al., 2005; Wiatrak et al., 2004). However, Halvorson et al. (2000a, 2000b) reported that spring wheat yielded more in conventional or minimum tillage compared to no-tillage within a crop-fallow system or in rotation with sunflower (Helianthus annuus L.).

Changing tillage systems also may impact the growth and population dynamics of weedy species (Martin and Felton, 1993; Navarrete and Fernandez-Quintanilla, 1993; Mas and Verdu, 2003). Sterile oat is one of the most common and troublesome grass weeds of winter cereals grown in Mediterranean countries (Damanakis, 1983; Navarrete and Fernandez-Quintanilla, 1993; Dhima et al., 2000). Also, wild oat (Avena fatua L.) is the most economically harmful annual grass weed occurring in cultivated land in North America, central and northern Europe, and Australia (Carlson and Hill, 1985; Cousens et al., 1991; Martin and Field, 1987; Wilson and Wright, 1990). Barley and triticale yield reduction due to competition with sterile oat can range from 8 to 67% (Dhima and Eleftherohorinos, 2001; Dhima et al., 2000). The effect of tillage system on the population dynamics of sterile oat is not clearly defined. For example, Navarrete and Fernandez-Quintanilla (1993) found less sterile oat emerged seedlings and less viable seeds produced in CT (moldboard-plow) plots than in CT (shallow cultivation) plots. Mas and Verdu (2003) also reported that mean biomass of sterile oat was less under conventional than under minimum tillage. However, Martin and Felton (1993) found no consistent tillage effects on wild oat density, seed production, or carry over of seeds in the soil.

Published data on barley response to different tillage systems as well as data related to the effect of tillage practices on barley grown with sterile oat under Mediterranean conditions are limited. The objective of this research was to assess the short-term impact of three tillage systems (CT, RT, and MT) on growth and yield components of two winter barley cultivars grown in presence or absence of sterile oat.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
A field experiment was conducted and repeated during 2003–2004 (Yr 1) and 2004–2005 (Yr 2) growing seasons at the University Farm of Thessaloniki (northern Greece) (22°59'6.17'' E, 40°32'9.32'' N) to determine the effect of three tillage systems on growth and yield of six-row winter barley grown with sterile oat. Experiments were established on a silty clay, well-drained soil (Typic Xerorthent) whose physicochemical characteristics were silt 455 g kg–1, clay 502 g kg–1, sand 43 g kg–1, organic C content 13.5 g kg–1, pH (1:2 H2O) 7.8, and CaCO3 39 g kg–1. Mean monthly temperature and rainfall data recorded near the experimental area are given in Fig. 1 .


Figure 1
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  		Fig. 1. Total monthly rainfall and mean monthly temperature during the experiment.

 
Cropping history at the experimental site in the previous 5 yr comprised a winter wheat crop under CT. Winter wheat was harvested in mid-June of each growing season approximately 20 to 25 cm from the soil level. Wheat straw (3500 kg ha–1) was baled and removed after harvest. The experimental area was infested with natural sterile oat populations, which were controlled by fenoxaprop {(±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoic acid} applied POST at 0.083 kg a.i. ha–1. The broadleaf weeds present in the area were controlled by tribenuron {2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)metrhylamino]carbonyl]amino]sulfonyl]benzoic acid} applied POST at 0.015 kg a.i. ha–1 during 1998–1999, 2000–2001, and 2002–2003.

The experiment was configured as a split-split-plot design with four replicates. Main plot size was 21 by 7 m and all plots were separated by a 2-m buffer zone. The main plots consisted of three tillage systems: MT (cultivator to a depth of approximately 12 cm), RT (heavy offset harrow disc to a depth of approximately 18 cm and cultivator to a depth of approximately 12 cm), and CT (four-bottom moldboard plow to a depth of approximately 22 cm, tandem harrow disc to a depth of approximately 12 cm, and cultivator to a depth of approximately 12 cm). The main plots were prepared in autumn, 1 wk before cereal planting. Nitrogen and P2O5 as ammonium sulfo-phosphate (20–10–0) at 90 and 45 kg ha–1, respectively, were incorporated into the soil during cultivation in all tillage treatments. Also, 50 kg N ha–1 was applied as ammonium nitrate (33.5–0–0) in all plots in early March. The two most commonly grown winter barley cultivars (‘Athinaida’ and ‘Plaisant’) for the last 10 yr in Greece were planted in 21 by 3 m subplots at 170 kg ha–1 within last week of November of each year. The planter was equipped with 33-cm diam. disc openers and adjusted to plant at 3- to 4-cm depth in 16-cm rows.

Each barley cultivar subplot was split into two sub-subplots 10 by 3 m in size. One of the sub-subplots was sprayed POST with 0.45 kg a.i. ha–1 of imazamethabenz whereas the other sub-subplot was untreated. Imazamethabenz was applied on 17 February each growing season when sterile oat was at the three- to four-leaf stage and barley was beginning to tiller (Feekes growth stage [FGS] 2) (Large, 1954). A propane-pressurized hand-field plot sprayer (AZO-SPRAYERS, P.O. Box 350-6710 BJ EDE, the Netherlands), with a 2.4-m wide boom fitted with six 8002 flat fan nozzles (Teejet Spray System Co., P.O. Box 7900, Wheaton, IL 60188) was calibrated to deliver 300 L ha–1 of water at 250 kPa pressure. Herbicide for broadleaf weed control was not applied in either growing seasons because the density of the weed species [corn poppy (Papaver rhoeas L.), wild mustard (Sinapis arvensis L.)] present in the experimental area was very low. The experiment was located on top of the same exact plot area in both years.

Barley and sterile oat densities were determined by counting plant number in a 1- by 1-m area on the center of each sub-subplot on 25 January of both growing seasons (8 wk after planting) when both crop and most of sterile oat seedlings had emerged. Also, barley and sterile oat plants were harvested in a 1- by 1-m area on the 10 central rows of each untreated sub-subplot 0, 3, 6, and 9 wk after tillering (WAT) to evaluate the barley competitive ability against sterile oat. The first sampling area was randomly determined in each of the sub-subplots. Subsequent sampling areas were separated from the first sampling area and each other by 20 cm to avoid potential border effects. The sampling at 0 WAT was done on 24 Mar. 2004 and 26 Mar. 2005. Crop and weed stem number as well as fresh weight were determined at each sampling.

At harvest (on 17 June of both growing seasons), crop plants from a 1-m2 area near the center of each sub-subplot were hand-harvested. Total weight, ear number, grain yield adjusted to 13% grain moisture, and 1000-grain weight of both barley cultivars were recorded. Also, sterile oat total fresh weight and panicle number were recorded at the same time.

Barley straw was baled and removed after harvest, while no other treatment was made until autumn of the following growing season.

Statistical Analysis
A combined-over growing season analysis of variance (ANOVA) was performed for fresh weight and stem number for both barley and sterile oat by using a split-split plot factorial design (tillage system x barley cultivar x time of sampling). As the ANOVA indicated differences between growing season and growing season x treatments interaction, in most cases, a new ANOVA was performed separately for each growing season. Since these new ANOVA analyses did not clearly show a significant effect for tillage system x barley cultivar x duration of interference interaction, a multivariate analysis of variance (MANOVA) was performed for tillage systems and barley cultivars to determine barley and sterile oat growth parameters (Table 1). Because the MANOVA indicated, in most cases, no significant tillage system x barley cultivar interaction, the parameter means for barley and sterile oat were averaged across barley cultivars and regressed against time (WAT). Stem number and fresh weight data before the ANOVA or MANOVA were {surd}x+1 and log(x + 1) transformed, respectively, to reduce their heterogeneity, but means presented are back-transformed values. Linear, quadratic, hyperbolic, and logarithmic equations were tested for their suitability to describe the relationship between stem number or fresh weight response and time. The equation with the highest coefficient of determination (R2) values was judged to be the most appropriate. In these regression equations, stem number and fresh weight were the dependent variables (y) and time the independent variable (x).


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  		Table 1. Multivariate analysis of variance (MANOVA) for barley and sterile oat stem number and fresh weight data as affected by tillage system, barley cultivar, and tillage system x barley cultivar interaction during the 2003–2004 and 2004–2005 growing seasons.

 
Also, a combined-over growing season analysis of variance (ANOVA) was performed for crop total weight, ear number, grain yield, and 1000-grain weight, as well as of sterile oat total weight and panicle number data by using a split-split plot factorial design (tillage system x barley cultivar x sterile oat control). As the ANOVA indicated differences between growing season and growing season x treatments, in most cases, a new ANOVA was performed separately for each growing season (Table 2). Since the new ANOVA did not show significant barley cultivar effect or barley cultivar x treatment interaction, in most cases, the tillage system and sterile oat control means, averaged across barley cultivar, are only presented.


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  		Table 2. Analysis of variance of barley total weight, ear number, grain yield, and 1000-grain weight as well as sterile oat dry weight and panicle number as affected by tillage system, barley cultivar, and sterile oat control during the 2003–2004 and 2004–2005 growing seasons.

 
Fisher's protected LSD procedures were used to detect and separate mean treatment differences at P = 0.05. The program MSTAT (MSTAT-C, 1988) was used to conduct the ANOVA, while the SPSS program (SPSS, 1997a, 1997b) was used to conduct the regression and the multivariate analysis.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Sterile Oat Response
Sterile oat stems and fresh weight decreased as the season progressed. Linear regression equations (y = a – bx) were the best fit for sterile oat stem number changes vs. WAT whereas quadratic regression equations (y = a + bx – cx2) were used to describe fresh weight changes vs. WAT (Fig. 2 and 3) . Estimated initial stem number and fresh weight (the a parameter) values were greater in Yr 2 than those estimated for Yr 1. Avena spp. emergence has been reported to be greater when winter temperatures are above 9°C (Aibar et al., 1991). Therefore the warmer prevailing temperatures from December to January during Yr 2 (Fig. 1) could account for the increase in sterile oat emergence.


Figure 2
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  		Fig. 2. Temporal pattern in stem number of sterile oat grown with barley during the 2003–2004 and 2004–2005 growing seasons. Lines describe linear regression equations (data before the multivariate analysis of variance [MANOVA] were {surd}(x + 1)-transformed, but the mean values used were back-transformed). MT, minimum tillage; RT, reduced tillage; CT, conventional tillage.

 

Figure 3
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  		Fig. 3. Temporal pattern in fresh weight of sterile oat grown with barley during the 2003–2004 and 2004–2005 growing seasons. Lines describe quadratic regression equations (data before the multivariate analysis of variance [MANOVA] were log(x + 1)-transformed, but the mean values used were back-transformed). MT, minimum tillage; RT, reduced tillage; CT, conventional tillage.

 
At harvest, total weight and panicle number of sterile oat in Yr 1, averaged across barley cultivar, were lower than those in Yr 2 (Table 3). In addition, total weight and panicle number of sterile oat in Yr 1 were higher under CT than under RT or MT. However in Yr 2, sterile oat total weight and panicle number were lower under CT than under RT or MT.


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  		Table 3. Total weight and panicle number of sterile oat grown in barley as affected by three tillage systems during the 2003–2004 and 2004–2005 growing seasons. Means are averaged across barley cultivars.

 
The greater total weight and panicle number of sterile oat on untreated (no herbicide) sub-subplots in Yr 2 compared to those in Yr 1 could be attributed to the reported earlier environmental conditions differences between the two growing seasons. The greater total weight and panicle number of sterile oat grown in competition with barley under CT during Yr 1 could be the result of better soil conditions (better soil aeration and greater soil temperature) prevailing after CT that favored sterile oat growth. The lowest sterile oat total weight and panicle number under CT in Yr 2 could be attributed to the initial reduced emergence in CT recorded 8 wk after planting (data not shown) due to less seed brought to the soil surface by moldboard plowing compared to the tillage operations in MT and RT systems in the previous growing season. These results are in agreement with those reported by Tørresen et al. (1999) who found, in long-term experiment, that weed infestation in spring barley and oat increased when tillage intensity decreased.

The lack of cultivar effect on sterile oat total weight (Table 2), averaged across growing season and tillage system, is in contrast with those reported by Dhima et al. (2000) and O'Donovan et al. (2000) who found that shoot dry weight of sterile oat and wild oat, respectively, were affected by barley cultivars.

Crop Response
Linear regression equations were again the best fit for barley stem number changes vs. WAT whereas quadratic regression equations were used to describe fresh weight changes vs. WAT (Fig. 4 and 5) . The estimated value of a (intercept) for both stem number and fresh weight were greater in Yr 1 than in Yr 2 indicating reduced crop growth the second year. The differences in stem number and fresh weight between the 2 yr may be due to drier conditions during the April and May of the second year (Fig. 1). In both growing seasons, barley stem number decreased as the season progressed and this reduction could be attributed to the competition among tillers for water and nutrients. This result agrees with that reported by Baethgen et al. (1995) who found that competition among tillers of barley resulted in lower tiller survival rates. Also, barley fresh weight increased from 0 to 3 WAT but decreased 6 to 9 WAT due to loss of water and the death of the lower leaves (Fig. 4 and 5).


Figure 4
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  		Fig. 4. Temporal pattern in barley stem number in the presence of sterile oat during the 2003–2004 and 2004–2005 growing seasons. Lines describe linear regression equations (data before the multivariate analysis of variance [MANOVA] were {surd}(x + 1)-transformed, but the mean values used were back-transformed). MT, minimum tillage; RT, reduced tillage; CT, conventional tillage.

 

Figure 5
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  		Fig. 5. Temporal pattern in barley fresh weight in the presence of sterile oat during the 2003–2004 and 2004–2005 growing seasons. Lines describe quadratic regression equations (data before the multivariate analysis of variance [MANOVA] were log(x + 1)-transformed, but the mean values used were back-transformed). MT, minimum tillage; RT, reduced tillage; CT, conventional tillage.

 
Total weight, ear number, and grain yield of barley averaged over tillage and sterile oat were greater in Yr 1 compared to those parameters in Yr 2 (Tables 4 and 5). Also, in Yr 1, total weight, ear number, and grain yield of barley grown in weedy plots were reduced less by sterile oat interference (estimated as percent of herbicide treated ones) compared with the reduction measured in the second growing season (Table 5).


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  		Table 4. Yield components of barley as affected by tillage systems during the 2003–2004 and 2004–2005 growing seasons. Means are averaged across barley cultivars and sterile oat control.

 

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  		Table 5. Yield components of barley as affected by sterile oat and imazamethabenz postemergence (POST) application during the 2003–2004 and 2004–2005 growing seasons. Means are averaged across barley cultivars and tillage system.

 
Total weight of barley in Yr 2 was not affected by tillage system (Table 4). However, total weight of barley under MT and RT in Yr 1 were similar but both were lower than that of CT. In addition, total weight of barley, averaged across tillage system and barley cultivar grown in Yr 1, harvest from weedy plots (no herbicide) was 10% lower compared with weights from treated plots (Table 5). However, the total weight reduction due to sterile oat competition, during Yr 2, was 33% when compared to the weed-free control (Table 5).

Ear number, averaged across sterile oat control and barley cultivar, of barley grown in Yr 1 under CT was higher than that under MT and RT (Table 4). However, in Yr 2, ear number of barley grown under CT was similar to that under RT and higher than that under MT (Table 4). Barley ear numbers in Yr 1 and 2 in the weedy (no herbicide) treatment were 16 and 45% less, respectively than in weed-free treatments (Table 5).

Tillage system did not affect grain yield of barley (averaged across sterile oat control and barley cultivar) in Yr 1; however, in Yr 2, grain yield of barley grown under CT or RT was 14% higher than that under MT (Table 4). Grain yield of barley grown with sterile oat interference was reduced by 20% in Yr 1 and by 37% in Yr 2 (averaged across tillage system and barley cultivar) to that of yield in the weed-free plots (Table 5).

The 1000-grain weight of both barley cultivars was not significantly affected by tillage systems and by barley cultivar (Table 2). However, 1000-grain weight was higher in Yr 1 than in Yr 2 (data not shown).

The lack of tillage system effect on total weight of barley in Yr 2 is in agreement with results reported by Wiatrak et al. (2004) who found that wheat dry matter was not significantly affected by tillage system (CT and no-tillage). The 10% reduction of total weight due to sterile oat competition in Yr 1 agree with results reported by Dhima and Eleftherohorinos (2001) who found that the presence of 110 sterile oat plants m–2 reduced total weight of barley by only 6%.

The similar grain yield in all tillage system plots during Yr 1 is in agreement with results reported by Legere et al. (1997) who found that barley yields produced under no-tillage were comparable to those in a tillage system that includes moldboard plow in the autumn, followed by spring secondary tillage, and did not require a major increase in herbicide use. Some research has shown that tillage system did not affect winter wheat yields (Halvorson et al., 2002; Latta and O'Leary, 2003) or barley growth and yield (Cantero-Martinez et al., 2003). In contrast, Tørresen et al. (1999) found that spring barley and oat yield decreased when tillage intensity decreased in long-term experiments, which agree with our findings in Yr 2. Plots with no herbicide treatment showed a large spring barley and oat yield reduction on only harrowed and no-tillage plots compared to spring or autumn plowed plots. Halvorson et al. (2000a, 2000b) found that spring wheat yielded more in CT or MT than in no-tillage within a crop-fallow system or in rotation with sunflower. The grain yield reduction due to sterile oat interference agree with results reported by Torner et al. (1991) and Wilson and Peters (1982) who found that high densities of wild oat (>300 panicles m–2) reduced yield of barley by 50 to 72%. The lack of tillage effect on 1000-grain weight of barley, combined with the respective 27% ear number reduction (averaged across growing season, barley cultivar, and tillage system), indicates that barley grain yield reduction due to sterile oat interference resulted mostly from reduction in ear number and less by 1000-grain weight. This result agrees with that reported by Dhima et al. (2000) and Dhima and Eleftherohorinos (2001).

The reduced barley yield components in Yr 2 could be attributed to the lower amount and distribution of rainfall during the critical period of crop growth (April–May) (Balyan et al., 1991), as well as to greater sterile oat competitive ability (greater stem number) due to favorable temperature prevailing from December 2004 to January 2005 as mentioned previously (Fig. 1). These results are in agreement with those reported by Torner et al. (1991) who found that barley yield was reduced by sterile oat through a reduction in the number of fertile tillers and yield losses were greatest in the drier seasons. Similar results were also found by others (Akey and Morrison, 1984; Dhima and Eleftherohorinos, 2001; Lithourgidis et al., 2005) who reported that spring climatic conditions (drought and high temperature) are the main factors which affect winter cereal growth.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
The results of this study indicated that although total weight and panicle number of sterile oat were affected by tillage system, its interference ability on barley remained similar in all tillage systems. However, sterile oat interference ability was greater during the dry growing season, where crop competition was poor, than the wet one. Barley yield components were slightly affected by tillage system, but they were less affected by sterile oat interference during the wet growing season compared with that during the dry season. These findings showed that short-term MT or RT could be used as alternative management systems for barley production under Mediterranean conditions, but these systems may not be viable under long-term application.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 





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