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CROP ECOLOGY, MANAGEMENT & QUALITY

Tillage Effects on Wheat Emergence and Yield at Varying Seeding Rates, and on Labor and Fuel Consumption

^a Dep. of Agronomy, University Farm, Aristotle Univ. of Thessaloniki, 570 01 Thermi, Greece
^b Technol. and Educ. Inst. of Thessaloniki, 541 01 Echedoros, Greece
^c Technol. and Educ. Inst. of Larissa, 411 01 Larissa, Greece
^d Lab. of Agronomy, Univ. of Thessaloniki, 541 24 Thessaloniki, Greece

^* Corresponding author (lithour{at}agro.auth.gr)

	ABSTRACT

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

 
Conservation tillage systems can play an important role in reducing soil erosion and improving soil quality with the extra benefit of being equal to or more economical than conventional tillage; however, yield variability still remains a major concern among farmers. Field experiments were conducted in 2003 through 2004 and 2004 through 2005 in northern Greece to determine the effect of seeding rate (100, 150, 200, and 250 kg ha^–1) on wheat establishment and grain yield under three tillage systems (minimum, reduced, and conventional tillage). In addition, labor time and fuel consumption for wheat production under these tillage systems were compared. For all tillage systems, the greatest number of wheat plants was recorded at the two highest seeding rates (P < 0.05). However, wheat plant numbers, averaged over seeding rates, were reduced by 11 to 17% in minimum tillage compared with conventional and reduced tillage systems in both growing seasons. Ear numbers were unaffected by tillage systems but generally increased with the increased seed rate. However, differences were not found in grain yield either among tillage systems or seeding rates. Regarding labor time and fuel consumption, 50 and 53% savings was achieved with minimum tillage, respectively, and 43 and 48% with reduced tillage in comparison with conventional tillage. These findings indicate that wheat can be grown successfully under conservation tillage systems with yields equal to those of conventional tillage and lower labor and fuel inputs. Increasing of seeding rate favored crop establishment in all tillage systems, but it did not provide any grain yield advantage.

	INTRODUCTION

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

 
CONSERVATION TILLAGE represents a broad spectrum of farming methods which are based on establishing crops in the previous crop's residues purposely left on the soil surface. The use of conservation tillage can play an important role in reducing soil erosion and improving soil quality (Uri et al., 1999) and can be an attractive alternative to conventional tillage for farmers because of its potential to minimize labor and fuel consumption and to lower total production cost (Uri, 2000).

Wheat response to conservation tillage practices is variable and yields are often inconsistent depending largely on climatic and soil factors. Thus, wheat yields with conservation tillage may be either higher or lower than with conventional tillage probably because of the considerable annual variation both within and between sites (Kirkegaard, 1995). In southern Spain, López-Bellido et al. (1996) found higher winter wheat yield under no tillage than under conventional tillage in dry seasons, whereas the opposite was true in wet seasons. In a number of studies, conservation tillage systems have been reported to provide wheat yields equal to or even higher than those achieved by conventional tillage (Gemtos et al., 1998; Mrabet, 2000; McMaster et al., 2002; Hemmat and Eskandari, 2004). However, other studies (Hammel, 1995) indicated lower wheat yields under no tillage than conventional or minimum tillage because of increased disease incidence under minimum or no tillage. In a 12-yr study in the U.S. northern Great Plains, Halvorson et al. (2000) reported that the order of spring wheat grain yields by tillage systems was conventional > minimum > no tillage. In addition, Camara et al. (2003) found that conservation tillage was less productive than moldboard plowing probably because of lack of downy brome (Bromus tectorum L.) control in the conservation tillage systems.

Differences among wheat cultivars both across and possibly within studies may contribute to the inconsistency in yield response to changes in tillage. For example, the relative ranking of four soft white spring wheat cultivars across three tillage systems changed for grain yield in the U.S. Pacific Northwest, prompting the recommendation that cultivars must be developed for specific tillage environments (Ciha, 1982). A similar recommendation resulted when cultivars were compared in tilled and untilled environments in South Dakota (Hall and Cholick, 1989). However, in contrast to these findings, Carr et al. (2003a, 2003b) reported that the ranking of contrasting hard red spring wheat cultivars for yield components was unchanged under conventional, reduced, or no tillage system.

Conservation tillage planting causes special demands related to uneven seedbeds and surface crop residue. Thus, when residue from the previous crop is unevenly distributed, correct and uniform planting depth is very difficult to be achieved; this may result in poor seedling emergence, thin stands, slow vegetative growth, and consequently reduced grain yield. In particular, Wilkins et al. (1989) indicated that fewer plants had been established when winter wheat was seeded in a seedbed with no preplant tillage compared with a tilled seedbed. Also, fewer plants and lower yields were found in preliminary field studies with no tillage wheat in Greece compared with conventional tillage (Lithourgidis and Tsatsarelis, 2002). As a result, increasing seeding rate is a common practice in minimum tillage systems because of the belief that crop residue at the soil surface reduces the effectiveness of seed delivery systems and results in poor seed-soil contact (Lithourgidis and Tsatsarelis, 2002; Carr et al., 2003a, 2003b). On the other hand, certain studies showed that the increase of seeding rates did not have any significant effect on grain yield of wheat grown under conservation tillage (Sunderman, 1999; Hemmat and Taki, 2001).

Minimum tillage, in addition to its ability to reduce drastically soil erosion, has the extra benefit of being equal to or more economical than conventional tillage (Liu and Duffy, 1996). In particular, many studies with different crops indicated that conservation or no tillage systems reduce input costs such as labor, fuel, machinery use, and repair expenses (Hernánz et al., 1995; Gemtos et al., 1998; Sijtsma et al., 1998; Ribera et al., 2004; Lithourgidis et al., 2005). However, other studies showed that although conservation tillage provided major savings in labor, fuel, and machinery compared with conventional tillage, these savings were largely offset by increases in the energy input for herbicide use or higher nitrogen rates (Zentner et al., 2002, 2004).

Wheat, in Greece and other Mediterranean countries, is mainly grown in dry land and the yield produced is much lower than that obtained in north-central Europe or in some areas of USA with longer growing seasons, better rainfall distribution, and mild temperatures during grain filling (Lloveras et al., 2004). Therefore, reduction of wheat production cost through reduced tillage and establishment of optimum seeding rate is of particular importance for wheat growers. However, as reported earlier, yield response of wheat to reduced tillage practices is inconsistent because of the differences resulting from the tillage systems in N availability, soil temperature, soil moisture, seedbed, and cropping conditions (Kirkegaard, 1995; Gemtos et al., 1998; Halvorson et al., 2000; Carr et al., 2003a, 2003b; Hemmat and Eskandari, 2004). There are also concerns that suboptimal stands result from reduced tillage and, as a consequence, seeding rate adjustments may be needed to reflect changes in tillage system used in various regions (Wilkins et al., 1989; Lithourgidis and Tsatsarelis, 2002; Carr et al., 2003a, 2003b). In addition, comparison of costs from different tillage systems and seeding rates is often difficult because costs vary considerably between crops, tillage systems, soil and climatic conditions, and other management practices. These findings indicate clearly that any conservation tillage practice and seeding rate should be evaluated for their suitability before their adoption in any particular region.

The objective of this study was to determine the effect of seeding rate on growth and productivity of winter wheat (Triticum aestivum L.) under minimum and reduced tillage practices as compared with conventional tillage. Fuel and labor inputs for wheat production under conventional and conservation tillage practices were determined.

	MATERIALS AND METHODS

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

 
A field experiment was conducted during 2003 through 2004 and 2004 through 2005 growing seasons in the University Farm of Thessaloniki in northern Greece. The experiment was established in a silty clay soil with pH 7.8 and organic matter content 27 g kg^–1 (0- to 30-cm depth). The previous crop was winter wheat (variety Yecora) and was harvested in mid June. Wheat straw (3500 kg ha^–1) was baled and removed after harvest, while the remaining stubble (20–25 cm tall) ranged from 1000 to 1200 kg ha^–1.

Winter wheat (variety Yecora) was planted at seeding rates of 100, 150, 200, and 250 kg ha^–1 (corresponding 210, 315, 420, and 525 seeds m^–2) within the first week of November of both growing seasons in three tillage systems (minimum, reduced, and conventional tillage). The experimental design was a randomized complete block in a split-plot arrangement with four replications. The three tillage systems were considered the main plots (separated by a 2-m buffer zone) and the four seeding rates were considered the subplots. Main plot size was 12 x 202 m, which allowed the use of commercial-size farm equipment. In each main plot, four subplots sized 5 x 100 m were created for the four seeding rate treatments. All subplots were separated by a 2-m buffer zone.

The three tillage management systems were: (i) MT (minimum tillage), where wheat sowing was made after shallow tillage with cultivator to a depth of 12 cm (operation speed of 8 km/h), (ii) RT (reduced tillage), where wheat was sown after tillage with heavy offset harrow disc to a depth of 18 cm and followed by cultivator to a depth of 12 cm (respective operation speed 10 and 8 km/h), and (iii) CT (conventional tillage), where wheat was sown after tillage with a four-bottom moldboard plow to a depth of 22 cm (speed of 7 km/h), followed by a tandem harrow disc to a depth of 12 cm (speed of 11 km/h), and by cultivator to a depth of 12 cm (speed of 8 km/h); the latter is the common tillage practice for wheat production in Greece and was considered as the control. An 88 HP (64.7 kW) Ford tractor (Model 6640 Powerstar SL)¹ was used for all operations, running at 1700 to 2100 rpm engine speed (according to load). In all plots, wheat was planted with farmer's equipment (16-row sowing machine, Model 400, Co., Bekam, Greece)¹. The planter was equipped with a disc opener (33-cm diameter) and was adjusted to plant at a depth of 3 to 4 cm in rows 16 cm apart, at a planting speed of 6 km/h.

Nitrogen and P₂O₅ as ammonium sulfo-phosphate (20–10–0) at 120 and 60 kg ha^–1, respectively, were incorporated into the soil before cultivation in all tillage treatments. In all plots, weed control was achieved with chlorsulfuron (2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide) (15 g a.i. ha^–1) applied preemergence and also with clodinafop-propargyl [(R)-2-[4[5-chloro-3-fluoro-2-pyridinyl)oxy]phenoxy]propanoic acid)](40 g a.i. ha^–1) applied postemergence for the control of sterile oat (Avena sterilis L.). The second growing season, a week before wheat planting, paraquat dichloride (1,1'-dimethyl-4,4'-bipyridinium dichloride) (0.4 kg a.i. ha^–1) was applied in minimum tillage plots to control weeds.

Plant number, ear number, grain yield, and 1000-grain weight of wheat were determined for all plots in each year. Wheat plants were counted 6 wk after planting in two random areas of 1 m² each in all subplots. At harvest, plants from the same areas were selected to determine ear number. Wheat was harvested the second half of June of each growing season and grain yield was adjusted to 130 g kg^–1 grain moisture. Grain yield was determined by harvesting a 4 by 50 m area of each subplot with an appropriate grain harvesting machine (Model Hege 140, Co., Hans-Ulrich-Hege, Germany). Wheat straw (3500 kg ha^–1) was baled and removed after harvest, while the remaining stubble (20–25 cm tall) ranged from 1000 to 1200 kg ha^–1_. Labor time and diesel fuel consumption were calculated for each main tillage plot in each treatment and year. Labor and fuel requirements for tillage, planting, fertilization, herbicide application, and harvest were directly associated with field operations and did not include time spent for equipment repairs and preparations. Fuel consumption was calculated after operation in each plot of each tillage treatment topping up the fuel tank of tractor with a graduated cylinder. Fuel consumption included fuel spent for tractor turning in the headlands between the plots. Labor was measured with a stop watch for each tillage treatment.

The experiment was located in the same area each year and was repeated in the second growing season following exactly the same procedure (with the exception of paraquat application before planting in minimum tillage plots as previously described) using the same tractor and machinery. Climatic data during the cultivation periods are given in Fig. 1 . Statistical analysis of data was performed using the SPSS (version 10) program. A separate analysis of variance (ANOVA) for each year was performed for the plant number, ear number, and yield data because the Bartlett's test for homogeneity of variances indicated that they were heterogeneous. The ANOVA was performed in a randomized block design in a split plot arrangement, where the three tillage systems were the main plots and the four seeding rates were the subplots (Tables 1 and 2). However, the ANOVA for labor time and fuel consumption was performed over years using a randomized block design with three tillage systems replicated four times (Table 3). This was made because labor time and fuel consumption measurements were not taken for the subplot seeding rate treatments (as they were exactly the same) but only for the main plot tillage treatments. Differences between treatment means were examined by the protected LSD test at the 0.05 probability level.

View larger version (24K): [in this window] [in a new window]   Fig. 1. Total monthly rainfall and mean monthly temperature during the experiments.

	RESULTS AND DISCUSSION

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

Number of Wheat Ears
Ear number, in both growing seasons, was not affected by tillage system, averaged over seeding rates or by tillage system x seeding rate interaction (Tables 1, 2, and 5). However, there were significant differences in ear number among seeding rates. In particular, averaged over tillage systems, in both growing seasons no significant differences were observed in ear number among the two lower or among the two higher seeding rates, but ear number in the two lower rates were lower than that in the two higher seeding rates. These findings also mean that, averaged over tillage systems, there were 2.20 and 2.25 ears per plant at the lowest seeding rate in 2004 and 2005, respectively, and 1.53 and 1.38 ears per plant at the highest seeding rate in 2004 and 2005, respectively. In addition, the initial 41% plant number difference (157 vs. 266 plants m^–2) between the lowest and highest seeding rate in the first growing season decreased to 15% in terms of ear number (346 vs. 407 ears m^–2). In the second growing season, the initial 52% plant number difference (145 vs. 304 plants m^–2) decreased to 22% ear number difference (326 vs. 418 ears m^–2). These findings indicate that increased tillering and consequently increased ear formation has taken place to compensate the reduced stand density of plants grown under lower seeding rates. Such compensating effect for low plant densities through increased tillering is common in wheat (Whaley et al., 2000; Gooding et al., 2002; Lloveras et al., 2004). Carr et al. (2003b) also reported that more ear-bearing tillers per square meter occurred as the seeding rate increased, but there were fewer tillers per plant. Similarly, Sunderman (1999) found that seed density of hard red winter wheat had little effect on the final number of ears per unit area under no-tillage. Hemmat and Taki (2001) also found that seeding rate did not have a significant effect on wheat heads per unit area when averaged across stubble-tillage management systems.

Our findings agree with those reported by other researchers who found that overall grain yield of wheat was unaffected by seeding rate (Sunderman, 1999; Hemmat and Taki, 2001; Carr et al., 2003a, 2003b). On the contrary, López-Bellido et al. (1996) found higher winter wheat yield under no-tillage than under conventional tillage in dry seasons, whereas the opposite was true in wet seasons. In addition, Halvorson et al. (2000) and Camara et al. (2003) reported lower grain yield of spring or winter wheat in conservation tillage systems compared with moldboard plowing.

Labor Time and Fuel Consumption for Wheat Production
Labor time and fuel consumption were similar for both growing seasons, but they were affected by tillage system (Table 3). In particular, labor time and fuel consumption under minimum tillage during seedbed preparation was 75.9 and 73.7% less than conventional tillage, while the corresponding reduction under reduced tillage was 65.7 and 65.8% (Table 6). In addition, total labor time and fuel use under minimum tillage, during all growing operations (tillage to harvest), was 49.7 and 53.3% less than conventional tillage. The labor and fuel reductions were 43.0 and 47.6% respectively, under reduced than conventional tillage.

	CONCLUSIONS

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

 
The results of this study indicate that winter wheat can be grown successfully under conservation tillage systems with lower labor and fuel inputs and without any detrimental effect on grain yield. The increase of seeding rate increased wheat density and ear number, but it did not produce any significant advantage on grain yield. Even when herbicide application before planting is needed in minimum tillage, its effect on labor and fuel inputs is low considering that grain yields in minimum tillage are equal to those of conventional tillage and that conventional tillage requires higher inputs in labor time and fuel during seedbed preparation than minimum tillage. These findings mean that conservation tillage systems could become a viable alternative tillage system for wheat growers under Mediterranean conditions without the need of any particular adjustment in seeding rates to optimize grain yield.

	NOTES

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

 
¹ This does not imply endorsement of the manufacturer over others, or something to that effect.

Received for publication September 21, 2005.

	REFERENCES

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

 

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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Lithourgidis, A. S. Articles by Eleftherohorinos, I. G. Search for Related Content PubMed Articles by Lithourgidis, A. S. Articles by Eleftherohorinos, I. G. Agricola Articles by Lithourgidis, A. S. Articles by Eleftherohorinos, I. G. Related Collections Crop Growth and Development Other Crop Management Best Management Practices Tillage