Tillage effects on corn emergence, silage yield, and labor and fuel inputs in double cropping with wheat.
Delayed crop emergence and reduced plant population are problems sometimes associated with corn production under conservation tillage practices. Poor crop establishment, low plant populations, and delayed early plant growth due to higher mechanical impedance of soil were the primary cause of low corn forage yields on no-tillage plots observed by Hughes et al. (1992). On the other hand, a number of studies have reported that corn yields were similar with reduced tillage systems or traditional moldboard plow tillage (Al-Darby and Lowery, 1986; Mehdi et al., 1999; Beyaert et al., 2002). However, most of research has shown a great variability in corn yield response to no-tillage treatments, which often depends on previous crop and soil drainage characteristics (Dick and Van Doren, 1985; Griffith et al., 1988).
In general, well-drained soils, crop rotation, and warmer climates often account for higher corn yields with no-tillage than poorly drained soils, continuous cropping, and cooler climates (Griffith and Wollenhaupt, 1994). Thus, no-tillage corn produced greater yield on well-drained sandy loam and silt loam soils but less yield on a dark and poorly drained soil than moldboard plow for continuous corn (Griffith et al., 1973). However, continuous corn yield in no-tillage and moldboard plow systems did not differ on a poorly drained loam and a well-drained sandy loam (Hesterman et al., 1988). Yields of continuous corn have been less under no-tillage than moldboard plow tillage on silt loam or finer textured soils (Dick and Van Doren, 1985; Griffith et al., 1988; Meese et al., 1991). A yield reduction due to no-tillage can often be offset, at least partially, by rotating corn with other crops (Oriffith et al., 1988; Chase and Dully, 1991; Dick et al., 1991). Thus, Meese et al. (1991) reported a yield decrease of about 10% for continuous corn in no-tillage compared with moldboard plow tillage, whereas corn yields under these two tillage systems were generally similar in a corn-soybean [Glycine max (L.) Merr.] rotation. Corn yield was found to be significantly higher under plow tillage in 1992, following alfalfa (Medicago saliva L.) but similar to no-tillage in 1993 on a clay loam soil (Karunatilake et al., 2000). On the contrary, Brown et al. (1989) reported that no-tillage corn yield was less than yield with moldboard plow, disking, and field cultivation in a corn-soybean rotation. Similarly, corn forage yields on no-tillage plots were, on average, 16% lower than on full-tillage plots in a 10-yr corn-oats (Auena saliva L.) rotation (Hughes et al., 1992).
No-tillage systems are characterized by high levels of previous crop residues on soil surface. The presence of residues can reduce soil erosion, conserve soil moisture, decrease evaporation and runoff and increase rainfall infiltration (Pierce et al., 1992). On the other hand, the presence of residue may delay plant emergence and reduce crop yields mainly because of cooler soil temperatures (Opoku et al., 1997). Lund et al. (1993) reported reduction of 6% in no-tillage corn yields where corn followed wheat rather than soybean. High levels of wheat straw mulch on no-tillage plots reduced corn yields in Nebraska (Wicks et al., 1994). Reducing the amount of wheat residues increased early-season corn plant height and yield (Swanton et al., 1995). When all wheat residue was completely removed, no-tillage corn yields were not different from those obtained with fall tillage systems (Opoku et al., 1997). On the contrary, with a wheat-sorghum [Sorghum bicolor (L.) Moench] rotation retaining mulch on the soil surface during the growing season increased grain sorghum yield 9 to 11% when compared with no mulch (Unger and Jones, 1981).
Acceptance of no-tillage or reduced tillage systems for corn depends more on its profitability rather than grain yield alone. Profitability for corn depends on revenue (grain yield x price for grain) and total production cost (Al-Kaisi and Yin, 2004). In general, greater economic returns and lower production cost of reduced tillage systems result in reduced energy and operator time requirements compared with conventional tillage systems (Smart and Bradford, 1999). Thus, reduced tillage systems have lower costs in labor, fuel, and machinery inputs (Raper et al., 1994), although the presence of difficult-to-control weeds can greatly elevate herbicide and total production costs (Smith et al., 1996). Therefore, the expected higher economic return with no-tillage corn because of labor and fuel saving is questionable. The economic return for no-tillage may vary considerably with many factors such as soil characteristics, management practices, crop rotation, and labor inputs compared with conventional or other conservation tillage systems. Karunatilake et al. (2000) reported that long-term use of reduced tillage systems was more economic than conventional tillage systems on well-structured clay loam soils. Similarly, Smart and Branford (1999) found in a 4-yr tillage study that conservation tillage systems (reduced and no-tillage) had greater economic returns compared with a conventional tillage system because of both greater yield in dry years and lower production costs in all years. However, Chase and Duffy (1991) found that the economic return for corn under no-tillage was similar to that under moldboard plow, ridge, or chisel plow tillage in a corn-soybean rotation. Moreover, Doster et al. (1983) reported that no-tillage ranked second in economic return for corn, next to ridge tillage, among six tillage systems in both continuous corn and corn-soybean rotations.
The objective of this study was to investigate the effect of no-tillage (direct drilling) and reduced tillage on corn establishment and silage yield and to determine consumption of fuel and human labor required for corn production under these tillage systems compared with conventional tillage in double cropping with winter wheat. The effect of tillage systems on grain yield of winter wheat was also evaluated.
MATERIALS AND METHODS
One field experiment was conducted during the 1997-1998, 1998-1999, 1999-2000, and 2000-2001 growing seasons in the University Farm of Thessaloniki in northern Greece. The experiment was established in a clay loam, well-drained soil with pH 8 and organic matter content 12.5 g [kg.sup.-1] (0- to 30-cm depth). The previous crop was winter wheat (variety Yecora), which was harvested in mid June of each growing season approximately 20 to 25 cm from the soil level. Wheat straw (4000 kg [ha.sup.-1]) was baled and removed after harvest.
Corn (Pioneer hybrid PR 3245) was sown within the first week of July (a common period for planting corn as double crop following wheat) of each growing season at the same field where winter wheat was previously grown. The experimental design was a randomized complete block of the three tillage systems replicated ten times. Plot size was 6.00 x 50.00 m, which allowed the use of commercial-size farm equipment; each plot included eight corn rows. Tillage treatments were separated by a 2-m buffer zone.
The three tillage management systems were (i) NT (notillage), i.e., corn sowing with direct drilling (after wheat harvest) without any seedbed preparation, using four-row sowing machine (Model Annodi Fondazione, Co., Gaspardo, Italy), designed especially for direct drilling. The planter was equipped with two single fluted coulter blades in one line (45- and 30-cm diameter, respectively) to cut a slit, followed by two inclined plain disks (28-cm diameter) to form a V-groove in which the seed was placed, and a single 10-cm-wide wheel (45-cm diameter) for furrow closing. (ii) RT, i.e., corn sowing after reduced tillage (heavy offset harrow disc to a depth of 18 cm and cultivator to a depth of 12 cm, speeds of operations 10 and 8 kin/h, respectively). (iii) CT, i.e., corn sowing after conventional tillage (four-bottom moldboard plow to a depth of 22 cm at a speed of 7 kin/h, tandem harrow disc to a depth of 12 cm at a speed of 11 km/h, and cultivator to a depth of 12 cm at a speed of 8 km/h), which is the common tillage practice for corn production in Greece and was considered as control. A 88 HP (64.7 kW) Ford tractor (Model 6640 Powerstar SL) was used for all operations, running at 1700 to 2100 rpm engine speed (according to load). In conventional tillage and reduced tillage plots, corn was sown with farmer's equipment (four-row pneumatic sowing machine, Model sp. 520, Co., Gaspardo, Italy). The planter was equipped with a runner opener, 3-cm-wide angled press wheels (35-cm diameter), and a clod deflector attached in front of the runner opener. Both planters were adjusted to plant at a depth of 4 to 5 cm, with planting speed of 6 km/h. Distance between rows was 75 cm. In all plots, corn was sown at approximately 85 000 seeds [ha.sup.-1].
Nitrogen as ammonium sulfate (21-0-0) and [P.sub.2][O.sub.5] as superphosphate (0-20-0) at 240 and 70 kg [ha.sup.-1], respectively, were incorporated into the soil before disc harrowing in conventional tillage and reduced tillage plots, whereas it was applied to the soil surface before corn sowing in no-tillage plots. In all plots, weed control was achieved with alachlor, 2-chloroN-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide, plus atrazine, 6-chloro-N2-ethyl-N-4-isopropyl-1,3,5-triazine- 2,4-diamine, (Lasso-AT 33.6/14.4 SC at 5 L [ha.sup.-1]) applied preemergence, and also with rimsulfuron, 1-(4,6-dimethoxypyrimidin2-yl)-3-(3-ethylsulfonyl-2-pyridylsulfonyl)urea, (Rush 25 WG at 50 g [ha.sup.-1]) applied postemergence for the control of johnsongrass (Sorghum halepense L.). In 1998, 1999, and 2000, mechanical cultivation was also used to control weeds in conventional and reduced tillage treatments when corn was at the V-5 to V-6 stage of growth. The mechanical cultivation was used to follow exactly the standard agronomic practices commonly used for corn production by most farmers in Greece. The experimental area was irrigated similarly with sprinklers eight times in the first year with a 350-ram total amount of water, seven times for the other 2 yr with a 360-mm total amount of water, and eight times in the last year with a 400-mm total amount of water. First irrigation took place within the first week after corn sowing for all years, with the exception of last year where it was applied a week before sowing because of dry soil conditions prevailing.
Plant number (4 wk after sowing) and silage yield (at approximately 0.5-kernel milk line stage) were determined for all plots in each year. Labor time and diesel fuel consumption were calculated totally for all plots 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 all plots of each treatment (totally 10 plots) 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 treatment. The middle six rows of each eight-row plot of corn were harvested in mid October of each growing season (about 105 d after sowing) with an appropriate two-row silage harvesting machine (Rottinger Mex-profi k, Austria). At this time, random samples of 1 kg biomass from each plot were taken and dried in oven for 72 h at 65[degrees]C to determine the relative water content. Then, silage yield was calculated on a 650 g [kg.sup.-1] water basis.
After corn harvest, conventional tillage was applied to all the experimental area and winter wheat, variety Yecora, was sown around mid November at 150 kg [ha.sup.-1] (16-cm row widths) at the same experimental plots used for conventional, reduced tillage, and no-tillage corn. Nitrogen and [P.sub.2][O.sub.5] as diammonium phosphate (20-10-0) at 120 and 60 kg [ha.sup.-1], respectively, were incorporated into the soil before wheat sowing. In all plots, weed control was achieved with tribenuron methyl (Granstar 75 WG at 15 g [ha.sup.-1]) applied postemergence.
The experiment was located in the same area each year, with the same plot layout, and was repeated in each growing season following exactly the same procedure, and using the same tractor and machinery. Climatic data during both summer and fall cultivation periods are given in Table 1. Statistical analysis of data was performed by the SPSS (version 10) program. A combined analysis of variance (ANOVA) over years was performed for the plant number and yield data. This was made after the use of Bartlett's test to check for homogeneity of variances of each parameter among years. However, the ANOVA for labor and fuel consumption was performed with the four year measurements as replicates. All treatment means were compared by the protected least significant difference (LSD) at the 0.05 probability level.
RESULTS AND DISCUSSION
Number of Corn Plants
The number of emerged plants for all treatments in each year is presented in Table 2. The number of plants with each of the three tillage systems did not differ in 1997 and 2000. In contrast, in 1998 and 1999 the number of plants was lower (by 26.4 and 16.2%, respectively) with no-tillage than with conventional tillage. The number of plants in 1998 was lower by 15.5 to 35.6% for all treatments compared with those of the previous year. This could be attributed to the unfavorable soil conditions during corn sowing (early July). In particular, the low level of soil moisture due to low precipitation before sowing (2 mm from June to July) (Table 1), resulted in difficulties during sowing in all tillage systems. This was more pronounced in no-tillage plots apparently because of the incapacity of the sowing machine to penetrate the dry soil surface resulting in lower number of emerged plants per hectare. In the last year (2000), because of irrigation in all plots before sowing, the situation appeared improved and the number of plants did not differ in any case. In all years, reduced tillage plots had always similar number of plants compared with conventional tillage plots. Moreover, there was always a greater uniformity regarding plant population in the control treatment and in reduced tillage treatment compared with no-tillage. This could be attributed to the tillage technique and also to the different technology of the sowing machines used. Differences in plant population between tillage systems resulting in lower corn yields in some years have been previously reported (Potter et al., 1996). Also, reductions in early corn growth and, in some cases, in final grain yields have been reported and were attributed to lower early season soil temperatures under notillage (Vyn and Raimbault, 1993). Similarly, Smith et al. (1992) reported that no-tillage reduced corn emergence by 8 to 20% compared with conventional tillage. By contrast, plant density of corn following alfalfa was found to be significantly higher under no-tillage than plow tillage (Karunatilake et al., 2000).
Earlier emergence and faster growth rate for corn plants were observed in no-tillage plots during the early growth stages (data not shown). This was probably due to both higher level of soil moisture in no-tillage plots (because of lower loss of soil moisture under no-tillage practice) and shading by the residue (straw) of the previous crop. However, no significant differences in corn growth were observed between treatments later in the growing season. On the other hand, Wicks et al. (1994) reported that early corn growth was retarded by increasing wheat residues because of reduced soil temperatures, but after tasseling, corn grew taller because of increased soil moisture. In addition, no-tillage corn has been found to require an average of two more days to reach 50% emergence compared with conventional and chisel tillage and much of this delay in the emergence was attributed to reduced soil temperatures (Hayhoe et al., 1993) and to the presence of high levels of wheat residues on the soil surface (Opoku et al., 1997) in no-tillage treatments.
Corn Silage Yield
Corn silage yield for all treatments in each year is presented in Table 3. Silage yield did not differ among treatments in 1997, 1999, and 2000; however, in 1998, it was lower in no-tillage than in conventional tillage cropping. In that year, as mentioned previously, the number of plants was also lower (by 26.4%) in no-tillage than in conventional tillage (Table 2). However, silage yield reduction was not proportional to the plant number reduction. Thus, silage yield in no-tillage was only 13.5% lower than conventional tillage (Table 3). Moreover, differences in plant number between no-tillage and conventional tillage in 1999 (by 16.2%) did not have any significant effect on silage yield. This could be attributed to the corn plants compensation for low population. In addition, a substantial number of those plants (about 40%) gave one extra thin tiller with ear (data not shown), reducing thereby the effect of lower plant number on silage yield. In 1998, however, there was a significant difference in silage yield because the difference in plant number that year was much greater than in 1999. The lower corn yields which were observed with no-tillage than with other tillage practices were associated with plant population differences between tillage systems, with low plant populations in no-tillage plots restricting corn yield in some years (Potter et al., 1996).
The findings of this experiment agree with those of Smart and Bradford (1999) who found that yields for no-tillage were lower than for conventional tillage of the first cropping year, whereas, yields were equivalent or greater than conventional tillage yields in the next 2 yr. Similarly, Griffith et al. (1973) and Hesterman et al. (1988) reported that no-tillage corn produced greater or similar yield on well-drained soils than moldboard plow tillage. On the other hand, the results are in contrast to other previous studies (Pierce et al., 1992; Swanton et al., 1995; Opoku et al., 1997), where corn following wheat always had higher yields in conventional tillage than no-tillage systems, especially, where wheat residues remained in the zone above the corn row.
Despite differences among growing seasons (overall mean of yields was 3.66, 5.50, 4.00, and 4.95 Mg [ha.sup.1] in 1998, 1999, 2000, and 2001, respectively), no significant differences were observed in wheat yield among tillage practices. Yield differences among years could be attributed to rainfall variation among growing seasons, particularly to the amount and distribution of rainfall during the critical period of wheat growth (March-May). This is important since spring climatic conditions (drought and high temperature) are the main factors that affect winter wheat growth under Mediterranean conditions (Garcia del Moral et al., 2003; Matsi et al., 2003). Thus, the lower yields recorded in 1998 and 2000 could be attributed to the unequal distribution of rainfall in the spring of 1998 and to the low amount of rainfall in the spring of 2000 (Table 1), whereas the satisfactory amount of rainfall, evenly distributed during the critical period of growth could account for the higher yields in 1999 and 2001.
Labor Time and Fuel Consumption for Corn Production
Labor time and fuel required during the various corn stages are presented in Table 4. There was considerable saving in time and fuel during seedbed preparation and crop establishment. Thus, labor time use with no-tillage was 63.2% in 1997, 70.0% in 1998, 50.9% in 1999, and 62.2% in 2000 less than conventional tillage. The fuel required with no-tillage was 75.1% in 1997, 83.0% in 1998, 69.4% in 1999, and 73.8% in 2000 less than conventional tillage. In addition, labor and fuel use in reduced tillage was 9.0 to 14.9%, and 13.8 to 23.0% less than conventional tillage. In 1998, greater fuel consumption and time required for crop establishment with conventional tillage and reduced tillage than the other years (Table 4). This was due to the unfavorable soil conditions during seedbed preparation which required extra soil tillage. Despite the extra soil tillage, the number of plants and silage yield were lower in 1998 compared with the other years (Table 2) and only that year (1998) showed a significant reduction in silage yield (Table 3). This unfavorable situation was avoided the next years, particularly in 1999, because of rainfall before sowing (Table 1), and in 2000, because of irrigation of the experimental field to facilitate soil tillage or no-tillage before corn establishment.
On the average, during seedbed preparation and crop establishment labor use was 3.58 h [ha.sup.-1] less, a 62.7% reduction, and fuel consumption 27.20 L ha 1 less, a 76.5% reduction, under no-tillage than conventional tillage. The labor and fuel reductions were 0.70 h [ha.sup.-1] (12.3%) and 6.34 L [ha.sup.-1] (17.8%), respectively, under reduced than conventional tillage. Similarly, Sijtsma et al. (1998) reported that fuel usage for seedbed preparation and crop establishment was lower with several minimum tillage practices (10.0-23.7 L [ha.sup.-1]) than conventional moldboard ploughing (27.6 L [ha.sup.-1]).
In addition, overall total labor and fuel use, during all growing operations (tillage to harvest), was 4.54 h ha-1 and 31.50 L [ha.sup.-1] less, respectively, under no-tillage than conventional tillage, a 35.9 and 36.0% reduction, respectively. The labor and fuel reductions were 5.6 and 7.2% respectively, under reduced than conventional tillage. The findings of this experiment were similar with those of Franzluebbers and Francis (1995) who found that fuel consumption was 48% less with no-tillage than with traditional tillage for different types of corn and sorghum management systems. Significant reductions in labor and fuel consumption have also been reported for corn grown under reduced tillage compared with a moldboard plow system (Weersink et al., 1992; Archer et al., 2002; Luna and Staben, 2002).
The effect of no-tillage, reduced tillage, and moldboard plow tillage on corn emergence and silage yield and on wheat grain yield in double cropping sequence was investigated. Moreover, labor and fuel consumption required for corn production under these three tillage systems was calculated. The data of this study indicate that reduced tillage or no-tillage practices did not greatly affect corn silage yield compared with conventional tillage. Furthermore, these practices provided significant saving in labor and fuel consumption required for corn production, mainly during the period of crop establishment, and did not influence yield of wheat followed corn. The level of soil moisture at sowing may affect corn emergence and establishment particularly with no-tillage. Lack of adequate moisture can be overcome by irrigation before sowing. Furthermore, a significant advantage of no-tillage corn in double cropping with wheat is that corn can be planted immediately after wheat harvest and no additional herbicide application is necessary. Reduced tillage or no-tillage for late-planted corn following wheat could be successfully implemented under favorable soil conditions at sowing with significant economical benefits for the farmers as an attractive alternative to conventional tillage practices.
The authors are grateful to Professor N. Fotiadis and Professor A. Gagianas, Aristotle University, Faculty of Agriculture, for their critical review and helpful comments regarding a previous draft of the manuscript.
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Anastasios S. Lithourgidis, * Constantinos A. Tsatsarelis, and Kico V. Dhima
A.S. Lithourgidis, Dep. of Agronomy, University Farm, Aristotle Univ. of Thessaloniki, 570 01 Thermi, Greece; C.A. Tsatsarelis, Dep. of Agricultural Engineering, Aristotle Univ. of Thessaloniki, 541 24 Thessaloniki, Greece; K.V. Dhima, Technol. and Educ. Inst. of Thessaloniki, 541 01 Sindos, Greece. Received 11 Feb. 2005. * Corresponding author (email@example.com).
Published in Crop Sci. 45:2523-528 (2005). Crop Ecology, Management & Quality doi:10.2135/cropsci2005.0141
Table 1. Monthly total precipitation and mean air temperature at the Farm of the Aristotle University of Thessaloniki during the four growing seasons of experimentation. Total precipitation 1997-1998 1998-1999 1999-2000 2000-2001 mm Corn cropping season July 31 1 28 10 August 29 6 0 0 September 8 32 45 22 October 74 26 53 84 Season 142 65 126 116 Wheat cropping season November 19 155 84 34 December 43 22 35 11 January 50 40 66 53 February 50 24 34 8 March 3 45 3 0 April 0 28 20 72 May 78 53 7 93 June 1 27 0 22 Season 244 394 249 293 Mean temperature 1997-1998 1998-1999 1999-2000 2000-2001 [degrees] C Corn cropping season July 25.6 28.2 27.5 27.8 August 23.0 28.5 27.4 27.1 September 18.7 22.0 22.2 21.6 October 12.0 17.3 17.6 15.9 Season 19.8 24.0 23.7 23.1 Wheat cropping season November 10.5 11.5 11.0 13.8 December 6.7 4.3 7.6 7.7 January 6.6 4.9 1.7 3.9 February 8.7 5.0 5.0 6.3 March 7.7 10.3 8.2 9.7 April 15.8 15.1 15.8 15.9 May 19.4 19.9 20.7 21.0 June 26.1 25.3 25.1 25.8 Season 12.7 12.0 11.9 13.0 Table 2. Number of corn plants as affected by tillage systems in each growing season. No. plants [ha.sup.-1] Treatment 1997 1998 1999 2000 No-tillage 76 700a ([dagger]) 49 300a 64 700a 69 700a Reduced tillage 80 500a 66 000b 71 100ab 73 500a Conventional tillage 79 300a 67 000b 77 200b 77 300a ([dagger]) Means in the same column followed by the same letter do not differ significantly according to the LSD test (P = 0.05). Table 3. Corn silage yield as affected by tillage systems in each growing season. Silage yield Treatment 1997 1998 1999 2000 Mg [ha.sup.-1] ([dagger]) No-tillage 36.68a ([double 27.93a 34.32a 38.90a dagger]) Reduced tillage 39.62a 30.66ab 38.58a 40.02a Conventional tillage 38.69a 32.28b 38.51a 39.73a ([dagger]) Silage yield is reported on a 650 g [kg.sup.-1] water basis. ([double dagger]) Means in the same column followed by the same letter do not differ significantly according to the LSD test (P = 0.05). Table 4. Labor time and fuel inputs in corn as affected by tillage systems in each growing season. Tillage and sowing Year Tillage system Time Fuel h [ha.sup.-1] L [ha.sup.-1] 1997 No-tillage 1.96 8.17 Reduced 4.61 26.89 Conventional 5.33 32.83 1998 No-tillage 2.28 8.64 Reduced 6.91 43.72 Conventional 7.60 50.72 1999 No-tillage 2.38 8.36 Reduced 4.14 21.06 Conventional 4.85 27.36 2000 No-tillage 1.91 8.22 Reduced 4.36 25.16 Conventional 5.06 31.29 Average No-tillage 2.13a ([dagger]) 8.35a Reduced 5.01b 29.21b Conventional 5.71b 35.55b Other operations Year Tillage system Time Fuel h [ha.sup.-1] L [ha.sup.-1] 1997 No-tillage 6.04 47.19 Reduced 6.04 47.19 Conventional 6.04 47.19 1998 No-tillage 5.54 48.75 Reduced 7.01 55.25 Conventional 7.01 55.25 1999 No-tillage 6.08 47.52 Reduced 7.37 53.02 Conventional 7.37 53.02 2000 No-tillage 6.26 47.29 Reduced 7.33 52.49 Conventional 7.33 52.49 Average No-tillage 5.98a 47.69a Reduced 6.94b 51.99b Conventional 6.94b 51.99b Total operations Year Tillage system Time Fuel h [ha.sup.-1] L [ha.sup.-1] 1997 No-tillage 8.00 55.36 Reduced 10.65 74.08 Conventional 11.37 80.02 1998 No-tillage 7.82 57.39 Reduced 13.92 98.97 Conventional 14.61 105.97 1999 No-tillage 8.46 55.88 Reduced 11.51 74.08 Conventional 12.22 80.38 2000 No-tillage 8.17 55.51 Reduced 11.69 77.65 Conventional 12.39 83.78 Average No-tillage 8.11a 56.04a Reduced 11.94b 81.20b Conventional 12.65b 87.54b ([dagger]) Means in the same column followed by the same letter do not differ significantly according to the LSD test (P = 0.05).
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|Author:||Lithourgidis, Anastasios S.; Tsatsarelis, Constantinos A.; Dhima, Kico V.|
|Date:||Nov 1, 2005|
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