Effects of Conventional and Reduced Tillage Methods on Some Traits of Wheat in Cotton-Wheat System

Tillage is one of the most important agronomical practices especially for plant height (PH), grain yield (GY) and yield components in wheat production. This study was carried out in 2007–08 and 2008– 09 growing seasons in Kahramanmaras, Turkey, to investigate response of five wheat cultivars (Adana, Ceyhan, Dogankent, Menemen and Yuregir) to conventional (CT) and reduced tillage (RT) systems after cotton harvest for PH, number of fertile spikes per m2 (SM), spike length (SL), number of fertile spikelets spike–1 (SS), number of grains spike–1 (GS), 1000–kernel weight (KW) and GY components. The soil was ploughed at a depth of 25–30 cm in CT system, while it was not used in RT. The results indicated that all traits had greater values in 2008–09 than in 2007–08 except KW and GY. The tillage systems significantly affected PH, SM, SL, SS, GS and GY except KW. Over the two years, values of all traits in CT were higher than those of RT. There was a significant and positive correlation for GY, SS, GS and KW between CT and RT. The cultivars were affected by year and tillage system. Dogankent cultivar had better performance and stable for most of the traits compared to others under CT and RT in both years. DOI:10.18016/ksudobil.382413 Article History Received : 22.01.2018 Accepted : 09.04.2018


INTRODUCTION
Cotton and wheat have important roles in field crops production of Turkey.Cotton is produced only in western and southern regions of the country while wheat is produced country-wide.In the southern regions, wheat is produced fallowing cotton as a winter crop.
Depending on the climate of the year, the planting date of wheat is delayed in some years because of the delay of cotton harvest to late November (Nasrullah et al., 2010).Some studies reported that delaying in sowing of wheat decreases the yield (Gangwar et al., 2004;Buttar et al., 2012).After cotton harvest, reduced tillage may be a solution to prevent delayed wheat sowing (Nasrullah et al., 2010).Reduced tillage system, also known as limited tillage, is any type of farming system that involves less cultivation than conventional tillage (Buttar et al., 2012).Normally, reduced tillage system does not involve plowing and disc cultivation, and it is generally used in the second crop soil preparation (shallow disc cultivator and harrow) after the first crop harvest (Nasrullah et al., 2010).Reduced tillage has some advantages such as higher profits from reduced inputs including labor and fuel costs, reduced land degradation, improvements of soil structure and organic matter (Micucci and Taboada, 2006), improved soil moisture retention and less leaching of chemicals and nutrients (Logsdon et al., 1987;Varsa et al., 1997;Dexter, 2004;Humphreys et al., 2010;Dexter and Czyż, 2011).The soil compaction is reduced in reduced tillage compared to conventional tillage system because of less traffic in the field (Zhang et al. 2006;Ji 2013).In addition, Buttar et al. (2011) and Ram et al. (2012) reported that reduced tillage system reduced wheat production cost.Jug et al., (2011) said that the effect of reduced tillage system on wheat yield is dependent on where it is applied.Under a no-tillage conservation system, the soil conditions were better for plants compared to under conventional system in arid and semi-arid conditions (Mosaddeghi et al., 2009).In contrast to the above opinion, Vita et al. (2007) found that plough tillage gives better results for grain yield under higher rainfall.Khan and Khaliq (2005) compared conventional wheat production after cotton harvest to delayed surface seeding of wheat and reported that surface seeding yielded higher than conventional production.
In Turkey, early fall precipitations after cotton harvest causes difficulties in soil preparation for wheat planting.Therefore, growers frequently use reduced tillage after cotton harvest.In this study, reduced tillage after cotton harvest was performed to determine the effects on the traits such as plant height, yield and yield components of wheat compared to conventional tillage.1).The total rainfall in growing season of 2008-09 was 16.8% higher than average of long-term while rainfall of the growing season of 2007-08 was 19.9% lower than average of long-term.April is an important month for anthesis and grain filling period of wheat in this region.Unlike in the growing season of 2007-08 and the usual trend in long-term, dry and warm southern winds in the growing season of 2008-09 caused grain yield reductions.The experimental field soil was loamy, slightly alkaline and highly limy, and containing adequate potassium but low organic matter.

MATERIALS and METHODS
The experiment was a randomized complete block in a split plot design with three replications.The main plots were two levels of tillage, one of which was conventional tillage (CT) and the other was reduced tillage (RT).The sub-plots were five bread wheat cultivars which were Adana, Ceyhan, Dogankent, Menemen and Yuregir.Mentioned cultivars were used because of being widely grown in Kahramanmaras.CT and RT were applied after harvesting the previous cotton crop on November in both growing seasons.In CT system, the soil was firstly ploughed at a depth of 25-30 cm (1), then shallow disc cultivator at a depth of 10-15 cm was applied (2) and it was harrowed for flatting (3).Under RT System, shallow disc cultivator tillage at a depth of 10-15 cm was applied (1) and it was harrowed (2).Under each tillage system, cotton stalks were mixed into the soil by shallow disc cultivator.Wheat cultivars were sown on 17 November 2007 and 12 November 2008 via seed plotter.Each subplot was sown in 6 rows, 7 meters length and 20 cm apart.The sowing density was 500 seeds m -2 .Fertilization process was made according to farmers' application.Fertilizer DAP (150 kg ha -1 ) was applied before planting and AN (200 kg ha -1 ) was used at the shooting stage, while weed-control was performed by herbicide application at the main shoot stage (Zadoks et al., 1974).Irrigation was one time applied with flood water system in milk stage in both CT and RT.
In the study, plant height (PH), number of fertile spikes per m 2 (SM), spike length (SL), number of fertile spikelets spike -1 (SS), number of grains spike -1 (GS), 1000-kernel weight (KW) and grain yield (GY) were determined.PH and SL were measured (cm) with average of ten plants.SM was counted in one meter square prior to harvest.SS and GS were counted in ten spikes and their means were calculated.The data collected were subjected to statistical analysis using MSTAT-C software.

Plant height (PH)
According to the results, PH was significantly affected by year (Y), tillage system (T), cultivar (C), and C × T and Y × C × T interactions (

Spike length (SL)
Spike length varied throughout the years, tillage systems, and interactions of Y and T (Table 2).But, there were insignificant differences between the cultivars, and among all of traits interactions for the mean of SL.In 2008-09 growing season with the highest rainfall, the mean SL of cultivars was higher than in 2007-08 (2.7%).Conventional tillage was also higher in SL than RT (8%) in the mean of years.In the contrary, the mean values of cultivars were found insignificant between CT and RT in each year (Table 3).
Number of fertile spikes per m 2 (SM) Number of fertile spikes per m 2 responded significantly to the years, tillage systems, cultivars, and Y × C, C × T and Y × G × T interactions (Table 2).In 2008-09 growing season, the mean of SM of cultivars was higher than in 2007-08 (5.5%).Also, in respect to SM values CT was significantly higher than RT (10.6%).A measure of SM was highly affected by tillage systems in 2008-09, while it was not affected in 2007-08 (Table 4).Dogankent cultivar had the highest SM under CT in both two years, while it had less under RT.In the contrary, Adana cultivar had the highest SM under RT in both experiment years.
Number of fertile spikelets spike -1 (SS) The results show that SS was significantly affected by the years, tillage systems, cultivars, and Y × C and C × T interactions ( A measure of GS was significantly influenced by years, tillage systems and cultivars.But, GS was not affected by their interactions (Table 2).Cultivars responded separately to the precipitation.All cultivars in 2008-09 had higher GS numbers than in 2007-08 except Yuregir (Table 5).Dogankent cultivar had higher mean number of GS in both 2007-08 and 2008-09 years (39.2 and 40.9 grains spike -1 , respectively) and was also higher under CT and RT.Yuregir cultivar had similar values for GS (39.1 grains spike -1 ) between tillage systems and years.According to the results, KW was significantly affected by years and cultivars, and their interactions (Table 2).However, KW was not affected by tillage systems.In the contrary, to expectations, in 2007-08 growing season, the mean KW of cultivars were higher (38 g) than in 2008-09 (37 g) (Table 2).In each years, KW values of cultivars were significantly varied by tillage systems except RT in first year (Table 5).The KW values of cultivars under CT were higher than under RT except Adana cultivar in second year.Ceyhan cultivar had the highest KW values under CT and RT in 2008-09.Under CT in first year, Dogankent cultivar had the highest KW (39.2 g) which was followed Ceyhan, Adana and Menemen (38.0, 37.9 and 37.9 g, respectively).

Grain yield (GY)
The analysis of variance revealed that GY was significantly affected by years, tillage systems and cultivars (Table 2).However, GY was not affected by interactions of experimental factors.Although, high rainfall in 2008-09, the mean GY of cultivars in this year was lower than in 2007-08.GY values were found variable for each year and cultivars.In average of two years, the highest GY was obtained from Dogankent cultivar (6909 kg ha -1 ) which was followed by Adana and Ceyhan (6623 and 6257 kg da -1 , respectively).
Irrespective of the cultivar, wheat had a higher GY under CT than under RT.GY of CT was increased at the rate of 11.5% compared to RT in both combined and separated years (Table 2 and Table 6).
In higher rainfall year, GY values of cultivars under RT were significant compared to CT, while it was viceversa in 2007-08 (Table 6).Dogankent cultivar was the most stable cultivar under CT compared to other cultivars in both experiment years, which was followed by Adana cultivar.2.0 1.9 1.3 1.7 1.4 1.0 1 -0.9 0.8 1.1 0.6 **Significant at 1%, * significant at 5% and ns: not significant b Tillage system × Cultivar in each year 1000-kernel weight (KW) Table 6.Effects of two level tillage systems and five cultivars on grain yield (kg ha -1 ) of wheat.
Grain yield (kg ha

Correlations among traits in tillage systems
There was a significant and positive correlation for GY, SS, GS and KW between CT and RT (r ꞊ 0.724*, r ꞊ 0.727, r ꞊ 0.854** and r ꞊ 0.0814**, respectively) (Table 7).Under RT system, KW and GY were correlated highly and positively (r ꞊ 0.732*).There was a positive and significant relation between SS and GS (r ꞊ 0.603*).Under CT, there was a positive and significant relation between PH and SM (r ꞊ 0.638*).The correlation between SM and SL was significant and positive (r ꞊ 0.669*).In addition, there also was a positive correlation between SM and GS (r ꞊ 0.922**) and SL and GS (r ꞊ 0.642*).

DISCUSSION and CONCLUSION
Results of current experiment indicated that all traits were highly significant between the CT and RT system except KW which had higher values under CT than RT (Table 2).There were also significant differences among cultivars for all traits except SL.There were differences between two experimental years for SM, SL, SS, GS, KW and GY and PH.All studied traits sustained greater values in 2008-09 than in 2007-08 except KW and GY.
The years were also evaluated separately for each trait for their differences.There was a difference for plant height for both experiment years.The mean PH of cultivars under CT was higher than under RT in both 2007-08 and 2008-09 growing seasons.Similar results also reported in a study by Buttar et al. (2012).In 2008-09 growing season, the cultivars were found variable in both CT and RT while they were found variable only in CT in 2007-08.
The mean SM of the cultivars was higher in the first year than the second year.Besides, in both 2007-08 and 2008-09 growing seasons, the SM performance of the cultivars under CT was higher than those of RT which was consistent with the findings of Malecka et al. (2012).Dogankent cultivar had the highest SM under CT while Adana cultivar had the highest SM under RT.CT showed in a significantly higher SL than RT in the mean of years.Contrarily, the mean values of cultivars were found insignificant between CT and RT for each year.Interestingly; SL was not affected by tillage systems in each experiment year.CT system had higher the mean of GS than RT in combined years.Malecka et al. (2012) reported that GS was not significant in combined years.All cultivars in 2008-09 sustained higher GS numbers than in 2007-08 except Yuregir.Yuregir cultivar was stable between tillage systems and in both experiment years.Dogankent cultivar had the higher number of GS in both years and also under CT and RT.
CT system had higher GY than RT in combined years (Malecka et al., 2004;Malecka et al., 2012;Woźniak, 2013).The cultivars under CT except Adana were higher than under RT for GY in second year.Dogankent cultivar was the most stable cultivar for GY under CT compared to other cultivars in both experiment years and it was followed by Adana cultivar.CT system had higher KW than RT in combined years.In contrast to our result, Malecka et al., (2012) found that CT system had lower KW than RT.The highest KW were recorded in Ceyhan under CT and RT in 2008-09.Under CT in first year, Dogankent cultivar had the highest KW value and was followed by Ceyhan, Adana and Menemen cultivars.Although high rainfall in 2008-09, the mean GY of cultivars in 2008-09 was lower than in 2007-08.There was also similar result for KW.The climatic conditions of Kahramanmaras was extremely different in 2008-09 winter wheat growing season compared to 2007-08 and the long-term (Table 1).In April 2009, there was extremely a dry southern wind, and furthermore there was high moisture in the soil caused by high rainfall.In Kahramanmaras, the early milk stage of grain filling period is in April.Therefore, the climatic changes in 2008-09 growing season caused environmental stress on early milk stage of wheat, and negatively affected KW and GY.Sharma and Smith (1986) and Lihua et al. (2013) reported negative effects of dry winds on GY.Additionally, Jia et al. (2009) reported negative effect of high precipitation and soil moisture on milk stage and GY of wheat.On the contrary, Vita et al. (2007) reported positive effect of higher precipitation on grain yield.Barasel et al (2008) and Woźniak (2013) reported that yield and yield components are greatly influenced by plant genotype and environmental conditions.
Between CT and RT there was a significant and positive correlation for GY, SS, GS and KW.There was a positive relation between KW and GY under RT system.Virk and Anand (1970), Iftikhar (2012) and Haq et al. (2010) reported similar results while Khan et al. (1999) reported otherwise.There was a positive and significant relation between SS and GS and this finding was in agreement with Cantrell's (1986).Under CT, there was a positive and significant relation between PH and SM.These findings were comparable to Eunus et al. (1986) and Belay et al. (1993).However, Iftikhar (2012) reported negative relation between these traits.The correlation between SM and SL was significant and positive just as Cantrell and Haro-Arias (1986) indicated despite the fact that Mohsin et al. (2009) reported a negative correlation for the two traits.In addition, there was also a positive correlation between SM and GS and SL and GS.Cantrell and Haro-Arias (1986) also reported a positive correlation between SM and GS which supported our findings.Eunus et al. (1986) andSahah et al. (1988) reported positive relation between SL and GS, while Iftikhar et al. (2012) andNarwal et al. (1999) found negative correlations.
All of the investigated traits of bread wheat cultivars in this study were affected by tillage systems, except KW, and climate at different levels.According to the results, plant height, grain yield and yield components under RT system decreased depending on cultivars compared to CT. Repeating the study with multi locations and years including economic analysis and different sowing dates in upcoming years is needed.

Table 1 .
The total rainfall, number of rainy days and maximum and minimum temperatures per month during 2007-08 and 2008-09 growing seasons and over thelong-term (between 1970 and 2011) in *The Kahramanmaras Meteorology Station located at 37° 35' N latitude, 36° 56' E longitude at an altitude of 572 m above sea-level W = West; E = East; S = South; N = North KW was determined by counting of 1000 seeds and were weighted in gram.Plot yields in harvest were converted to hectare yields.

Table 2 .
Table2).The mean SS value of cultivars was higher in 2008-09 compared to 2007-08 (Table4).Numbers of fertile spikelets was affected by tillage systems in each year.Dogankent cultivar had 18.3 fertile spikelet spike -1 in 2008-09, while Ceyhan and Dogankent cultivars had 17.1 fertile spikelet spike -1 in 2007-08 (Table4).In addition, Dogankent and ceyhan cultivars were characterized by high SS stability under CT and RT for both two years.The average data of years, cultivars and tillage systems for studied traits.

Table 3 .
Effects of two level tillage systems and five cultivars on plant height and spike length of wheat.

Table 4 .
Effects of two level tillage systems and five cultivars on number of fertile spikes per meter-square and number of fertile spikelets per spike of wheat.

Table 5 .
Effects of two level tillage systems and five cultivars on number of grains per spike and 1000-kernel weight of wheat.