Abstract: To study the effects of four types of primary tillage implements separately and seed densities on the yield of rain fed wheat using deep drill planting with press wheel and drill planting with end wheels, an experiment was conducted in research farm of Gonbad Agricultural faculty during 3 years (1997-2000), split block factorial design with three replications was used as experimental design. The primary tillage implements included: Moldboard Plow (MP), Disc Plow (DP), Chisel Plow (CP) and Offset Disc (OD). TAJEN wheat cultivar was planted at the rates of 140, 150 and 160 kg ha-1. Crop yields for different treatments were measured at the end of the study. The results showed that grain yield was not affected by seed density and types of tillage machines. But year, replicationxyear, planting machine and interaction effect of yearxplanting machine had significant effects on the grain yield (p<1%). As a result, considering the priority of soil physical properties, reduced tillage could be recommended as a promising strategy to improve soil physical quality, preventing soil erosion and to ensure moisture control, less energy consumption and fast preparation of soil as well as reducing costs of production, using of Chisel Plow with 140 or 150 kg ha-1 seed density with deep drill planting machine is suggested to increase wheat yield.
INTRODUCTION
Wheat is one of the most demanded, valuable and strategic crop worldwide. Apart from its use as food it has been used widely in industry especially for alcohol production. For example, in Iran, it makes up to 66.5% of seeds produced and meets 60-65% of required protein of the country (Amin, 1998). The planting area is about 145000 hectare with irrigation and 226000 hectare for rain-fed wheat according to the latest report (Agricultural Jihad of Golestan Province in 2005). If it could be possible to make a 200 kg ha-1 improvement then we could make a considerable yield increase of 75000 tones. Wheat is mostly used in supplying bread which forms the most important food of the majority of the population of the country. As a result of increasing population and essential needs of mankind to this vital and strategic crop and by considering the lack of enough resources of the production, making attempts to increase the production per each single unit of planting area and decreasing the production costs seem necessary. Most of the researches conducted in Iran have been in the field of genetic issues and a few projects have been done on technical and arable issues like cultivation density, application of tillage implements and planting, while 60% of energy costs in agricultural practices is usually allocated to tillage practice (Iqbal et al., 1994). Therefore, to reach wheat production independence in Iran, conducting deeper studies to pick out the best agricultural machines and practices that could be used for rain-fed wheat, seem inevitable.
The purposes of tillage practices are to make an appropriate environment for the germination of the seeds, growth of roots and for weeds control as well as increasing the preservation of soil moisture or facilitating the water penetration into soil. Apart from the items mentioned earlier, soil softening and stability in order to increase seed contact with soil, reduction of soil tolerance, cohesion and soil erosion are results of a good tillage practice. It is important to consider moisture control, burying vegetative remains, mixing fertilizers, pesticides and reforming materials with soil and unsetting soil inappropriate capillaries to reduce evaporation as other important desired consequents of good tillage programs (Shafieei, 1992).
To achieve mentioned goals, special tillage implements could be applied and each tillage implement has special usability and has its own advantages and disadvantages and that`s why researchers have been trying to find and use the appropriate ones by having the knowledge of the appropriate purposes according to the farm situation.
In each climate and region, appropriate tillage implements should be used concerning soil texture,precipitation, underground water depth, evaporation amount and perspiration from soil and plant, or different tillage implements should be compared and the most appropriate one should be determined in each region.
Seed density (sowing rate) is an important factor on the final yield. If it is less or more than the optimal amount, it leads to a yield reduction. When it is more than the optimal amount, the grains become weak; consequently fewer yields will be obtained. Among the three yield components, heads per unit area and kernel per head considered more important than kernel weight for determining wheat grain yield (Donaldson et al., 2001; Shah et al., 1994; Schillinger et al., 2005). Heads per unit area is generally the most important yield component for wheat (Garcia del Moral et al., 2003) but under drought conditions, kernel per head often has the greatest effect on grain yield (Arnon, 1972; Schillinger and Young, 2004). High sowing rates often result in increased head per unit (Guberac et al., 2000; Stougaard and Xue, 2004) with corresponding reduction in kernel per head (Carr et al., 2003). In response to increasing sowing rate, cereal grain yield will generally rise rapidly, reach a broad plateau and then decline slowly (Carr et al., 2003; Paulsen, 1987).
The most widely recommended sowing rate for dry land spring wheat in the northern Great Plains and the pacific North West is 200 seeds m-2 (Paulsen, 1987), but some farmers sow up to 350 seeds m-2. Considerable variability in optimum sowing rate for cereals often involve interactions with tillage, cultivar and environmental factors. The common sowing rate for dry land spring cereals in the less than 300 mm annual precipitation zone of the pacific North West is 195 seeds m-2. Sowing rates as high as 800 seeds m-2 are reported for oat production in Finland (Peltonensainio and Jarvinen, 1995).
So, concerning this issue and the fact that the cost of plantation rises with increase of seed density, reaching the optimal seed density is one of the purposes of the research.
Planting machines should also be based on the climate of each region considering mainly soil texture and precipitation. If planting machine doesn`t fit the regional conditions, it would lead to failures like, yield reduction and earlier amortization of the planting machine.
One of tillage disadvantages is increasing soil compaction that leads to a hardpan after a few years under the surface of arable soil that makes researchers think of the possibility of reducing tillage practices because the hardpan is not only preventing root growth deeply inside the soil but also caused early amortization of the machinery. By reducing tillage activities, mechanization expenditure is saved as well (Hargrave et al., 1982). But in most of lands in Iran, plantation without tillage practices does not have satisfactory results because soil of those regions is too heavy (Hemat and Asadi, 1997).
In presented study the effect of different primary tillage methods (including Moldboard Plow, Disc Plow, Chisel Plow and Offset Disc) and seed density of Tajen wheat at the rate of 140, 150 and 160 kg ha-1 with two planting machines (deep drill planting with press wheels and drill planting with end wheels) on the yield of Tajen wheat cultivar was studied in Gonbad rain-fed regions.
Touchton and Jonson (1982) conducted an experiment on the effect of 3 different methods of tillage and plantation on the yield of wheat and soybean. The 3 tillage methods included chisel, Moldboard plow and no tillage. The results were that the yield of soybean in the 2 mentioned tillage methods didn`t differ, but yield of wheat in case of Plow with Chisel Plow was less than Moldboard plow. It was indicated that when the soil was plowed by Moldboard or Chisel Plow, before plantation, the yield was better than no tillage.
Cox (1986) studied the effect of different methods of preparation of soil and 2 different types of wheat seed on the amount of yield. In that study, different methods of soil preparation included the conventional method of the region with keeping the vegetative remains in the field with plowing and tillage and without plowing or tillage. From the view point of the amount of yield, no significant difference was observed between treatments.
Baloch et al. (1991) conducted a farm experiment in order to compare the yield after using implements like Moldboard, Disc, Chisel Plow and cultivator. These experiments were conducted in two types of soil, clay-loam and loam-silt. The results showed that Disc plow needed more pulling power in loam-clay soil compared to loam-silt. When comparing the yield (field capacity) cultivators had increased the yield for 48.5 and 59.1% in comparison with Moldboard Plow and compared with Disc plow, respectively.
MATERIALS AND METHODS
Farm characteristics and the used cultivar: The experiment was conducted in research farm of Gonbad Agricultural faculty. Average annual precipitation is more than 450 mm. Rain fall occurs mainly during autumn, winter and early spring. The annual average temperature of the region was 17.7°C. According to Ambrotermic meteorology records, this region is considered as a Mediterranean climate. Soil texture was silt-clay-loam (64 silt, 30 clay and 6% sand) with electrical conductivity of 1.5 mμ m-1 and the acidity of 7.8. TAGEN; A domestic high producing rain-fed cultivar was used in this experiment.
Machinery: Two types of planting machines (deep drill with press wheels (Hussia) with 24 cm distance of plantation lines and drill planting with end wheels (Danish) with 12 cm distance of plantation lines) were used. A Tractor MF 285 was used to provide pulling power as well.
The primary tillage machinery used included Moldboard Plow with 3 bottoms mounted and one way, Disc Plow with 3 bottoms mounted, Chisel Plow with nine tines/shanks and Offset Disc 2 way 1 angle with 18 tensile discs.
Experimental design and conducting the experiment: A factorial split blocks experimental design was conducted in 3 replications. Factors including (A) Planting machines in two levels (B) Primary tillage machines in four levels and (C) seed density in three levels 140, 150 and 160 kg ha-1 (The seed density of rain-fed wheat is currently 130-160 kg ha-1 in Gonbad region that depends on soil texture and in soil with heavier texture, higher density is also possible because of more preservation of rain).
The size of each main plot of the experiment for soil preparation using each mentioned tillage machine was 72 square meters (18x4 m2, excluding the borders). Soil moisture was about 20% based on the soil texture at the time of plowing (tillage practice) and at the end of plowing a tandem Disc (2 angle) was applied on the already plowed soil, so on the whole there were 4 main plots. Then plantation with different seed density started perpendicular to the tillage direction or to the main plots forming subplots of 96 m2 (16x6 m) and there were 3 replications for each treatment.
Clean, equal in size, healthy and adore less with 13-16% moisture TAJEN wheat seeds were prepared. Purity Percentage, Germination Percentage and weight of 1000 seeds were 100, 95% and 39 g, respectively. In order to prevent fungal diseases, Carboxin nad Vitarax fungicides were used (150 g/100 kg seeds).
Plantation by mentioned planting machines was done considering seed rate and planting depth of the region (2-5 times the biggest seed`s dimensions meaning approximately 3 cm) right after soil preparation (late December to early January) and crop protection practices including removing weeds, preventing pests and diseases and applying chemical fertilizers were carried out as follows: based on soil analysis, 100 kg ha-1 phosphate fertilizer at the time of plantation and 75 kg ha-1 while digitate in March (top-dressing fertilizer were given to the experimented plots.
After complete digitate until the growth of main stems (20-25 cm tall), removing weeds was done using chemical poisons; 100 g ha-1 Granestar and 1 L ha-1 Pumasuper by sprayer machine. The amount of the poison sprayed was determined based on weeds densities and the type of the Sprayer (1-1/5 L of poison diluted with 200-400 L water ha-1). Other special cares were done during crop protection practice including removing yellow, black and brown blight/rust (after founding blight/rust by spraying 2 L Zineb poison in 1000 L water). Harvest time (when crop moisture is 14-16%, leaves are yellow and seeds are firm) was in late spring considering high regional temperature.
Harvesting practice was carried out by a sickle under mast level, in the middle of each plot far from the borders and the harvested crops were put in the gunny sack labeled accordingly and transferred to Agricultural research center of Gonbad for threshing by small combine machine. After threshing practice (crop moisture 14%), the yield at each square meter and finally at each hectare was calculated.
Required statistical calculations were done using statistical software SPSS and the mean average test was performed by Donkan Multi-Amplitude examination at p<5%.
RESULTS AND DISCUSSION
Table 1 shows a summary of the results of the variance analysis of the average yields of rain-fed wheat. Duncan multi amplitude test was used to carry out the comparison of the averages (Table 2). Results indicate that year and interaction effect of yearxreplication had significant effects (p<1%) on the rain-fed wheat yield every year.
Annual precipitation in the first year of the experiment (1997-1998) was 593.4 mm and it was 369.2 and 582.3 mm for the second and the third years respectively.
And these noticeable differences in precipitation and the fact of having
rotation in the year before conducting the experiment as well as the irregular
distribution of rainfall in the third year of the experiment have led
to significant differences in terms of yield within the 3 years of conducting
the experiment.
| Table 1: | Variance analysis of different factors within 3 years of the experiment |
| The type of tillage machine did not show any significant effects on the yield (Table 1). | |
The data in the present study shows that when deep drill was used for planting, in terms of yield increase Disc Plow was ranked first and Offset Disc, Chisel Plow and Moldboard Plow were second to fourth, respectively, so apparently Disc Plow made a better seedbed compared to other methods resulting in a higher yield although it was not significantly different (p = 0.46).
Although Disc Plow has made a non-significant yield increase of 5.5, 7.6 and 8.3% compared to Offset Disc, Chisel Plow and Moldboard Plow. respectively but because Chisel Plow needs less pulling power therefore it can be used at higher speeds and it can cover a wider area as well. As a result, saving energy, reducing costs and required time for soil preparation, improving physical characteristics of soil, moisture control and preventing soil erosion are the advantages could be made by using Chisel Plow, so based on the obtained data on this research this tillage machine is recommended for Golestan province and similar climates and soils for the priority of reducing tillage practices and maintaining plant residues. Interaction effect of yearxtillage machine on the yield was not significant (Table 1) meaning that both mentioned factors had same effects on the yield, so it could be concluded that each year the tillage machines have had the same effect on soil preparation and consequently on the yield
The results obtained by French and Schultz (1984) are in line with the findings of the resent study. Tanaka`s findings (1989) on the comparison of the yield of pea while using different tillage treatments including no tillage, reduced tillage and conventional tillage (Moldboard Plow) supports the obtained results in the present study as it was indicated in their study that the yield difference for the mentioned tillage treatments was not significant and even no tillage showed a better yield trend. In a study of the effect of different tillage methods on the yield of wheat, Ciha (1982) concluded that plowing by Chisel Plow Led to a higher yield than other tillage methods. Hodgson et al. (1989) obtained similar results.
However, some researchers have found significant yield increase when applying Moldboard Plow for irrigated wheat compared to other tillage methods (Hemat and Asadi, 1997). Afuni and Mosadeghi (2001) and Mahboubi et al. (1993) reported that considering the fact that the type of tillage does not have any significant effects on the yield, it`s recommended to apply either of the two methods of soil preparation by Chisel Plow or Disc Plow which brings along the advantages of saving required finance and time of the soil preparation practice and reducing tillage as well, that is in line with the results of the present research.
There were significant differences on the yield between planting machines
(p<1%) (Table 1). Comparing the average yield of each year with different
precipitation for each planting machine within the 3 years of the experiment.
Table 2 shows that deep drill planting has increased the yield on the
average 35% compared to drill planting with end wheels especially in the
first year which there was more rainfall and more appropriate soil due
to the rotation in the year before beginning of the experiment. The reasons
that led to such an increase could be explained as follows: deep drill
planting machines plant seeds deeply at the bottom of furrows providing
a good attachment to earth. This attachment especially when soil moisture
is moderate accelerates the germination of the seeds. Besides, while raining,
rain water can penetrate through furrows and consequently soil erosion
and flow of water throughout farm and organic materials wash-out could
be prevented.
| Table 2: | Comparison of the effect of the planting machines on the average yield of rain-fed wheat in different years of the experiment with different precipitation |
| Values with different superscripts are significantly different at 5% level | |
| Table 3: | Comparison of the effect of different planting machines and seed density on the average yield of rain-fed wheat |
| Values with different superscripts in two planting machines separately are significantly different at 1% level | |
The interaction effect of yearxplanting machine on the yield was significant (p<1%) (Table 1). It means that the two factors of year and planting machine didn`t have the equal effects on the yield. On the other hand, in some years, deep drill with press wheels was better and caused a higher yield as a result of appropriate amount and distribution of rainfalls (Table 2).
Seed density didn`t have a significant effect on the yield (Table 1). The comparison of the average yield of rain-fed wheat with different seed densities for each planting machine has shown in Table 3, as it is indicated seed density at the rate of 140 kg ha-1 has made a non-significant yield increase of up to 7-9% when compared with the other 2 densities. That could be due to less competition for nutrients among seeds or enough moisture or less plants in each plot leading to an increase in the number of spikelets in each wheat kernel. Besides, one reason of obtaining non-significant results could be due to the small differences among seed density treatments.
So, considering the yield increase of 7-9% although not significant, but in order to reduce the production costs, it is recommended to reduce seed density to 140 kg ha-1.
Khajepoor (1986) also obtained similar results and 100 kg ha-1 was recommended among seed densities of 70, 100, 150 kg ha-1, but Saif (1976) suggested that seed density had no significant effect on the yield. However, the seed density of 180 kg ha-1 was recommended Table 1 shows that interaction effect of yearxseed density; planting machinextillage machine; yearxseed densityxtillage machine and seed densityxtillage machine; yearxplanting machinextillage machine and seed densityxplanting machine; yearxseed densityxplanting machine; seed densityxplanting machinextillage machine; yearxseed densityxplanting machinextillage machine didn`t have significant effects on the yield of rain-fed wheat meaning that all the studied factors were effective independently or all mentioned factors in this experiment have had equal effects on the yield of Tajen rain-fed wheat.
COMMENTS AND SUGGESTIONS
To reach more exact results it`s suggested that the following points should be considered in similar researches:
| • | Difference in seed density should be chosen up to 15-20 kg. |
| • | The farm chosen for the experiment shouldn`t be in fallow farmed before conducting the research to reserve the nutrients for the research plants. The rotation of crop should be considered with the current products of the region as well. |
| • | Soil moisture should be monitored, especially while seed formation because the results could be more accurate. |
| • | The depth of the hardpan layer should be measured frequently. |
| • | Average precipitation and temperature, related to the years of conducting the experiment should be recorded as the rain distribution is important on the results analysis. |
| • | Soil physical characteristics for different tillage methods should be studied too. |
| • | Mean Weight Diameter (MWD) of cultivar plot used in the experiment that affects soil sustainability, before and after the tillage practice should be measured. |
| • | Amount of produced straw should be measured as different tillage machines might have significant effects on the amount of straw produced. |
ACKNOWLEDGMENTS
The author would like to appreciate Dr. Biabani, Eng. Jafarzade, Dr. Soltani, his daughter F. Shamsabadi and Mrs. A. Janati, who cooperated with and helped him in conducting the research including soil preparation, plantation, crop protection and harvesting also typing and aid in primary translating into English and would like to ask God for the best of their health while wishing them prosperity and success.