Abstract: This research was carried out on dry farming areas in four locations around Van lake Basin in the eastern Turkey between 1998 and 2001. The aim of the experiment was to determine the effects of fallow and winter lentil (Lens culinaris) on wheat (Triticum aestivum) yield and the available water content in soil layers between 0 and 120 cm after fallow and lentil treatments. The experimental design was a randomized block with 4 replications. The results indicated that the highest water contents occurred in fallow plots in all locations. The highest fallow efficiency was observed in Ercis (9.4%) and the lowest was in Adilcevaz (-8.8%). Wheat yield was significantly reduced by lentil in all locations. Growing winter lentil was more profitable than fallow. Therefore, wheat-winter lentil rotation system is recommended in all locations.
INTRODUCTION
Wheat (Triticum aestivum) is the major crop in dry farming areas in Turkey. In Van Lake Basin (Turkey), water is the most limiting factor of crop production in dryland farming. Fallow has been a traditional strategy to capture and store water. For this purpose, weeds in fields are removed by tillage or herbicide by the time of planting (Lampurlanes et al., 2002). Fallow period is approximately 15 months, for winter wheat, from harvest in July to planting in October of the next year. Summer fallow has been the most common cultural practice for soil water conservation in the eastern Anatolia. It also provides an efficient weed control, yield increase and release in plant nutrients (Connor and Loomis, 1991). Fallow is applied to conserve water in many places in the world (Bonfil et al., 1999). Up to 25% of the annual precipitation is held in the soil during fallow period (Farahani et al., 1998). The effectiveness of fallow depends on soil type, tillage practices, rainfall, topography, temperature and soil water-storage capacity. However, all the researchers are not in agreement regarding the effects of fallow in water conservation in semi-arid regions (Godwin, 1990). Farahani et al. (1998) stated that the most of water conserved is lost during the last summer of fallow.
There are also some disadvantages of fallow. It may lead to poor soil water storage efficiency and enhanced soil erosion (Aase and Pikul, 2000). Additionally, growing only wheat can cause exploitation of the same soil profile and also tillage for fallow can cause hard and impermeable soil formation in time; root systems of cereals can not grow in this profile and active root zone gets smaller. Decreases of infiltration during fallow may enhance the loss of water through surface flow and evaporation. To avoid these, legumes that are deep rooted and consume less water can be utilized during fallow. Eser et al. (1999), reported from Shultz (1927), indicated that annual legumes form deep root canals that are reach in nitrogen and organic matter, thus enhancing biological soil process. There are some reports regarding growing legumes in fallow years. In Western Australia, white lupine, blue lupine, faba bean and field pea preceding cereals are used in fallow (Thomson et al., 1997). In Canada, field pea, lentil and chickpea in sequences with spring wheat have been proposed to use in fallow (Miller et al., 2002; Miller at al., 2003). Larney and Lindwall (1995), found that the amount of available water for winter wheat in fall in Canada was least 45 mm after canola, 59 mm after winter wheat, 74 mm after lentils and 137 mm after fallow. Additionally, Gan et al. (2003) stated that grain yield and protein increase much better if pulses are grown before spring wheat than if spring wheat precedes spring wheat.
Approximately 5 million ha of land is left for fallow in Turkey. Application of legume-wheat rotation system in places where annual precipitation is sufficient will provide crop production every year and biological process of soil in deep profiles. Even decrease in the amount of water because of consumption by legumes in fallow may limit wheat yield at the beginning, this will become reverse because infiltration and organic matter content of soil will increase in time.
The objective of present study was to investigate the effects of fallow and alternative crop (winter lentil) on soil-water content and wheat yield in Van-Lake Basin in dry farming areas. To investigate different perspectives, the studies were pursued in four locations (Van, Erciş, Adilcevaz ve Gevaş) that included sandy, sandy-loam, sandy-loam-clay soils and in slopped and smooth lands.
MATERIALS AND METHODS
Field experiments were carried out in four locations in Van-Lake Basin in the east of Turkey between 1998 and 2001. The locations were Van (38°25’ N, 43°21’ E; altitude: 1720 m; average temperature: 8.8°C; average rainfall: 381.3 mm), Erciş (39°00’ N, 43°28’ E; altitude: 1730 m; average temperature: 7.9°C; average rainfall: 458.0 mm), Adilcevaz (38°58’ N, 42°48’ E, altitude: 1730 m; average temperature: 9.0°C; average rainfall: 578.2 mm) and Gevaş (38°18’ N, 43°07’ E, altitude: 1710 m; average temperature: 8.8°C; average rainfall: 516.9 mm). Soil samples were analyzed at the laboratories of Erzurum Village Affairs Research Institute. The soil types of experimental locations were sandy-loam-clay in Van and Gevaş, Sandy-loam in Erciş and sandy in Adilcevaz. Soils of all locations were slightly alkaline, poor in organic matter, N and P.
Sazak-91 (lentil) and Tir (wheat) cultivars were used in the study. Experimental areas, except Gevaş (8 % slopped) were flat. Each plot was 5x10 m = 50 m2. The experiment was done in a randomized complete block design with 4 replications. Wheat and lentil were sown in early October each year, using plot drill. Plant density was 250 seeds m-2 for lentil and 450 seeds m-2 for wheat in rows spaced 20 cm apart. Lentil and wheat were harvested in early and late July, respectively. Fertilizer, 140 kg ha-1 Diamoniumphosphate (18% N, 46% P2O5) was applied to each plot at sowing. In addition, wheat plots received 50 kg ha-1 N as Ammonium Sulfate (21% N) at the stem elongation stage. In the first season (1998-1999), all plots were sown with wheat; in the second year (1999-2000), some plots were sown with winter lentil and the other plots left for fallow. All plots were sown with wheat in the third year (2000-2001). Soil water storage and wheat yield between fallow-wheat and winter lentil-wheat rotation systems were compared. The soil samples were taken from 0-30, 30-60, 60-90 and 90-120 cm depths at the beginning (July-1999) and end (October-2000) of fallow in all plots. The soil water content was obtained by Gravimetric Method (Kacar, 1995).
The data were analyzed using ANOVA (SAS, 1996). Mean separation was performed for the significant main effects through Duncan test at p = 0.05 (Montgomery, 1991).
RESULTS AND DISCUSSION
The highest precipitation during fallow was observed in Gevaş (421.9 mm), followed by Adilcevaz (338.4 mm), Van (312.0 mm) and Erciş (247.3 mm). The WSE in Gevaş was lower than in the other locations because experimental area was 8% slopped (Table 1).
The highest soil water content was obtained in Van (151.8 mm) while the least occurred in Adilcevaz (74.3 mm). The rates of water that could be conserved through fallow, but consumed by lentil were 28.5% in Van, 24.8% in Erciş, 42.7% in Adilcevaz and 19.8% Gevaş (Table 2).
The highest water storage efficiency during fallow was observed in Erciş and Van locations as 9.42 and 7.70 %, respectively (Table 1). Erciş had less precipitation, but higher WSE than Van during the fallow. This could be because Van had higher average temperature than Erciş, which was conducive to higher evaporation during the fallow. The WSE was the lowest (-8.81%) in Adilcevaz location because the soil of this location was sandy and water holding capacity was very low. The similar results were reported by Lampulanes et al. (2001). Although Gevaş had the same soil structure with Van and Erciş, it had lower WSE (0.50%) because the soil was slopped in that location. The amounts of water conserved and WSE were highest in sandy-loam and smooth soils, while the least amounts were found sandy and also smooth soils. They decreased in slopped soils (Fig. 1). The results of studies by Farahani et al. (1998) about water storage efficiency are similar to the results of this study.
After lentil, the highest soil water content was observed in Van (108.6 mm) and least was in Adilcevaz (42.6 mm). The highest WSE was obtained from Erciş (4.90%) while the least was in Adilcevaz (-18.20%) (Table 2). The differences in WSE values could be attributed to the differences in topography rather than precipitation.
Table 1 Precipitation during fallow and fallow efficiency in four locations.
Table 2 shows the water contents in soil depths between 0 and 120 cm were higher in fallow plots than in lentil plots in all locations. Similarly, Güngör (1991), Adak (2001) and Larney and Lindwall (1995) also states that the highest water is obtained from fallow plots. WSE depending on different soil depths varied in locations. The highest amount of water was accumulated in 90-120 cm in Van (6.6%) and Gevaş (2.4%) and in 0-30 cm in Erciş (5.2%) and Adilcevaz (4.7%). After lentil, the highest WSE values were found in 0-30 cm in all locations (Van, Erciş and adilcevaz 3.5, 0.4 and 0.8%), except Gevaş (Fig. 1).
| Table 1: | Precipitation during fallow and fallow efficiency in four locations |
| W-F-W: Wheat-Fallow-Wheat and W-L-W: Wheat-Lentil-Wheat rotation system | |
| Fig. 1: | WSE values in different soil depths in the locations. (a) Van (sandy-loam-clay) (b) Esciş (sandy-loam) (c) Asilcevaz (sandy) (d) Gevas (sandy-loam-clay and slopped) |
In all locations, except Gevaş, as the soil depth increased after fallow, the WSE started decreasing from 0-30 cm depth and increased again in 60-90 cm. In Gevaş that has slopped land, WSE increased as the soil depth increased (Table 2 and Fig. 1).
Main purpose of fallow is to conserve water to guarantee wheat germination in fall. Therefore, humidity in 0-30 cm soil depth is important at the beginning of growth. But lack of humidity in 30-60 (like in Adilcevaz ve Gevaşta), especially in the cases of decrease in fall rains may cause moisture stress. The decreases in wheat and lentil yields in Adilcevaz and Gevaş could be attributed to this phenomenon. Therefore, the soils of Van (sandy-loam-clay) and Erciş (sandy-loam) seem safer compared to soils of Gevaş (slopped) and Adilcevaz (sandy).
Table 2 soil water content during, at the beginning and end of fallow on wheat-fallow and wheat-lentil rotation systems.
Wheat yield was significantly affected from fallow-wheat and lentil-wheat rotation systems. All of the yields in fallow treatments were higher than in winter lentil treatments in all locations (Table 3).
The effects of fallow-wheat and winter lentil-wheat rotations systems on biological, grain and straw yield of wheat Adilcevaz location had the lowest biological, grain and straw yield. This could be due to the fact that the soil of Adilcevaz location was sandy; So, water holding capacity of this site was very low (Table 3 and Fig. 2).
Wheat yields in the fallow treatment plots were higher than in the lentil treatment plots. The highest grain yield (1356 kg ha-1) in fallow-wheat rotation system was obtained from Van location that had the highest soil water content (151.8 mm). There was a relationship between soil water content and yield in both fallow-wheat and lentil-wheat rotation systems (Fig. 2). The similar results on the effects of soil structure and topography on yield were reported by Tan et al. (1989), Adak (1994), Lyon et al. (1998), Eser et al. (1999) and Lampulanes et al. (2001).
Despite the fact that the fallow-wheat system improves soil water storage efficiency and wheat yield,the fallow has not received a great attention in the region.
| Table 2: | Soil water content during beginning and end of fallow on wheat-fallow and wheat-lentil rotation systems |
| Table 3: | The effects of fallow-wheat and winter lentil-wheat rotations systems on biological, grain and straw yield of wheat |
| Values having different alphabets are significantly different at p <0.05 | |
| Fig. 2: | The relationships between wheat grain yield and the water contents of soils. YAL: Yield after fallow, YAL: Yield after lentil, WCAF: Water content after fallow, WCAL: Water content after lentil |
The May-September fallow period is not enough for water accumulation. Therefore, the total water storage efficiency is low. Especially, sandy soil (Adilcevaz) and slopped area (Gevaş) caused decreases in water storage efficiency.
The traditional fallow-crop rotation is not economically feasible for the region. Instead of this, use of annual legumes (with low water consuming crops such as lentil and chickpea) with should take place to protect soil from erosion. Growing lentil in fallow years should be considered to improve other aspects such as deep biological process of soil, thus increasing permeability and water holding capacity of soil, optimization of N, weed control and increasing farmer’s additional income.
ACKNOWLEDGMENT
This study was funded by The Scientific and Technical Research Council of Turkey (TOGTAG-TARP-1956 project).