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Dep. of Plant Sci., Faculty of Agric. and Food Sci., Am. Univ. of Beirut, P.O. Box 11-0236, Beirut, Lebanon
* Corresponding author (sy00{at}aub.edu.lb)
Received for publication July 9, 2001.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: EG, early planting with early clipping or grazing • ENG, early planting with no clipping or grazing • NNG, normal planting with no clipping or grazing
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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In the region, some farmers allow sheep grazing on barley crops in their early stage of growth and then let the crops recover for grain harvesting (Yau and Mekni, 1987). This practice of grazing cereals in early growth stages occurs in Morocco (Belaid and Morris, 1991), Syria (Nordblom, 1983; Mazid and Hallagian, 1983), and Tunisia (Amara et al., 1985).
Farmers in some other areas of the world also allow green-stage grazing on winter cereals. The most outstanding example is in the USA where winter wheat in the southern Great Plains is widely used for grazing by cattle (Redmon et al., 1995). In Australia, the practice is common in the Tablelands of New South Wales where oat (Avena sativa L.) has been the most popular cereal for this purpose (FitzGerald et al., 1995). The practice is also reported from Mediterranean Europe, like Cyprus (Hadjichristodoulou, 1983) and Spain (Royo et al., 1994), and from Canada (Poysa, 1985). Earlier, the practice was common in Argentina, the British Isles, New Zealand, South Africa, and Uruguay (Holliday, 1956).
The practice of green-stage grazing of barley in West Asia and North Africa arose from a lack of feed for the increasing numbers of sheep in the region (Anderson, 1985; Belaid and Morris, 1991). Some barley farmers follow the practice because they believe that it can increase tillering and grain yield. Despite an increase in tiller numbers after grazing, head numbers usually decrease because of higher tiller mortality (Yau et al., 1989a). Green-stage grazing also commonly causes grain yield reduction in winter cereals (Holliday, 1956; Redmon et al., 1995). However, the practice may be economically beneficial even if grazing reduces grain yield (Nordblom, 1983; Yau et al., 1989b).
Green-stage grazing may not reduce grain yield if environmental conditions are favorable. The recent review of experiments on grazing in the southern USA by Redmon et al. (1995) concluded that cattle grazing would have minimal effect on wheat grain yield if soil water is adequate throughout the growing season. In an earlier study on barley in arid areas, grain yield after grazing by sheep did not decrease in a season with above-average rainfall and good rainfall distribution (Yau et al., 1989b). This led the author to believe that in semiarid (300–600 mm) areas, grazing by sheep might not decrease barley grain yield and that this practice could be encouraged.
Date of planting usually has a large effect on seed yield of barley in West Asia and North Africa. Experiments showed that early planting results in higher barley grain yield by producing early ground cover to make better use of precipitation (ICARDA, 1984, 1987; Ketata, 1987). In arid environments, farmers always plant their barley crops before the first rainfall of the season, which allows for seed germination. On the contrary, farmers in semiarid environments normally plant their barley after the first rain. However, if the barley is going to be used for grazing, farmers usually plant their crops as early as possible. They probably learned by experience that early planting gives earlier availability and higher amount of forage for grazing and that combination of late planting and grazing has a higher chance of reducing grain and straw yields.
Although many studies have been conducted on wheat grazing by cattle in the USA, little research has been done on grazing of barley by sheep in Mediterranean regions. The objective of this study was to test the hypothesis that under semiarid conditions of West Asia and North Africa, clipping or grazing by sheep before stem elongation on a suitable early planted barley cultivar may not lead to reduction in grain and straw yields.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Two barley cultivars, Rihane and ER/Apam, were tested in 1997–1998. Rihane is a facultative six-row variety released in Lebanon in 1987 and is the most productive and most widely cultivated variety in the country. It is also a good dual-purpose type for green-stage grazing plus grain harvesting (Yau and Mekni, 1987). ER/Apam is a new variety released in Lebanon in 1997 only for the milder and drier northern Bekaa. It is a spring two-row type that is shorter and matures earlier than Rihane. Based on the results of 1997–1998, only Rihane was used in the following two seasons.
The experiments had three treatments: ENG, EG, and NNG. Early and normal planting were defined as before or after the first occurrence of rain, respectively. Farmers in the Bekaa usually plant winter cereals after the first occurrence of rain in November; thus, the NNG treatment was the control. Dates of planting, seedling emergence, and clipping or grazing are given in Table 1. In 1997, the first rain came on 3 November. However, in 1998 and 1999, rain came as late as 17 and 14 December, respectively.
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In 1997–1998 and 1998–1999, hand clipping of the appropriate plots at 10 cm above ground level was performed. Clipping did not remove any apical meristems. From each clipped plot, the clippings from a 1-m row in the center of the plot were collected, dried at 80°C for 24 h, and weighed. The rest of the clippings were then removed from the plots.
Actual grazing was conducted in 1999–2000 to confirm the effects of clipping in the two earlier seasons. Sheep grazing took place during a period when the surface soil was dry. Before introducing the sheep, a cage was placed in the center of the plots (covering two 28-cm rows of plants) to protect the plants from grazing. Five ewes were allowed to graze in each plot for about 15 min. Average plant height after grazing was around 2 cm above ground level. To estimate the amount of forage removed by the grazing animals, the protected plants in the center of the plots were clipped at 2 cm above ground, and the clippings were collected for measurement of dry matter production.
In each season, heading date, head-bearing tillers, plant height, biological (grain + straw) yield, and grain yield were measured. Heading date was recorded when heads emerged from 50% of the shoots in the plot. Days to heading were calculated from date of seedling emergence. The number of head-bearing tillers from one (two in 1999–2000) representative meter of plants in a central row was counted and plant height (the average plot height from ground level to the tip of heads excluding awns) measured near maturity. In 1997–1998 and 1998–1999, one representative meter of plants at ground level was harvested at maturity by hand from each of the two central rows, dried in the oven at 60°C for 24 h, weighed to give biological yield, and threshed to give grain yield. In 1999–2000, the central 3 m by eight rows of plants was harvested for biological and grain yield measurement. Straw yield and harvest index were calculated from biological and grain yield.
Additional traits were measured in the last two seasons. Dry matter yield (from one row of 1-m length and two rows of 3-m length of plants in 1998–1999 and 1999–2000, respectively) at heading and thousand-grain weight after threshing were measured in both seasons. Grains per head were calculated from grain yield, grain weight, and head number.
The experiments were in randomized complete block designs. In 1997–1998, the experiment was in a factorial arrangement of three treatments by two cultivars with three replicates. In 1998–1999 and 1999–2000, there were four replicates. The ANOVA directive of the GENSTAT package (Genstat 5 Committee, 1993) was used to perform the analyses of variance for individual seasons and for the imbalanced three-season data set of Rihane. In the ANOVA of multiple years, the random-season and fixed-treatment model was adopted (McIntosh, 1983). Under such a model, mean squares of seasons, treatments, and season x treatment were tested against the mean squares of blocks within seasons, season x treatment, and pooled error, respectively. Barlett's test of homogeneity of variances was applied to error mean square from individual ANOVAs of the three seasons when season x treatment interaction was significant. For those traits that showed heterogeneity of variance, the square root or power-of-0.25 transformations were found to be effective in removing or reducing the heterogeneity. As results of the ANOVAs using transformed or original data were essentially the same, the original data were presented. Statistical significance was accepted at P 
0.05. Fisher's protected LSD procedure (Steel and Torrie, 1980) was used for mean separation at P = 0.05.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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The treatment x season interaction was not significant for grain yield. In 1998–1999, both early plantings gave higher grain yield than that of the NNG treatment (Table 3). However, there were no significant differences between treatments in mean grain yield of the three seasons. Mean grain yield of 1997–1998 was higher than that of 1998–1999, which was higher than that of 1999–2000.
For straw yield and biological yield, treatment x season interaction was significant (Table 3). The straw yield of the NNG treatment ranked the lowest among the treatments in 1997–1998 and 1998–1999 but highest in 1999–2000. The NNG treatment had less biological yield than the ENG and EG treatments in 1997–1998 and 1998–1999, but there were no significant differences in 1999–2000. Treatments had no significant effects on mean straw and biological yields over years. Mean straw yield was higher in 1998–1999 than in 1997–1998. In contrast, mean biological yield was higher in 1997–1998 than in 1998–1999. Mean straw and biological yields were lower in 1999–2000 than in 1997–1998 and 1998–1999.
For harvest index, significant differences existed between seasons but not between treatments and in the treatment x season interaction (Table 3). Mean harvest index was higher in 1997–1998 than in 1998–1999 and 1999–2000.
Yield Components
Treatment x season interaction was significant for number of heads per square meter (Table 4). The NNG treatment had less heads than the ENG and EG treatments in 1997–1998; however, there were no significant differences between treatments in 1998–1999 and 1999–2000. Treatments did not affect 3-yr mean numbers of heads significantly. The mean number of heads was higher in 1998–1999 than in 1997–1998 and 1999–2000 seasons.
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Other Agronomic Traits
Heading time expressed a significant treatment x season interaction (Table 5). The differences in heading time between the ENG and EG treatments and between the ENG and NNG treatments were larger in 1999–2000 than in 1997–1998 and 1998–1999. Significant differences also existed between treatments and seasons. Relative to the ENG treatment, the EG treatment delayed the mean heading time by 1 d. As expected, the NNG treatment took less time to head than the ENG and EG treatments. In 1997–1998, plants took more time to head than in 1998–1999 and 1999–2000.
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For plant height near maturity, differences between treatments and the treatment x season interaction were not significant, but the differences between seasons were significant. In 1999–2000, mean plant height was about half that of the two earlier seasons (Table 5). Lodging was observed in the ENG treatment in 1997–1998 only. Lodging did not occur in the last two seasons.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Results of this study are consistent with those on cattle grazing winter wheat in the southern USA (see review by Redmon et al., 1995) where grazing usually has a minimal effect on subsequent grain yield if soil moisture at planting and subsequent precipitation during the growing season are adequate. This consistency was unexpected in terms of the large differences in farming systems (cattle grazing on winter wheat vs. sheep grazing on barley) and climatic conditions (summer rainfall sub humid vs. dry summer semiarid) prevailing in the southern USA compared with West Asia and North Africa. This indicates the similarity in response of winter wheat and barley after grazing. If external conditions are favorable after grazing, the crops will recover and produce grains.
Planting barley crops early and allowing grazing by sheep will help in solving the problems of inadequate feed supplies and high feed prices, which were ranked by farmers as two of the top problems in a recent survey of small-ruminant production systems in the Bekaa (Hamada et al., 1994). In case farmers do not own any sheep, cutting the forage for sale or leasing pastures may be a profitable option. However, farmers who allow green-stage grazing must be careful in choosing the right cultivar and in the timing of grazing. Farmers must use a cultivar like Rihane, which has a good ability to grow after grazing. Besides, grazing must not remove apical meristems. If apical meristems are removed by grazing animals or the cutter, grain yield will be substantially reduced. The latest time for safe grazing that also allows reasonable production of forage is when leaf sheaths are strongly erect (growth stage 30; Tottman, 1987).
The prevention of excessive vegetative growth probably was the reason why clipping or grazing did not reduce grain yield in this study, especially for the latter two drier seasons. According to Holliday (1956), there are two conditions under which grazing does not adversely affect grain yield. One is where prolific growth in the vegetative stage limits grain yield due to early soil moisture depletion. The other is where this practice reduced lodging. In semiarid areas, lodging usually is not a serious problem. Thus, the usual condition whereby grazing does not reduce grain yield is by preventing prolific vegetative growth from depleting soil moisture early. Results of 1999–2000 showed that the dry weight at heading was lower for the grazed than the nongrazed treatments. In fact, many farmers in Syria allow grazing when early vegetative growth is abundant due to milder- or wetter-than-usual winters. These farmers probably learned by experience that a large dry matter yield does not mean high grain yield in semiarid Mediterranean environments.
This study suggested that farmers in the Bekaa should plant their barley crops early even if they do not intend to allow grazing. Results of the nonclipped or nongrazed treatments tend to support earlier studies conducted in Jordan and Syria, which showed that early sowing of barley gave higher yield than later sowing (ICARDA, 1984, 1987). Thus, a situation like this is much simpler than the case in the southern Great Plains of the USA where winter wheat solely for grain production should be planted later than that for grazing plus grain production (Epplin et al., 2000).
Winter temperature appeared to have a bigger influence than precipitation on barley grain and straw yield in the Bekaa. In 1998–1999, although precipitation was the lowest of the three seasons, the warm winter allowed barley plants to grow rapidly and produce a yield close to the wet season of 1997–1998. In comparison, the cooler 1999–2000 had a higher precipitation than 1998–1999, yet the yield was much lower. This result does not agree with longer-term studies in lower-latitude, semiarid areas, in which precipitation had a dominant influence on crop yield over seasons (Blum and Pnuel, 1990; Erskine and El-Ashkar, 1993; Van Oosterom et al., 1993). Whether temperature has a real dominant influence in the high-elevation Bekaa or the result of the three seasons was just a short-term artifact warrants further study.
Result of 1997–1998 illustrated the differences between the two cultivars in response to green-stage clipping. The earlier, shorter, and lodging-resistant ER/Apam was more sensitive to clipping than the taller and later Rihane. The existence of barley cultivar differences in response to clipping or grazing was reported earlier (Anderson, 1985; Yau and Mekni, 1987). Similar results were reported for winter wheat in southern USA where it was shown that two modern lodging-resistant semidwarf cultivars with earlier heading were more sensitive to grazing than a tall cultivar (Winter et al., 1990).
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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ACKNOWLEDGMENTS |
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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