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Tanner, D.G.

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Tanner
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D.G.
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Tanner, D.G.

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End date: 1999 × Start date: 1990 ×

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    Agro-ecological decision support systems for wheat improvement in Ethiopia: Climatic characterisation and clustering of wheat growing regions
    (African Crop Science Society, 1999) Belay Simane; Tanner, D.G.; Tarekegne, A.T.; Asefa Taa
    Wheat production environments in Ethiopia are highly heterogeneous with respect to natural resource characteristics, cropping systems, biotic and abiotic constraints. This paper analyses the agro-climatic resources of 20 representative wheat growing sites in the country and groups them by cluster analysis to develop homogeneous environmental groupings for wheat improvement research. The wheat growing sites are defined and clustered based on precipitation, temperature, altitude, longitude, and length of growing season. Annual precipitation decreases along a west-east axis, ranging from 1784 to 585 mm. The major feature of the precipitation pattern is its seasonality with distinct dry and rainy seasons. Generally, rainy season duration extends from 2.5 to 6.5 months. In the western, central and northern parts of the country, rainfall distribution is generally monomodal. In the eastern part of the country (i.e., 39.4 to 42.5° E) the distribution is bimodal, resulting in two cropping seasons, viz. "belg" (short) and "meher" (main). Of the parameters studied, annual and main season precipitation, and length and end of growing period were negatively correlated with longitude (r = -0.73**, -0.82**, -0.64** and -0.43*). Altitude was negatively correlated only with maximum and minimum temperatures (r = -0.64** and -0.86**). Three main environmental groups (C1, Western; C2, High Altitude; C3, Eastern) and six subgroups (C1-1, C1-2, C2, C3-1, C3-2, C3-3) were identified in the cluster analysis. Such clustering into homogeneous environmental groups should assist the national wheat improvement programme in making decisions about test site selection and proper targeting of released varieties.
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    Improvement of durum wheat yield and associated effects on morpho-physiological characters
    (African Crop Science Society, 1995) Tarekegne, A.T.; Tanner, D.G.; Tesfaye Tesemma; Getinet Gebeyehu
    Six durum wheat ( Triticum turgidum var. durum check for this species in other resources ) cultivars released in the central highlands of Ethiopia from 1967 to 1992, were evaluated to estimate progress in improving grain yield, and to determine changes in crop morphological and physiological attributes. The six durum wheat cultivars differed in all crop parameters studied. Over the 25 year period represented by the varietal releases, grain yield increased by 68 kg ha-1y-1 (1.58%y-1). Grain yield of durum wheat was positively correlated with harvest index, grains m-2, grains spike-1, grains spikelet-1, and thousand grain weight, all of which increased significantly over time. Spike density (ie., spikes m-2) decreased slightly while the other parameters did not exhibit significant temporal trends. Protein yield increased over time along with grain yield, while grain protein was unchanged. The national durum improvement programme has substantially improved the grain yield of rainfed durum wheat by increasing the magnitude of the grain sink and the efficiency of assimilate partitioning into grain. Durum breeders in Ethiopia should emphasise spike fertility and kernel size as reliable selection criteria for continued improvement in yield potential.
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    Yield stability analysis of nine spring bread wheat genotypes in the central highlands of Ethiopia
    (African Crop Science Society, 1995) Solomon Assefa; Abeyo Bekele Geleta; Tanner, D.G.
    Eight promising bread wheat lines and one standard check cultivars were evaluated for grain yield performance, stability and adaptation across nine environments of the central highlands of Ethiopia. Results of the combined analysis of variance for grain yield showed highly significant effects of genotypes, environments, and genotype by environment interaction. The mean grain yields for individual lines ranged from 3249 to 4762 Kh ha-1. When the genotypic grain yields were subjected to stability analysis against an environmental index, the regression coefficients for individual lines ranged from 0.406 to 1.451. Among the lines tested, HAR 1696 and Enkoy were the two most stable genotypes across all environments, while two of the four highest yielding lines, HAR 1349 and HAR 1709, appeared to be specifically adapted to favorable growing conditions. The test line HAR 1685 exhibited superior yield performance across all environments, and was recommended for release in 1994 for commercial production in Ethiopia.
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    Competitive ability of Ethiopian spring bread wheat cultivars with Avena fatua L.
    (African Crop Science Society, 1995) Tanner, D.G.; Giref Sahile; Workiye Tilahun
    Competitive interactions of four spring bread wheat cultivars ( Triticum aestivum check for this species in other resources L.) with four wild oat ( Avena fatua check for this species in other resources L.) seedling densities were assessed in field studies in southeastern Ethiopia during three cropping seasons (1991-93). Grain yield of wheat was linearly proportional to the seedling density of wild oats, but yield reductions at the maximum density of 90 weed seedlings m-2 ranged from 26 to 63% across the wheat cultivars. The semidwarf cultivar Dashen was the most sensitive to wild oat competition, while the intermediate height cultivar Enkoy was the least affected. Wheat cultivars varied markedly in their ability to suppress A. fatua tillering and seed production, differentially affecting wild oat seed and straw yield, panicle production, seed number panicle-1, and thousand kernel weight. Given the limited access of Ethiopian peasant farmers to grass herbicides, wheat breeders should be encouraged to exploit such variability, and develop germplasm with a greater inherent ability to compete with wild oats.
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    Improvement in yield of bread wheat cultivars released in Ethiopia from 1949 to 1987
    (African Crop Science Society, 1995) Tarekegne, A.T.; Tanner, D.G.; Getinet Gebeyehu
    Thirteen bread wheat ( Triticum aestivum check for this species in other resources L.) cultivars popular in the highlands of Ethiopia and representative of the period from 1949 to 1987 were studied for two cropping seasons in Ethiopia to estimate progress made in improving grain yield. The selected cultivars were grown with the effects of other genetic changes minimized by using fungicides to control foliar diseases, nets to prevent lodging, and periodic hand weeding to control weeds. Adequate levels of nutrients were also supplied. Significant differences were observed among cultivars for all crop parameters studied. The grain yield of bread wheat cultivars released since 1949 has increased at a mean rate of 77 kg ha-1yr-1 (2.21%) as measured in central Ethiopia and 50 Kg ha-1y-1(1.77%) under warmer and drier conditions in southeastern Ethiopia. Grain Yield was significantly and positively correlated with harvest index, grains m-2, spikelets spike-1 and grains spike-1. Genetic improvement has substantially increased the grain yield of rainfed bread wheat in the highlands of Ethiopia, resulting from an improved harvest index associated with an increased number of grains spike-1 and, as a result, grains m-2. Wheat breeders in Ethiopia should continue to emphasize spike fertility as a selection criterion for high grain yield.
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    Response of bread wheat to rate and timing of nitrogen application in marginal rainfall zone in Ethiopia
    (African Crop Science Society, 1994) Zewdu Yilma; Tanner, D.G.
    Nitrogen fertilizer rate by timing trials were conducted on bread wheat (Triticum aeslivum L) in peasant farmers' fields during two annual cropping seasons for three years in a drought-prone district of southeastern Ethiopia. Nitrogen rates had an incremental effect on grain yield, but the response to N was economically acceptable only up to 41 kg N ha-1, and then only in the more reliable second growing season. Mean grain yields obtained in different growing seasons were correlated with seasonal rainfall totals, but nitrogen response was not. Early application of N, either all at sowing or split applied between sowing and mid-tillering, resulted in the highest yield increments, and also significantly increased the number of wheat spikes m-2, grains spike-1 grains m-2, plant height, and biomass yield, while decreasing harvest index. Thousand kernel weights and broadleaf weed seedling densities were unaffected by N rate and timing. Split application of N should be recommended as an economic risk-aversion strategy in this marginal rainfall zone.
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    On-farm evaluation of alternative bread wheat production technologies in northwestern Ethiopia
    (African Crop Science Society, 1995) Asmare Yallew; Tanner, D.G.; Regassa Ensermu; Alemu, H.
    Wheat ( Triticum spp.) is a major crop grown in northwestern Ethiopia. The primary wheat production constraints in this area include low soil fertility, use of unimproved and disease-susceptible varieties, and high weed infestation. Technology packages, combining three nutrient levels (92-20, 41-20 and 0-0 kg N-P ha-1), the improved bread wheat cultivar (ET13), the local line (Israel), and two weed management methods (hand weeding and application of 2,4-D), were evaluated on farmers’ fields. Highly significant grain yield differences were observed among the treatments. The highest grain yield (2,991 kg ha-1) and the greatest benefit were obtained from application of 92-20 kg N-P ha-1 and 2,4-D herbicide on ET13. Adoption of the improved bread wheat cultivar was highly profitable regardless of fertilizer usage. The effect of fertilizer on grain yield and economic return was much greater than the effect of 2,4-D used alone for weed control.
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    The effects of several crop management systems on bread wheat yields in the Ethiopian Highlands
    (African Crop Science Society, 1997) Tarekegne, A.T.; Tanner, D.G.; Amanuel Gorfu; Tilahun Geleto; Zewdu Yilma
    Crop management (CM) research conducted in Ethiopia has tended to quantify yield gains and losses associated with single management factors, making it difficult to determine the relative importance of main effects and interactions among factors. During 1987 and 1988, exploratory trials examining several CM factors for bread wheat (Triticum aestivum) production were conducted at four research centres situated in the priority wheat production zones of Ethiopia. In the two cropping seasons of 1990, five similar trials were executed in south-eastern Ethiopia to examine the differential responses to four CM factors between farmers' fields and a research site. All 13 trials examined differences between local and improved bread wheat varieties, and response to fertiliser and hand weeding. A fourth factor of local significance such as fungicide, insecticide, or sowing date was added at each site to complete a 24 design. Treatment main effects exerted the predominant influence on grain yield (GY). Relative to unimproved traditional germplasm, GY increments from modern varieties ranged from 13 to 315%. Fertiliser application reduced GY by 9% in one trial due to enhanced lodging, but, in nine others, increased yield from 20 to 88%. Hand weeding increased GY in nine trials; the increases ranged from 17 to 94%. Fungicide increased GY by 5% in two trials, primarily by increasing the yield of a susceptible semi-dwarf variety under a heavy epidemic of stripe rust (Puccinia striiformis). Seed treatment with insecticide for control of shoot fly (Delia arambourgi) increased GY by 13 to 46% in four trials. Two way interactions involving variety emphasised the greater responsiveness of modern varieties to improved management and higher levels of inputs. Overall, the interactions demonstrated the beneficial impact of combining improved production practices in one cultural package. From the comparison of on-farm and on-station results, it was apparent that station conditions differ dramatically from farmers' circumstances in terms of heat crop response to hand weeding, fertiliser application and insecticidal seed treatment. This has obvious implications for the extrapolation of research results generated on station to the surrounding small-scale farming community.
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    Effect of nitrogen fertiliser applied to tef on the yield and N response of succeeding tef and durum wheat on a highland vertisol
    (African Crop Science Society, 1999) Selamyihun Kidanu; Tanner, D.G.; Tekalign Mamo
    A trial was conducted on an Ethiopian Vertisol from 1990 to 1995 to determine the residual effect of fertiliser N applied to tef (Eragrostis tef) following chickpea (Cicer arietinum) on the grain and straw yield, N content, and N uptake of succeeding crops of durum wheat (Triticum turgidum var. durum) and tef. Measures of N use efficiency across the interval 0 to 60 kg ha-1 of applied N contrasted between the two consecutive tef crops: tef following chickpea exhibited lower mean values for agronomic efficiency (AE), namely 11.7 vs 16.8 kg grain per kg applied N, and apparent recovery (AR), 37.8 vs. 66.4%, of N compared to the second consecutive tef crop. The magnitude and consistency of the beneficial carryover effect of N applied to tef on the succeeding tef and durum wheat crops was dramatic. The mean AE of 60 kg ha-1 of N applied to tef and wheat in the current season (using 0 N as the base) was 16.8 and 13.0 kg grain per kg fertiliser N, respectively; the mean AE of 60 kg N applied to tef in the previous season was 6.1 for both crop species. The results demonstrated a residual fertiliser N benefit equivalent to 36.3 and 46.9% of the response to current season N application for tef and durum wheat, respectively (i.e., across the interval from 0 to 60 kg fertiliser N ha-1). Across the same interval, the mean rates of apparent recovery of fertiliser N in tef and wheat were 66.4 and 65.4% for current season N application, and 25.7 and 36.1% for previous season N application. The carryover effects of applied fertiliser N on succeeding cereal crops on Vertisols in the Ethiopian highlands have several beneficial implications. Tef and wheat grain comprise the principal dietary components of the Ethiopian highland populace, while tef and wheat straw represent the major dry season feed source for Ethiopia=s livestock population. The current study demonstrates that the carryover benefit of applied fertiliser N enhanced the yields and N contents of the grain and straw of both wheat and tef, resulting in significant increases in total N uptake. Thus, both human and livestock populations in the Ethiopian highland Vertisol zones would benefit from an increase in dietary protein intake as well as an increase in the quantity of dietary staples. Any analysis of the profitability of fertiliser N response should reflect the multi-year benefit period.
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    On-farm evaluation of an animal-drawn implement developed in Ethiopia for row placement of wheat seed and basal fertilizer
    (African Crop Science Society, 1997) Asefa Taa; Tanner, D.G.; Melesse Temesgen; Kefyalew Girma
    Grass weeds are difficult to control by hand weeding in a broadcast wheat crop because several species are not easily distinguished from the crop at an early stage. Chemical weed control, on the other hand, can be highly effective, but is limited in Ethiopia by the unavailability and high cost of herbicides. Further, dependence on high efficacy herbicides to control grass weeds can result in weed species shifts and/or the development of resistant weed biotypes. Row sowing of wheat can facilitate hand and/or mechanical weeding by enabling farmers to identify grass weeds in the inter-row spaces. However, manual row seeding is extremely labour intensive and unacceptable to peasant farmers in Ethiopia. Row seeders developed elsewhere have not been accepted in Ethiopia because they were either too labour inefficient or ineffective in cloddy and rough fields. Therefore, a four-row seeder has been developed in Ethiopia with a new type of seed metering mechanism
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