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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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Start date: 1990 × AGROVOC: WHEAT ×

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Now showing 1 - 10 of 12
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    Estimation of optimum plot dimensions and replication number for wheat experimentation in Ethiopia
    (African Crop Science Society, 2000) Girma Taye Awake; Tarekegne, A.T.; Tanner, D.G.
    Bread wheat was row and broadcast sown using uniform crop management practices on a research station soil classified as a haplic Nitisol, situated in a major wheat producing region of Ethiopia, during the 1996 and 1997 crop seasons. The harvested area was divided into basic units measuring 1 m by 1 m. Resultant basic unit grain yields were combined to simulate different plot sizes and shapes, and Smith's empirical model and subsequent derivations were used to estimate soil heterogeneity. The broadcast sown trials generally resulted in lower estimates of soil heterogeneity, higher coefficients of variation, and higher values for adjacent plot correlation due to both modified inter-plant competition, and a more variable distribution of wheat plants and basal fertiliser within plots. Parameter estimates from the broadcast sown trials were less consistent over the two year trial period relative to those from the row sown trials. The analyses suggested a marginal superiority for square plot shapes for broadcast sown trials, while for row sown trials rectangular and square plot shapes were equally precise in measuring soil heterogeneity. A comparison of the trial design parameters currently favoured by wheat researchers in Ethiopia with the optimal parameters estimated in the current study suggests that: (a) the design characteristics of broadcast sown wheat agronomic trials appear close to optimal, but (b) the net plot areas harvested from row sown wheat breeding trials are markedly suboptimal.
    Publication
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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.
    Publication
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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.
    Publication
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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.
    Publication
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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
    Publication
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    Grass weed competition and calculated economic threshold densities in bread wheat in Ethiopia
    (African Crop Science Society, 1997) Taye Tessema; Tanner, D.G.
    Competition effects of four of the predominant grass weed species in Ethiopia (Avena abyssinica Hoechst, Lolium temulentum L., Snowdenia polystachya Fresen (Pilg), and Phalaris paradoxa L.) on the grain yield, yield components and morphological characters of bread wheat (Triticum aestivum L.) were studied in Western Shewa Zone of Ethiopia. The four grass species varied significantly in their effects on wheat tillering, leaf area index (LAI), number of fertile spikes m^-2, grains per spike, spike length, thousand grain weight, straw, biomass and grain yield, harvest index and plant height. Avena abyssinica and S. polystachya were the most competitive, reducing wheat yield components and morphological characters to a greater extent than L. temulentum and P. paradoxa. Grass species by seedling density interaction effects were significant for most of the crop and weed characters measured, indicating a differential rate response for individual species. The reduction in wheat grain yield at the maximum weed density of 320 seedlings m^-2 ranged from 48 to 86% across the four grass species studied. The wheat yield components most affected by weed competition were number of fertile spikes m^-2 and number of seeds spike-1. Weed morphological characters (i.e., number of tillers, LAI, number of panicles, and plant height) varied markedly among species and in direct proportion with weed seedling density. Plant height and LAI appeared to be the factors most closely associated with weed competitive ability with bread wheat. Competitive yield losses were fitted to a rectangular hyperbola model to facilitate the prediction of wheat grain yield loss, and to derive economic thresholds for herbicidal intervention in relation to weed seedling density.
    Publication
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    Grain yield of barley as affected by cropping sequence and fertilizer application in Southeastern Ethiopia
    (African Crop Science Society, 1997) Asefa Taa; Tanner, D.G.; Kefyalew Girma; Amanuel Gorfu
    Cropping systems in the Ethiopian highlands involve rotations of cereals with grain legume and oilseed crops; the proportional allocation among crop species varies with altitude, rainfall, and soil type. Barley (Hordeum vulgare) tends to dominate in the highest altitudinal zones, while bread wheat (Triticum aestivum) is more common at medium altitudes. A trial was established in 1992 at the Bekoji research site in southeastern Ethiopia to evaluate interactions among barley-based cropping sequences and annual applications of inorganic nitrogen (N) and Phosphorus (P) fertiliser. Rotational crops included Ethiopian rapeseed (Brassica carinata), faba bean (Vicia faba), and bread wheat
    Publication
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    Grass weed competition with bread wheat in Ethiopia. II: Prediction of grain yield loss and implications for economic weed control
    (African Crop Science Society, 1996) Taye Tessema; Tanner, D.G.; Mohammed Hasenna
    Two multi-year studies were conducted in Ethiopia to examine the effects of competition by the predominant grass weed species on bread wheat (Triticum aestivum L.). In the first experiment, the effects of four grass weed species (Avena abyssinica Hoechst, Lolium temulentum L., Snowdenia polystachya Fresen (Pilg), and Phalaris paradoxa L.) at eight seedling densities (from 0 to 320 m^2) on wheat grain yield were studied. A. abyssinica and S. polystachya were highly competitive, resulting in a greater reduction of wheat grain yield (i.e., 85 and 86%, respectively, at 320 seedlings m^-2) than L temulentum and P. paradoxa. L temulentum exerted a greater competitive effect than P. paradoxa. Competitiveness of the grass weeds varied with weed seedling density. The second experiment studied the competitive interactions of Avena fatua L. sown at four seedling densities (from 0 to 90 m^-2) in competition with four bread wheat cultivars commonly grown by peasant farmers in Ethiopia. The semi dwarf cultivar Dashen was the most sensitive to A. fatua competition, exhibiting a yield loss of 63% at the maximum density of 90 wild oat seedlings m^-2. Competitive indices were derived from each experiment to facilitate the prediction of wheat grain yield loss, and to derive economic thresholds for herbicidal intervention in relation to weed seedling density.
    Publication
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    Grass weed competition with bread wheat in Ethiopia. I. Effects on selected crop and weed vegetative parameters and yield components
    (African Crop Science Society, 1996) Taye Tessema; Tanner, D.G.; Mengistu Hulluka
    Competition effects of four of the predominant grass weed species in Ethiopia (Avena abyssinica Hoechst, Lolium temulentum L., Snowdenia polystachya Fresen (Pilg), and Phalaris paradoxa L.) on the morphological characters, grain yield, and yield components of bread wheat (Triticum aestivum L.) were studied in western Shewa Zone of Ethiopia. The four grass species varied significantly in their effects on wheat plant height, tillering, leaf area index (LAI), number of fertile spikes m^-2, grains per spike, spike length, thousand grain weight, straw, biomass, harvest index and grain yield. A. abyssinica and S. polystachya were the most competitive, reducing wheat morphological characters and yield components to a greater extent than L. temulentum and P. paradoxa. The reduction in wheat grain yield was linearly proportional to the square root of weed seedling density. Grass species by seedling density interaction effects were significant for most of the crop and weed characters measured, indicating a differential rate response for individual species. The reduction in wheat grain yield at the maximum weed density of 320 seedlings m^-2 ranged from 48 to 86% across the four grass species studied. The wheat yield components most affected by weed competition were number of fertile spikes m^2 and number of seeds/spike. Weed vegetative and reproductive characters (i.e., number of tillers, LAI, number of panicles, and plant height) varied markedly among species and in direct proportion with weed seedling density. Plant height and LAI appeared to be the factors most closely associated with weed competitive ability with bread wheat.
    Publication
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    Potential for cereal-based double cropping in Bale Region of Southeastern Ethiopia
    (African Crop Science Society, 1994) Tanner, D.G.; Zewdu Yilma; Lemma Zewdie; Girmay Gebru
    A double cropping trial was conducted under bimodal rainfall conditions for two years at the Sinana Research Centre in southeastern Ethiopia. Compared to the traditional farmers’ practice of fallowing land during one of the two annual cropping seasons, double cropping increased total farm grain output and net income. The best crop combination, both in agronomic and economic terms, consisted of field pea (Pisum arvense L.) grown during the first rainy season followed by bread wheat (Triticum aestivum L.) in the second season. Double cropping cereals in both seasons appeared to be the least desirable combination, although this system still outperformed the traditional fallow practice during the two years of this study. Double cropping in Sinana “woreda” district could minimize several negative aspects of the fallow systems: (1) soil erosion could be reduced by maintaining a crop vegetative cover in both cropping season; (2) the rate of expansion of cultivation onto pasture land could be reduced by intensifying production on the currently cropped areas; (3) weed control could be facilitated by rotating non-cereal crops with the second season wheat crop; and (4) human and ox labour could be utilized more efficiently in a double cropping system than in a fallow-wheat system.
    Publication