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Tanner, D.G.

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Tanner
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Tanner, D.G.

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    Implication of rate and time of nitrogen application on wheat (Triticum aestivum. l .) yield and quality in Kenya
    (Elewa BioSciences, 2011) Ooro, P.A.; Malinga, J.N.; Tanner, D.G.; Payne, T.S.
    In Kenya, Nitrogen is the first limiting macro-element on many farms where bread wheat (Triticum aestivum) has been grown continuously for more than a decade. On-farm trials were conducted in Kenya by superimposing the treatments on farmers? fields in Nakuru (5 sites), Uasin Gishu (3 sites), and Timau (2 sites) districts during the main growing seasons of 1997-99. This was to study the effect of rate and time of application of fertilizer nitrogen (N) on bread wheat (Triticum aestivum) grain yield, yield components, and grain quality. Wheat grain samples from the ten (N) nitrogen rates and timing treatments combined across replications were analysed at the Small Grain Institute, Bethlehem, Republic of South Africa for milling and baking quality in accordance with standard analytical procedures (Pyler, 1973; Kent, 1983; Hoseney, 1986). Results revealed that flour protein content (FPC) and grain nitrogen (GN) increased significantly in response to N rate. Nitrogen application increased timing of sedimentation (SDSS) rate and loaf volume, but decreased the kernel weight, falling number (FLN) and flour yield (FLY) percentage. N application had P<0.05 effects only on mixing development time (MDT), FLN and (SDSS). Split application of N resulted in superior quality attributes than when the entire N was applied at once. The sensitivity of rate and time of N application was found to be greater in the wheat quality attributes than the grain yield and yield components. These results can therefore be used in situations where good wheat prices are determined on the basis of grain quality.
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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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    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.
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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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    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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    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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    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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    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.
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